Optical System and Assembly Method

- LASER LIGHT ENGINES

An optical system which includes some or all of the following parts: a laser light source which illuminates a spatial light modulator such that optical characteristics are preserved; a stereoscopic display which has a polarization-switching light source; a stereoscopic display which includes two infrared lasers, two optical parametric oscillators, and six second harmonic generators; two light sources processed by two parts of the same spatial light modulator; a method of assembly using an alignment plate to align kinematic rollers on a holding plate; an optical support structure which includes stacked, compartmented layers; a collimated optical beam between an optical parametric oscillator and a second harmonic generator; a laser gain module with two retroreflective mirrors; an optical tap which keeps the monitored beam co-linear; an optical coupler which includes an optical fiber and a rotating diffuser; and an optical fiber that has a core with at least one flat side.

Skip to: Description  ·  Claims  · Patent History  ·  Patent History
Description
BACKGROUND OF THE INVENTION

Movie theaters have traditionally relied on projectors which use an arc-lamp as the source of light. This is a highly inefficient source for projecting an image onto a screen due to the extended size of the source, its low brightness, its broadband light, and the relatively short lifetime of the lamp itself. The cost of ownership to theater owners is large due to the frequent lamp changes required, the cost of electricity to operate the multi kilowatt lamps as well as the cooling required to keep the projector room at a normal operating temperature.

The move to digital cinema further reduces the efficiency of the lamp due to the requirement that the light needs to be separated into component red/green/blue bands to illuminate three modulation arrays in a uniform manner before recombining the beams for projection. Finally, 3-D digital cinema requires even more light as the projected image must be alternated between scenes for the left and right eyes which reduces the apparent brightness of the image on the screen.

Red, Green, Blue solid state lasers seem to be a viable solution to these problems while reducing the total cost of ownership. The pump lasers have very long rated lives, on the order of 20,000 hours, eliminating the need for lamp replacements. Semiconductor pump lasers have high electrical to optical efficiency meaning much less heat generation for a given output power as compared to arc lamps. The lasers are narrow-band which makes them easier to separate with little light loss. They also are much brighter sources which allows high optical throughput. Finally lasers are typically polarized which provides a big power advantage for some 3-D display technologies.

Solid-state lasers are not without problems, however. The typical high purity TEM00 Gaussian spatial mode is difficult to convert to a uniform source over the digital modulators. The narrow line width of a laser leads to speckle patterns over the viewed image which may lead to an unacceptable loss of image quality.

The optical designs of most digital image projectors use spatial light modulators (SLMs) to switch each pixel on and off in order to create a visual image. The SLMs may be reflective, such as liquid crystal on silicon (LCOS) devices and digital micromirror devices (DMDs), or may be transmissive such as liquid crystal display (LCD) panels.

Some of the commonly used components of laser optical systems include optical parametric oscillators (OPOs), and laser gain modules. OPOs may be used to generate multiple wavelengths of laser light from one pump laser beam. In the OPO, parametric amplification in a nonlinear crystal converts the pump laser wavelength into two more wavelengths of light, so an optical system with one pump laser and one OPO may produce at total of three wavelengths of visible light which are useful for applications such as full-color digital image projection. Laser gain modules are used to optically amplify laser light. A laser is used to pump a gain slab which is composed of a gain medium. Optical energy is transferred from the pump beam into a main beam of light which is also traveling through the gain slab.

Many other optical components are used in laser light sources, projectors, and optical systems in general. Commonly used abbreviations are as follows: ultra-high performance (UHP) lamp, polarizing beamsplitter (PBS), dichroic beamsplitter (DBS), second harmonic generation (SHG) unit, total-internal-reflection (TIR) prism, antireflection (AR) coating, neodymium-doped yttrium lithium fluoride (Nd:YLF) laser, neodymium-doped yttrium aluminum perovskite (Nd:YAP) laser, neodymium-doped yttrium lithium fluoride (Nd:YLF) laser, lithium triborate (LBO) crystal, short wave pass (SWP) filter, long wave pass (LWP) filter, subminiature A (SMA) connector, and light emitting diode (LED). Some of the concepts used in optics and their abbreviations are full-width half maximum (FWHM) bandwidth, angle of incidence (AOI), and ultraviolet (UV) light. The organizations and industry standards that apply include the Digital Cinema Initiative (DCI), the Commission Internationale de l'Eclairage (CIE), and the International Telecommunication Union Radiocommunication (ITU-R) Recommenation 709 (Rec. 709).

Assembly and alignment of optical systems generally require that the optical components be placed in a desired position with high accuracy and that the components be held in that position throughout shipping and over the lifetime of the product. In manufacturing quantities of thousands or more, conventional optical assembly techniques do not provide cost-effective methods for assembling optical devices with high tolerances such as complex laser systems. Optical systems are typically assembled on the upper surface of a flat optical support structure. Each optical component of the optical system is aligned and attached to the flat optical support structure in its desired location.

A stereoscopic projector forms still or moving images that can be seen in three dimensions. Stereoscopic projection systems may be formed by using polarized light to form distinct images for the left eye and the right eye. These images simulate the images that would be seen in an actual three-dimensional scene. One polarization state is used for the left-eye image and the orthogonal polarization is used for the right-eye image. Glasses with polarizing filters are used to allow the left image to pass through to the left eye and the right image to pass through to the right eye, while blocking the left image from reaching the right eye, and blocking the right image from reaching the left eye. In other words, the image for the left eye is directed to the left eye and not to the right eye, whereas the image for the right eye is directed to the right eye and not to the left eye.

Instead of using polarized light, stereoscopic left and right images may be formed by using spectral selection, for example as described in U.S. Pat. No. 6,283,597, the complete disclosure of which is incorporated herein by reference. In the spectral selection method, first wavelength bands of red, green, and blue are passed to the left eye, and second wavelength bands of red, green, and blue are passed to the right eye. The first bands and second bands are distinct so that there is little or no overlap between the first and second bands.

Stereoscopic projection systems can be characterized as one of three basic types: (1) time-sequential projection that uses one SLM per color and alternately shows left eye images and right eye images in rapid sequence, (2) simultaneous projection that uses two SLMs per color, one for the left eye images and one for the right eye images, and (3) split image projection, where there is only one SLM per color, and the left and right eye images are formed simultaneously on separate parts or pixels of the single SLM.

In summary, the main problems facing digital image projectors are providing a bright image with a long operation lifetime, especially in the case of stereoscopic systems, and providing an alignment and assembly method that is feasible in full-scale production.

SUMMARY OF THE INVENTION

In embodiments, in one aspect, an optical system including a laser light source and an SLM where the SLM includes a liquid crystal material. The laser light source emits light only in a range of wavelengths that preserves an optical characteristic of the SLM.

In embodiments, in one aspect, a stereoscopic display system including a polarization-switching light source and a polarization-preserving projector which is illuminated by the polarization-switching light source.

Implementations may include one or more of the following features. The polarization-preserving projector may form a left-eye digital image and a right-eye digital image, and the polarization state of the polarization switching light source may be changed in synchronization with an alternating projection of the left-eye digital image and the right-eye digital image.

In embodiments, in one aspect, a stereoscopic projection system including a first infrared laser, a first gain module that amplifies the light beam from the first infrared laser, a first SHG that frequency doubles the light beam from the first gain module, a first OPO that parametrically amplifies the light beam from the first SHG, a second SHG that frequency doubles the first light beam from the first OPO; a third SHG that frequency doubles the second light beam from the first OPO, a second infrared laser, a second gain module that amplifies the light beam from the second infrared laser; a fourth SHG that frequency doubles the light beam from the second gain module, and the like. Part of the light beam from the first SHG passes through the first OPO to form a remaining light beam which is green. The light beam from the second SHG is red, the light beam from the third SHG is blue, and the light beam from the fourth SHG is a second color of green.

Implementations may include one or more of the following features. The remaining light beam, the light beam from the second SHG, and the light beam from the third SHG may combine to form an image that is directed to one eye of the viewer and is not directed to the other eye of the viewer. There may be a switch that switches the light beam from the first SHG, a second OPO that parametrically amplifies the light beam from the first SHG, a fifth SHG that frequency doubles the first light beam from the second OPO, a sixth SHG that frequency doubles the second light beam from the second OPO. The switch may send the light beam from the first SHG alternately to the first OPO and the second OPO, and the like. The light beam from the fifth SHG may be a second color of red light, and the light beam from the sixth SHG may be a second color of blue light. There may be a third infrared laser, a third gain module that amplifies the light beam from the third infrared laser, a fifth SHG that frequency doubles the light beam from the third gain module; a second OPO that parametrically amplifies the light beam from the fifth SHG, a sixth SHG that frequency doubles the first light beam from the second OPO, a seventh SHG that frequency doubles the second light beam from the second OPO, and the like. The light beam from the sixth SHG may have a second color of red light, and the light beam from the seventh SHG may have a second color of blue light.

In embodiments, in one aspect, an optical system including a first light source, a second light source; and an SLM. The first light source has a first optical output which is processed by a first part of the SLM and the second light source has a second optical output which is processed by a second part of the SLM.

Implementations may include one or more of the following features. The first light source may have an etendue lower than 0.1 mm2 sr. The first part of the SLM may be used to form an image for the left eye of the viewer and the second part of the SLM may be used to form an image for the right eye of the viewer. The first optical output may include a first wavelength band and the second optical output may include a second wavelength band and the first wavelength band may be different than the second wavelength band.

In embodiments, in one aspect, a method of assembly including the steps of placing an alignment plate on a holding plate, inserting a roller and a holding block into the alignment plate, fastening the holding block to the holding plate to hold the roller, fastening the roller to the holding plate, removing the alignment plate, mating an optical module to the roller on the holding plate, and the like.

Implementations may include the following feature. The final alignment may be achieved without further adjustments.

In embodiments, in one aspect, an optical support structure including first and second compartmented support structures adapted to support optical modules. The second compartmented support structure is stacked on top of the first compartmented support structure.

Implementations may include one or more of the following features. There may be a first compartment in the first compartmented support structure, a second compartment in the second compartmented support structure, a hole between the first compartment and the second compartment that allows a beam of light to pass through, and the like. There may be a third compartment in the second support structure, and a hole between the second compartment and the third compartment that allows a beam of light to pass through.

In embodiments, in one aspect, an optical system including an OPO, an SHG, a first lens which passes light between the OPO and the SHG, a second lens which passes light between the OPO and the SHG, a third lens which passes light between the OPO and the SHG, and the like.

Implementations may include the following feature. The first lens may pass a collimated beam segment to the second lens.

In embodiments, in one aspect, an apparatus including a laser gain slab which carries a main laser beam, a pump laser which optically pumps the laser gain slab, a retroreflective minor positioned adjacent to the laser gain slab, and the like. The retroreflective minor reflects the main laser beam.

In embodiments, in one aspect, an optical tap including a first plate, a second plate, a detector, and the like. A first beam of light enters the first plate and a small fraction of the first beam of light is reflected to the detector. A second beam of light exits the first plate and enters the second plate. The second plate shifts the second beam of light to be co-linear with the first beam of light.

Implementations may include the following feature. The first plate may be an uncoated plate of glass.

In embodiments, in one aspect, an optical coupler including an optical fiber and a despeckler. A laser light beam illuminates the optical fiber, the output from the first optical fiber illuminates an integrating rod, and the output from the integrating rod illuminates a digital image projector.

Implementations may include one or more of the following features. There may be a second optical fiber, another laser light beam which illuminates the second optical fiber, the output from the second optical fiber may illuminate the despeckler, and the like. There may be a third optical fiber and a third laser light beam which illuminates the third optical fiber, and the output from the third optical fiber may illuminate the despeckler. The first laser light beam may be red, the second laser light beam may be green, and the third laser light beam may be blue. The first optical fiber may be attached to the second optical fiber to form an optical fiber bundle.

In embodiments, in one aspect, an optical system including a laser light source, an optical fiber with a core, and a digital image projector. The laser light source illuminates the core, the core illuminates the digital image projector, and the core has at least one flat side.

Implementations may include one or more of the following features. The core may have a rectangular cross section. The polarization direction of the laser light source may be oriented orthogonal to the flat side of the core.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a block diagram of an optical system which includes at least one laser light source, at least one coupler, and at least one set of SLMs;

FIG. 2 is a top view of a projector system using LCOS SLMs;

FIG. 3 is a top view of a projector system using LCD SLMs;

FIG. 4 is a graph of the spectrum of a xenon lamp;

FIG. 5 is a graph of the shortwave spectrum of a xenon lamp;

FIG. 6 is a graph of the safe blue spectrum of a xenon lamp;

FIG. 7A is a graph of the spectrums of two narrow-band blue lasers;

FIG. 7B is a graph of the spectrum of a wide-band blue laser;

FIG. 8 is a color chart of two xenon-projector color gamuts compared to the DCI standard;

FIG. 9 is a color chart of two laser-projector color gamuts compared to the DCI standard;

FIG. 10 is a color chart of a laser-projector color gamut compared to the Rec. 709 standard;

FIG. 11 is a graph of the spectrum of a UHP lamp;

FIG. 12 is a side view of a stereoscopic display system;

FIG. 13 is a side view of a stereoscopic display system with a polarization-switching light source;

FIG. 14 is a top view of a polarization-preserving projector;

FIG. 15 is a side view of a polarization-switching light source;

FIG. 16 is a front view of a rotating disk in a polarization switch;

FIG. 17 is a flowchart of a method of stereoscopic projection;

FIG. 18 is a top view of stereoscopic projection;

FIG. 19 is a block diagram of a projector light engine;

FIG. 20 is a block diagram of a laser light system based on two lasers;

FIG. 21 is a block diagram of a laser light system based on three lasers;

FIG. 22 is a flowchart of a method of generating light based on two lasers;

FIG. 23 is a flowchart of a method of generating light based on three lasers;

FIG. 24 is a top view of a projector optical design with dual illumination using LCOS SLMs;

FIG. 25 is a top view of a projector optical design with dual illumination using DMD SLMs;

FIG. 26 is a top view of a projector optical design with dual illumination using transmissive LCD SLMs;

FIG. 27 is a front view of a portrait-oriented SLM with two images located one above the other;

FIG. 28 is a front view of a landscape-oriented SLM with two images located one above the other;

FIG. 29 is a front view of a portrait-oriented SLM with two images far apart and located one above the other;

FIG. 30 is a front view of a landscape-oriented SLM with two images located on the left and right of each other;

FIG. 31 is a front view of a landscape-oriented SLM with two images located one diagonal to the other;

FIG. 32 is a front view of a landscape-oriented SLM with an anamorphic pattern of pixels;

FIG. 33 is a front view of a landscape-oriented SLM with a checkerboard pattern of pixels;

FIG. 34 is a top view of low etendue illumination compared to high etendue illumination;

FIG. 35 is a flow chart of a method of dual illumination;

FIG. 36 is a flowchart of an assembly method;

FIG. 37 is a flowchart of an assembly method with pre-alignment;

FIG. 38 is a flowchart of an assembly method with a chassis plate;

FIG. 39A is a top view of a base plate;

FIG. 39B is a side view of a base plate;

FIG. 40A is a side view of an optical module;

FIG. 40B is a bottom view of an optical module;

FIG. 41 is a side view of a mated base plate and optical module;

FIG. 42 is a side view of a mated base plate and optical module attached to a chassis plate;

FIG. 43A is a top view of a chassis plate with multiple optical modules attached;

FIG. 43B is a side view of a chassis plate with multiple optical modules attached;

FIG. 44 is a flowchart of an assembly method with an alignment plate;

FIG. 45A is a top view of an alignment plate;

FIG. 45B is a side view of an alignment plate and a holding plate;

FIG. 46A is a schematic diagram of alignment error bars for the assembly method of FIG. 36;

FIG. 46B is a schematic diagram of alignment error bars for the assembly method of FIG. 37;

FIG. 47A is a top view of an optical assembly on a flat support structure;

FIG. 47B is a side view of an optical assembly on a flat support structure;

FIG. 48A is a top view of a compartmented support structure;

FIG. 48B is a side view of a compartmented support structure;

FIG. 48C is a top view of a compartmented support structure with a feedthrough hole in a different location;

FIG. 48D is a side view of a compartmented support structure with a feedthrough hole in a different location;

FIG. 49A is a top view of an optical assembly in a compartmented support structure;

FIG. 49B is a side view of an optical assembly in a compartmented support structure;

FIG. 50A is a side view of a stacked compartmented support structure;

FIG. 50B is a top view of a stacked compartmented support structure;

FIG. 51 is a flowchart of an assembly method for a stacked compartmented support structure assembled in parallel;

FIG. 52 is a flowchart of an assembly method for a stacked compartmented support structure assembled in series;

FIG. 53 is a schematic view of an optical system with an optical parametric oscillator;

FIG. 54 is a schematic view of a recirculating optical subsystem with four relay lenses;

FIG. 55 is a schematic view of a recirculating optical subsystem with four relay lenses showing additional details of the optical beams;

FIG. 56 is a schematic view of a non-rectilinear recirculating optical subsystem;

FIG. 57 is a flowchart of a method of generating light;

FIG. 58 is a top view of a gain module with flat mirrors;

FIG. 59 is a side view of a gain module with flat minors;

FIG. 60 is a top view of a gain module with retroreflective mirrors;

FIG. 61 is a flowchart of a method of using retroreflective mirrors;

FIG. 62 is a block diagram of an optical system with an optical tap;

FIG. 63A is a side view of an optical tap with two plates;

FIG. 63B is a side view of an optical tap with three plates;

FIG. 64 is a side view of an optical plate with an incident ray of light;

FIG. 65 is a graph of reflection from an optical plate;

FIG. 66 is an expanded graph of reflection from an optical plate;

FIG. 67 is a block diagram of a color adjusting system with optical taps; and

FIG. 68 is flowchart of a method of optical tapping;

FIG. 69 is a flowchart of an optical coupler method;

FIG. 70 is a side view of an optical coupler with a center-driven diffuser;

FIG. 71 is a side view of an optical coupler with an edge-driven diffuser;

FIG. 72 is a side view of an optical coupler with a collimated output beam;

FIG. 73 is an isometric end view of an optical fiber bundle;

FIG. 74 is a side view of an optical coupler with an optical fiber bundle;

FIG. 75 is a side view of an optical coupler with a reflective beam combiner;

FIG. 76 is a side view of an optical system with a fiber;

FIG. 77 is a cross sectional view of a flat-sided fiber;

FIG. 78 is a cross sectional view of a rectangular fiber with glass cladding;

FIG. 79 is a cross sectional view of a rectangular fiber with air cladding; and

FIG. 80 is a method of illuminating a digital projector using a flat-sided fiber.

 DETAILED DESCRIPTION

FIG. 1 is a block diagram of optical system 100 which has a number of novel parts that will be explained in the following description. First laser light source 102 may include OPO 104, laser gain module 106, and optical tap 108. Light is generated in OPO 104, passes through gain module 106, then through tap 108. The light then passes through first coupler 110 which includes flat-sided fiber 112, and then is processed by first SLMs 114. The light is then projected out of the optical system.

Second laser light source 116 may optionally be included for stereoscopic optical systems. The light from second laser light source 116 passes through second coupler 118 and then through first SLMs 114. The light is then projected out of the optical system. Alternatively, third laser light source 120 may optionally be included for stereoscopic optical systems. The light from third laser light source 120 passes through third coupler 122 and then through second SLMs 124. The light is then projected out of the optical system. Second laser light source 116 and third laser light source 120 may also include OPOs, gain modules, and optical taps (not shown).

In one aspect of the optical system shown in FIG. 1, instead of filtering out damaging wavelengths of light from the light source as is typically done with conventional arc lamp sources, a light source may be used that does not generate the damaging wavelengths, thereby avoiding the need to filter. By proper selection of the wavelength, specifications for color gamut and brightness may be met while utilizing all of the blue efficiently and maximizing the lifetime of liquid crystal materials in the SLM. First laser light source 102, second laser light source 116, or third laser light source 120 may be used to provide laser light without damaging wavelengths. Specific embodiments follow but are not meant to be limiting in any way.

High energy light may damage the internal parts of SLMs. Liquid crystal materials that are used in SLMs are particularly sensitive to shortwave radiation. LCD and LCOS SLMs include liquid crystal materials. The light with highest energy photons is at the short end of the visible spectrum such as the short-wave end of the blue light region and UV light. In a conventional projector, these bands are filtered out so as to prevent degradation to the liquid crystal materials.

For a display system with a white light source, the brightness is in part determined by the amount of blue light that can be filtered out of the original white light. Filtering the light source to remove damaging wavelengths of light at the shortwave end has the disadvantage of lowering the amount of blue light available to the overall optical system. If the blue bandwidth is increased by moving the longwave end of the band up towards green, the separation between blue and green may be lost. If the total system brightness is limited by the amount of blue light, the other colors of light (green and red) must also be lowered if the amount of blue light is reduced in order to keep the desired white point. Reducing all three colors then results in a large decrease in total system brightness.

Another disadvantage of filtering out shortwave portions of the light source is that the color of the blue primary is changed if the shortwave end of the blue band is eliminated. This may cause the projector's color gamut to fall outside of the desired specification.

One type of display system projects an image onto an external screen. This is commonly known as a projector. Other types of display systems may have the screen contained internally. FIG. 2 shows the optical design of a projector system that uses LCOS SLMs. Light source 200 produces first beam segment 202 which is spread by first lens system 204 to make second beam segment 206. Second beam segment 206 is homogenized by mixing rod 208 to produce third beam segment 210. Third beam segment 210 is spread by second lens system 212 to form fourth beam segment 214. Fourth beam segment 214 is collimated by third lens system 216 to make fifth beam segment 218. Fifth beam segment 218 partially reflects from first DBS 220 to form sixth beam segment 250 and partially transmits to form seventh beam segment 222. Sixth beam segment 250 reflects from mirror 252 to form eighth beam segment 254. Eighth beam segment 254 enters first PBS 256 and is reflected to form ninth beam segment 258. Ninth beam segment 258 is processed by first SLM 260 which rotates the polarization of each pixel depending on the desired brightness of the pixel and reflects ninth beam segment 258 back along its input path to reenter first PBS 256. On a pixel-by-pixel basis, if the polarization is not changed relative to the input beam, the light reflects inside first PBS 256 to go back towards light source 200. If the polarization has been changed relative to the input beam, some or all of the light (depending on how much the polarization has been changed) passes through first PBS 256 to form tenth beam segment 262.

Seventh beam segment 222 partially reflects from second DBS 224 to form eleventh beam segment 240 and partially transmits to form twelfth beam segment 226. Eleventh beam segment 240 enters second PBS 242 and is reflected to form thirteenth beam segment 244. Thirteenth beam segment 244 is processed by second SLM 246 which rotates the polarization of each pixel depending on the desired brightness of the pixel and reflects thirteenth beam segment 244 back along its input path to reenter second PBS 242. On a pixel-by-pixel basis, if the polarization is not changed relative to the input beam, the light reflects inside second PBS 242 to go back towards light source 200. If the polarization has been changed relative to the input beam, some or all of the light (depending on how much the polarization has been changed) passes through second PBS 242 to form fourteenth beam segment 248.

Twelfth beam segment 226 enters third PBS 228 and is reflected to form fifteenth beam segment 230. Fifteenth beam segment 230 is processed by third SLM 234 which rotates the polarization of each pixel depending on the desired brightness of the pixel and reflects fifteenth beam segment 230 back along its input path to reenter third PBS 228. On a pixel-by-pixel basis, if the polarization is not changed relative to the input beam, the light reflects inside third PBS 228 to go back towards light source 200. If the polarization has been changed relative to the input beam, some or all of the light (depending on how much the polarization has been changed) passes through third PBS 228 to form sixteenth beam segment 236.

Beam combiner 238 combines tenth beam segment 262, fourteenth beam segment 248, and sixteenth beam segment 236 to form seventeenth beam segment 264. Seventeenth beam segment 264 passes through fourth lens system 266 to form eighteenth beam segment 268 which passes outside of the projector to make a viewable image on a projection screen (not shown).

Beam combiner 238 may be an X-prism. First lens system 204, second lens system 212, third lens system 216, and fourth lens system 266 may be formed from a single lens or any number of lenses that guide the light beams into the desired positions. First lens system 204 may be an optical fiber or fiber bundle. The sizes of components and distances between components are not shown to scale in FIG. 2. Some optical components may be positioned against other optical components so that there is no gap between the components. Auxiliary optical components such as polarizers, relay lenses, skew ray plates, polarization rotation plates, and trim filters are not shown in FIG. 2. The three SLMs shown in FIG. 2 may be each assigned to a primary color so that one is red, one is green, and one is blue. Light source 200 may output polarized light. Mixing rod 208 may be replaced by a fly's eye lens or other homogenization component in which case first lens system 204, second lens system 212, and third lens system 216 may take a different form in order to guide the light properly through the homogenization component.

FIG. 3 shows the optical design of a projector system that uses transmissive LCD SLMs. Light source 300 produces first beam segment 302 which is spread by first lens system 304 to make second beam segment 306. Second beam segment 306 is homogenized by mixing rod 308 to produce third beam segment 310. Third beam segment 310 is spread by second lens system 312 to form fourth beam segment 314. Fourth beam segment 314 is collimated by third lens system 316 to form fifth beam segment 318. Fifth beam segment 318 partially reflects from first DBS 320 to form sixth beam segment 342 and partially transmits to form seventh beam segment 322. Sixth beam segment 342 reflects from first mirror 344 to form eighth beam segment 346. Eighth beam segment 346 is processed by first SLM 348 which rotates the polarization of each pixel depending on the desired brightness of the pixel. On a pixel-by-pixel basis, depending on the amount of polarization rotation, the light is transmitted or absorbed to a varying degree by a polarizer (not shown) to form ninth beam segment 350.

