Abstract: A projection display apparatus in which a light emitted from a reflective light valve is made incident on a prism member and a light having passed through the prism member is projected by a projection lens, comprises a dust proofing cover that provides a seal between an emergence surface of the reflective light valve and an incidence surface of the prism member.

Abstract: A display apparatus (10) comprises a light source (20) for forming a beam of light. Illumination optics shapes and directs the beam of light. A splitter for splits the beam of light into at least three color beams of light. A modulation optical system (120) for each of the three color beams of light comprises a pre-polarizer (160), a wire grid beamsplitter (170), a reflective spatial light modulator (30), and a polarization analyzer (165). An imaging relay lens (130) in each color provides an intermediate image of the reflective spatial light modulator from the modulated light for that color. A dichroic combiner (26) recombines the modulated light for each given color, such that the multiple color beams form the respective intermediate images along a common optical axis to form a combined intermediate image. A projection lens (32) images the combined intermediate image to a display screen. An imager field lens (140) provides nominally telecentric light to the spatial light modulators.

Abstract: Beam splitter designs for interferometers provide a phase difference between the two resulting interference beams that are independent of the polarization status of the incident beam. The polarization independent phase coating is achieved by making the internal beam splitting coating of an unpolarized beam splitter to be symmetrical. A symmetrical coating will produce the phase matching condition, &PSgr;SR−&PSgr;SR′=&PSgr;PR−&PSgr;PR′=0.

Abstract: A display apparatus (10) comprises a light source (20) for forming a beam of light. Illumination optics shapes and directs the beam of light. A splitter for splits the beam of light into at least three color beams of light. A modulation optical system (120) for each of the three color beams of light comprises a pre-polarizer (160), a wire grid beamsplitter (170), a reflective spatial light modulator (30), and a polarization analyzer (165). An imaging relay lens (130) in each color provides an intermediate image of the reflective spatial light modulator from the modulated light for that color. A dichroic combiner (26) recombines the modulated light for each given color, such that the multiple color beams form the respective intermediate images along a common optical axis to form a combined intermediate image. A projection lens (32) images the combined intermediate image to a display screen. An imager field lens (140) provides nominally telecentric light to the spatial light modulators.

Abstract: Disclosed is a technology that corrects astigmatism introduced by crossing beam splitting/combining plates. This technology may be used in the context of video projection systems, whereby the plates may be used for combining and/or splitting beams between two or more light modulating panels. In one embodiment, a system is provided for projecting an optical image, where the system includes a lens configured to receive and focus light rays to project the image. The system also includes a first beam splitting/combining plate that refracts light rays passing therethrough, where the refracting creates pluralities of light rays having corresponding optical paths causing each of the pluralities to be focused on corresponding focal planes by the lens.

Abstract: Provided is a head-up display having a prism sheet interposed between a display device and the position of an observer's eye. Control is extended so that points from which light rays having different wavelengths emerge are made different by a predetermined distance from each other so as not to form images at different points by light rays from a point source, relative to the difference between the wavelengths. Otherwise, a distance to an image in a vertical direction is made shorter by a predetermined distance than a distance thereto in a horizontal direction. The vertical angle of each of prisms included in the prism sheet is asymmetrical to a normal to the surface of the prism sheet.

Abstract: A rotating periodic color-regulating module of the image display device is disclosed to improve the usage of light. The rotating periodic color-regulating module comprises a color separating light guide and a color-regulating processor. By using a grating element installed in front of the color separating light guide, the incident light is interleaved into three parts of different wavelengths, red (R), green (G) and blue (B), propagating toward the corresponding color filters. Part of the light is reflected by the color filters, then reflected by the mirror around the grating element, and goes back to the color filters. The incident light is divided into three uniform beams of light, R, G and B, to the color-regulating processor. The color-regulating processor changes the outgoing position and order of the light beams periodically and rapidly for displaying image.

Abstract: There is provided a projection display apparatus using a polarization beam splitter having two splitting surfaces, which can simplify its structure and reduce its cost. The projection display apparatus includes the polarization beam splitter that has a first splitting surface for transmitting or reflecting a red light and a second splitting surface for transmitting or reflecting a green light and a blue light. A polarization state converter that is provided in the polarization beam splitter converts the polarization states of the green and blue lights and applies the converted green and blue lights to the polarization beam splitter.

Abstract: A single plate type optical unit and display device to utilize light with high efficiency in a simple method is configured so a dichroic mirror separates light into a plurality of colors, and the plurality of colors of light reflected by the dichroic mirror are beamed onto a rotating multisurface element, the plurality of colors of light emitted from the rotating multisurface element are each beamed onto different locations on the display element, and by rotating the rotating multisurface element, the plurality of colors of light are moved in one direction along the display element, and a color image is beamed from a projection lens.

Abstract: A high-efficiency, compact color illuminating system and a projection type image display apparatus using the color illuminating system are provided. The color illuminating system includes a light source, a spiral lens disc that periodically scrolls light by rotational movement, and an optical unit that isolates light beams of different wavelengths from white light emitted from the light source and guides the isolated light beams to enter at least two effective regions of the spiral lens disc. The projection type image display apparatus includes the color illuminating system, an image forming unit that generates images using scrolling light from the spiral lens disc, and a projection lens unit that enlarges and projects the images formed by the image forming unit on a screen.

Abstract: A bi-directional wavelength division multiplexing/demultiplexing device is disclosed. In an exemplary embodiment, the bi-directional wavelength division multiplexing/demultiplexing device comprises a diffraction grating for combining a plurality of monochromatic optical input beams into a multiplexed, polychromatic optical output beam, and for separating a multiplexed, polychromatic optical input beam into a plurality of monochromatic optical output beams; and a transmissive/reflective optical element for transmitting the plurality of monochromatic optical input beams on an optical path toward the diffraction grating, and for reflecting the plurality of monochromatic optical output beams received on an optical path from the diffraction grating.

Abstract: An extreme ultraviolet (EUV) lithography system may include a spectral purity filter including diffractive gratings. The diffractive gratings may be formed in a silicon substrate using anisotropic etching techniques to produce smooth, flat facets defined by (111) crystallographic planes.

Abstract: An objective lens for an optical pickup has a single lens element. One surface of the objective lens is divided into a central area and a peripheral area, and a step providing a level difference along a direction of the optical axis is formed at a boundary therebetween. The step provides a phase shift between light passing through the central area and the peripheral area. The level difference is formed such that a thickness on the peripheral area side is greater than a thickness on the central area side at the boundary. In one case, the objective lens satisfies a condition: 0.83<hx/hmax<0.97, where hx is a radius of the boundary, and hmax is an effective radius defining a numerical aperture of the surface formed with the step.

Abstract: A beam splitter (24)for splitting light in a wavelength range of about 500 nm to about 600 nm is arranged in a relay optical system of a taking lens (12). A green light beam reflected from the beam splitter (24) is directed through a relay lens (R3) to a focusing state determination imaging unit (26). The imaging unit (26) comprises three imaging elements (A, B, C) for capturing the directed green light beam to determine the focusing state. Thus, a device for determining the focusing state of the taking lens is provided, in which the green light beam is separated as an object light for determining the focusing state from the object light entering the taking lens (12), so that the focusing state can be determined with high accuracy on the basis of the high-frequency components of the image signal generated by capturing the green light beam by means of the imaging elements (A, B, C) having different optical path lengths.

Abstract: The present invention relates to a method and system for expanding a laser beam. An illumination system includes a horizontal reflective multiplexer and a vertical reflective multiplexer. The horizontal reflective multiplexer replicates the input beam along a first dimension to