Seventh beam segment 322 partially reflects from second DBS 324 to form tenth beam segment 352 and partially transmits to form eleventh beam segment 326. Tenth beam segment 352 is processed by second SLM 354 which rotates the polarization of each pixel depending on the desired brightness of the pixel. On a pixel-by-pixel basis, depending on the amount of polarization rotation, the light is transmitted or absorbed to a varying degree by a polarizer (not shown) to form twelfth beam segment 356.

Eleventh beam segment 326 reflects from second mirror 328 to form thirteenth beam segment 330. Thirteenth beam segment 330 reflects from third minor 332 to form fourteenth beam segment 334. Fourteenth beam segment 334 is processed by third SLM 336 which rotates the polarization of each pixel depending on the desired brightness of the pixel. On a pixel-by-pixel basis, depending on the amount of polarization rotation, the light is transmitted or absorbed to a varying degree by a polarizer (not shown) to form fifteenth beam segment 338.

Beam combiner 340 combines ninth beam segment 350, twelfth beam segment 356, and fifteenth beam segment 338 to form sixteenth beam segment 358. Sixteenth beam segment 358 passes through fourth lens system 360 to form seventeenth beam segment 362 which passes outside of the projector to make a viewable image on a projection screen (not shown).

Beam combiner 340 may be an X-prism. First lens system 304, second lens system 312, third lens system 316, and fourth lens system 360 may be formed from a single lens or any number of lenses that guide the light beams into the desired positions. First lens system 304 may be an optical fiber or fiber bundle. The sizes of components and distances between components are not shown to scale in FIG. 3. Some optical components may be positioned against other optical components so that there is no gap between the components. Auxiliary optical components such as polarizers, relay lenses, skew ray plates, polarization rotation plates, and trim filters are not shown in FIG. 3. The three SLMs shown in FIG. 3 may be each assigned to a primary color so that one is red, one is green, and one is blue. Light source 300 may output polarized light. Mixing rod 308 may be replaced by a fly's eye lens or other homogenization component in which case first lens system 304, second lens system 312, and third lens system 316 may take a different form in order to guide the light properly through the homogenization component.

FIG. 4 shows a graph of the spectrum of a xenon lamp. Xenon lamps are a type of high-intensity-discharge lamp based on the optical emission of xenon gas and are commonly used for illumination of large-venue digital projectors. The x-axis of FIG. 4 represents wavelength in nanometers and the vertical axis represents normalized intensity. Curve 400 shows the spectrum of a typical short-arc xenon lamp of the type used in digital projectors. There is a substantial amount of the spectrum in wavelengths below 430 nm that may be harmful to liquid crystal materials in LCD or LCOS SLMs.

FIG. 5 shows a graph of the shortwave spectrum of a xenon lamp. The x-axis of FIG. 5 represents wavelength in nanometers and the vertical axis represents normalized intensity. Curve 500 is obtained by filtering out the wavelengths longer than 500 nm in curve 400 of FIG. 4. Curve 500 shows the spectrum of the blue channel in a xenon-lamp-based digital projector if the entire shortwave spectrum is used to make the blue primary color. In this case, the blue channel of the digital projector would be subject to damage from wavelengths shorter than 430 nm, so the spectrum shown in FIG. 5 may be considered unsafe with respect to the lifetime of LCD or LCOS SLMs.

FIG. 6 shows a graph of the portion of the blue spectrum of a xenon lamp that is safe for liquid crystal materials. The x-axis of FIG. 6 represents wavelength in nanometers and the vertical axis represents normalized intensity. Curve 600 is obtained by filtering out the wavelengths shorter than 430 nm in curve 500 of FIG. 5. Curve 600 shows the spectrum of the blue channel in a xenon-based digital projector if only the safe wavelengths are used to make the blue primary color. The case shown in FIG. 6 would result in an improved SLM lifetime for the blue channel as compared to the case shown in FIG. 5.

FIG. 7A shows a graph of the spectrums of two blue lasers with wavelengths of 450 and 455 nm. The x-axis of FIG. 7A represents wavelength in nanometers and the vertical axis represents normalized intensity. The blue lasers have each a single wavelength with a narrow bandwidth, so the two spectrums appear as first vertical line 700 at 450 nm and second vertical line 702 at 455 nm. In these two examples, there are no wavelengths less than 430 nm, so there would be improved SLM lifetime for the blue channel as compared to the case shown in FIG. 5. For the purposes of this disclosure, narrow band is considered to be a full-width-half-maximum of less than 1 nm and wide band is considered to be a full-width-half-maximum of more than 1 nm.

FIG. 7B shows a graph of the spectrum of a wide-band blue laser that covers the range of wavelengths between 450 and 455 nm. The center wavelength is 452.5 nm. The x-axis of FIG. 7B represents wavelength in nanometers and the vertical axis represents normalized intensity. In this example, there are no wavelengths less than 430 nm, so there would be improved SLM lifetime for the blue channel as compared to the case shown in FIG. 4. The wide-band laser spectrum is shown as square wave form 704 in FIG. 7B, but may have other shapes such as a Gaussian form, and it may have peaks and dips at specific wavelengths. In the case of complex shapes, the center wavelength is generally defined as the wavelength midway between the two half-maximum points.

FIG. 8 shows a color chart of two xenon-projector color gamuts compared to the DCI standard. The x and y axes of FIG. 8 represent the x and y coordinates of the CIE 1931 color space. Each color gamut is shown as a triangle formed by red, green, and blue primary colors that form the corners of the triangle. All other colors of the projector are made by mixing various amounts of the three primaries to form the colors inside the gamut triangle. Colors outside the gamut triangle cannot be made by the projector. First triangle 800 shows the DCI standard which is commonly accepted for digital cinema in large venues such as movie theaters and museums. Second triangle 802 shows a projector gamut with the unsafe spectrum of a xenon lamp, as shown in FIG. 5, forming the blue primary. Third triangle 804 shows a projector gamut with the safe spectrum of a xenon lamp, as shown in FIG. 6, forming the blue primary. The green and red primaries of second triangle 802 and third triangle 804 are chosen to be the same as the green and red primaries of the DCI standard for the purposes of this example. It is desirable to choose projector primary colors such that the projector gamut includes the entire gamut of the applicable standard so that all of the colors in the standard may be formed by the projector. Note that second triangle 802 covers more of first triangle 800 than does third triangle 804. This shows that the safe spectrum's color gamut is significantly worse than the unsafe spectrum's color gamut. In the blue and purple regions of the color chart, the safe spectrum is not able to reproduce some of the colors required by the DCI standard that are available with the unsafe spectrum.

FIG. 9 shows a color chart of two laser-projector color gamuts compared to the DCI standard. The x and y axes of FIG. 9 represent the x and y coordinates of the CIE 1931 color space. First triangle 900 shows the DCI standard. Second triangle 902 shows a projector gamut with a blue laser at 450 nm (as shown by first vertical line 700 in FIG. 7A) forming the blue primary. Third triangle 904 shows a projector gamut with a blue laser at 455 nm (as shown by second vertical line 702 in FIG. 7A) forming the blue primary. The green primaries of the laser projectors are at 523.5 nm and the red primaries are at 625 nm for the 450 nm blue primary and 615 nm for the 455 nm blue primary. These green and red wavelengths are the result of using OPO laser light sources as described in U.S. Pat. No. 5,740,190, the complete disclosure of which is incorporated herein by reference. Other laser wavelengths may be utilized with similar results. Second triangle 902 and third triangle 904 each include first triangle 900 showing that both examples of laser projectors are able to form all the colors required by the DCI standard.

FIG. 10 shows a color chart of a laser-projector color gamut compared to the Rec. 709 standard. The Rec. 709 standard is commonly accepted for digital projection of high definition content in homes. The x and y axes of FIG. 10 represent the x and y coordinates of the CIE 1931 color space. First triangle 1000 shows the Rec. 709 standard. Second triangle 1002 shows a projector gamut with a blue laser at 455 nm (as shown by second vertical line 702 in FIG. 7A) forming the blue primary. The green primaries of the laser projector is at 523.5 nm and the red primary is at 615 nm. Other laser wavelengths may be utilized with similar results. Second triangle 1002 includes first triangle 1000 showing that the example laser projector is able to form all the colors required by the Rec. 709 standard.

FIG. 11 shows a graph of the spectrum of a UHP lamp. UHP lamps are a type of short-arc high-intensity-discharge lamp based on the optical emission of mercury vapor and are commonly used for illumination of home digital projectors. The x-axis of FIG. 11 represents wavelength in nanometers and the vertical axis represents normalized intensity. Curve 1100 shows the spectrum of a typical UHP lamp of the type used in home digital projectors. As with the spectrum of the xenon lamp shown in FIG. 4, FIG. 11 shows that a UHP lamp also has a substantial amount of the spectrum in wavelengths below 430 nm that may be harmful to liquid crystal materials in LCD or LCOS SLMs.

SLMs may be formed from a variety of light valve technologies. Some are based on polarized light such as LCD and LCOS technologies whereas some do not depend on polarized light such as DMDs. DMD SLMs are usually not as sensitive to shortwave optical radiation as LCD and LCOS SLMs, but even DMD SLMs may be adversely affected if the intensity of the shortwave radiation is high enough. Other types of light valves are less commonly used and depending on their materials, may or may not be affected by shortwave optical radiation. Liquid crystal materials are used to rotate the polarization of light in LCD and LCOS SLMs. For example, if polarized light is incident on a liquid crystal pixel, by controlling the voltage across the liquid crystal material, the polarization state of light passing through the pixel may be variably changed depending on the voltage. A polarizer or PBS acts as a filter on the exit side of the light valve to allow through only light that is of the desired polarization. A dark pixel is formed when the polarizer or PBS does not allow transmission out of the projector and a bright pixel is formed when the polarizer or PBS does allow transmission out of the projector. Any intermediate state of polarization can make an intermediate brightness pixel. The primary optical characteristic of the SLM (and associated optical elements such as the polarizer and PBS) is contrast between the darkest possible state and the brightest possible state. Other optical characteristics include switching speed and maximum possible transmission. Light with wavelengths shorter than 430 nm may degrade the optical characteristics of the SLM and its associated optical elements. The degradation may take the form of decreased contrast, decreased light transmission, increased switching speed, or a degradation of any other optical characteristic necessary for the proper functioning of the SLM. If only light above 430 nm is used, the optical characteristics of the SLM will be preserved leading to an improved lifetime for the optical system.

There are two types of LCOS SLMs: organic and inorganic. Organic LCOS SLMs use an organic material such as a polyimide plastic to align the liquid crystal layer, whereas inorganic LCOS SLMs use an inorganic alignment material such as SiO2. Although LCOS SLMs with organic alignment layers are more easily damaged by shortwave optical radiation, inorganic LCOS SLMs are also damaged given enough time and intensity.

In order to achieve the desired brightness, a light source of sufficient output should be used in a projection system. For a given light source technology, light output tends to scale with light-source power consumption (wattage), but there are limits on the maximum wattage light source that can be efficiently utilized in a projection system. For example, arc lamps for cinema projectors are typically limited to about 7 kilowatts for DMD-based projectors because at higher powers, the arc becomes too long and the etendue of the light source exceeds the etendue of the DMD projection system. This prevents efficient use of the light generated in the light source. For LCOS projectors, a 7 kilowatt lamp might be accepted by the etendue of a given LCOS projection system, but the limiting factor may instead be the amount of damaging shortwave optical radiation that is generated by the arc lamp. At even higher powers, the etendue of the lamp may still become the limiting factor. An unfiltered laser light system has the advantage that an arbitrarily large power can be used without the limitations of damage by shortwave optical radiation.

The 430 nm definition of shortwave optical radiation is an approximation because the wavelengths of light that can cause damage depend on the exact construction of the SLM, the composition of the liquid crystal material, and the material of the associated optical components such as polarizers or PBS s among other factors. Wavelengths below approximately 200 nm are emitted by arc lamp sources, but are strongly absorbed by the air, so they are not a factor in causing damage to SLMs. The most damaging rays are generally in the range of 200 nm to 430 nm which is the region considered shortwave optical radiation. The range of wavelengths from 200 nm to 380 nm is considered UV light and the range of wavelengths from 380 nm to 430 nm is considered shortwave blue light. The range of wavelengths between 430 nm and 500 nm is considered longwave blue light.

In order to eliminate damaging wavelengths of light from an arc lamp illumination source, projectors usually use optical filters. These are typically shortwave cut-off filters that operate on principles of multilayer interference or absorption or both. These filter designs have a gradual cut-off rather than an infinitely sharp cut-off, so for the purposes of this description, the cutoff wavelength may be considered as the wavelength where 10% of the light is transmitted. Even in the transmission band at longer wavelengths than the cut-off wavelength, there is reduced transmission due to reflections or absorptions in the filter at the longer wavelengths. These losses contribute to the desirability of using illumination systems that do not have a cut-off filter.

A stereoscopic projection system may be formed by using the principle of spectral selection to separate left and right images as described in U.S. Pat. No. 6,283,597. In the spectral selection method, first primary colors of red, green, and blue are passed to the left eye, and second primary colors of red, green, and blue are passed to the right eye. The first group of primaries and the second group of primaries are distinct so that there is little or no overlap between the first and second groups. To achieve sufficient separation between the two blue primaries, the two wavelengths may be approximately 10 to 20 nm apart. The first blue primary wavelength may be in the range of 450 nm to 460 nm and the second blue primary wavelength may be in the range of 430 nm to 445 nm. With an OPO light source, an effective first blue primary wavelength may be 445 nm and an effective second blue primary wavelength may be 440 nm. Unfiltered illumination sources have a particular advantage in the case of spectrally selective stereoscopic projection systems because the filters used to cut out the short wave blue light typically decrease the amount of light available for the second (shorter wave) blue primary.

Blue light in the safe region may be generated by methods other than an OPO. Other types of blue lasers may be used instead or other types of blue light sources that generate blue light in the safe region such as semiconductor light sources. One type of semiconductor light source is a blue LED. Individual LEDs may be arrayed in bars or other configurations to produce powerful sources of blue light. Also, diode-pumped solid-state lasers may be used to generate blue light with non-linear optical elements. The green wavelengths may be likewise be produced by lasers or LEDs centered at various wavelengths such as 520 nm, 532 nm, or 540 nm, and the red wavelengths may be produced by lasers or LEDs centered at various wavelengths such as 620 nm, 630 nm, or 640 nm.

In another aspect of the optical system shown in FIG. 1, a polarization-switching light source is used to form stereoscopic images by transmission through a polarization-preserving projection device. First laser light source 102 may be a polarization switching light source. First coupler 110 and first SLMs 114 may be polarization-preserving parts of a polarization-preserving projection device. Specific embodiments are described in the following paragraphs but are not meant to be limiting in any way.

First laser light source 102, second laser light source 116, or third laser light source 120 may be used to provide polarization-switched light. Polarized light may be used to project stereoscopic images when there are two orthogonal states of polarization. Orthogonal polarization states mean that two different orientation or types of polarizing filters are able to fully and distinctly separate the two polarization states without overlap. For example, linearly polarized light with an electric field vector oscillating in the horizontal direction is orthogonal to linearly polarized light with the electric field vector oscillating in the vertical direction. Similarly, linearly polarized light with an electric field vector oscillating in the −45 degree direction is orthogonal to linearly polarized light with the electric field vector oscillating in the +45 degree direction. Also, circularly polarized light with an electric field vector rotating in the clockwise (right-hand) direction is orthogonal to circularly polarized light with an electric field vector rotating in the counter-clockwise (left-hand) direction. If two states of non-orthogonal polarized light are used for stereoscopic viewing, the left eye image will leak into the right eye and vice versa to make ghosting artifacts which detract from the quality of the stereoscopic viewing experience.

Circularly polarized light is commonly used for stereoscopic projection because viewer head tilt does not significantly change the viewing experience. In contrast, when using linearly polarized light, severe ghosting artifacts will appear if the viewer's head is tilted too far. Also if the projector alone produces linearly polarized light, an external device may be placed in front of the projector to rapidly change the polarization between left-hand and right-hand circular polarization states. The external device may be an electrically-controlled liquid-crystal polarization rotator which is driven in synchronization with the projection of left-eye images and right-eye images.

By alternating the polarization states of left-eye images and right-eye images, stereoscopic content may be displayed and viewed. By rapidly alternating the polarization and images at faster than the flicker-fusion frequency, the appearance of moving images may be obtained.

Polarization preserving optical elements are used to transmit or reflect light without changing its polarization state. If two orthogonal polarization states are transmitted and reflected multiple times by the optical elements in a polarization preserving optical system, the two orthogonal polarization states are maintained in the original two orthogonal polarization states. Birefringence is the property of optical elements that describes the case where different directions have different indices of refraction. Birefringence generally leads to changes in polarization state, so low birefringence is usually desirable when designing polarization preserving optical systems.

FIG. 12 shows a stereoscopic display system. Light source 1200 illuminates projector 1202. Projector 1202 projects an image with lens 1204. Projector 1202 and lens 1204 illuminate polarizing filter 1206 which polarizes the light into one polarization state. After polarizing filter 1206, the light passes into polarization switch 1208 which actively switches the light into two orthogonal polarization states in synchronization with projector 1202 displaying left and right eye images. The light then passes to polarization-preserving screen 1210 to form projected image 1212 on polarization-preserving screen 1210. In this system, the images for one eye are displayed with one orthogonal polarization state while the images for the other eye are displayed with the other orthogonal polarization state.

FIG. 13 shows a stereoscopic display system with a polarization-switching light source. Polarization-switching light source 1300 illuminates polarization-preserving projector 1302. Polarization-preserving projector 1302 projects an image with lens 1304. Polarization-switching light source 1300 switches the light into two orthogonal polarization states in synchronization with polarization-preserving projector 1302 displaying left and right eye images. Polarization-preserving projector 1302 and polarization-preserving lens 1304 illuminate polarization-preserving screen 1310 to form projected image 1312 on polarization-preserving screen 1310. As in the system of FIG. 12, the images for one eye are displayed with one orthogonal polarization state while the images for the other eye are displayed with the other orthogonal polarization state.

FIG. 14 shows the details of a polarization-preserving projector design. Light from polarization-switching light source 1420 enters lens system 1400. Lens system 1400 passes the light to TIR prism 1422 which consists of first TIR subprism 1402 and second TIR subprism 1412. The light enters first TIR subprism 1402 and reflects off the interface between first TIR subprism 1402 and second TIR subprism 1412. Then the light exits first TIR subprism 1402 and enters Philips prism 1424 which consists of first Philips subprism 1404, second Philips subprism 1406, and third Philips subprism 1408. The light enters first Philips subprism 1404 and passes to the interface between first Philips subprism 1404 and second Philips subprism 1406. At the interface between first Philips subprism 1404 and second Philips subprism 1406, the blue wavelength region of the light is reflected and the green and red wavelength regions of the light are transmitted. The blue light reflects off the surface of first Philips subprism 1404, then reflects from blue polarization-preserving SLM 1416, then reflects off the surface of first Philips subprism 1404, then reflects off the interface between first Philips subprism 1404 and second Philips subprism 1406 to rejoin the main beam to exit from Philips prism 1424. The green light passes into second Philips subprism 1406, then into third Philips subprism 1408, then reflects from green polarization-preserving SLM 1410, then rejoins the main beam to exit from Philips prism 1424. The red light reflects from the interface between second Philips subprism 1406 and third Philips subprism 1408, reflects off the surface of second Philips subprism 1406, then reflects from red polarization-preserving SLM 1418, then reflects from the interface of first Philips subprism 1404 and second Philips subprism 1406, then reflects from the interface of second Philips subprism 1406 and third Philips subprism 1408 to join the main beam and to exit from Philips prism 1424. The beam with all three colors modulated by polarization-preserving SLMs 1410, 1416, and 1418 passes again through TIR prism 1422 and then passes through polarization-preserving lens 1414 to form a projected digital image.

FIG. 15 shows a polarization-switching light source. Linearly polarized light source 1500 forms linearly polarized light beam 1502. Linearly polarized light beam 1502 passes through quarter wave plate 1504 which produces right-hand circularly polarized light beam 1506. Right-hand circularly polarized light beam 1506 passes through polarization switch 1518 which consists of dummy plate 1508, half wave plate 1512, rotor 1514, and motor 1516. Dummy plate 1508 and half wave plate 1512 form rotating disk 1520 which spins around rotor 1514 and is powered by motor 1516. Right-hand circularly polarized light beam 1506 passes alternately through dummy plate 1508 and half wave plate 1512 as they spin around rotor 1514. When right-hand circularly polarized light beam 1506 passes through dummy plate 1508, there is no effect on the polarization and beam 1510 is still right-hand circularly polarized. When right-hand circularly polarized light beam 1506 passes through plate 1512, the polarization of beam 1510 is changed to become left-hand circularly polarized. Polarization switch 1518 is synchronized with a projector to produce left-eye images polarized with one circular polarization state (e.g. right-hand) and right eye images with the orthogonal circular polarization state (e.g. left-hand). Alternately, quarter wave plate 1504 may be arranged to produce left-hand circularly polarized light in which case half wave plate 1512 changes the polarization to right-hand circularly polarized light.

FIG. 16 shows a front view of rotating disk 1520 in polarization switch 1518. Disk 1520 rotates clockwise as shown by arrow 1602. Right-hand circularly polarized light beam 1506 passes through disk 1520 at the position shown by arrow 1600. Alternately, the disk may rotate counterclockwise.

FIG. 17 shows a method of stereoscopic projection. In step 1700, polarization-switched light is generated. In step 1702, the polarization switched light is modulated to make a left-eye digital image and a right-eye digital image. In step 1704, the left-eye digital image and the right-eye digital image are projected for viewing. The modulation in step 1702 may be in synchronization with the polarization of the polarization-switched light so that the image for the left eye is polarized in one state, and the image for the right eye is polarized in the orthogonal state.

Polarization-switching light sources may be constructed by polarizing a naturally unpolarized source of light such as an arc lamp. In this case, the polarizer may be an absorptive polarizer such as polarizing film that absorbs the unwanted polarization of light. A more efficient system makes use of polarization recovery to repolarize the unwanted polarization state so that there is more light in the desired polarization state. Another method is to start with an inherently polarized light source such as a polarized laser that may be a solid state laser, diode pumped solid state laser, gas laser, or OPO.

A polarization switch may be used to actively change the polarization state of the polarization-switching light source. A polarization switch may be mechanical such as the one shown in FIG. 15, or it may be an electro-optical or magneto-optical device such as a polarization cell based on the Pockels effect, Faraday effect, Kerr effect, or any other polarization-controlling optical element. The polarization switch may be built into the light source or it may be a separate element immediately after the light source which operates on light emitted by the light source in which case the light source and polarization switch together are considered to be a polarization-switching light source. When utilized for stereoscopic projection, the polarization switch should not spend significant time switching between states because the time between states may contribute to ghosting.

Wave plates may be also used to change polarization states of light. Achromatic wave plates make the same change in polarization across all wavelengths in a certain design region. When held at the proper rotational orientation relative to the beam direction of propagation, quarter wave plates make a 90 degree phase difference in the horizontal and vertical electric field vectors such that linearly polarized light is converted to circularly polarized light and vice versa. Half wave plates make a 180 degree phase difference such that linearly or circularly polarized light is converted to the orthogonal polarization state. Wave plates may be made of birefringent crystals cut as a specific orientation, or they may be made from birefringent plastic film with specific retardation in each axis. Achromatic wave plates may be made from a stack of multiple layers of plastic film at specific orientations such as those manufactured by ColorLink Inc. (Boulder, Colo.).

A polarization-preserving projector may be constructed by using optical components that are themselves polarization preserving. If all the lenses, prisms, SLMs, minors and other optical components of the projector are polarization preserving, the overall projector will be polarization preserving. Optical components are polarization preserving if they cause an acceptably low level of polarization changes for two orthogonal polarization states. Optical effects which can cause polarization changes include scattering, retardation, and polarization splitting. Scattering is an inherently depolarizing process. Retardation may occur from randomly distributed birefringence regions in plastic optical elements. Polarization splitting is caused at optical surfaces by differences in reflected or transmitted intensities of light that are of two different polarization states. Optical surfaces with a very high transmission or reflection throughout the wavelengths of operation generally have minimal polarization splitting. Certain AR coatings and all total internal reflection surfaces have minimal polarization splitting as long as the wavelengths and angles fall within their designed range of operation. Also, most coatings and materials have minimal polarization splitting when the AOI is low. The AOI for a ray of light incident on a surface is defined as the angle between the incident ray of light and the perpendicular to the surface. If the AOI is zero degrees, mirrors and transmissive surfaces have zero polarization splitting. If the AOI is 5 degrees, aluminum mirrors have approximately 0.1% polarization splitting and typical AR coatings have approximately 0.01%. If the AOI is 10 degrees, aluminum mirrors have approximately 0.2% polarization splitting and typical AR coatings have approximately 0.05% in the photopically significant middle of the visible region of light which extends from approximately 500 nm to approximately 600 nm.

Optical elements constructed of high quality optical glass are generally inherently polarization preserving in the bulk of the material because the index of refraction is uniform throughout. Plastic optical elements, on the other hand, sometimes have retardation which leads to depolarizing or non-uniform polarization if the index of refraction varies throughout the plastic material.

Polarization preserving SLMs may be designed using DMDs such as those available from Texas Instruments (Dallas, Texas). Since the mirrors of a DMD are coated with a highly-reflecting material such as aluminum, the polarization splitting is low at small angles of operation which are typically 5 to 10 degrees AOI. If lower polarization splitting is desired, higher reflection coatings or other coatings with reduced polarization splitting may be used on the minors. In addition, AR coatings on the DMD window may help reduce polarization splitting of the DMD.

Glass TIR prisms may be designed to be polarization preserving. The interface between the two subprisms of a TIR prism has an air gap with AR coatings on both of the surfaces that form the air gap. In the example of FIG. 14, the AOI at the point where the beam passes through the air gap and AR coatings is 36 degrees. The transmission through the AR-coated surfaces of the TIR prism may have low polarization splitting if the AR-coating is designed to minimize polarization splitting. Between 500 and 600 nm, the polarization splitting may be less than 0.2%.

Philips prisms may be used for color splitting and recombining as described in detail in U.S. Pat. No. 3,659,918 the complete disclosure of which is incorporated herein by reference. Philips prisms with low polarization splitting may be constructed as described in “Design of Non-Polarizing Color Splitting Filters used for Projection Display System” by W. Chen et al., Displays, Elsevier, 2005, the complete text of which is incorporated herein by reference. The Philips prisms used by Chen have coatings designed with standard techniques of optical thin film design so that polarization splitting is reduced to near zero for all wavelengths of operation.

Polarization-preserving front-projection screens are commercially available with matte metallic coatings that diffusely reflect light while maintaining the polarization state with low depolarization. These screens are commonly used with polarization-based stereoscopic projection systems. Polarization-preserving rear projection screens are also available for use in rear projection systems.

Instead of using a projector that is polarization preserving, a projector that makes a known change in polarization states may be used as long as optical elements are included that perform compensating polarization adjustments after the light passes through the projector or internally in the projector so that the left and right eye images are still orthogonal. ColorLink filters may be helpful compensation elements for this purpose because they may be designed to change the polarization of different colors by different amounts. For example, if the polarization state of a specific color is rotated because of polarization splitting in the Philips prism, the polarization of that color can be corrected by rotating that color back to the desired polarization state by adding a ColorLink filter at the output of the projector.

An advantage of using a polarized-laser light source with a polarization-preserving projector is the high efficiency compared to systems that start with an unpolarized light source. With DMD light valves, typical polarized projection systems lose at least 50% of the light when using an unpolarized light source. Even with polarization recovery, 20% of the light is generally lost when converting from unpolarized to polarized light.

As opposed to SLM-based projectors, scanning projectors do not use an SLM. Instead they have a spot or line of light that is scanned over the area of the screen to form an image. Scanning projectors are typically based on laser light sources because the high collimation of the laser beam allows the projector to form a small spot at a distance. When compared to scanning projectors, SLM-based projectors typically have advantages in construction simplicity, alignment stability, and safety due to lower peak beam intensity.

In another aspect of the optical system shown in FIG. 1, a stereoscopic projection system separates left and right images by using spectral selection, for example as described in U.S. Pat. No. 6,283,597. In the spectral selection method, first wavelength bands of red, green, and blue are passed to the left eye, and second wavelength bands of red, green, and blue are passed to the right eye. The first bands and second bands are distinct so that there is little or no overlap between the first and second bands. First laser light source 102 may be used to provide the first bands of red, green, and blue light and second laser light source 116 or third laser light source 120 may be used to provide the second bands of red, green, and blue light. Specific embodiments are described in the following paragraphs but are not meant to be limiting in any way.

FIG. 18 shows the general layout of a stereoscopic image projection system. Projector 1800 emits light beam 1804 from lens 1802. Light beam 1804 impinges on screen 1806 and reflects light beam 1808 through filter glasses 1810 to the eyes 1812 of viewer 1814. Projector 1800 may form distinct images for each eye 1812 by time sequencing different images for each eye 1812. Alternately, projector 1800 may be two separate projectors, one forming the image for the left eye and one forming the image for the right eye.

FIG. 19 shows an example of the operation of projector 1800 which includes light system 1918 and projection engine 1916. Light system 1918 emits first light beam segment 1900 into projection engine 1916. First light beam segment 1900 enters mixing rod 1902 which forms second light beam segment 1904. Second light beam segment 1904 enters lens 1906 which forms third light beam segment 1920. Third light beam segment 1920 enters splitting prism 1908 which forms fifth light beam segment 1922. Fifth light beam segment 1922 enters color prism 1910 and is separated into three colors which then impinge on light valves 1912. Each light valve 1912 forms an image in a distinct color and then the imaged light beams are combined by color prism 1910 and sent back along the path of fifth light beam path segment 1922 into splitting prism 1908. Splitting prism 1908 outputs the imaged light beam as sixth light beam segment 1914 to form an image on screen 1806. Splitting prism 1908 may be a total TIR prism and color prism 1910 may be a Philips prism.

FIG. 20 shows one embodiment of light system 1918 which is based on two lasers. Nd:YLF laser 2000 generates light at 1047 nm which enters Nd:YLF gain module 2002, is optically amplified by gain module 2002, then enters SHG unit 2004 where it is converted to green light at 523.5 nm. The green light is rapidly switched by left/right switch 2006 so that it passes to either OPO 2008 or OPO 2010. A fraction of the 523.5 nm light in OPO 2008 is converted to 910 nm and a fraction is converted to 1230 nm. The 910 nm light exits OPO 2008 and is converted by SHG unit 2036 into 455 nm blue light. The 1230 nm light exits OPO 2008 and is converted by SHG unit 2038 into 615 nm red light. The 532.5 nm green light that is not lost in OPO 2008 or converted into blue or red light by OPO 2008, exits OPO 2008. The left/right switch 2006 may be synchronized with the display of left and right images to use the green laser light efficiently.

A fraction of the 523.5 nm light in OPO 2010 is converted to 880 nm and a fraction is converted to 1288 nm. The 880 nm light exits OPO 2010 and is converted by SHG unit 2042 into 440 nm blue light. The 1288 nm light exits OPO 2010 and is converted by SHG unit 2044 into 644 nm red light. The 532.5 nm green light that exits OPO 2010 goes into beam dump 2012.

Nd:YAP laser 2028 generates light at 1079.5 nm which enters Nd:YAP gain module 2030, is optically amplified by gain module 2030, then enters SHG unit 2040 where it is converted to green light at 539.7 nm.

The 455 nm blue light from OPO 2008 and the 440 nm blue light from OPO 2010 pass through blue filter 2014 and form light beam 2020. The 523.5 nm green light from OPO 2008 and the 539.7 nm green light from SHG unit 2040 pass through green filter 2016 and form light beam 2022. The 615 nm red light from OPO 2008 and the 644 nm red light from OPO 2010 pass through red filter 2018 and form light beam 2024. Light beams 2020, 2022, and 2024 are combined together to form light beam 1900.

OPO 2008, SHG unit 2036, and SHG unit 2038 form light generation unit 2032 which is used to form images for the left eye. Nd:YAP laser 2028, ND:YAP gain module 2030, SHG unit 2040, OPO 2010, SHG unit 2042, beam dump 2012, and SHG unit 2044 form light generation unit 2034 which is used to form images for the right eye. Alternately, light generation unit 2032 may be used for the right eye and light generation unit 2034 may be used for the left eye.

Light system 1918 as described in FIG. 20 may produce at least 50 watts of optical power including all six colors of output in light beams 2020, 2022, and 2024. If the total optical power output is 100 watts, Nd:YLF laser 2000 may produce about 2 watts of 1047 nm light and Nd:YLF gain module 2002 may produce about 300 watts of 1047 nm light. Nd:YAP laser 2028 may produce about 2 watts of 1079.5 nm light and Nd:YAP gain module 2030 may produce about 60 watts of 1079.5 nm light.

FIG. 21 shows another embodiment of light system 1918 which is based on three lasers. Nd:YLF laser 2100 generates light at 1047 nm which enters Nd:YLF gain module 2102, is optically amplified by gain module 2102, then enters SHG unit 2104 where it is converted to green light at 523.5 nm and enters OPO 2108. A fraction of the 523.5 nm light in OPO 2108 is converted to 910 nm and a fraction is converted to 1230 nm. The 910 nm light exits OPO 2108 and is converted by SHG unit 2136 into 455 nm blue light. The 1230 nm light exits OPO 2108 and is converted by SHG unit 2138 into 615 nm red light. The 532.5 nm green light that is not lost in OPO 2108 or converted into blue or red light by OPO 2108, exits OPO 2108.

Nd:YLF laser 2148 generates light at 1047 nm which enters Nd:YLF gain module 2150, is optically amplified by gain module 2150, then enters SHG unit 2152 where it is converted to green light at 523.5 nm and enters OPO 2110. A fraction of the 523.5 nm light in OPO 2110 is converted to 880 nm and a fraction is converted to 1288 nm. The 880 nm light exits OPO 2110 and is converted by SHG unit 2144 into 440 nm blue light. The 1288 nm light exits OPO 2110 and is converted by SHG unit 2146 into 644 nm red light. The 532.5 nm green light that exits OPO 2110 goes into beam dump 2112.

Nd:YAP laser 2128 generates light at 1079.5 nm which enters Nd:YAP gain module 2130, is optically amplified by gain module 2130, then enters SHG unit 2142 where it is converted to green light at 539.7 nm.

The 455 nm blue light from OPO 2108 and the 440 nm blue light from OPO 2110 pass through blue filter 2114 and form light beam 2120. The 523.5 nm green light from OPO 2108 and the 539.7 nm green light from SHG unit 2142 pass through green filter 2116 and form light beam 2122. The 615 nm red light from OPO 2108 and the 644 nm red light from OPO 2110 pass through red filter 2118 and form light beam 2124. Light beams 2120, 2122, and 2124 are combined together to form light beam 2100. The blue, green, and red filters may be band pass filters that block visible colors and infrared light of wavelengths outside the pass band.

Nd:YLF laser 2100, Nd:YLF gain module 2102, SHG unit 2104, OPO 2108, SHG unit 2136, and SHG unit 2138 form light generation unit 2132 which is used to form images for the left eye. Nd:YLF laser 2148, Nd:YLF gain module 2150, SHG unit 2152, OPO 2110, SHG unit 2144, beam dump 2112, SHG unit 2146, Nd:YAP laser 2128, ND:YAP gain module 2130, and SHG unit 2142, form light generation unit 2134 which is used to form images for the right eye. Alternately, light generation unit 2132 may be used for the right eye and light generation unit 2134 may be used for the left eye.

Light system 1918 as described in FIG. 21 may produce at least 50 watts of optical power including all six colors of output in light beams 2120, 2122, and 2124. If the total optical power output is 100 watts, Nd:YLF lasers 2100 and 2148 each produce about 2 watts of 1047 nm light and Nd:YLF gain module 2102 and 2150 each produce about 300 watts of 1047 nm light. Nd:YAP laser 2128 produces about 2 watts of 1079.5 nm light and Nd:YAP gain module 2130 produce about 60 watts of 1079.5 nm light.

FIG. 22 shows a method of generating light based on two lasers which corresponds to the laser light system shown in FIG. 20. In step 2200, a first beam of infrared laser light is generated. In step 2202, the first beam of infrared light is amplified. In step 2204, a first green light is generated by converting the first beam of infrared light to green light. In step 2206, the first green light is switched between left eye and right eye beams. In step 2208, the left, first green light is converted to second and third beams of infrared light. In step 2210, first red light and first blue light are generated by converting the second and third beams of infrared light. In step 2212, the remaining first green light, first red light, and first blue light are output by the method. In step 2214, the right, first green light is converted to fourth and fifth beams of infrared light. In step 2216, second red light and second blue light are generated by converting the fourth and fifth beams of infrared light. In step 2218, the remaining right, first green light is absorbed by a beam dump. In step 2222, a sixth beam of infrared laser light is generated. In step 2224, the sixth beam of infrared light is amplified. In step 2226, a second green light is generated by converting the sixth beam of infrared light to green light. In step 2220, the second green light, second red light, and second blue light are output by the method.

FIG. 23 shows a method of generating light based on three lasers which corresponds to the laser light system shown in FIG. 21. In step 2300, a first beam of infrared laser light is generated. In step 2302, the first beam of infrared light is amplified. In step 2304, a first green light is generated by converting the first beam of infrared light to green light. In step 2306, the first green light is converted to second and third beams of infrared light. In step 2308, first red light and first blue light are generated by converting the second and third beams of infrared light. In step 2310, the remaining first green light, first red light, and first blue light are output by the method. In step 2312, a fourth beam of infrared laser light is generated. In step 2314, the fourth beam of infrared light is amplified. In step 2316, a second green light is generated by converting the first beam of infrared light to green light. In step 2318, the second green light is converted to fifth and sixth beams of infrared light. In step 2320, second red light and second blue light are generated by converting the fifth and sixth beams of infrared light. In step 2322, the remaining second green light is absorbed by a beam dump. In step 2326, a seventh beam of infrared laser light is generated. In step 2328, the seventh beam of infrared light is amplified. In step 2330, a third green light is generated by converting the seventh beam of infrared light to green light. In step 2324, the third green light, second red light, and second blue light are output by the method.

OPOs such as those shown in elements 2008, 2010, 2108, and 2110 in FIGS. 20 and 21 use parametric amplification to convert a fraction of the input light into two other wavelengths. By suitably designing the OPO and controlling operation parameters such as temperature, when the input light is green, the outputs may be blue and red, thus making all three colors required for a full-color projection display. By mixing red, green, and blue light, other colors may be generated in projector 1800. In FIG. 20, OPO 2008 and OPO 2010 are controlled at different temperatures in order to make different output wavelengths. In FIG. 21, OPO 2108 and OPO 2110 are controlled at different temperatures in order to make different output wavelengths. In order to achieve the desired color of white light (also called the white point), there must be a certain fraction of red light, blue light, and green light mixed together. If the OPO under converts green light into blue light and red light, some green light must be wasted when forming white light. If the OPO over converts green light into blue light and red light, the OPO conversion efficiency can be controlled by slightly detuning the OPO in order to attain the desired white point. An optical sensor such as a color sensor may be employed for real time sensing of the white point and real time control of the OPO tuning to maintain the desired white point over time. An intensity sensor may likewise be employed for real time sensing of the output power and real time control of the light system output to maintain the desired output intensity over time. Alternately, each color channel can be monitored separately with an optical sensor to achieve the desired white point and overall output intensity. The outputs from the color or intensity sensors may be electrical signals that feed into electronic circuits that control the intensity of each color channel.

The OPOs shown in FIGS. 20 and 21 may be constructed from LBO crystals operated in the type I, noncritical phase matching mode. In this condition, the temperature of OPO 2008 and OPO 2108 may be 131 degrees Celsius and the temperature of OPO 2010 and OPO 2110 may be 137 degrees Celsius. The resultant output wavelengths of the laser light systems in FIGS. 20 and 21 may be 523.5 nm, 539.7 nm, 615 nm, 644 nm, 455 nm, and 440 nm. The wavelengths may vary 1 or 2 nm from these values without changing the essential nature of operation.

Laser light systems enable light to be generated in the narrow bands required by the spectrally selective stereoscopic glasses. This allows high brightness images even when projected on large screen sizes. Conventional projector light sources, such as Xenon bulbs, must be filtered to produce narrow bands and thus are highly inefficient leading to brightness limitations, especially for large screen sizes. Laser light systems also produce narrower bands than filtered Xenon sources which allow the colors to be better placed for achieving optimal color gamut and optimal isolation between the two eyes to reduce ghosting.

Gain modules such as those shown in FIGS. 20 and 21 use stimulated emission from a gain medium to amplify light so that the output beam has higher power than the input beam. The detailed operation of gain modules is described in U.S. Pat. No. 5,774,489, the complete disclosure of which is incorporated herein by reference. Gain modules include one or more stages of gain where each stage of gain includes one gain slab and associated pump lasers.

SHG units such as those shown in SHG units 2004, 2036, 2038, 2040, 2042, 2044, 2104, 2136, 2138, 2152, 2142, 2144, and 2146 in FIGS. 20 and 21 use nonlinear optical processes to convert the wavelength of the original light into a harmonic wavelength such as half the original wavelength. The detailed operation of SHG units is described in U.S. Pat. No. 4,019,159, the complete disclosure of which is incorporated herein by reference.

The wavelengths of light used for spectrally-selective stereoscopic imaging can be any wavelengths that can be filtered such that one set of wavelengths arrives only at one eye, and the other set arrives only at the other eye. There may be one wavelength for each eye, two wavelengths for each eye, three wavelengths for each eye, or more. The case of three wavelengths for each eye (six colors total) is the minimum number of wavelengths to produce a full color image. In the case of four wavelengths for each eye, a larger gamut of colors can be expressed than in the case of three wavelengths for each eye. The wavelengths described in FIGS. 20 and 21 may be adjusted to fit the requirements of the individual projection systems or available wavelength selective glasses.

The FWHM bandwidths of the wavelength bands may be as narrow as 0.05 nm or as wide as 20 nm depending on the types of lasers used and the construction of the OPOs, gain modules, SHG units, and filters. Narrow wavelength bands are generally subject to increased visible speckle when compared to wider bands. Laser light systems allow a larger color gamut than conventional light sources such as Xenon lamps. Particularly in the green region of the color gamut, an alternate color space is available because laser light systems allow substantial generation of light at 532.5 nm rather than the typical green wavelength of Xenon lamps which is centered near 546 nm.

The color gamut of the laser light system may be tuned by changing the operation temperature of the nonlinear element in the OPO or other parameter of the OPO such that the red and blue wavelengths are shifted. Typically, when the red wavelength shifts towards the center of the visible wavelength band, the blue also shifts towards the center of the visible. This makes a direct tradeoff between size of the color gamut and brightness because when the red and blue are shifted towards the center of the visible wavelength band, the human eye perceives higher brightness according to the photopic sensitivity curve whereas when the red and blue are shifted away from the center of the visible wavelength band, the color gamut is larger, but the human eye perceives less brightness.

Q-switched lasers are often best to achieve the high power densities required for the nonlinear effects in OPOs and SHG units. The Q-switching frequency may be in the range of 20 kHz to 300 kHz, with pulse widths of 5 ns to 100 ns. Continuous wave (also called oscillator) lasers may alternately be used in some cases such as is shown in lasers 2028 and 2128 of FIGS. 20 and 21.

Spectrally selective glasses, as shown in FIG. 18, allow left eye images to be transmitted to only the left eye and right eye images to be transmitted to only the right eye. The narrow bands of light from laser light systems enable the efficient use of narrow transmission bands in the spectrally selective glasses which has the benefits of reduced ghosting and improved rejection of ambient light. Glasses may be active (shutter) glasses or passive (non-shutter) glasses. In the case of active glasses, the glasses may be synchronized with the pulses of the laser light system to attain high system efficiency.

Various projector types can be used with laser light systems. In addition to the DMD design shown in FIG. 19, laser light systems can be used with LCOS light valves, LCD light valves, and other types of light valves. The design of the projector will be different for each type of light valve, but the laser light system may generally be substituted for a xenon or other broad band light source with very few or no changes in the projector design. This allows after-market substitution of the laser light system. If the projector is to be designed specifically for operation with a laser light system, the projector may be designed with a low etendue that matches the low etendue of the laser light system. This may allow the projector to generate higher contrast images compared to a projector with higher etendue. Polarized laser light systems may allow more efficient light throughput when combined with light valves that operate with polarized light such as LCD and LCOS light valves. The polarization may be linear or circular.

In another aspect of the optical system shown in FIG. 1, dual illumination is used to illuminate two parts of each SLM in a projector. First laser light source 102 may be used to illuminate the first part of the SLMs and second laser light source 116 may be used to illuminate the second part of the SLMs. Dual illumination may allow reduced complexity in the optical system compared to using separate sets of SLMs. Specific embodiments are described in the following paragraphs but are not meant to be limiting in any way.

Split image projection has the advantage of using fewer SLMs and other optical components compared to simultaneous projection. Split image projection also has the advantage of not requiring active glasses such as those used in time sequential projection. Technological progress leads towards ever higher and higher pixel counts per SLM which also tends to favor using more than one image per SLM while still allowing sufficient pixels in each image to achieve high resolutions such as 1920×1080 pixels (full high definition) which is also known as 2K. Very high resolution 4K SLMs, (which may be 4096×2160 resolution) are available for cinema applications. Two 2K images may be processed on two parts of one 4K SLM. In the case of stereoscopic projection, one of the 2K images may be viewed by the left eye, and the other 2K image may be viewed by the right eye. Dual illumination allows one low-etendue light source to illuminate one part of the SLM, and a second low-etendue light source to illuminate a second part of the same SLM. Other advantages of low-etendue light sources will also be seen in the following examples.

FIG. 24 shows a projector optical design with dual illumination using LCOS SLMs. First light source 2400 produces first beam segment 2402 which is spread by first lens system 2404 to make second beam segment 2406. Second beam segment 2406 is homogenized by first mixing rod 2408 to produce third beam segment 2410. Third beam segment 2410 is collimated by second lens system 2412 to form fourth beam segment 2414. Fourth beam segment 2414 partially reflects from first DBS 2432 to form fifth beam segment 2472 and partially transmits to form sixth beam segment 2436. Fifth beam segment 2472 reflects from first mirror 2475 to form seventh beam segment 2476. Seventh beam segment 2476 enters first PBS 2480 and is reflected to form eighth beam segment 2484. Eighth beam segment 2484 is processed by first SLM 2485 which rotates the polarization of each pixel depending on the desired brightness of the pixel and reflects eighth beam segment 2484 back along its input path to reenter first PBS 2480. On a pixel-by-pixel basis, if the polarization is not changed relative to the input beam, the light reflects inside first PBS 2480 to go back towards first light source 2400. If the polarization has been changed relative to the input beam, some or all of the light (depending on how much the polarization has been changed) passes through first PBS 2480 to form ninth beam segment 2486.

Sixth beam segment 2436 partially reflects from second DBS 2438 to form tenth beam segment 2458 and partially transmits to form eleventh beam segment 2442. Tenth beam segment 2458 enters second PBS 2460 and is reflected to form twelfth beam segment 2464. Twelfth beam segment 2464 is processed by second SLM 2466 which rotates the polarization of each pixel depending on the desired brightness of the pixel and reflects twelfth beam segment 2464 back along its input path to reenter second PBS 2460. On a pixel-by-pixel basis, if the polarization is not changed relative to the input beam, the light reflects inside second PBS 2460 to go back towards first light source 2400. If the polarization has been changed relative to the input beam, some or all of the light (depending on how much the polarization has been changed) passes through second PBS 2460 to form thirteenth beam segment 2468.

Eleventh beam segment 2442 enters third PBS 2444 and is reflected to form fourteenth beam segment 2446. Fourteenth beam segment 2446 is processed by third SLM 2450 which rotates the polarization of each pixel depending on the desired brightness of the pixel and reflects fourteenth beam segment 2446 back along its input path to reenter third PBS 2444. On a pixel-by-pixel basis, if the polarization is not changed relative to the input beam, the light reflects inside third PBS 2444 to go back towards first light source 2400. If the polarization has been changed relative to the input beam, some or all of the light (depending on how much the polarization has been changed) passes through third PBS 2444 to form fifteenth beam segment 2454.

First beam combiner 2488 combines ninth beam segment 2486, thirteenth beam segment 2468, and fifteenth beam segment 2454 to form sixteenth beam segment 2490. Sixteenth beam segment 2490 reflects from second minor 2491 to form seventeenth beam segment 2493. Seventeenth beam segment 2493 reflects from third DBS 2492 to form beam segment 2494.

Second light source 2416 produces eighteenth beam segment 2418 which is spread by third lens system 2420 to make nineteenth beam segment 2422. Nineteenth beam segment 2422 is homogenized by second mixing rod 2424 to produce twentieth beam segment 2426. Twentieth beam segment 2426 is collimated by fourth lens system 2428 to form twenty-first beam segment 2430. Twenty-first beam segment 2430 partially reflects from first DBS 2432 to form twenty-second beam segment 2474 and partially transmits to form twenty-third beam segment 2434. Twenty-second beam segment 2474 reflects from first minor 2475 to form twenty-fourth beam segment 2478. Twenty-fourth beam segment 2478 enters first PBS 2480 and is reflected to form twenty-fifth beam segment 2482. Twenty-fifth beam segment 2482 is processed by first SLM 2485, which rotates the polarization of each pixel depending on the desired brightness of the pixel and reflects twenty-fifth beam segment 2482 back along its input path to reenter first PBS 2480. On a pixel-by-pixel basis, if the polarization is not changed relative to the input beam, the light reflects inside first PBS 2480 to go back towards first light source 2400. If the polarization has been changed relative to the input beam, some or all of the light (depending on how much the polarization has been changed) passes through first PBS 2480 to form twenty-sixth beam segment 2487.

Twenty-third beam segment 2434 partially reflects from second DBS 2438 to form twenty-seventh beam segment 2456 and partially transmits to form twenty-eighth beam segment 2440. Twenty-seventh segment 2456 enters second PBS 2460 and is reflected to form twenty-ninth beam segment 2462. Twenty-ninth beam segment 2462 is processed by second SLM 2466, which rotates the polarization of each pixel depending on the desired brightness of the pixel and reflects twenty-ninth beam segment 2462 back along its input path to reenter second PBS 2460. On a pixel-by-pixel basis, if the polarization is not changed relative to the input beam, the light reflects inside second PBS 2460 to go back towards first light source 2400. If the polarization has been changed relative to the input beam, some or all of the light (depending on how much the polarization has been changed) passes through second PBS 2460 to form thirtieth beam segment 2470.

Twenty-eighth beam segment 2440 enters third PBS 2444 and is reflected to form thirty-first beam segment 2448. Thirty-first beam segment 2448 is processed by third SLM 2450, which rotates the polarization of each pixel depending on the desired brightness of the pixel and reflects thirty-first beam segment 2448 back along its input path to reenter third PBS 2444. On a pixel-by-pixel basis, if the polarization is not changed relative to the input beam, the light reflects inside third PBS 2444 to go back towards first light source 2400. If the polarization has been changed relative to the input beam, some or all of the light (depending on how much the polarization has been changed) passes through third PBS 2444 to form thirty-second beam segment 2452.

First beam combiner 2488 combines twenty-sixth beam segment 2487, thirtieth beam segment 2470, and thirty-second beam segment 2452 to form thirty-third beam segment 2489. Thirty-third beam segment 2489 passes through third DBS 2492 to combine with seventeenth beam segment 2493 in forming thirty-fourth beam segment 2494. Thirty-fourth beam segment 2494 passes through fifth lens system 2495 to form thirty-fifth beam segment 2496 which passes outside of the projector to make a viewable image on a projection screen (not shown).

First beam combiner 2488 may be an X-prism. Second mirror 2491 and third DBS 2492 form second beam combiner 2497. First lens system 2404, second lens system 2412, third lens system 2420, fourth lens system 2428, and fifth lens system 2495 may be formed from a single lens or any number of lenses that guide the light beams into the desired positions. The sizes of components and distances between components are not shown to scale in FIG. 24. Some optical components may be positioned against other optical components so that there is no gap between the components. Auxiliary optical components such as polarizers, relay lenses, skew ray plates, polarization rotation plates, and trim filters are not shown in FIG. 24. The three SLMs shown in FIG. 24 may be each assigned to a primary color so that one is red, one is green, and one is blue. First light source 2400 may output sub-bands red 1, green 1, and blue 1 whereas second light source 2416 may output sub-bands red 2, green 2, and blue 2. First DBS 2432 may reflect blue while passing green and red. Second DBS 2438 may reflect green while passing red. Third DBS 2492 may reflect sub-bands red 1, green 1, and blue 1 while passing sub-bands red 2, green 2, and blue 2. First light source 2400 and second light source 2416 may output polarized light.

FIG. 25 shows a projector optical design with dual illumination using DMD SLMs. First light source 2502 produces first beam segment 2504 which is spread by first lens system 2506 to make second beam segment 2508. Second beam segment 2508 is homogenized by first mixing rod 2510 to produce third beam segment 2512. Third beam segment 2512 is collimated by second lens system 2514 to form fourth beam segment 2516. Fourth beam segment 2516 enters first subprism 2534 and reflects from the interface of first subprism 2534 and second subprism 2568 to form fifth beam segment 2538. Fifth beam segment 2538 partially reflects from the interface between third subprism 2540 and fourth subprism 2556 and then from the entrance face of third subprism 2540 to form sixth beam segment 2544. Fifth beam segment 2538 also partially transmits from the interface between third subprism 2540 and fourth subprism 2556 and partially transmits from the interface between fourth subprism 2556 and fifth subprism 2548 to form seventh beam segment 2552. Fifth beam segment 2538 also partially reflects from the interface between fourth subprism 2556 and fifth subprism 2548 and then reflects from the interface between fourth subprism 2556 and third subprism 2540 to form eighth beam segment 2560. Sixth beam segment 2544 is processed by first SLM 2546 which flips micromirrors for each pixel depending on the desired brightness of the pixel. For darker pixels, more light is directed back through the prism systems until the light is absorbed in a beam dump (not shown) and for brighter pixels, more light is directed to the output path which reflects from the entrance face of third subprism 2540 and then from the interface between third subprism 2540 and fourth subprism 2556 to form ninth beam segment 2566.

Seventh beam segment 2552 is processed by second SLM 2554 which flips micromirrors for each pixel depending on the desired brightness of the pixel. For darker pixels, more light is directed back through the prism systems until the light is absorbed in a beam dump (not shown) and for brighter pixels, more light is directed to the output path which passes through the interface between fifth subprism 2548 and fourth subprism 2556, then passes through the interface between fourth subprism 2556 and third subprism 2540 to join sixth beam segment 2544 in forming ninth beam segment 2566.

Eighth beam segment 2560 is processed by third SLM 2562 which flips micromirrors for each pixel depending on the desired brightness of the pixel. For darker pixels, more light is directed back through the prism systems until the light is absorbed in a beam dump (not shown) and for brighter pixels, more light is directed to the output path which reflects from the interface between fourth subprism 2556 and third subprism 2540, then reflects from the interface between fourth subprism 2556 and fifth subprism 2548, then passes through the interface between fourth subprism 2556 and third subprism 2540 to join sixth beam segment 2544 and seventh beam segment 2552 in forming ninth beam segment 2566.

Ninth beam segment 2566 passes through first subprism 2534 and second subprism 2568 to form tenth beam segment 2572. Tenth beam segment 2572 passes through first DBS 2578 to form eleventh beam segment 2580.

Second light source 2518 produces twelfth beam segment 2520 which is spread by third lens system 2522 to make thirteenth beam segment 2524. Thirteenth beam segment 2524 is homogenized by second mixing rod 2526 to produce fourteenth beam segment 2528. Fourteenth beam segment 2528 is collimated by fourth lens system 2530 to form fifteenth beam segment 2532. Fifteenth beam segment 2532 enters first subprism 2534 and reflects from the interface of first subprism 2534 and second subprism 2568 to form sixteenth beam segment 2536. Sixteenth beam segment 2536 partially reflects from the interface between third subprism 2540 and fourth subprism 2556 and then from the entrance face of third subprism 2540 to form seventeenth beam segment 2542. Sixteenth beam segment 2536 also partially transmits from the interface between third subprism 2540 and fourth subprism 2556 and partially transmits from the interface between fourth subprism 2556 and fifth subprism 2548 to form eighteenth beam segment 2550. Sixteenth beam segment 2536 also partially reflects from the interface between fourth subprism 2556 and fifth subprism 2548 and then reflects from the interface between fourth subprism 2556 and third subprism 2540 to form nineteenth beam segment 2558. Seventeenth beam segment 2542 is processed by first SLM 2546 which flips micromirrors for each pixel depending on the desired brightness of the pixel. For darker pixels, more light is directed back through the prism systems until the light is absorbed in a beam dump (not shown) and for brighter pixels, more light is directed to the output path which reflects from the entrance face of third subprism 2540 and then from the interface between third subprism 2540 and fourth subprism 2556 to form twentieth beam segment 2564.

Eighteenth beam segment 2550 is processed by second SLM 2554 which flips micromirrors for each pixel depending on the desired brightness of the pixel. For darker pixels, more light is directed back through the prism systems until the light is absorbed in a beam dump (not shown) and for brighter pixels, more light is directed to the output path which passes through the interface between fifth subprism 2548 and fourth subprism 2556, then passes through the interface between fourth subprism 2556 and third subprism 2540 to join seventeenth beam segment 2542 in forming twentieth beam segment 2564.

Nineteenth beam segment 2558 is processed by third SLM 2562 which flips micromirrors for each pixel depending on the desired brightness of the pixel. For darker pixels, more light is directed back through the prism systems until the light is absorbed in a beam dump (not shown) and for brighter pixels, more light is directed to the output path which reflects from the interface between fourth subprism 2556 and third subprism 2540, then reflects from the interface between fourth subprism 2556 and fifth subprism 2548, then passes through the interface between fourth subprism 2556 and third subprism 2540 to join seventeenth beam segment 2542 and eighteenth beam segment 2550 in forming twentieth beam segment 2564.

Twentieth beam segment 2564 passes through first subprism 2534 and second subprism 2568 to form twenty-first beam segment 2570. Twenty-first beam segment 2570 reflects from first mirror 2574 to form twenty-second beam segment 2576 and then reflects from first DBS 2578 to join tenth beam segment 2572 in forming eleventh beam segment 2580. Eleventh beam segment 2580 passes through fifth lens system 2582 to form twenty-third beam segment 2584 which passes outside of the projector to make a viewable image on a projection screen (not shown).

First subprism 2534 and second subprism 2568 form TIR prism 2588. Third subprism 2540, fourth subprism 2556, and fifth subprism 2548 form Philips prism 2586. Minor 2574 and DBS 2578 form beam combiner 2590. First lens system 2506, second lens system 2514, third lens system 2522, fourth lens system 2530, and fifth lens system 2582 may be formed from a single lens or any number of lenses that guide the light beams into the desired positions. The sizes of components and distances between components are not shown to scale in FIG. 25. Some optical components may be positioned against other optical components so that there is no gap between the components. Auxiliary optical components such as polarizers, relay lenses, skew ray plates, polarization rotation plates, and trim filters are not shown in FIG. 25. The three SLMs shown in FIG. 25 may be each assigned to a primary color so that one is red, one is green, and one is blue. First light source 2502 may output sub-bands red 1, green 1, and blue 1 whereas second light source 2518 may output sub-bands red 2, green 2, and blue 2. The interface between third subprism 2540 and fourth subprism 2556 may reflect blue while passing green and red. The interface between fourth subprism 2556 and fifth subprism 2548 may transmit green while reflecting red. First DBS 2578 may transmit sub-bands red 1, green 1, and blue 1 while reflecting sub-bands red 2, green 2, and blue 2.

FIG. 26 shows a projector optical design with dual illumination using transmissive LCD SLMs. First light source 2600 produces first beam segment 2602 which is spread by first lens system 2604 to make second beam segment 2606. Second beam segment 2606 is homogenized by first mixing rod 2608 to produce third beam segment 2610. Third beam segment 2610 is collimated by second lens system 2612 to form fourth beam segment 2614. Fourth beam segment 2614 partially reflects from first DBS 2632 to form fifth beam segment 2664 and partially transmits to form sixth beam segment 2636. Fifth beam segment 2664 reflects from first minor 2668 to form seventh beam segment 2672. Seventh beam segment 2672 is processed by first SLM 2674 which rotates the polarization of each pixel depending on the desired brightness of the pixel. On a pixel-by-pixel basis, depending on the amount of polarization rotation, the light is transmitted or absorbed to a varying degree by a polarizer (not shown) to form eighth beam segment 2676.

Sixth beam segment 2636 partially reflects from second DBS 2638 to form ninth beam segment 2681 and partially transmits to form tenth beam segment 2640. Ninth beam segment 2681 is processed by second SLM 2682 which rotates the polarization of each pixel depending on the desired brightness of the pixel. On a pixel-by-pixel basis, depending on the amount of polarization rotation, the light is transmitted or absorbed to a varying degree by a polarizer (not shown) to form eleventh beam segment 2684.

Tenth beam segment 2640 reflects from second minor 2644 to form twelfth beam segment 2648. Twelfth beam segment 2648 reflects from third mirror 2650 to form thirteenth beam segment 2654. Thirteenth beam segment 2654 is processed by third SLM 2656 which rotates the polarization of each pixel depending on the desired brightness of the pixel. On a pixel-by-pixel basis, depending on the amount of polarization rotation, the light is transmitted or absorbed to a varying degree by a polarizer (not shown) to form fourteenth beam segment 2660.

First beam combiner 2662 combines eighth beam segment 2676, eleventh beam segment 2684, and fourteenth beam segment 2660 to form fifteenth beam segment 2685. Fifteenth beam segment 2685 reflects from fourth mirror 2687 to form sixteenth beam segment 2688. Sixteenth beam segment 2688 reflects from third DBS 2690 to form seventeenth beam segment 2691.

Second light source 2616 produces eighteenth beam segment 2618 which is spread by third lens system 2620 to make nineteenth beam segment 2622. Nineteenth beam segment 2622 is homogenized by second mixing rod 2624 to produce twentieth beam segment 2626. Twentieth beam segment 2626 is collimated by fourth lens system 2628 to form twenty-first beam segment 2630. Twenty-first beam segment 2630 partially reflects from first DBS 2632 to form twenty-second beam segment 2666 and partially transmits to form twenty-third beam segment 2634. Twenty-second beam segment 2666 reflects from first minor 2668 to form twenty-fourth beam segment 2670. Twenty-fourth beam segment 2670 is processed by first SLM 2674 which rotates the polarization of each pixel depending on the desired brightness of the pixel. On a pixel-by-pixel basis, depending on the amount of polarization rotation, the light is transmitted or absorbed to a varying degree by a polarizer (not shown) to form twenty-fifth beam segment 2678.

Twenty-third beam segment 2634 partially reflects from second DBS 2638 to form twenty-sixth beam segment 2680 and partially transmits to form twenty-seventh beam segment 2642. Twenty-sixth beam segment 2680 is processed by second SLM 2682 which rotates the polarization of each pixel depending on the desired brightness of the pixel. On a pixel-by-pixel basis, depending on the amount of polarization rotation, the light is transmitted or absorbed to a varying degree by a polarizer (not shown) to form twenty-eighth beam segment 2683.

Twenty-seventh beam segment 2642 reflects from second mirror 2644 to form twenty-ninth beam segment 2646. Twenty-ninth beam segment 2646 reflects from third minor 2650 to form thirtieth beam segment 2652. Thirtieth beam segment 2652 is processed by third SLM 2656 which rotates the polarization of each pixel depending on the desired brightness of the pixel. On a pixel-by-pixel basis, depending on the amount of polarization rotation, the light is transmitted or absorbed to a varying degree by a polarizer (not shown) to form thirty-first beam segment 2658.

First beam combiner 2662 combines twenty-fifth beam segment 2678, twenty-eighth beam segment 2683, and thirty-first beam segment 2658 to form thirty-second beam segment 2686. Thirty-second beam segment 2686 passes through third DBS 2690 to combine with sixteenth beam segment 2688 in forming seventeenth beam segment 2691. Seventeenth beam segment 2691 passes through fifth lens system 2692 to form thirty-third beam segment 2693 which passes outside of the projector to make a viewable image on a projection screen (not shown).

First beam combiner 2662 may be an X-prism. Second mirror 2687 and third DBS 2690 form second beam combiner 2694. First lens system 2604, second lens system 2612, third lens system 2620, fourth lens system 2628, and fifth lens system 2692 may be formed from a single lens or any number of lenses that guide the light beams into the desired positions. The sizes of components and distances between components are not shown to scale in FIG. 26. Some optical components may be positioned against other optical components so that there is no gap between the components. Auxiliary optical components such as polarizers, relay lenses, skew ray plates, polarization rotation plates, and trim filters are not shown in FIG. 26. The three SLMs shown in FIG. 26 may be each assigned to a primary color so that one is red, one is green, and one is blue. First light source 2600 may output sub-bands red 1, green 1, and blue 1 whereas second light source 2616 may output sub-bands red 2, green 2, and blue 2. First DBS 2632 may reflect blue while passing green and red. Second DBS 2638 may reflect green while passing red. Third DBS 2690 may reflect sub-bands red 1, green 1, and blue 1 while passing sub-bands red 2, green 2, and blue 2. First light source 2600 and second light source 2616 may output polarized light.

FIG. 27 shows a portrait-oriented SLM with two images located one above the other. First image 2702 is formed in one part of SLM 2700 and second image 2704 is formed in another, distinct part of SLM 2700. First image 2702 and second image 2704 are located such that most of the un-used pixels are above and below each image. In the case of stereoscopic systems, first image 2702 may be the left eye image and second image 2704 may be the right eye image.

FIG. 28 shows a landscape-oriented SLM with two images located one above the other. First image 2802 is formed in one part of SLM 2800 and second image 2804 is formed in another, distinct part of SLM 2800. First image 2802 and second image 2804 are located such that most of the un-used pixels are on the left and right of each image. In the case of stereoscopic systems, first image 2802 may be the left eye image and second image 2804 may be the right eye image.

FIG. 29 shows a portrait-oriented SLM with two images far apart and located one above the other. First image 2902 is formed in one part of SLM 2900 and second image 2904 is formed in another, distinct part of SLM 2900. First image 2902 and second image 2904 are located such that most of the un-used pixels are between the two images. In the case of stereoscopic systems, first image 2902 may be the left eye image and second image 2904 may be the right eye image. By placing first image 2902 far from second image 2904 an increased guard band is formed between the two images that may reduce the amount of cross-talk or light spillage between the two images.

FIG. 30 shows a landscape-oriented SLM with two images located on the left and right of each other so that they form a central band across the horizontal center of the SLM. First image 3002 is formed in one part of SLM 3000 and second image 3004 is formed in another, distinct part of SLM 3000. First image 3002 and second image 3004 are located such that most of the un-used pixels are formed into one band above the images and one band below the images. In the case of stereoscopic systems, first image 3002 may be the left eye image and second image 3004 may be the right eye image.

FIG. 31 shows a landscape-oriented SLM with two images located one diagonal to the other. First image 3102 is formed in one part of SLM 3100 and second image 3104 is formed in another, distinct part of SLM 3100. First image 3102 and second image 3104 are located such that most of the un-used pixels are above and below the two images in diagonally opposite corners. In the case of stereoscopic systems, first image 3102 may be the left eye image and second image 3104 may be the right eye image.

FIG. 32 shows a landscape-oriented SLM with an anamorphic pattern of pixels with one image located above the other. First image 3202 is formed in one part of SLM 3200 and second image 3204 is formed in another, distinct part of SLM 3200. First image 3202 and second image 3204 use substantially all of the pixels in SLM 3200. An anamorphic lens may be used to compress the horizontal axis (relative to the vertical axis) or expand the vertical axis (relative to the horizontal axis) such that the final viewable images are formed with the desired aspect ratio. In the case of stereoscopic systems, first image 3202 may be the left eye image and second image 3204 may be the right eye image.

FIG. 33 shows a landscape-oriented SLM with a checkerboard pattern of pixels. Pixels of the first image on SLM 3300 are shown cross-hatched such as pixel 3302 and pixels of the second image on SLM 3300 are shown not cross-hatched such as pixel 3304. A 31×15 array of pixels is shown for clarity, but SLMs typically have many more pixels to form high resolution images. The checkerboard pattern uses substantially all the pixels of the SLM. In the case of stereoscopic systems, the first image may be the left eye image and second image may be the right eye image.

FIG. 34 shows low etendue illumination of an SLM and an optical component compared to high etendue illumination of the same SLM and optical component. First beam segment 3400 passes through optical component 3402 to form second beam segment 3404. Second beam segment 3404 passes through SLM 3406 to form third beam segment 3408. Alternatively, fourth beam segment 3410 passes through optical component 3402 to form fifth beam segment 3412. Fifth beam segment 3412 passes through SLM 3406 to form sixth beam segment 3414. First beam segment 3400, second beam segment 3404, and third beam segment 3408 have high etendue. Fourth beam segment 3410, fifth beam segment 3412, and sixth beam segment 3414 have low etendue. First beam segment 3400, second beam segment 3404, and third beam segment 3408 can be seen to have higher angles of incidence for rays near the edges of the beam segments. Fourth beam segment 3410, fifth beam segment 3412, and sixth beam segment 3414 can be seen to have lower angles of incidence for rays near the edges of the beam segments. Optical component 3402 may be any component that processes light such as a polarizer, skew ray plate, polarization rotation plate, interference filter, beamsplitter, minor, or lens assembly. Skew ray plates are used to compensate the polarization state of rays at high angle of incidence. Polarization rotation plates make a controlled change in polarization such as changing linear polarization to circular polarization. SLM 3406 may be any sort of SLM such as DMD, LCD, or LCOS. Optical component 3402 and SLM 3406 are shown operating in transmission, but may alternatively operate in reflection. Optical component 3402 is shown to in the light path before SLM 3406, but alternatively, optical component 3402 may be after SLM 3406. The included angles of beam segments shown in FIG. 34 are for illustrative purposes only. The actual beam angles may be larger or smaller depending on the design of the actual optical system.

FIG. 35 shows a flow chart of a method of dual illumination. In this method, an SLM is illuminated by two light sources. In step 3500, a first beam of light is generated. In step 3502, the first beam of light is processed by the first part of an SLM. In step 3504, a second beam of light generated. In step 3506, the second beam of light is processed by the second part of the same SLM. In optional step 3508, the first beam of light after processing is combined with the second beam of light after processing.

When considering a light source, etendue is an optical property that characterizes how spread out the light beam is in both area and angle. In simple terms, the approximate etendue of a light source may be computed by multiplying the emitting area of the source by the solid angle that the light beam subtends. Lasers have low etendue whereas arc lamps, filament lamps, and LEDs have high etendue. If the light source has sufficiently low etendue, it is possible to focus light through a subsequent optical system with high efficiency. Laser light sources enable the independent illumination of more than one part of an SLM with high brightness. As an example, the beam from a semiconductor laser may have a cross-sectional area of 1 mm2 and a beam divergence of 10 milliradians which makes an etendue of approximately 0.01 mm2 sr. Most lasers have etendues less than 0.1 mm2 sr, which allows effective illumination of multiple parts of an SLM. An example of a high etendue light source is an arc lamp which may have an emitting area of 3 mm2 and a beam divergence of 12.6 radians which makes an etendue of approximately 38 mm2 sr.

When considering an optical system which accepts light from a light source, etendue is the optical property that characterizes how much light the optical system can accept in both aperture area and angle. In simple terms, the approximate etendue of an optical system may be computed by multiplying the area of the entrance pupil by the solid angle of the light path as seen from the entrance pupil. For an optical system of a fixed etendue such as a projector SLM, associated lens systems, and auxiliary optical components, the etendue of the light source should be lower than or equal to the etendue of the optical system in order to efficiently illuminate the optical system without vignetting. Additional advantages may be gained by using an even lower source etendue. Low source etendue means that the angle of incidence is smaller, especially for rays that are near the edge of the beam. A low angle of incidence means that certain optical components may be simplified or may operate more effectively. For example, polarization uniformity may be improved in LCD and LCOS SLMs, skew ray plates may not be necessary, PBSs and polarization filters may have higher extinction ratios, multilayer interference filters may have less angle shift, and lens assemblies may be less subject to optical aberrations.

Prisms and beamsplitters are used in projectors and other optical systems to control the path of light beams. DBSs split or combine wavelength bands of light that form various colors and are usually constructed from interference coatings on flat substrates or prism surfaces. PBSs split or combine different polarizations of light and may be constructed from interference coatings, prisms, or by other techniques such as wire grids. Philips prisms consist of three subprisms with DBSs on two of the internal faces. TIR prisms have an air gap inside that makes total internal reflection when the incidence angle of the beam is greater than the critical angle. X-prisms consist of 4 subprisms assembled into a cube such that the internal surfaces have DBSs along both diagonal faces. Depending on their roles in the light path, prisms and beamsplitters may act as beam separators, beam combiners, or both at the same time.

SLMs may be one, two, or three-dimensional. In each case, an SLM processes an incoming beam of light to produce an outgoing beam of light which has pixels formed in a two-dimensional array. A one-dimensional SLM has a single pixel which is scanned in two directions to form a two-dimensional image. A one-dimensional SLM has pixels arranged in a one-dimensional line segment which is scanned in one direction to form a two-dimensional image. A two-dimensional SLM has pixels arranged in a two-dimensional shape such as a rectangle.

A mixing rod is used to make a light beam more spatially uniform and to form the beam into a specific cross-section, such as rectangular, so that the beams can better match the shape of an SLM. A mixing rod may be constructed from a solid rectangular parallelepiped where total internal reflection guides the rays of light inside to make multiple bounces within the mixing rod. In the case of dual illumination, there are two mixing rods, and a thin air gap may be used to keep the light within each rod while keeping the rods as close as possible. If the light sources are linearly polarized, orthogonal orientation of the mixing rods relative to the polarization state of the light will maintain the linear polarization state of the light sources. If circular polarization is desired at the output of the projectors, a quarter-wave rotation plate may be used to convert linear polarization to circular polarization. Alternatively, instead of mixing rods, other types of beam homogenizers may be used such as fly's eye lenses or diffusers.

Anamorphic lenses expand or compress one axis relative to the other, orthogonal axis. For example, an anamorphic lens may be used to compress the horizontal axis relative to the vertical axis, so that the 4:1 aspect ratios of the images in FIG. 32 become 2:1 aspect ratios. The use of an anamorphic lens allows substantially all of the pixels of SLM 3200 to be used for imaging so that there are few or no un-used pixels. A small number of un-used pixels may surround the images as guard bands if necessary to allow for alignment tolerances.

Projection lens systems such as fifth lens system 2495 in FIG. 24, fifth lens system 2582 in FIG. 25, and fifth lens system 2692 in FIG. 26 may consist of many individual lens elements that are combined into one lens system designed to project a large image onto a screen that is located many meters away from the projector. Functions such as image shifting, zooming, focusing, and other image control features may be built in the projection lens system. FIGS. 24 through 26 show a second beam combiner and one projection lens system, but alternatively, two projection lens systems may be used, one for each image. A second beam combiner is not necessary if two projection lens systems are used, but a beam separator may be required to increase the spacing between the two beams so that the beams can pass through the two projection lens systems.

Dual illumination of a projector is advantageous because light output may be increased relative to designs that use only one light source. This is particularly important for 3D projection systems that are often operated below desired brightness levels. Also, the light is efficiently used in a dual illumination system because the light is directed only to the pixels that form the images, and does not illuminate un-used pixels. In the configurations of FIGS. 32 and 33, a double benefit is that all the light is used and also all the pixels are used.

In one example of dual illumination, a wider gamut can be obtained by using more than three primary colors where the colors come from more than one light source. Red, green, and blue, may be generated by one light source whereas yellow (or yellow and cyan) may be generated by another light source. The two light sources may illuminate separate parts of an SLM or may overlap to illuminate the same part of the SLM.

In another example of dual illumination, an SLM may be illuminated with different wavelengths of the same primary color in order to reduce speckle. The checkerboard pattern of FIG. 33 may be illuminated such that the pixels that are cross-hatched process one wavelength of light, and the pixels that are not cross-hatched process another wavelength of light. The two wavelengths of light may be generated by two separate light sources, or may be generated by one light source with two output wavelengths. In the case where most of the speckle results from the green band, only the green band need be broken into two sub-bands to significantly reduce visible speckle.

Other optical systems include those with more than two light sources which may be utilized to illuminate two or more parts of each SLM, optical systems that are not imaging such as laser-beam spatial-shaping systems, optical systems that include non-visible light such as ultraviolet or infrared radiation, optical systems that use infrared radiation to simulate night-vision scenes, and optical systems that use inexpensive SLMs with resolution of 2K or less that are subdivided into more than one part.

In another aspect of the optical system shown in FIG. 1, novel assembly methods may be used to align and fasten the components of the optical system. In particular, the optical components of first laser light source 102, second laser light source 116, and third laser light source 120 need precise alignment and stable positioning over the operating lifetime of the optical system. Specific embodiments are described in the following paragraphs but are not meant to be limiting in any way.

The conventional method of assembling and aligning optical devices may be characterized as serial alignment. In this method, each optical component is placed into its approximate final location, and alignment is a sequential process where each optical component is aligned using the beam of light of the final device. Each component's position is adjusted in as many as six degrees of freedom to find a local optimum for that component, and then the process is repeated for every component until a satisfactory overall alignment is found. This is an iterative process where the local optimums depend upon each other, so each component may need to undergo the alignment process multiple times.

As an example, consider the alignment of a laser system which may have various optical components such as minors, lenses, optical gain stages, prisms, filters, polarization control elements, wavelength doublers, taps, and other optical components. Starting at the beginning of the light generation path, each optical component is aligned to a local maximum one by one in turn. If a proper combination of component positioning cannot be found by the time the last component is being aligned, prior components must be readjusted. There is no deterministic method to find which components must be readjusted or by how much, so a high level of skill and experience is required to decide which parts should be readjusted and by how much. This process is very time consuming and has no guarantee of success at the end.

As an aid to proper positioning of each optical component, kinematic mounts may be used to place optical components into a fixed location. Kinematic mounts consist of plates with locating features, such as balls and rollers, which exactly constrain the six degrees of freedom such that an optical component is held in a unique position without wobble. The optical component combined with one side of the kinematic mount forms an optical module. The mating side of the kinematic mount is held by a base plate. When the optical module is removed from the base plate and then put back onto the base plate, it will go back into the same position with high repeatability.

Referring now to the drawings, FIG. 36 shows a method of assembly for optical components. In step 3600, kinematic mounts of an optical module are mated to the matching kinematic mounts of a base plate. In step 3602, the optical module is held to the base plate by magnets or other holding mechanism. In step 3604, the module is aligned with the beam of the final optical device which is called the actual beam. In step 3606, steps 3600 through 3604 are repeated for each optical module in the optical system. In step 3608, the overall optical system is checked for proper functionality. If it is properly functional, step 3610 shows the assembly is finished. If not, step 3612 is to realign an optical module with the actual beam and return to step 3608 to check system functionality. Steps 3608 and 3612 are repeated until the system is properly functional.

FIG. 37 shows a method of assembly using pre-alignment with a reference beam rather than the actual beam. In step 3700, an optical module is aligned to a reference beam outside of the final optical device. In step 3702, the kinematic mounts of the optical module are mated to the matching kinematic mounts of a base plate. In step 3704, the optical module is held to the base plate by magnets or other holding mechanism. In step 3706, steps 3700 through 3704 are repeated for each optical module in the optical system. In step 3708, the overall optical system is checked for proper functionality. If it is properly functional, step 3712 shows the assembly is finished. If not, step 3710 is to adjust an alignment module with the actual beam. After the single adjustment in step 3710, the overall optical alignment of the system is finished as shown in step 3712.

FIG. 38 shows a method of assembly using pre-alignment with a reference beam, a chassis plate, and removal of the base plates. In step 3800, an optical module is aligned to a reference beam outside of the final optical device. In step 3802, the kinematic mounts of the optical module are mated to the matching kinematic mounts of a base plate. In step 3804, the optical module is held to the base plate by magnets or other holding mechanism. In step 3806, steps 3800 through 3804 are repeated for each optical module in the optical system. In step 3808, the overall optical system is checked for proper functionality. If it is properly functional, step 3812 is to fasten the optical modules to a chassis plate. If it is not properly functional, step 3810 is to adjust an alignment module with the actual beam. After the single adjustment in step 3810, the overall optical alignment of the system is finished and in step 3812, the optical modules are fastened to a chassis plate. In step 3814, the base plates are removed and the assembly is finished as shown in step 3816. Alternately, the base plates may not be removed so that they are present in the final assembly.

FIG. 39A shows a top view of base plate 3910 and FIG. 39B shows a side view of base plate 3910. The purpose of the base plate is to position and hold the optical module with kinematic mounts. Bottom plate 3900 has cavities 3902 which hold rollers 3904. Magnet 3906 is attached to bottom plate 3900.

FIG. 40A shows a side view of optical module 4020 and FIG. 40B shows a bottom view of optical module 4020. Module plate 4000 has balls 4002 mounted in its bottom surface. Optical component 4010 is attached to upper surface 4008 of module plate 4000. Light beam 4012 passes through optical component 4010. Magnet 4006 is attached to module plate 4000.

FIG. 41 shows a side view of optical module 4020 and base plate 3910 mated together with kinematic mounting. Balls 4002 fit against rollers 3904 to determine a unique kinematic mounting position for optical module 4020. Magnets 3906 and 4006 come close together but do not touch, in order to hold together optical module 4020 and base plate 3910.

FIG. 42 shows a side view of optical module 4020 and base plate 3910 mated together with kinematic mounting and chassis plate 4200 attached to the optical module. After chassis plate 4200 is attached to the optical module, base plate 3910 may be removed without disturbing the alignment of the optical module.

FIG. 43 shows six optical modules attached to chassis plate 4300. Each optical module has an optical component 4304, 4306, 4310, 4312, or 4314, and a module base plate 4302. Beam of light 4320 passes through the optical components 4304, 4306, 4310, 4312, and 4314. In this example, optical components 4304, 4308, 4310, and 4314 are beamsplitter and beam combining optical elements. Optical components 4306 and 4312 may be any optical elements that act on beam 4320 such as a lenses, gain stages, prisms, filters, polarizers, wavelength doublers, taps, etc. The balls and magnets of the optical modules are not shown in FIG. 43. More complex systems may be built using additional optical components in addition to those shown in FIG. 43.

FIG. 44 shows an assembly method using an alignment plate. In this method, an alignment plate forms a template that is used to align kinematic rollers on a holding plate. In step 4400, the alignment plate is placed on the holding plate. In step 4402, rollers and holding blocks are placed into holes in the alignment plate. In step 4404, the holding blocks are fastened to the holding plate to hold the rollers in the proper position as determined by the alignment plate. In step 4406, the rollers are fastened to the holding plate. In step 4408, the alignment plate is removed. In step 4410, optical modules are mated to the rollers on the holding plate in the kinematic positions determined by the rollers.

In FIG. 45A, a top view of an alignment plate and a holding plate are shown which may be used for the assembly method described in FIG. 44. Alignment plate 4502 has holes 4504. FIG. 45B shows the corresponding side view of the alignment plate. Alignment plate 4502 is placed on holding plate 4500. Rollers 4508 and holding blocks 4506 are placed in rectangular holes 4504. Holding blocks 4506 are pressed against rollers 4508 which are located against the sides of holes 4504. Holding blocks 4506 are fastened to holding plate 4500 to hold rollers 4508 in the proper position which is determined by the sides of holes 4504 in alignment plate 4502. The reference surfaces of alignment plate 4502 include the sides of holes 4504 and the bottom of alignment plate 4502. The reference surfaces may be formed by a high tolerance machining method such as electrical discharge machining so that tolerances can be kept on the order of a few micrometers. Holding plate 4500 may be manufactured by an inexpensive method such as casting without further high-precision machining steps.

The method shown in FIG. 37 results in an optical system alignment that is much quicker and easier to accomplish than the method shown in FIG. 36. In fact, the method shown in FIG. 36 may not converge to a functioning optical system for a fixed set of optical components. For the method in FIG. 37, no special skill is required for the alignment of the optical system because no iterations are required where guessing is necessary to figure out which optical elements to adjust and by how much. Also, the method in FIG. 36 generally requires large adjustment ranges on the order of 5 mm to cover the entire span that might be required. Finding the best alignment position in this large range is time-consuming. The method in FIG. 37 requires much smaller adjustment ranges on the order of 200 micrometers and finding the best alignment position in the small range is very quick. Another advantage of the method in FIG. 37 is that by changing pre-aligned optical modules, the system may be easily repaired. Also each optical module may be made and aligned in a different location or at a different company and then shipped to one location for assembly with only minimal final adjustment.

An advantage of the method shown in FIG. 38 and the device shown in FIG. 42 is that the base plates may be removed and the relatively inexpensive chassis plate may be substituted instead for the final assembly. Once the optical modules are fastened to the chassis plate, the base plates are no longer required to hold the optical modules in the proper position.

An advantage of the method shown in FIG. 44 and the device shown in FIGS. 45A and 45B is that the relatively high-tolerance and expensive alignment plate may be reused many times to align the optical modules. Once the rollers are held in the proper position, the alignment plate may be removed. The alignment plate is in effect “printing” the alignment positions onto the less expensive parts such as the holding plate.

FIG. 46A shows a schematic diagram of the alignment error bars of each optical component for the method of FIG. 36. FIG. 46B shows the alignment error bars of each optical component for the method of FIG. 37. The vertical axis represents the amount of error from nominal beam path 4600. The horizontal axis represents travel through the optical system. Note how ranges 4606 of FIG. 45B are smaller and close to nominal position 4600 compared to ranges 4602 in FIG. 45A. The result is that aligned beam 4608 is closer to nominal beam 4600 than aligned beam 4604. Whereas in the method of FIG. 36, the alignment objective is to align each module to the previous one, in the method of FIG. 37, the alignment objective is to make the beam of light travel in the correct location. Some optical components may require high tolerances such as apertures, and some may require lower tolerances such as lenses, but for the purpose of FIGS. 46A and 46B all tolerances are shown as equal.

In addition to the kinematic mounting method with three balls and three groves as described in FIGS. 39 through 41, other kinematic mounting methods may be used. Six points of contact are required to exactly determine the six degrees of freedom (three linear and three angular) of each optical component. As an example of a different kinematic mounting method, a flat-groove-pyramid kinematic mount has one ball that contacts a pyramid in three points, one ball that contacts a groove in two points, and one ball that contacts a flat at one point.

Holding methods are intended for temporary positioning during assembly. Various methods may be used to hold together the kinematic mounts of the optical module and the base plate. Magnets are shown in FIGS. 39 through 41. Other methods may include bolts, springs, and flexure blades. These methods generally allow the optical module to be easily removed from the base plate.

Flexure blades are thin strips of metal that are strong in two directions and flexible in one direction. Two orthogonal flexure blades fix an optical component in all six degrees of freedom.

Fastening methods are intended for permanent or semi-permanent attachment. Fastening methods include adhesives such as two-part epoxies or ultraviolet-cure epoxies, soldering, brazing, and welding. If an adhesive is used, the thickness of the bond line should be minimal so that there is no possibility of the glue expanding or contracting over time or with temperature changes. In the case of repair or rework, the fastening may be removed and a new component installed, aligned, and fastened again in place of the previous component. Robotic assembly techniques may be used if advantageous for cost, cleanliness, throughput, or other reasons.

When fastening methods are used rather than optical adjustment mounts such as angular or linear positioners, there are no adjustments to drift during the lifetime of the optical system. Also, there is a cost savings when no angular or linear positioners are required in the final product.

Kinematic mounts are not capable of withstanding large shocks such as those that might occur during transportation. Even when the balls and rollers are made of hard materials such as silicon nitride or hardened stainless steel, the point contacts of the curved surfaces tend to get flattened if there is too much pressure applied. Kinematic mounts made with conventional materials can withstand up to approximately 90 newtons (20 pounds) of force per ball before damage becomes a problem. Once flattened, the kinematic mount may have unacceptable wobble. An advantage of using the chassis as shown in FIG. 42 is that the kinematic mounts are removed so the entire assembly is ruggedized to withstand transportation or other environmental shock and vibration.

Using the method of FIG. 37 or 38, the entire optical system may be shipped to its final destination of usage in the unaligned state and then easily aligned on site. During shipping, the mating parts of the kinematic mounts may be separated completely or they may be separated only slightly to avoid damage from shock or vibration. A cam mechanism may be used to lift the optical modules from the base plates during shipping and then reseat them when the optical system is ready to be used.

The balls, rollers, and magnets in FIGS. 39A, 39B, 40A, 40B, 41, and 42 may be attached to their respective plates using epoxy. The minimum thickness of the plates to keep optical tolerances may be in the range of 5 mm thick to 15 mm thick depending on the size of the part. Many optical parts for laser applications must be controlled to a tolerance of a few arc-seconds in two angular directions and a few micrometers in two linear dimensions.

The segments of the beam path may form a rectilinear shape (meaning all angles between the segments are 180 degrees or 90 degrees) to reduce the alignment changes that result from thermal expansion and contraction of the entire optical assembly. All the vertical supporting structures may be constructed from the same material and all the horizontal supporting structures may be from the same material which may be different than the material of the vertical supporting structures. For example, all the vertical supporting structures may be constructed from stainless steel and all the horizontal supporting structures may be constructed from aluminum. Since there is generally more material in the horizontal supporting structures, a lightweight material such as aluminum may be used for the horizontal supporting structures. The base plate may be the primary horizontal supporting structure and the primary vertical supporting structures may be in the optical modules.

The method of FIG. 36 may result in a situation where the optical system may be functioning but close to the non-functioning state if it experiences thermal stress, aging, or other natural changes. For low-duty cycle systems such as medical laser applications, this may be sufficient, but for consistent operation for many hours per day, the method of FIG. 37 results in a more reliable optical system.

The object of the method in FIG. 37 is to position the path of the light beam into the proper location. The position of the optical modules depends on the proper position of the path of the light beam. Low tolerance parts may be used for the optical modules because the parts are aligned using the reference beam. The optical system may be aligned to reach the global maximum. In the method of FIG. 36, the opposite approach is used; the optical modules are positioned into desired locations and the position of the light beam depends on the position of each optical module. High tolerance parts are generally used to help make the alignment go quicker, but the optical system may only be aligned to a local maximum. The global maximum may not be reached.

In laser optical systems, collimated light beams generally have two angular degrees of freedom, azimuth and elevation, and two linear degrees of freedom, x and y, that must be adjusted to high tolerances. The remaining two degrees of freedom, roll and z, generally do not need to be adjusted. The z-direction is defined as the linear direction along the path of the beam.

In another aspect of the optical system shown in FIG. 1, a support structure with compartments and stackable layers may be used for the optical assembly of first laser light source 102, and if used, second laser light source 116 and third laser light source 120. The stacked compartmented support structure makes a stable optical assembly with low weight. Specific embodiments are described in the following paragraphs but are not meant to be limiting in any way.

The conventional method of assembling optical systems utilizes a rigid, flat, support structure that may be a solid block of metal or, to reduce weight, a honeycomb structure with a flat top. An optical system consists of a number of optical components. Each component needs to be aligned and fastened into the proper position for the entire system to function correctly. The optical components must be held in place over temperature changes and as the structure ages. There is a trade-off between rigidity and weight, because more material in the structure is generally necessary to make it more rigid.

FIG. 47A shows a top view of an optical assembly built on a flat support structure and FIG. 47B shows a side view of the same assembly. The optical assembly consists of optical modules which each have one or more optical components and the supporting structure. First light beam segment 4708 enters first optical module 4710 and is processed by first optical module 4710 to form second light beam segment 4712. Second light beam segment 4712 enters second optical module 4714 and is processed by second optical module 4714 to form third light beam segment 4716. Third light beam segment 4716 enters third optical module 4718 and is processed by third optical module 4718 to form fourth light beam segment 4720. Fourth light beam segment 4720 enters fourth optical module 4722 and is processed by fourth optical module 4722 to form fifth light beam segment 4724. Fifth light beam segment 4724 enters fifth optical module 4726 and is processed by fifth optical module 4726 to form sixth light beam segment 4728. The optical modules are mounted to flat support structure 4700. Each optical module performs an optical function such as focusing the light beam, amplifying the light beam, reflecting the light beam, or changing the wavelength of the light beam with nonlinear optics. The optical modules may be simple, consisting of single components such as lenses, minors, or filters, or the optical modules may be complex, consisting of multiple components in each optical module that form lasers, gain stages, second harmonic generators, or optical parametric oscillators. The optical modules may be mounted to the flat support structure using kinematic mounts. The light beams in FIG. 47 may be laser beams or may be other light beams such as incoherent beams formed by lenses.

FIG. 48A shows a top view of a compartmented support structure and FIG. 48B shows a side view of the same structure. Compartmented support structure 4800 has first compartment 4802, second compartment 4804, and third compartment 4806. First hole 4830 is a feedthrough hole that enables a beam of light to enter first compartment 4802. Second hole 4832 enables a beam of light to travel between first compartment 4802 and second compartment 4804. Third hole 4834 enables a beam of light to travel from second compartment 4804 to third compartment 4806. Compartmented support structure 4800 has sufficient height so that optical modules may be mounted within its compartments. More or fewer compartments may be included and the compartments may have various shapes depending on how many optical modules are desired inside compartmented support structure 4800, the shapes of the optical modules, and the desired layout of the optical modules. Compartmented support structure 4800 may be constructed of one solid piece of material, or it may be constructed from separate pieces of material that are attached together.

FIG. 48C shows a top view of a compartmented support structure with a feedthrough hole in a different location compared to FIG. 48A. FIG. 48D is a side view of the same structure shown in FIG. 48C. Compartmented support structure 4810 has first compartment 4812, second compartment 4814, and third compartment 4816. First hole 4840 is a feedthrough hole that enables a beam of light to enter first compartment 4812. Second hole 4842 enables a beam of light to travel between first compartment 4812 and second compartment 4814. Third hole 4844 enables a beam of light to travel from second compartment 4814 to third compartment 4816. In FIG. 48A, the light circulates through the compartments clockwise, whereas in FIG. 48C, the light circulates through the compartments counter-clockwise.

FIG. 49A shows a top view of an optical assembly built with a compartmented support structure and FIG. 49B shows a side view of the same assembly. FIGS. 49A and 49B show the optical modules of FIGS. 47A and 47B mounted inside the compartmented support structure of FIGS. 48A and 48B. First light beam segment 4908 travels through first hole 4930 to enter optical module 4910 in first compartment 4902 and is processed by first optical module 4910 to form second light beam segment 4912. Second light beam segment 4912 travels through second hole 4932 to enter second optical module 4914 in second compartment 4904 and is processed by second optical module 4914 to form third light beam segment 4916. Third light beam segment 4916 enters third optical module 4918 in compartment 4904 and is processed by third optical module 4918 to form fourth light beam segment 4920. Fourth light beam segment 4920 travels through third hole 4934 to enter fourth optical module 4922 in compartment 4906 and is processed by fourth optical module 4922 to form fifth light beam segment 4924. Fifth light beam segment 4924 enters fifth optical module 4926 in compartment 4906 and is processed by fifth optical module 4926 to form sixth light beam segment 4928. The optical modules are mounted to compartmented support structure 4900. The functions of the light beam segments and optical modules may be the same as in FIGS. 1A and 1B. First light beam segment 4908 vertically enters first optical module 4910 from the bottom of compartmented support structure 4900. Sixth light beam segment 4928 vertically exits fifth optical module 4926 from the top of compartmented support structure 4900. The dots representing first light beam segment 4908 and sixth light beam segment 4928 in FIG. 49A signify that the light beams are traveling towards the viewer. The cross representing third light beam segment 4916 in FIG. 49B signifies that the light beam is traveling away from the viewer.

FIG. 50A shows a side view of a stacked compartmented support structure and FIG. 50B shows a side view of the same assembly. The stacked compartmented support structure may be populated by optical modules to form a stacked optical assembly. The stacked compartmented support structure shown in FIGS. 50A and 50B is composed of five compartmented support structures of the type shown in FIGS. 48A, 48B, 48C, and 48D. The five compartmented support structures, first compartmented support structure 5000, second compartmented support structure 5002, third compartmented support structure 5004, fourth compartmented support structure 5006, and fifth compartmented support structure 5008, are stacked vertically one on top of the other with lid 5010 on top of fifth compartmented support structure 5008. First compartmented support structure 5000 is of the type shown in FIGS. 48A and 48B except that it has no feedthrough hole. Third compartmented support structure 5004 and fifth compartmented support structure 5008 are of the type shown in FIGS. 48A and 48B. Second compartmented support structure 5002 and fourth compartmented support structure 5006 are of the type shown in FIGS. 48C and 48D. Optical modules and beams of light are not shown in FIGS. 50A and 50B, but may be installed as shown in FIGS. 49A and 49B. The initial light beam is generated in first compartment 5020 of first compartmented support structure 5000 and travels through holes 5060, 5064, 5068, 5070, 5072, 5076, 5080, 5082, 5084, 5086, 5088, and other holes not shown as it goes through compartments 5022, 5026, 5030, 5032, 5034, 5038, 5042, 5044, 5046, 5048 and other compartments not shown, rising through the stack to exit from final hole 5088 in lid 5010.

FIG. 51 shows an assembly method for a stacked compartmented support structure assembled in parallel. In this method, each layer of compartmented support structure is assembled in parallel and then all the compartmented support structures are stacked. In step 5100, optical modules are mounted in a compartmented support structure. In step 5102, the optical modules are aligned in the compartmented support structure. Reference beams may be used for this alignment. In step 5104, steps 5100 and 5102 are repeated for all of the compartmented support structures that will form the stacked compartmented support structure. In step 5106, the compartmented support structures are assembled into a vertical stack. In step 5108, final alignment is performed if necessary. The final alignment points of interior optical modules may be reached through alignment holes in the stacked compartmented support structure. In step 5110, the lid is attached to the stacked compartmented support structure.

FIG. 52 shows an assembly method for a stacked compartmented support structure assembled in series. In this method, each layer of compartmented support structure is assembled in series and assembled into the stacked compartmented support structure before the next layer of compartmented support structure is assembled. In step 5200, optical modules are mounted in the first compartmented support structure which will form the bottom of the stacked compartmented support structure. In step 5202, the optical modules are aligned in the first compartmented support structure. Reference beams may be used for this alignment. In step 5204, an additional compartmented support structure is attached to the top of the previous compartmented support structure. In step 5206, optical modules are mounted in the additional compartmented support structure. In step 5208, optical modules are aligned in the additional compartmented support structure. In step 5210, steps 5204, 5206, and 5208 are repeated for all the additional compartmented support structures that will form the stacked compartmented support structure. In step 5212, the lid is attached to the stacked compartmented support structure.

Kinematic mounting techniques may be used for mounting the optical modules to the compartmented support structures. Kinematic mounting techniques may also be used for stacking each layer of compartmented support structure to the underlying layer. The stacked compartmented support structure may be held together by bolts that go through the entire assembly from the bottom of the bottom compartmented support structure to the top of the top compartmented support structure or there may be bolts that attach each compartmented support structure only to its underlying compartmented support structure. Kinematic mounting techniques are helpful to enable quicker assembly and to allow optical modules or an entire layer of compartmented support structure to be replaced in case of malfunction. A kinematic mount may be located in the compartmented support structure, on the exterior surface of an optical module, on the exterior surface of the compartmented support structure, or on the mating surfaces between the compartmented support structures.

The vertical optical beams and vertical feedthrough holes shown in FIGS. 50A and 50B pass through points on only one side of the stacked compartmented support structure. Alternatively, some vertical optical beams may pass through one side of the support structure and some vertical optical beams may pass through the other side of the support structure. Using both sides of the support structure may increase the ruggedness of the assembly. The transfer of light between compartments or between layers of compartmented support structure may be performed by conventional relay optics consisting of lenses which are designed to gather light beams and transmit them over the appropriate distances without significant losses.

In FIGS. 47A, 47B, 48A, 48B, 48C, 48D, 49A, 49B, 50A, and 50B, certain mechanical and optical features are shown, but supporting electrical features are not shown. Appropriate wires and electrical feedthroughs are required for electrically active optical modules such as those that contain semiconductor lasers, gain stages, gas discharges, or other electrical components.

The compartmented support structures may be composed of any stiff and optically opaque material. Metals such as aluminum and stainless steel may be used. If weight is a primary consideration, lighter materials such as high-strength plastic or graphite composite materials may be used. If optical transparency is desired in certain regions of the compartmented support structure, transparent glass or crystal window material may be used in those regions. Alternately, some regions of the compartmented support structure may be left open.

Although FIGS. 48A, 48B, 48C, 48D, 49A, 49B, 50A, and 50B show three compartments per compartmented support structure, one, two, or more compartments may be formed in each compartmented support structure. Each compartment isolates the optical modules in that compartment. Stray light is therefore contained within each compartment. Black-painted surfaces or the use of black structural materials may be used to absorb stray light. The layout of the compartments may be of any design to fit the desired optical modules inside. Each compartmented support structure in the stacked optical assembly may have a different layout of its compartments.

Although FIGS. 50A and 50B show five compartmented support structure layers in the stacked optical assembly, there may be any number of compartmented support structure layers in the stacked optical assembly. If many optical modules are required to build a complex optical system, more compartmented support structure layers may be added to the design to accommodate the increased complexity. Alternately, more compartments may be added to the design of each layer. The overall shape of the stacked compartmented support structure may be a rectangular parallelepiped as shown in FIGS. 50A and 50B, or it may be another shape such as cylindrical, pyramidal, irregular polygonal or any other three-dimensional shape.

The wall thickness of the compartmented support structure should be sufficient to ensure stable positioning of the optical modules inside. The wall thickness may be in the range of 2 mm to 15 mm or in the range of 5 mm to 10 mm. High tolerances may be required for the optical modules inside the compartmented support structure. Optical modules of precision systems such as lasers may require positioning with linear tolerances on the order of three micrometers and angular tolerances on the order of three arc-seconds.

The layout of optical modules within compartments may be determined by many factors such as the required order of the optical modules, thermal considerations, and electrical considerations. Some of the modules in the compartmented support structure may not have optical components as they may be supporting electrical components or serve other non-optical functions.

As an example of an optical system using a stacked compartmented support structure, a multicolor laser system may have services such as water cooling and electrical power supplies in the bottom (first) compartmented support structure, Q-switched laser oscillators in the next (second) compartmented support structure, optical gain modules in the next (third) compartmented support structure, another layer of optical gain modules in the next (fourth) compartmented support structure, OPOs in the top (fifth) compartmented support structure, and a lid on the top compartmented support structure. In this example, each compartmented support structure may be 3.5 cm high and the entire size of the stacked compartmented support structure may be 48 cm long by 43 cm wide by 18 cm high. The second layer of gain modules may not be necessary if the desired output power of the multicolor laser system may be attained with a single layer of gain modules.

There are a number of advantages to using the stacked compartmented support structure relative to using the flat support structure. The stacked compartmented support structure is stiffer, has less weight, smaller linear dimensions, less overall volume, less surface area, and is more rugged for the same number of optical modules. The structural pieces may be made thinner to obtain equivalent stiffness and optical positioning tolerances.

For optical systems that include lasers, there are also improvements in laser safety during assembly because each layer of the compartmented support structure may be sealed and eye safe in serially assembled sections when the next layer is stacked. The entire system is also laser safe after final assembly. Light leakage between compartments and layers can also be controlled so that light leakage does not adversely impact the optical function of the system. Air flow may also be controlled between compartments and layers if desired. The compartmented support structure is also more modular and interchangeable allowing easy repair of individually tested modules and known working subsystems. Service may consist of taking apart and replacing a layer of compartmented support structure without disturbing the alignment of the other layers.

The compartmented support structure may be adapted to support optical modules by using kinematic mounts, by the layout of the compartments and holes between the compartments, by designing with stiffness sufficient for high tolerance optical positioning, by separating or absorbing light in each compartment, or by any other means that enable an optical system to function properly when mounted in the compartmented support structure.

In another aspect of the optical system shown in FIG. 1, a stabilized OPO 104 may be constructed by using collimated beams of light between optical modules in the OPO. The OPO may be quicker and easier to align and stay in alignment for a longer period of time when using collimated beams of light. Specific embodiments are described in the following paragraphs but are not meant to be limiting in any way.

A detailed description of an optical system generating three colors of visible light using an OPO may be found in U.S. Pat. No. 5,740,190, the complete disclosure of which is incorporated herein by reference. Starting with a visible pump beam, an OPO makes an infrared signal beam and an infrared idler beam. By choosing a specific temperature and other characteristics of the OPO crystal, the signal beam and idler beam may be tuned as desired. For example, if the pump beam has a wavelength of 523.5 nm, the two additional beams created may be at 898 nm and 1252 nm which are in the infrared region. By using two second-harmonic generators, the 898 nm light can be frequency doubled to 449 nm light which is blue, and the 1252 nm light can be frequency doubled to 626 nm which is red. This produces red, green, and blue colors of visible light that may be used by a digital image projection system. By choosing a different temperature of the OPO, the infrared wavelengths may be 904 nm and 1242 nm which can be frequency doubled to visible wavelengths of 452 nm and 621 nm which fit the color gamut specified for digital cinema. Other wavelengths within the blue or red range may give acceptable color performance for digital cinema projection or other types of digital image projection. Blue wavelengths may be in the range of 430 nm to 480 nm and red wavelengths may be in the range of 600 nm to 680 nm. The pump beam may be in the middle of the green region of visible light which extends from 510 nm to 550 nm. The pump laser may be a Nd:YLF laser which emits light at 1047 nm that can be frequency doubled to 523.5 nm, a Nd:YAP laser which emits light at 1079.5 nm that can be doubled to 540 nm, or other lasers with other wavelengths.

FIG. 53 shows an optical system with an optical parametric oscillator that generates two additional colors of light from one pump beam. Pump beam segment 5302 passes through first SWP filter 5304 and enters OPO 5306 which converts part of pump beam segment 5302 into colocated signal, idler, and remaining pump beam segment 5308. Colocated signal, idler, and remaining pump beam segment 5308 passes to second SWP filter 5310 which reflects first idler beam segment 5312 and passes colocated signal and remaining pump beam segment 5334. First idler beam segment 5312 is focused by first lens 5314 to form second idler beam segment 5316. Second idler beam segment 5316 reflects from first mirror 5318 to form third idler beam segment 5320. Third idler beam segment 5320 passes into first SHG 5322. First SHG 5322 converts part of third idler beam segment 5320 to form colocated second harmonic and remaining idler beam segment 5324. Colocated second harmonic and remaining idler beam segment 5324 passes to third SWP filter 5326 which reflects fourth idler beam segment 5328 and passes first second-harmonic beam segment 5340. Fourth idler beam segment 5328 is focused by second lens 5330 to form fifth idler beam segment 5332. Fifth idler beam segment 5332 reflects from first SWP filter 5304 to join together with pump beam segment 5302.

First SWP filter 5304, OPO 5306, second SWP filter 5310, first lens 5314, first mirror 5318, first SHG 5322, third SWP filter 5326, and second lens 5330 form recirculating optical subsystem 5300. Recirculating optical subsystem 5300 recirculates the idler beam so it passes multiple times through OPO 5306 and first SHG 5322. The optical input to recirculating optical subsystem 5300 is pump beam 5302 and the optical outputs are colocated signal and remaining pump beam segment 5334 and first second-harmonic beam segment 5340.

After leaving recirculating optical subsystem 5300, colocated signal and remaining pump beam segment 5334 passes to fourth SWP filter 5336 which reflects first signal beam segment 5350 and passes remaining pump beam segment 5338. First signal beam segment 5350 reflects from second mirror 5352 to form second signal beam segment 5354. Second signal beam segment 5354 is focused by third lens 5356 to form third signal beam segment 5358. Third signal beam segment 5358 passes into second SHG 5360 which consists of first SHG crystal 5362 and second SHG crystal 5364. First SHG crystal 5362 and second SHG crystal 5364 form a walk-off SHG system which converts part of third signal beam 5358 to form colocated second harmonic and remaining signal beam 5366. Colocated second harmonic and signal beam 5366 passes to LWP filter 5368 which reflects second second-harmonic beam segment 5372 and passes remaining signal beam 5370. Remaining signal beam 5370 passes into beam dump 5378 and is absorbed in beam dump 5378. Second second-harmonic beam segment 5372 reflects from third minor 5374 to form third second-harmonic beam segment 5376.

Fourth SWP filter 5336, second mirror 5352, third lens 5356, first SHG crystal 5362, second SHG crystal 5364, LWP filter 5368, third minor 5374, and beam dump 5378 form beam separation and conversion system 5380. The optical input to beam separation and conversion system 5380 is colocated signal and remaining pump beam segment 5334 and the optical outputs are remaining pump beam segment 5338 and third second-harmonic beam segment 5376.

FIG. 54 is a schematic view of a recirculating optical subsystem with four relay lenses rather than two relay lenses as shown in FIG. 53. Pump beam segment 5402 passes through first SWP filter 5404 and enters OPO 5406 which converts part of pump beam segment 5402 into colocated signal, idler, and remaining pump beam segment 5408. Colocated signal, idler, and remaining pump beam segment 5408 passes to second SWP filter 5410 which reflects first idler beam segment 5412 and passes colocated signal and remaining pump beam segment 5442. First idler beam segment 5412 is focused by first lens 5414 to form second idler beam segment 5416. Second idler beam segment 5416 is focused by second lens 5418 to form third idler beam segment 5420. Third idler beam segment 5420 reflects from mirror 5422 to form fourth idler beam segment 5424. Fourth idler beam segment 5424 passes into SHG 5426. SHG 5426 converts part of fourth idler beam segment 5424 to form colocated second harmonic and remaining idler beam segment 5428. Colocated second harmonic and remaining idler beam segment 5428 passes to third SWP filter 5430 which reflects fifth idler beam segment 5432 and passes second-harmonic beam segment 5444. Fifth idler beam segment 5432 is focused by third lens 5434 to form sixth idler beam segment 5436. Sixth idler beam segment 5436 is focused by fourth lens 5438 to form seventh idler beam segment 5440. Seventh idler beam segment 5440 reflects from first SWP filter 5404 to join together with pump beam segment 5402. First SWP filter 5404, OPO 5406, second SWP filter 5410, first lens 5414, second lens 5418, minor 5422, SHG 5426, third SWP filter 5430, third lens 5434, and fourth lens 5438 form recirculating optical subsystem 5400.

FIG. 55 shows additional details of the recirculating optical subsystem shown in FIG. 54. In FIG. 55, the beam extents are shown schematically as two lines, whereas in FIG. 53, the beams are shown schematically as single lines. Pump beam segment 5402 is focused so that it forms beam waist 5450 in OPO 5406. First idler beam segment 5412 is focused by first lens 5414 to collimated second idler beam segment 5416 which is collimated. Second idler beam segment 5416 is focused by second lens 5418 to form third idler beam segment 5420 and fourth idler beam segment 5424 which forms beam waist 5452 in SHG 5426. Fifth idler beam segment 5432 is focused by third lens 5434 to form sixth idler beam segment 5436 which is collimated. Sixth idler beam segment 5436 is focused by fourth lens 5438 to form seventh idler beam segment 5440 which joins together with pump beam segment 5402 to form beam waist 5450 in OPO 5406. The beam extent shown in FIG. 55 is exaggerated to more clearly show the difference between focused and collimated.

FIG. 56 shows a non-rectilinear recirculating optical subsystem. Relative to the rectilinear recirculating optical subsystem shown in FIG. 55, the non-rectilinear recirculating optical subsystem shown in FIG. 56 has second SWP 5410 moved farther away from OPO 5406 and third SWP 5430 moved farther away from SWG 5426. Also first SWP 5404, second SWP 5410, minor 5422, and third SWP 5430 are rotated approximately five degrees clockwise relative to FIG. 54. This produces a non-rectilinear recirculating optical subsystem. The shape of the recirculating optical subsystem in FIG. 56 is a parallelogram. By changing the positions of first SWP 5404, second SWP 5410, minor 5422, and third SWP 5430 and adjusting those four components to the appropriate angles so that the specular reflections circulate the beams around the recirculating optical subsystem, various quadrilateral shapes may be produced. A cross shape may also be formed by adjusting the SWPs and minor so that the beams cross in the middle.

FIG. 57 shows a method of generating light. In this method, two additional colors of light are generated from one pump beam. Including the remaining pump beam, the total output is three colors of light. In step 5700, a pump beam is focused into an OPO. In step 5702, the OPO forms a signal beam and an idler beam. In step 5704, the idler beam is separated from the signal beam and pump beam. In step 5706, the idler beam is focused through at least two lenses into an SHG. In step 5708, the SHG forms a second-harmonic beam from the idler beam. In step 5710, the second-harmonic beam is separated from the idler beam and the second-harmonic beam is output. In step 5712, the idler beam is focused back through at least two lenses to join the pump beam and enter the OPO. In step 5714, the remaining pump beam is separated from the signal beam and the remaining pump beam is output. In step 5716, the signal beam is focused through a lens into an SHG. In step 5718, the SHG forms a second-harmonic beam from the signal beam. In step 5720, the second-harmonic beam is separated from the remaining signal beam and the second-harmonic beam is output. In step 5722, the remaining signal beam is directed into a beam dump that absorbs the remaining signal beam.

A detailed description of OPOs may be found in U.S. Pat. No. 5,740,190. The wavelengths of the pump, signal, and idler beam are related by the following mathematical expression: 1/λp=1/λs+1/λi, where λp is the wavelength of the pump beam, 1/λs is the wavelength of the signal beam, and 1/λi is the wavelength of the idler beam. The wavelengths also depend on various parameters of the crystal such as its size, orientation, and temperature. Some of the requirements for high efficiency conversion include phase matching, good beam quality, and sufficiently high beam density. Q-switched lasers may be used achieve sufficient beam density by using short pulses and low duty cycles. The OPO may be an x-cut LBO crystal with propagation along the x-axis, noncritical phase matching, and temperature controlled at 159.29 degrees Celsius.

A detailed description of SHGs may be found in U.S. Pat. No. 4,019,159, the complete disclosure of which is incorporated herein by reference. SHGs use nonlinear optical processes to convert the wavelength of the original light beam into a harmonic wavelength such as half the original wavelength. This is equivalent to doubling the frequency of the light beam. The SHGs shown in FIGS. 53, 54, 55, and 56 may be constructed from LBO.

Phase matching in OPOs and SHGs may be divided into two types. Type I is defined as the condition where two input beams have the same polarization and type II is defined at the condition where two input beams have orthogonal polarization. In the case where there is one input beam, it can be considered two input beams with the same polarization. In FIGS. 53, 54, 55, and 56, OPOs 5306 and 5406 may be of type I. In FIG. 53, first SHG 5322 may be of type II and second SHG 5360 may be of type I. In FIGS. 54, 55, and 56, SHG 5426 may be of type II.

SWP and LWP filters may be formed by conventional methods such as the deposition of multilayer interference filters with alternating layers of high index and low index of refraction materials that are designed to transmit certain wavelengths while reflecting other wavelengths. The SWP and LWP filters shown in FIGS. 53, 54, 55, and 56 may be vacuum-deposited interference filters on flat, glass substrates.

Optical lenses are used to focus the beams into the nonlinear crystals of the OPOs and SHGs. A narrow focal point (beam waist) is helpful to reach the high power density required for nonlinear optical processes. Additionally, in order for the recirculating optical subsystem to work efficiently, the beam must go around the recirculation path repeating the position of each beam waist within a variation of approximately 10% of the width of the beam waist after 10 circuits. For example, if the beam waist is 80 micrometers wide, the idler beam must go around the recirculating optical subsystem 10 times while drifting less than 8 micrometers.

The recirculating optical subsystem shown in FIGS. 54, 55, and 56 with four lenses has a number of advantages over the recirculating optical subsystem shown in FIG. 53 which has only two lenses. One advantage of the four-lens system is that the beams which travel between the OPO and the SHG may be collimated. This makes the collimated section insensitive to length changes that may result from temperature changes or drift over the lifetime of the system. By placing first SWP filter 5404 and second SWP filter 5410 close to and in the same optical module as OPO 5406, those three components become one optical module which minimizes possible position changes in that module. In the same manner, by placing mirror 5422 and third SWP filter 5430 close to and in the same optical module as SHG 5426, those three components become one optical module. Collimated beams which are insensitive to misalignment are used to cover the relatively long distance between the OPO optical module and the SHG optical module.

A second advantage of the four-lens system is that alignment is much easier because more configurations are possible solutions for optical alignment of the recirculating optical subsystem. Two-lens systems such as the one shown in FIG. 53 generally must be rectilinear to a high accuracy. The four-lens system in FIGS. 54 and 55 has many possible alignment solutions that are not rectilinear such as the parallelogram shape shown in FIG. 56.

A third advantage of the four-lens system is that the issue of keeping the beam waist centered in the crystal can be separated from the issue of keeping the beam waist coming back into the same position each time it travels around the recirculating system. These two issues are closely interrelated during the alignment of the two-lens system.

In another aspect of the optical system shown in FIG. 1, an improved laser gain module 106 may be constructed by using retroreflective minors. In addition to being easier to align, the laser gain module may more efficient when retroreflective minors are used. Specific embodiments are described in the following paragraphs but are not meant to be limiting in any way.

A detailed description of transversely-pumped solid state lasers may be found in U.S. Pat. No. 5,774,489. When a transversely-pumped solid state laser is utilized to amplify laser light from an external laser, the transversely-pumped solid state laser can be considered to be a laser gain module. Optical side pumping of a gain medium in the laser gain module sets up a gain sheet which is used to optically amplify the external laser by stimulated emission in the gain sheet.

FIG. 58 shows a top view of the operation of laser gain module 5824. Legend 5820 defines the X, Y, Z, and φ directions. Angle φ is defined as a rotation in the X-Z plane. External laser 5822 produces input laser beam segment 5800 which enters gain slab 5802. Pump lasers 5816 produce pump beams 5818 which also enter gain slab 5802. Input laser beam segment 5800 is optically amplified by an inversion population of excited atoms in gain slab 5802 created by pump beams 5818. Input laser beam segment 5800 reflects off mirror 5804 to form laser beam segment 5806. Laser beam segment 5806 reflects off minor 5808 to form laser beam segment 5810. Laser beam segment 5810 reflects off minor 5804 to form laser beam segment 5812. Laser beam segment 5812 reflects off minor 5808 to form output laser beam segment 5814. The multiple laser beam segments crossing gain slab 5802 allow input laser beam segment 5800 to be amplified multiple times in the process of becoming output laser beam segment 5814. Output laser beam segment 5814 exits laser gain module 5824. Laser beam segments 5800, 5806, 5810, 5812, and 5814 combine to form a main laser beam which is distinct from pump beams 5818.

The number of times that the main laser beam crosses slab 5802 depends on the entrance angle of laser beam segment 5800 and the alignment angles of mirrors 5804 and 5808. Minors 5804 and 5808 may be flat or may have a slight curvature. Main laser beam segments 5800, 5806, 5810, 5812, and 5814 travel along paths that are substantially parallel to the Z direction. Pump beams 5818 travel along paths that are substantially parallel to the X direction.

FIG. 59 shows a side view of the operation of laser gain module 5824. Legend 5904 shows the X, Y, and Z directions which are rotated relative to legend 5820 in FIG. 58. Angle θ is defined as a rotation in the Y-Z plane. Gain sheet 5902 is in gain slab 5802. Gain sheet 5902 is formed by the optical pumping of pump lasers 5816 as shown in FIG. 58. Laser beams 5900 represent the main laser beam. Laser beams 5900 are optically amplified when they pass through gain sheet 5902.

FIG. 60 shows a top view of the operation of laser gain module 6024. Legend 6020 defines X, Y, Z, and φ as in FIG. 58. External laser 6022 produces input laser beam segment 6000 which enters gain slab 6002. Pump lasers 6016 produce pump beams 6018 which also enter gain slab 6002. Input laser beam segment 6000 is optically amplified by an inversion population of excited atoms in gain slab 6002 created by pump beams 6018. A gain sheet is created which is similar to the gain sheet shown in FIG. 59. Input laser beam segment 6000 reflects off TIR prism 6004 twice to form laser beam segment 6006. Laser beam segment 6006 reflects off TIR prism 6008 twice to form laser beam segment 6010. Laser beam segment 6010 reflects off TIR prism 6004 twice to form laser beam segment 6012. Laser beam segment 6012 reflects off TIR prism 6008 twice to form output laser beam segment 6014. The multiple laser beam segments crossing gain slab 6002 allow input laser beam segment 6000 to be amplified multiple times in the process of becoming output laser beam segment 6014. Output laser beam segment 6014 exits laser gain module 6024. Laser beam segments 6000, 6006, 6010, 6012, and 6014 combine to form a main laser beam which is distinct from pump beams 6018.

The number of times that the main laser beam crosses gain slab 6002 depends on the relative positioning of input laser beam segment 6022, TIR mirror 6004, and TIR mirror 6008. Main laser beam segments 6000, 6006, 6010, 6012, and 6014 travel along paths that are substantially parallel to the Z direction. Pump beams 6018 travel along paths that are substantially parallel to the X direction.

FIG. 61 shows a method of using retroreflective mirrors for optical amplification. In step 6100, a pump laser beam is injected into a laser gain slab. In step 6102, a main laser beam is injected into the laser gain slab. In step 61061, the main laser beam is reflected from a first retroreflecting minor. In step 6106, the main laser beam is amplified by passage through the laser gain slab. In step 6108, the main laser beam is reflected from a second retroreflecting mirror. In step 6110, the main laser beam is again amplified by passage through the laser gain slab. Steps 6104 through 6110 are repeated multiple times. In step 6112, the amplified main laser beam is output from the laser gain slab. Injecting is defined as focusing or otherwise introducing a beam of light into the laser gain slab. Lenses may be used to focus the beam into the laser gain slab.

Flat minors reflect light such that the angle of incidence equals the angle of reflection. In contrast, retroreflective mirrors reflect a beam of light back in the same direction as the incident direction. Retroreflective minors in two dimensions may be formed by placing two flat mirrors at right angles. Retroreflective minors in three dimensions may be formed by placing three flat mirrors at right angles to form a corner-cube reflector. TIR prisms are a form of retroreflective minors that use total internal reflection to form completely reflective mirrors on certain faces of the prism. When the index of refraction of the prism material is sufficiently high and the angle of the incident light on the face of the prism is sufficiently high, rays of light in the prism cannot exit the faces of the prism and are instead totally internally reflected according to Snell's law. To form TIR prisms that operate at internal incident angles of 45 degrees (such as TIR prisms 6004 and 6008), the index of refraction must be greater than 1.41 at the wavelength of the main laser beam. Many optical glass and crystal materials satisfy this index of refraction criterion. TIR prisms 6004 and 6008 are two-dimensional retroreflective minors. TIR prisms 6004 and 6008 may alternately be replaced by other types of retroreflective minors such as high-reflection flat minors positioned at right angles. Another type of TIR prism is an immersed design where the light travels in a high index material, but instead of being surrounded by air as in the previous examples, the high index material is surrounded by a lower index material such as low index glass on the sides of the prism designed to have total internal reflection.

External laser 6022 in FIG. 60 provides light pulses or continuous wave light to laser gain module 6024. External laser 6022 may be a Q-switched ND:YLF laser which produces light at 1047 nm or a Q-switched ND:YAP laser which produces light at 1079.5 nm. The optical power may be approximately 2 watts. The Q-switching frequency may be 125 kHz with a range of 20 kHz to 300 kHz, and the pulse width may be 25 nm with a range of 5 ns to 100 ns. The beam spatial profile may be Gaussian or another beam shape.

The gain slab carries the main laser beam inside while the main laser beam is reflecting back and forth between the two retroreflective mirrors. The gain slab is composed of a medium which allows stimulated emission. The gain slab may composed of the same material as the material used for the external laser. For example, if the external laser is of the ND:YLF type, the gain slab may also be composed of ND:YLF. If the external laser is of the ND:YAP type, the gain slab may also be composed of ND:YAP.

Pump lasers 6016 may be laser diode bars which may have collimation optics to guide their light into gain slab 6002 and efficiently from a gain sheet in gain slab 6002. The collimation optics may be substantially cylindrical lenses that focus the beam primarily in the Y direction. Pumps lasers 6016 may be collimated in the Y direction so that the gain sheet is well defined and has a quasi-Gaussian distribution of gain in the Y direction while being very uniform in the X-Z plane if the gain-slab absorption coefficient is suitably chosen. The optical power of the pump lasers may be over 1 watt per laser gain module, and the wavelength may be 808 nm.

An advantage of laser gain module 6024 relative to laser gain module 5824 is that laser gain module 6024 more uniformly fills the gain sheet volume with the main laser beam. In laser gain module 5824, the main laser beam is squeezed into a small volume in the regions near the reflection from minors 5804 and 5808. In these regions, the main laser beam overly depletes the population of excited atoms created by pump beams 5818. Other areas of the gain sheet are not filled by the main beam and therefore do not contribute to the optical amplification of the main beam. In laser module 6024, the main beam traverses the gain sheet volume more uniformly and therefore has the chance to utilize the full population of excited atoms in a large fraction of the gain sheet. In the Z-direction, also called the longitudinal direction, the uniformity of the main laser beam power density is improved by using retroreflective mirrors rather than flat minors. The components of laser gain module 6024 may be suitably designed to optimize the utilization of the excited atoms in the gain sheet by distributing the main laser beam uniformly throughout the gain sheet volume.

Another advantage of laser gain module 6024 relative to laser gain module 5824 is that laser gain module 6024 does not have parallel minors or minors close to parallel. Parallel or close to parallel mirrors such as mirrors 5804 and 5808 in laser gain module 5824 produce parasitic laser activity because a resonance condition is set up where spontaneous emission in gain slab 5802 will result in laser emission that depletes the excited atoms in gain slab 5802. Any parasitic laser activity removes excited atoms from the population of excited atoms in gain slab 5802 so those atoms are no longer available to optically amplify the main beam. To avoid parasitic laser activity, minors 5804 and 5808 must be slightly misaligned in both θ and φ angles. The misalignment is difficult to control and depends to some extent on the wedge angle of the optical faces of gain slab 5802. Laser gain module 6024 replaces minors 5804 and 5808 with TIR prisms that have no parallel or close to parallel faces. In addition, antireflection coatings at the lasing wavelength may be used on the end faces of gain slab 6002, and the end faces of the gain slab may be tilted to prevent additional parallel surfaces that can cause parasitic laser activity. The end faces of gain slab 6002 are the two faces that are closest to TIR prisms 6004 and 6008.

Multiple laser gain modules 6024 may be made interchangeable and easily replaceable by suitable alignment of gain slab 6002, TIR prisms 6004 and 6008, and other components of laser gain module 6024. An external alignment fixture may be used to align the components of laser gain module 6024 to produce a fixed and constant relationship between input laser beam segment 6000 and output laser beam segment 6014 for multiple laser gain modules. This allows for easy replacement of defective modules and easy alignment of the overall optical system that uses laser gain modules 6024.

Multiple laser gain modules 5824 cannot control output beam angle and position relative to the input accurately enough to chain laser gain modules 5824 without using location adjustments and mirror tilts of successive modules to correct errors of preceding modules. In other words, laser gain modules 5824 are not interchangeable. Multiple laser gain modules 6024, on the other hand, may be easily combined in series to amplify the main beam more than can be achieved by using a single laser gain module 6024. The limit of multiple gain modules is determined primarily by surface damage issues, not bulk damage in the gain sheets. But when the main beam reaches a sufficiently high power, the main beam may be optically steered by thermally induced changes in the index of refraction of the gain sheets. Compensation for beam steerage may be performed by additional optical elements dedicated to that task.

Thermal issues may affect the performance or alignment of the laser gain module if the laser gain module gets too hot or if the temperature of the module is not held sufficiently constant. Water cooling may be used to cool the laser gain module. Stability may be improved by splitting the water cooling into sections so that different parts of the laser gain module are cooled by different water cooling circuits.

The alignments of mirrors 5804 and 5808 in laser gain module 5824 are very sensitive to minor tilts and small errors which may lead to inefficient operation of laser gain module 5824. The alignment of laser gain module 6024 is much easier to perform because there are no angle misalignments in θ or φ required to avoid parasitic laser activity therefore the prisms may be aligned in the module with only relative alignments between the prisms in the X direction required. Even this alignment may be eliminated by templating if the parts of laser gain module 6024 are toleranced properly. Also, angle misalignments of TIR prisms 6004 and 6008 do not affect the angle of output laser beam 6014, only its location and beam separation from input laser beam 6000. An additional feature of laser gain module 6024 is that the number times the main laser beam passes through gain slab 6002 can be easily adjusted by changing the relative displacement of TIR prisms 6004 and 6008 in the X direction. Displacement of TIR prisms 6004 and 6008 in the X direction may also be used to null out any error in alignment of the components of laser gain module 6024.

In another aspect of the optical system shown in FIG. 1, an optical tap 108 may be formed to monitor and control a high-intensity beam of light. By using two uncoated glass plates, laser damage is avoided and the alignment of the original beam is not affected. Specific embodiments are described in the following paragraphs but are not meant to be limiting in any way.

Optical systems with high intensity light beams may experience drift or other instabilities. To enable feedback and control of the optical beam intensity, an optical tap may be utilized to monitor the high intensity beam. An optical tap takes a small amount of light from a high-intensity light beam and directs it to a detector where the small amount of light is converted to an electrical signal that represents the intensity of the high-intensity light beam.

FIG. 62 shows an optical system with an optical tap. First light processing element 6200 provides first beam segment 6202. First beam segment 6202 is collimated by first lens system 6204 to form second beam segment 6206. Second beam segment 6206 enters optical tap 6208. Optical tap 6208 outputs electrical signal 6218 which is used by electrical circuit 6220. Third beam segment 6210 exits optical tap 6208 and is focused by second lens system 6212 to form fourth beam segment 6214. Fourth beam segment 6214 enters second light processing element 6216. In this example, first beam segment 6202 and fourth beam segment 6214 are un-collimated beams of light, whereas second beam segment 6206 and third beam segment 6210 are collimated beams of light. Alternatively, all beams may be collimated so that first lens system 6204 and second lens system 6212 are not necessary. First light processing element 6200 may be a light source such as a laser, or it may be any optical component that provides a beam of light. Second light processing element 6216 may be any optical component that utilizes the light from first light processing element 6200. The final optical output of the optical system may be third beam segment 6210 in which case, there is no second light processing element 6216. Electrical signal 6218 is related to the intensity of second beam segment 6206. Electrical signal 6218 may be proportional to the intensity of second beam segment 6206. Electrical circuit 6220 may be a feedback circuit, control circuit for first light processing element 6200, or any other electrical circuit that uses electrical signal 6218 as an input.

FIG. 63A shows the detailed workings of an optical tap with two plates. Such a tap may be utilized by the optical system of FIG. 62. First beam segment 6300 partially reflects from first plate 6302 to form second beam segment 6314 and third beam segment 6304. Second beam segment 6314 is absorbed by beam dump 6316. Third beam segment 6304 is inside first plate 6302. Third beam segment 6304 exits first plate 6302 to form fourth beam segment 6306. Fourth beam segment 6306 partially reflects from second plate 6310 to form fifth beam segment 6318 and sixth beam segment 6308. Fifth beam segment 6318 is a small fraction of the intensity of first beam segment 6300. Fifth beam segment 6318 illuminates detector 6320 which produces electrical signal 6330. Sixth beam segment 6308 is inside second plate 6310. Sixth beam segment 6308 exits second plate 6310 to form seventh beam segment 6312. First plate 6302 and second plate 6310 may be composed of transparent solid materials such as glass or optical crystal. First beam segment 6300 is a collimated light beam. Second order reflections which produce beam segments of lower intensity are not shown in FIG. 63A. Second plate 6310 steers seventh beam segment 6312 so that it is co-linear with first beam segment 6300. Co-linear means that two beams lie on the same line. The angle of incidence of first beam 6300 on first plate 6302 is equal to the angle of incidence of fourth beam 6306 on second plate 6310. First plate 6302, second plate 6310, beam dump 6316, and detector 6320 form optical tap 6340. Alternatively, beam dump 6316 may not be included in the optical tap, but its function of absorbing second beam segment 6314 may instead be provided by the general enclosure (not shown) of optical tap 6340. Alternatively, beam dump 6316 and detector 6320 may be reversed so that the monitored reflection is from the first plate rather than the second plate.

FIG. 63B shows the detailed workings of an optical tap with three plates. Such a tap may be utilized by the optical system of FIG. 62. First beam segment 6342 partially reflects from first plate 6344 to form second beam segment 6350 and third beam segment 6346. Second beam segment 6350 is absorbed by first beam dump 6352. Third beam segment 6346 is inside first plate 6344. Third beam segment 6346 exits first plate 6344 to form fourth beam segment 6348. Fourth beam segment 6348 partially reflects from second plate 6354 to form fifth beam segment 6360 and sixth beam segment 6356. Sixth beam segment 6356 is inside second plate 6354. Sixth beam segment 6356 exits second plate 6354 to form seventh beam segment 6358. Fifth beam segment 6360 partially reflects from third plate 6362 to form eighth beam segment 6370 and ninth beam segment 6364. Ninth beam segment 6364 is inside third plate 6362. Ninth beam segment 6364 exits third plate 6362 to form tenth beam segment 6366. Tenth beam segment 6366 is absorbed by second beam dump 6368. Eighth beam segment 6370 is a small fraction of the intensity of first beam segment 6342. Eighth beam segment 6370 illuminates detector 6372 which produces electrical signal 6374. First plate 6344, second plate 6354, and third plate 6362 may be composed of transparent solid materials such as glass or optical crystal. First beam segment 6342 is a collimated light beam. Second order reflections which produce beam segments of lower intensity are not shown in FIG. 63B. Second plate 6354 steers seventh beam segment 6358 so that it is co-linear with first beam segment 6342. The angle of incidence of first beam 6342 on first plate 6344 is equal to the angle of incidence of fourth beam 6348 on second plate 6354. First plate 6344, second plate 6354, third plate 6362, first beam dump 6352, second beam dump 6368, and detector 6372 form optical tap 6380. Alternatively, first beam dump 6352 and second beam dump 6368 may not be included in the optical tap, but the function of absorbing second beam segment 6350 and tenth beam segment 6366 may instead be provided by the general enclosure (not shown) of optical tap 6380. Alternatively, first beam dump 6352 may be exchanged with third plate 6362, second beam dump 6368, and detector 6372 so that the monitored reflection is from the first plate and the third plate rather than the second plate and the third plate. The optical tap with three plates shown in FIG. 63B can be used to monitor higher power beams without saturation of the detector compared to the optical tap with two plates shown in FIG. 63A.

FIG. 64 shows an optical plate with an incident ray of light. The beam segments in FIGS. 63A and 63B consist of multiple rays of light which each act as shown in FIG. 64 when incident on first plate 6302 and second plate 6310. First ray segment 6402 enters plate 6400 and is partially refracted to form second ray segment 6412 and partially reflected to form third ray segment 6408. First angle 6406 is the angle between first ray segment 6402 and plate perpendicular 6404. First angle 6406 is the incidence angle of first ray segment 6402. Second angle 6410 is the angle between third ray segment 6408 and plate perpendicular 6404. Second angle 6410 is the reflection angle of second ray segment 6408. The magnitude of first angle 6406 is equal to the magnitude of second angle 6410. Second ray segment 6412 passes through plate 6400 until it reaches the back surface of plate 6400 where it exits plate 6400 and is partially refracted to form fourth ray segment 6414 and partially reflected to form fifth ray segment 6420. Fourth ray segment 6414 propagates in the same direction as first ray segment 6402, but is offset by distance 6418 from path 6416 that first ray segment 6402 would have taken in the absence of plate 6400. Fifth ray segment 6420 passes through the plate 6400 until it reaches the front surface of plate 6400 where it exits plate 6400 and is partially refracted to form sixth ray segment 6422 and partially reflected to form seventh ray segment 6424. Seventh ray segment 6424 continues reflecting back and forth inside plate 6400 growing weaker each time. Third ray segment 6408, sixth ray segment 6422, and similar ray segments (not shown) past seventh ray segment 6424 are reflected from plate 6400 and in combination make an overall reflected beam from plate 6400. Fourth ray segment 6414 and similar ray segments (not shown) past seventh ray segment 6424 are transmitted through plate 6400 and in combination make an overall transmitted beam through plate 6400.

FIG. 65 shows a graph of reflection from a plate such as first plate 6302, second plate 6310, first plate 6344, second plate 6354, third plate 6362, and plate 6400 in FIGS. 63A, 63B, and 64. The x-axis represents the angle of incidence in degrees and the y-axis represents the intensity of the reflection in percent of the intensity of the incident beam. First curve 6500 shows the reflection of s-polarized light and second curve 6502 shows the reflection of p-polarized light. S-polarized light has a large reflection at all angles of incidence, but the reflection of p-polarized light is close to zero for angles close to 56 or 57 degrees. The angle of zero reflection for p-polarized light is known as Brewster's angle. In the example of FIG. 65, the index of refraction of the plate is 1.52. If the index of refraction is different, Brewster's angle will also be different.

FIG. 66 shows an expanded graph of FIG. 65 centered near Brewster's angle. For many applications, a tap reflection of between 1×10−4 of 1×10−7 is an appropriate amount of power for the detector to accept without saturation on the high end or too much noise on the low end. Curve 6600 shows the reflection of p-polarized light. An effective range of angles for the optical tap may lie between 56.3 degrees and 57.0 degrees. In order to produce a tap reflection of 1×10−5, the angle of incidence must be close to 56.45 degrees or 56.87 degrees. In order to produce a tap reflection of 1×10−6, the angle of incidence must be close to 56.59 degrees or 56.72 degrees. If the high intensity beam being monitored is 100 watts these reflections make 1 milliwatt and 100 microwatts respectively, which is within the optimum range of conventional semiconductor detectors such as PIN (P-doped, Intrinsic, N-doped) photodiodes. The small amount of light removed from the high intensity beam does not significantly affect its use in most applications.

FIG. 67 shows a light generation system that uses three optical taps to control the output color. The three optical taps monitor three high-intensity beams of light and electronic control is used to keep the output color at a desired color point. First light processing element 6700 provides first beam segment 6702. First beam segment 6702 is collimated by first lens system 6704 to form second beam segment 6706. Second beam segment 6706 enters optical tap 6708. Optical tap 6708 outputs first electrical signal 6718 which is used by electrical circuit 6760. Third beam segment 6710 exits optical tap 6708 and is focused by second lens system 6712 to form fourth beam segment 6714. Fourth beam segment 6714 enters second light processing element 6716. Third light processing element 6720 provides fifth beam segment 6722. Fifth beam segment 6722 is collimated by third lens system 6724 to form sixth beam segment 6726. Sixth beam segment 6726 enters optical tap 6728. Optical tap 6728 outputs second electrical signal 6738 which is used by electrical circuit 6760. Seventh beam segment 6730 exits optical tap 6728 and is focused by fourth lens system 6732 to form eighth beam segment 6734. Eighth beam segment 6734 enters fourth light processing element 6736. Fifth light processing element 6740 provides ninth beam segment 6742. Ninth beam segment 6742 is collimated by fifth lens system 6744 to form tenth beam segment 6746. Tenth beam segment 6746 enters optical tap 6748. Optical tap 6748 outputs third electrical signal 6758 which is used by electrical circuit 6760. Eleventh beam segment 6750 exits optical tap 6748 and is focused by sixth lens system 6752 to form twelfth beam segment 6754. Twelfth beam segment 6754 enters sixth light processing element 6756. First light processing element 6700, first lens system 6704, optical tap 6708, second lens system 6712, second light processing element 6716, third light processing element 6720, third lens system 6724, optical tap 6728, fourth lens system 6732, fourth light processing element 6736, fifth light processing element 6740, fifth lens system 6744, optical tap 6748, sixth lens system 6752, sixth light processing element 6756, and electrical circuit 6760 form light generation system 6770.

In the example of FIG. 67, first beam segment 6702, fourth beam segment 6714, fifth beam segment 6722, eighth beam segment 6734, ninth beam segment 6742, and twelfth beam segment 6754 are un-collimated beams of light, whereas second beam segment 6706, third beam segment 6710, sixth beam segment 6726, seventh beam segment 6730, tenth beam segment 6746, and eleventh beam segment 6750 are collimated beams of light. Alternatively, all beams may be collimated so that first lens system 6704, second lens system 6712, third lens system 6724, fourth lens system 6732, fifth lens system 6744, and sixth lens system 6752 are not necessary. First light processing element 6700, third light processing element 6720, and fifth light processing element 6740 may be light sources such as lasers, or may be any optical components that provide a beam of light. Second light processing element 6716, fourth light processing element 6736, and sixth light processing element 6756 may be any optical components that utilize the light from first light processing element 6700, third light processing element 6720, and fifth light processing element 6740 respectively. The final optical output of the optical system may be a combination of third beam segment 6710, seventh beam segment 6730, and eleventh beam segment 6750 in which case, there is no second lens system 6712, fourth lens system 6732, sixth lens system 6752, second light processing element 6716, fourth light processing element 6736, or sixth light processing element 6756. First electrical signal 6718, second electrical signal 6738, and third electrical signal 6758 are related to the intensity of second beam segment 6706, sixth beam segment 6726, and tenth beam segment 6746 respectively. First electrical signal 6718 may be proportional to the intensity of second beam segment 6706, second electrical signal 6738 may be proportional to the intensity of sixth beam segment 6726, and third electrical signal 6758 may be proportional to the intensity of tenth beam segment 6746. Electrical circuit 6760 controls first light processing element 6700, third light processing element 6720, and fifth light processing element 6740 or other elements of the optical system (not shown) in order to balance the output color of light generation system 6770.

FIG. 68 shows a flowchart of a method of optical tapping. In step 6800, a first plate is illuminated with light. In step 6802, a small fraction of the light is reflected. In step 6804, the small fraction of light is captured in a detector. In step 6806, the remaining light is passed to a second plate. In step 6808, the remaining beam is shifted to be co-linear with the first beam.

Conventional beamsplitters may consist of transparent plates of glass with thin metal coatings or interference coatings that are operated at an incident angle of 45 degrees. For beam intensities greater than approximately 10 watts, it may not be practical to use a conventional beamsplitter to extract a portion of the beam for monitoring. Especially with pulsed laser systems such as Q-switched systems, the laser damage threshold of conventional beamsplitters may be exceeded and damage to the beamsplitter may result. In this case, the optical tap may be constructed from an uncoated glass plate so that the laser damage threshold of the plate is higher than the peak power of the high-intensity laser beam. The plates may be made of any material that is transparent to the light beam being monitored. Optical glasses such as BK7 may be used for their ruggedness and high transparency.

The amount of light reflected to the detector may be tuned by adjusting the angle of the plates of the tap. This is equivalent to adjusting the incident angle of the incident beam. The angle of the second plate of the tap may also be adjusted to keep the beam co-linear by making the angle of the second plate equal to the angle of the first plate. The tolerance of the angle is important to obtain the desired reflection intensity. In the example of FIG. 66, if the desired reflection from the plate is 1×10−6, the nominal angle of incidence would be 56.594 degrees, but to maintain 1×10−6 plus or minus 10%, the angle would be 56.590 degrees to 56.597 degrees. This is a range of 0.007 degrees. If the desired reflection is 1×10−5, the nominal angle of incidence would be 56.451 degrees, but to maintain 1×10−5 plus or minus 10%, the angle would be 56.440 degrees to 56.462 degrees. This is a range of 0.022 degrees. The beam being monitored should be collimated to within the angular range that gives the desired reflection. For example, if a reflection of 1×10−6 is desired, the beam being monitored should be collimated to within approximately 0.007 degrees for proper operation of the optical tap at the nominal angle of 56.594 degrees.

In order for the optical tap to reflect a suitably small amount of light, the high intensity beam being monitored must be close to 100% p-polarized. Even a small percentage of s-polarized light will cause a large reflection because s-polarized light has a reflection of approximately 27% near Brewster's angle. S-polarized light should be less than approximately 1×10−6 of the high intensity beam if a reflection on the order of 1×10−6 is desired at the nominal angle of 56.594 degrees.

Applications of optical taps include any optical system where high-intensity light beams must be monitored. Examples include laser projectors, laser light shows, laser cutting, laser engraving, laser beam processing of materials, and laser medical devices. Because the optical tap does not significantly affect the high-intensity beam of light in either beam path or intensity, the tap can be inserted or removed into a high-intensity beam without degrading the operation of the light system being monitored. This makes a modular system that can be easily adapted to existing optical designs without affecting the alignment of the optical system.

In another aspect of the optical system shown in FIG. 1, coupler 110 may be used to reduce speckle. Three colors of light may be transferred from laser light sources and combined in a form which is easy to retrofit to projectors that are designed for conventional light sources such as arc lamps. Specific embodiments are described in the following paragraphs but are not meant to be limiting in any way.

Digital projectors form projected digital images by modulating beams of light to form pixels. The modulation is performed by light valves that may be reflective or transmissive. For large-venue applications, the light sources must have high output power and high optical brightness, such as the conventionally used HID lamps. Laser light sources may also be used but are subject to visible speckle because of the long coherence length of laser light as compared to HID lamps.

Speckle refers to a random pattern of small bright and dark spots that is visible when laser light is reflected from a diffusing surface such as a projection screen. The speckle pattern moves with the head of the viewer. The size of the spots appears to be at the limit of visible resolution, and the spots may appear rainbow colored or may appear to have other colors depending on the color of the projected light. Speckle is usually considered an undesirable side effect of laser illumination.

Speckle may be reduced by a number of methods including time diversity (also called phase diversity), path length diversity (also called angle diversity), and wavelength diversity. These techniques average the bright spot and dark spots of speckle over time, space, or wavelength in order to reduce the amplitude of the brightness variations. A device which reduces speckle is called a “despeckler”. A moving element of the optical system such as a rotating diffuser will act as a despeckler as long as the frequency of motion is high enough so that the movement is not visible to the human eye. This is generally a movement frequency higher than approximately 100 Hz.

FIG. 69 shows a method of coupling a laser light source to a digital image projector. In step 6900, a laser light source generates a laser light beam which illuminates an input lens system. In step 6902, the input lens system collects and focuses the light beam so that it illuminates an optical fiber. In step 6904, the optical fiber passes the light into the proper location to illuminate an output lens system. In step 6906, the output lens system collects and focuses the light beam so that it illuminates a despeckler. In step 6908, the despeckler reduces the speckle of the light beam. In step 6910, the light beam passes into an integrating rod which improves the spatial uniformity of the light beam. In step 6912, a digital image projector uses the light beam to form a projected digital image. The word “illuminate” is used to mean that light is directly received by and passes into the object being illuminated.

For digital image projectors based on DMD light valves, an integrating rod is typically incorporated as part of the standard projector design. For digital image projectors based on LCOS or LCD light valves, there is typically no integrating rod, but the optical coupler may require an additional lens system to collimate the light beam before illuminating the projector.

FIG. 70 shows a side view of an optical coupler with a diffuser-based despeckler which is center driven. Laser light source 7002 generates a light beam which illuminates input lens system 7004. Input lens system 7004 collects and focuses the light beam so that it illuminates core 7008 of optical fiber 7006. Optical fiber 7006 passes the light beam into the proper location to illuminate output lens system 7010. Output lens system 7010 collects and focuses the light beam so that it illuminates diffuser 7012. Diffuser 7012 acts as a despeckler to reduce the speckle of the light beam and passes the light beam to illuminate integrating rod 7018. Integrating rod 7018 improves the spatial uniformity of the light beam and passes the light beam so that is illuminates digital image projector 7020. Mechanical vibrator 7022 vibrates optical fiber 7006 with core 7008 to provide additional despeckling. Diffuser 7012 is mounted on spindle 7014 which is rotated by motor 7016 in a center-driven configuration. Input lens system 7004, optical fiber 7006 with core 7008, output lens system 7010, diffuser 7012, vibrator 7022, spindle 7014, and motor 7016 form optical coupler 7000. For clarity, mechanical support structures to hold the components and optical isolation structures are not shown.

FIG. 71 shows a side view of an optical coupler similar to the optical coupler in FIG. 70 except that diffuser 7112 is edge driven by spindle 7114 and motor 7116. The edge-driven configuration may result in an optical coupler of smaller size than the center driven configuration of FIG. 70. Input lens system 7004, optical fiber 7006 with core 7008, output lens system 7010, diffuser 7112, vibrator 7022, spindle 7114, and motor 7116 form optical coupler 7100.

FIG. 72 shows a side view of an optical coupler similar to the optical coupler in FIG. 70 except that a collimation lens system 7222 is added so that the output of optical coupler 7200 forms collimated light beam 7224 that illuminates projector 7220. No integrating rod is necessary in this configuration, but projector 7220 may include light homogenization components such as a fly's eye lens. Input lens system 7004, optical fiber 7006 with core 7008, output lens system 7010, diffuser 7012, vibrator 7022, spindle 7014, motor 7016, and collimation lens 7222 form optical coupler 7200.

FIG. 73 shows a perspective view of the end of optical fiber bundle 7300. Optical fiber bundle 7300 has two ends, only one of which is shown in FIG. 73. One central optical fiber 7306 and six surrounding optical fibers 7302 are shown in optical fiber bundle 7300. Each surrounding optical fiber 7302 has a surrounding core 7304. Central optical fiber 7306 has central core 7308. Each surrounding core 7304 is capable of carrying light down the length of the corresponding surrounding optical fiber 7302. Central core 7308 is capable of carrying light down the length of central optical fiber 7306. Six surrounding optical fibers 7302 fit well around central optical fiber 7306 in optical fiber bundle 7300. Surrounding optical fibers 7302 and central optical fiber 7306 may have diameters in the range of 730 microns to 1000 microns and may be arranged within optical bundle 7300 in any geometric pattern. Surrounding cores 7304 have diameters larger than 50 microns, but smaller than the corresponding surrounding optical fibers 7302. Central core 7308 has a diameter larger than 50 microns, but smaller than the corresponding central optical fiber 7306.

FIG. 74 shows a side view of an optical coupler similar to the optical coupler in FIG. 70 except that an optical fiber bundle is used to combine two laser light sources. First laser light source 7430 generates first input light beam 7450 which illuminates first input lens system 7434. First input lens system 7434 collects and focuses first input light beam 7450 to form first focused light beam 7454. First focused light beam 7454 illuminates first core 7444 of first optical fiber 7440. First optical fiber 7440 passes the light into the proper location to illuminate output lens system 7410 with first intermediate light beam 7460. Second laser light source 7432 generates second input light beam 7452 which illuminates second input lens system 7436. Second input lens system 7436 collects and focuses second input light beam 7452 to form second focused light beam 7456. Second focused light beam 7456 illuminates second core 7446 of second optical fiber 7442. Second optical fiber 7442 passes the light into the proper location to illuminate output lens system 7410 with second intermediate light beam 7462. Third laser light source 7470 generates third input light beam 7472 which illuminates third input lens system 7476. Third input lens system 7476 collects and focuses third input light beam 7472 to form third focused light beam 7476. Third focused light beam 7476 illuminates third core 7486 of third optical fiber 7484. Third optical fiber 7484 passes the light into the proper location to illuminate output lens system 7410 with third intermediate light beam 7488.

Output lens system 7410 collects and focuses first intermediate light beam 7460, second intermediate light beam 7462, and third intermediate light beam 7488 to form first output light beam 7464, second output light beam 7466, and third output light beam 7490. First output light beam 7464, second output light beam 7466, and third output light beam 7490 illuminate diffuser 7012. Diffuser 7012 acts as a despeckler to reduce the speckle of first output light beam 7464, second output light beam 7466, and third output light beam 7490 and forms final light beam 7468 which is a combination of first output light beam 7464, second output light beam 7464, and third output light beam 7490. Final light beam 7468 illuminates integrating rod 7018. First input lens system 7434, second input lens system 7436, third input lens 7474, first optical fiber 7440 with first core 7444, second optical fiber 7442 with second core 7446, third optical fiber 7484 with third core 7486, output lens system 7410, diffuser 7012, vibrator 7022, spindle 7014, and motor 7016 form optical coupler 7400. First optical fiber 7440 with first core 7444, second optical fiber 7442 with second core 7446, and third optical fiber 7484 with third core 7486 form optical fiber bundle 7482. The offset between first intermediate light beam 7460, second intermediate light beam 7462, and third intermediate light beam 7488 and the offset between first output light beam 7464, second output light beam 7464, and third output light beam 7490 are exaggerated to show the individual light beams more clearly. In the example of FIG. 74, three laser light sources are shown, but two, four, or more laser light sources may also be combined in the same manner as shown in FIG. 74.

FIG. 75 shows a side view of an optical coupler similar to the optical coupler in FIG. 74 except that a dichroic beam combiner is used to combine the two laser light sources instead of an optical fiber bundle. First laser light source 7532 generates first input light beam 7574 which passes through first dichroic filter 7554 and second dichroic filter 7534 to illuminate input lens system 7536. Second laser light source 7572 generates second input light beam 7552 which reflects from first dichroic filter 7554 and passes through second dichroic filter 7534 to illuminate input lens system 7536. Third laser light source 7530 generates third input light beam 7570 which reflects from second dichroic filter 7534 to illuminate input lens system 7536. Input lens system 7536 collects and focuses first input light beam 7554, second input light beam 7552, and third input light beam 7570 so that first input light beam 7554, second input light beam 7552, and third input light beam 7570 combine to form focused beam 7556 which illuminates core 7544 of optical fiber 7540. Optical fiber 7540 passes the light into the proper location to illuminate output lens system 7510 with intermediate light beam 7560. Output lens system 7510 collects and focuses intermediate light beam 7560 to form output light beam 7564. Output light beam 7564 illuminates diffuser 7012. Diffuser 7012 acts as a despeckler to reduce the speckle of output light beam 7564 and forms final light beam 7568. Final light beam 7568 illuminates integrating rod 7018. First dichroic filter 7554, second dichroic filter 7534, input lens system 7536, optical fiber 7540 with core 7544, output lens system 7510, diffuser 7012, vibrator 7022, spindle 7014, and motor 7016 form optical coupler 7500. First dichroic filter 7554 and second dichroic filter 7534 form dichroic beam combiner 7580.

Laser light sources, such as those shown in FIGS. 70, 71, 72, 74, and 75, may be semiconductor lasers, gas discharge lasers, diode-pumped solid state lasers, optical parametric oscillators, or other any other type of light source which produces coherent light. The coherence length may be on the order of 1 mm. Each laser light source may emit 30 W to 1000 W of optical output. Q-switched lasers may be used to achieve high power densities so that nonlinear optical processes may convert the wavelengths to all of the colors required by the digital image projector.

Diffusers, such as those shown in FIGS. 70, 71, 72, 74, and 75, may be formed from ground and/or etched glass, holographic methods, or bulk diffusing materials. A high damage threshold is helpful to handle the large optical flux at the focal point of the beam on the diffuser. A rotating diffuser helps spread the heat load over a larger area so that the diffuser is self-cooling. With proper design of the diffuser, 7300 watts or more of optical power may be transmitted through the diffuser without overheating. In a well-designed optical coupler, as the optical power of the laser light sources is increased, at some point the optical absorption of the light valves or other components in the projector will become the limiting factor for overall system output. Although the diffuser slightly increases the spread of the light beam passing through it, by keeping the diffuser close to the integrating rod, most of the light that exits the diffuser will be captured by the acceptance cone of the integrating rod.

Diffusers reduce speckle even if not in motion due to path length diversity, but they reduce speckle more when rotated or otherwise moved because time diversity adds further averaging. The optimal rotation frequency depends on the size of the diffuser features, but greater than 50 rpm is typically sufficient to optimize the speckle reduction.

Optical fibers that carry a high flux of light should optimally have low absorption for the wavelength region in the light beam. SiO2 fibers may be used for this purpose. Fibers with a high concentration of hydroxyl radicals have reduced absorption in the blue region of the spectrum. Optical fiber bundles may be used such that the exit beams from the fibers are displaced by only a fraction of a millimeter. Keeping the exit beams close together is advantageous because the beams combine well into one beam that still has high throughput through the projector optical system. The laser light beam illuminating each fiber may have more than 10 watts of optical power when used by digital cinema projectors for large venues. By using seven optical fibers and laser light sources of 150 watts each, the total optical output from the coupler may be on the order of 800 watts after accounting for losses in the optical coupler. The fiber may be vibrated in order to perform despeckling. The vibration frequency may be greater than 100 Hz, and the vibration apparatus may be a piezo-electric actuator. The length of the fiber may be in the range of 1 to 50 meters to achieve suitable despeckling.

Lens systems may be a single lens, or a combination of multiple lens elements. Output lens system 7010 in FIG. 70 may be designed as a one-to-one imaging system so that the beam diameter at the output of optical fiber 7006 approximately equals the beam diameter at the input surface of diffuser 7012. The design of input lens system 7004 depends on the properties of the light beam exiting laser light source 7002. Input lens system 7004 needs to focus the beam of light from laser light source 7002 so that the light enters core 7008 of optical fiber 7006. Ray tracing software such as Zemax (Zemax Development Corporation, Bellevue, Wash.) may be used to design lens systems that effectively collect and focus light beams into the required locations.

Optical fiber bundle 7482 in FIG. 74 is one example of a beam combiner. Beam combiners may operate on various principles depending on the optical characteristics of the light beams being combined. These principles may include geometric combination, polarization combination, or wavelength combination. Fiber bundle 7482 operates on the principle of geometric combination. If the light beams are of different polarization states, the beam combiner may include a reflective polarizer. In this case, one polarization of light is transmitted and one is reflected. Another example is shown in FIG. 75 where the light beams have different colors. In this example, the beam combiner may consist of two dichroic filters that together form a dichroic beam combiner. In each filter, one region of colors is transmitted and another region of colors reflected. By using two filters, three colors may combined into one beam. Multiple beam combiners may be added in series or parallel to combine any number of light beams.

If feedback is necessary, an optical sensor may be incorporated into the optical coupler to sense the intensity of light passing through the optical coupler. The optical sensor may be a photodiode sensitive at the wavelengths of light used in the optical coupler. The sensor may be located at any convenient location. One such location is between output lens system 7010 and diffuser 7012 in FIG. 70.

An integrating rod may be formed from a rectangular piece of glass that confines the light inside using total internal refraction. Assuming the rod has sufficient length, light that enters with any spatial profile, but at angles below the acceptance angle of the integrating rod, will reflect inside the rod and become uniformly spread so that it exits the rod with a top-hat spatial distribution. The entry face of the integrating rod may be approximately 1 cm on the longer side for large-venue cinema projectors. The aspect ratio of the entry-face longer side to the entry-face shorter side may be the same aspect ratio as the light valve in order to homogenize the light over the aspect ratio of the light valve.

The optical couplers shown in FIGS. 70, 71, 72, and 74 which incorporate both vibrating fibers and rotating diffusers are capable of reducing the speckle to less than 4%. In large-venue applications, speckle of 4% or less may be considered acceptable and speckle of 1% or less is typically invisible to the naked eye.

The maximum power that can be coupled into one fiber is generally limited by the damage threshold of the input face of the fiber. The optical coupler described herein uses multiple fibers and/or beam combiners to enable higher optical power to be efficiently and reliably coupled into a digital projector. The multiple fibers or beam combiners may also be used to combine different colors of light such as red, green, and blue into a digital projector.

One example of the use of an optical coupler is the after-market replacement of high-intensity-discharge lamps with laser light sources for off-the-shelf cinema projectors. These high-intensity-discharge lamps are usually xenon lamps with short life spans. The optical coupler may be designed so that the laser light source is a drop-in retrofit to increase the optical output, light source lifetime, and power efficiency when compared to the original xenon bulb. The replacement may be as simple as removing the existing xenon bulb, and bolting the optical coupler into the area where the xenon lamp was mounted. The optical coupler conveniently combines the functions of coupling, color mixing, and despeckling into one subassembly. The alignment of the optical coupler is not sensitive to position and angle. As long as the output beam of the optical coupler enters the acceptance aperture and acceptance cone of the projector, the light from the optical coupler will be effectively coupled into the projector. A connector may be used to connect the optical fiber to the supporting structure than holds the fiber. The connector allows quick connection and disconnection of the optical coupler. The connector may be an SMA connector. Whether there is one optical fiber or a bundle of optical fibers, the same SMA connector may be used to provide a modular capability to increase power by changing optical couplers. No optical alignment is needed when attaching or changing the fibers with SMA connectors. Other types of lamps, such as mercury vapor lamps or tungsten lamps, may also be replaced by laser light sources in a similar manner.

The maximum repetition rate of a single Q-switched laser is limited because higher repetition rate generally means lower peak power in each pulse. High peak power is desirable for the nonlinear effects used in color conversion, but may not be achievable if the repetition rate is too high. On the other hand, a high repetition rate is desirable to avoid creating beat frequencies with DMD light valves or other periodic events in digital image projectors. The optical coupler described herein enables multiple laser light sources to be combined so that the repetition rate is high while maintaining high peak power. For example, two Q-switched lasers running at repetition rates of 100 kHz each can be combined without sacrificing peak power to have an effective repetition rate of 200 kHz.

In another aspect of the optical system shown in FIG. 1, flat-sided fiber 112 may be used to further reduce speckle. The flat-sided fiber may be used as one part of optical couplers such as those shown in FIGS. 70, 71, 72, 74, and 75. Specific embodiments are described in the following paragraphs but are not meant to be limiting in any way.

Optical fibers with rectangular cores are conventionally used for applications such as making rectangular power distributions. This purpose is shown in FIGS. 1 through 4 of Japanese patent publication No. 2003121664, published Apr. 23, 2003.

FIG. 76 shows the optical layout of an optical system with a laser light source, an optical fiber, and a digital image projector. Laser light source 7600 outputs laser light which is focused by input lens system 7602 so that it illuminates core 7606 of optical fiber 7604. The output of optical fiber 7604 is focused by output lens system 7608 so that it illuminates digital image projector 7610. Projector lens 7612 forms image 7616 on screen 7614. The digital image projector may include a mixing rod in which case output lens system 7608 couples the output of optical fiber 7604 into the mixing rod. Input lens system 7602 and output lens system 7608 may consist of any combination of optical elements such as lenses and minors that are able to transfer light into and out of the fiber. Laser light source 7600 may be a single laser or may include multiple lasers of different colors or with various optical properties. Optical fiber 7604 allows flexibility in the location of laser light source 7600 and digital image projector 7610 while allowing easy alignment of these two parts. Laser light source 7600 and digital image projector 7610 may be located far from each other, limited only by the length of optical fiber 7604. Alternately, optical fiber 7604 may be coiled such laser light source 7600, digital image projector 7610, and optical fiber 7604 are located in close proximity.

FIG. 77 shows a cross sectional view of a flat-sided fiber. Core 7700 has flat side 7710, height 7704 and width 7706. Glass cladding 7702 surrounds core 7700 and forms air cladding region 7708 adjacent to flat side 7710. Other than air cladding region 7708, the rest of core 7700 has a conventional glass cladding in contact with core 7700. Surrounding and in contact with cladding 7702 is a protective coating 7712 which is typically an acrylate or polyimide though other coatings may be used. The index of refraction of core 7700 is higher than the index of refraction of cladding 7702 or air cladding region 7708. Light travels primarily in core 7700 and is guided by TIR from the interface between core 7700 and cladding 7702 or air cladding region 7708. Cladding 7702 fulfills the function of keeping the light in the optical fiber core. Coating 7712 protects the fiber from contamination, abrasion, or other degradation from the environment outside core 7700. Alternately, glass cladding 7702 may be in contact with core 7700 all the way around core 7700 without an air cladding region. The term “flat-sided fiber” is used for optical fibers that have a flat-sided core even though the outside of the fiber may not have a flat side.

FIG. 78 shows a cross sectional view of a rectangular optical fiber with glass cladding. A rectangular core fiber is a specific case of a flat-sided optical fiber where there are four flat sides and the four sides are perpendicular. Core 7800 has a rectangular cross section with height 7804 and width 7806. Glass cladding 7802 surrounds core 7800 and is covered by coating 7812. The operation of the rectangular optical fiber is similar to the one-sided optical fiber shown in FIG. 77 except that there are 4 flat sides instead of one flat side and there is no air cladding region. In this example, the ratio of width 7806 to height 7804 is 2:1. Other ratios may be used to match the aspect ratio of the light valves in the digital image projector. For example, 4:3 and 16:9 may be used if the light valves have one of those aspect ratios.

FIG. 79 shows a cross sectional view of a rectangular optical fiber with air cladding. Core 7900 has a rectangular cross section with a height 7904 and a width 7906. Glass cladding 7902 forms air cladding regions 7908 because glass cladding 7902 surrounds core 7900 but only touches core 7900 at the corners of core 7900. Coating 7912 protects the fiber. In this example, the ratio of width 7906 to height 7904 is 2:1. The operation of the rectangular optical fiber is similar to the rectangular optical fiber shown in FIG. 3 except that there are air cladding regions surrounding all four sides of the rectangular core.

FIG. 80 shows a method of illuminating a digital projector with a flat-sided fiber. In step 8000, coherent light is generated from a laser light source. In step 8002, a flat-sided optical fiber is illuminated with the coherent light from the laser light source. In step 8004, a digital image projector is illuminated with the output from the flat-sided fiber. A flat-sided optical fiber refers to a fiber with a flat-sided core. The core may have one or more flat sides. If there are four flat sides perpendicular to each other, the core will have a rectangular cross section.

The fiber cores shown in FIGS. 77 through 79 are shown with sharp edges, but due to the fiber draw process as well as typical sleeving processes used in conventional fiber manufacture, the sharp edges will be softened slightly at the corners due to surface tension self-rounding effects. The cladding is shown fully collapsed around the core in FIG. 3, but this is not required as alternatively shown in FIGS. 77 and 79. The clad need only ensure that the light stays in the core.

One or more flat sides on the core give a number of benefits for illuminating a digital image projector with a laser light source. One advantage of this shape core is that the source is made highly uniform after propagating a short distance. The lack of circular symmetry causes a randomization of the input light distribution effectively making a top-hat intensity pattern the same size as the core. In the case of a rectangular fiber, from the physical optics point of view the spatial modes of the rectangular fiber do not individually overlap an input circularly symmetric beam well which means that a large number of guided modes are excited which causes a broad energy distribution. Since these modes dephase as they propagate with different modal indices, the original light distribution is lost and the light output more uniformly covers the fiber field. Since the rectangular fiber core may be matched in aspect ratio to the modulators used in a digital projector, the modulators may be uniformly filled.

Another benefit of the flat-sided core is speckle reduction in laser sources whose spectral bandwidth is at least a few tenths of a nanometer. If the spectral bandwidth is at least 1 nm wide, there may be very significant speckle reduction. Because a large number of modes are excited in a flat-sided fiber and each travels with its own phase velocity, provided the fiber is long enough, the modes will eventually be delayed by an amount greater than the source coherence length and the speckle will be reduced roughly by the square root of the number of the modes excited. This is a diminishing return effect and for a given source bandwidth, the fiber length must be balanced against speckle reduction, attenuation, and cost. The fiber length may be in the range of 1 to 500 meters. For the best balance of cost and speckle reduction, the fiber length may be in the range of 5 to 50 meters.

As a specific example of speckle reduction, for a laser light source with a central wavelength of 523 nm and a spectral bandwidth of 1 nm, a 100 micrometer by 200 micrometer rectangular-core fiber with a numerical aperture of 0.22 would be capable of supporting approximately 5000 modes. This implies that the best speckle reduction possible would be about 18 dB if every mode was incoherent and equally excited. The distance required to achieve this in a straight fiber would be very large but one could achieve approximately 13 dB reduction after only 20 meters.

In the case of fiber lengths that do not fully exceed the coherence length of modes with adjacent propagation constants, inter-modal interference will occur leading to a speckle-like spatial intensity pattern at the fiber output. Since the fiber acts like a long interferometer in this case, time averaging by perturbing the fiber eliminates this residual noise pattern. This may be accomplished by a variety of methods such as using a vibrating element to vibrate a section of the fiber thus temporally changing the relative mode phase delays at a rate sufficiently higher than the observer's detection rate to filter the residual noise. The vibrating element may be a piezoelectric transducer.

An advantage of a rectangular core is that it is capable of preserving the polarization of input light. This will be possible if the input polarization is aligned parallel to one of the core edges. This can be understood from the point of view of a ray propagating down the fiber. Since each total internal reflection is essentially a specular reflection from a flat surface, the polarization of the ray is unchanged.

The material of the fiber may be glass, plastic, or any material transparent at the wavelengths of operation. Glass is preferred for high power use due to its low absorption and high damage threshold. Silica glass with a high concentration of hydroxyl or deuteroxyl radicals has reduced absorption in the blue region of the spectrum. The maximum power that may be inserted into the fiber will be limited by laser damage threshold as well as possible nonlinear effects. Laser damage threshold of the cleaved or polished faces can be avoided if the power density is kept below a specific value such as 200 megawatts per cm2. Examples of nonlinear effects which could limit power carrying capability are stimulated Brillouin scattering and self focusing. These are well understood effects in single mode fiber but are not easily analyzed in multimode fiber.

The manufacturing of the flat-sided fiber made from glass may be performed using conventional fiber drawing techniques. The fiber preform may have a flat-sided core that may be machined to the desired shape such as rectangular with the desired aspect ratio. The cladding may be formed in the conventional way by doping the core to have a high index-of-refraction, and/or doping the cladding to have a low index-of-refraction. Air cladding may be formed by making the preform with the desired air region geometry and preserving the cross-sectional geometry of the air region during the fiber draw process.

Other implementations are also within the scope of the following claims.

Claims

1. An optical system comprising:

a blue light source;
a spatial light modulator (SLM);
wherein the blue light source emits light only in a range of wavelengths that preserves an optical characteristic of the SLM.

2. The system of claim 1 wherein the blue light source comprises a laser.

3. The system of claim 1 wherein the SLM comprises a liquid crystal material.

4. A stereoscopic display system comprising:

a polarization-switching light source characterized by a polarization state; and
a polarization-preserving projector which is illuminated by the polarization-switching light source.

5. The system of claim 4 wherein the polarization-preserving projector forms a left-eye digital image and a right-eye digital image, and the polarization state is changed in synchronization with an alternating projection of the left-eye digital image and the right-eye digital image.

6. A stereoscopic projection system comprising:

a first infrared laser;
a first gain module that amplifies a light beam from the first infrared laser;
a first second-harmonic generator (SHG) that frequency doubles a light beam from the first gain module;
a first optical parametric amplifier (OPO) that parametrically amplifies a light beam from the first SHG;
a second SHG that frequency doubles a first light beam from the first OPO;
a third SHG that frequency doubles a second light beam from the first OPO;
a second infrared laser;
a second gain module that amplifies a light beam from the second infrared laser; and
a fourth SHG that frequency doubles a light beam from the second gain module;
wherein part of the light beam from the first SHG passes through the first OPO to form a remaining light beam, the remaining light beam has a first wavelength of green light, a light beam from the second SHG has a first wavelength of red light, a light beam from the third SHG has a first wavelength of blue light; and a light beam from the fourth SHG has a second wavelength of green light.

7. The system of claim 6 wherein the remaining light beam, the light beam from the second SHG, and the light beam from the third SHG combine to form an image that is directed to one eye of a viewer and not directed to the other eye of the viewer.

8. The system of claim 6 further comprising:

a switch that switches the light beam from the first SHG;
a second OPO that parametrically amplifies the light beam from the first SHG;
a fifth SHG that frequency doubles a first light beam from the second OPO; and
a sixth SHG that frequency doubles a second light beam from the second OPO;
wherein the switch sends the light beam from the first SHG alternately to the first OPO and the second OPO, and a light beam from the fifth SHG has a second wavelength of red light, and a light beam from the sixth SHG has second wavelength of blue light.

9. The system of claim 6 further comprising:

a third infrared laser;
a third gain module that amplifies a light beam from the third infrared laser;
a fifth SHG that frequency doubles a light beam from the third gain module;
a second OPO that parametrically amplifies a light beam from the fifth SHG;
a sixth SHG that frequency doubles a first light beam from the second OPO; and
a seventh SHG that frequency doubles a second light beam from the second OPO;
wherein a light beam from the sixth SHG has a second wavelength of red light, and a light beam from the seventh SHG has a second wavelength of blue light.

10. An optical system comprising:

a first light source;
a second light source; and
an SLM;
wherein the first light source has a first optical output which is processed by a first part of the SLM and the second light source has a second optical output which is processed by a second part of the SLM.

11. The system of claim 10 wherein the first light source has an etendue lower than 0.1 mm2 sr.

12. The system of claim 10 wherein the first part of the SLM is used to form an image for a left eye of a viewer and the second part of the SLM is used to form an image for a right eye of the viewer.

13. The system of claim 10 wherein the first optical output comprises a first wavelength band and the second optical output comprises a second wavelength band; the first wavelength band being distinct from the second wavelength band.

14. A method of assembly comprising:

placing an alignment plate on a holding plate;
inserting a roller and a holding block into the alignment plate;
fastening the holding block to the holding plate to hold the roller;
fastening the roller to the holding plate;
removing the alignment plate; and
mating an optical module to the roller on the holding plate.

15. The method of claim 14 further comprising:

achieving final optical alignment without further adjustments.

16. An optical support structure comprising:

a first compartmented support structure adapted to support optical modules; and
a second compartmented support structure adapted to support optical modules;
wherein the second compartmented support structure is stacked on top of the first compartmented support structure.

17. The structure of claim 16 further comprising:

a first compartment in the first compartmented support structure;
a second compartment in the second compartmented support structure; and
a hole between the first compartment and the second compartment that allows a beam of light to pass between the first compartment and the second compartment.

18. The structure of claim 16 further comprising:

a third compartment in the second support structure; and
a hole between the second compartment and the third compartment that allows a beam of light to pass between the second compartment and the third compartment.

19. The structure of claim 16 further comprising:

a kinematic mount on the first compartmented support structure; and
a kinematic mount on the second compartmented support structure;
wherein the kinematic mount on the second compartmented support structure is mated to the kinematic mount on the first compartmented support structure.

20. An optical system comprising:

an OPO;
an SHG;
a first lens which passes light between the OPO and the SHG;
a second lens which passes light between the OPO and the SHG; and
a third lens which passes light between the OPO and the SHG.

21. The system of claim 20 wherein the first lens passes a collimated beam segment to the second lens.

22. An apparatus comprising:

a laser gain slab which carries a main laser beam;
a pump laser which optically pumps the laser gain slab; and
a retroreflective mirror positioned adjacent to the laser gain slab;
wherein the retroreflective minor reflects the main laser beam.

23. An optical tap comprising:

a first plate;
a second plate; and
a detector;
wherein a first beam of light enters the first plate, the first beam of light exits the first plate to form a second beam of light, the second beam of light enters the second plate, the second beam of light exits the second plate to form a third beam of light, the second plate forms the third beam of light to be co-linear with the first beam of light, the first beam of light is reflected from a plate selected from the group consisting of the first plate and the second plate to form a fourth beam of light, the fourth beam of light is a small fraction of the first beam of light, and the fourth beam of light illuminates the detector.

24. The tap of claim 23 further comprising:

a third plate;
wherein after the first beam of light reflects from the plate selected from the group consisting of the first plate and the second plate, the first beam of light reflects from the third plate to form the fourth beam of light.

25. The tap of claim 23 wherein the first plate comprises an uncoated plate of glass.

26. An optical coupler comprising:

a first optical fiber; and
a despeckler;
wherein a first laser light beam illuminates the first optical fiber; an output from the first optical fiber illuminates an integrating rod; and an output from the integrating rod illuminates a digital image projector.

27. The coupler of claim 26 further comprising:

a second optical fiber;
wherein a second laser light beam illuminates the second optical fiber; and an output from the second optical fiber illuminates the despeckler.

28. The coupler of claim 27 further comprising:

a third optical fiber;
wherein a third laser light beam illuminates the third optical fiber; an output from the third optical fiber illuminates the despeckler; the first laser light beam is red; the second laser light beam is green; and the third laser light beam is blue.

29. The coupler of claim 27 wherein the first optical fiber is attached to the second optical fiber to form an optical fiber bundle.

30. An optical system comprising:

a first laser light source;
an optical fiber with a core; and
a digital image projector;
wherein an output of the first laser light source illuminates the core, an output of the core illuminates the digital image projector, and the core has at least one flat side.

31. The system of claim 30 wherein the core has a rectangular cross section.

32. The system of claim 31 wherein the output of the first laser light source has a polarization direction and the polarization direction is oriented orthogonal to the flat side.

Patent History
Publication number: 20100253769
Type: Application
Filed: Sep 3, 2009
Publication Date: Oct 7, 2010
Applicant: LASER LIGHT ENGINES (Salem, NH)
Inventors: David A. Coppeta (Atkinson, NH), James J. Zambuto (Winchester, MA), Ian Turner (Stratham, NH), David Goodwin (Salem, NH), William Beck (Salem, NH)
Application Number: 12/553,890
Classifications
Current U.S. Class: Separation By Polarization (348/58); Optical Modulator (359/237); Polarizer (353/8); Stereoscopic (353/7); Harmonic Generator (359/328); Particular Pumping Type (e.g., Electrical, Optical, Nuclear, Magnetic, Etc.) (359/345); With Reflecting Element (359/726); Sequentially Associating Parts On Stationary Aligning Means (29/467); Supporting Base (248/346.01); Picture Reproducers (epo) (348/E13.075)
International Classification: H04N 13/04 (20060101); G02F 1/00 (20060101); G02B 27/26 (20060101); G02B 27/22 (20060101); G02F 1/37 (20060101); H01S 3/094 (20060101); G02B 17/00 (20060101); G02B 27/48 (20060101); B23P 11/00 (20060101); F16M 13/00 (20060101);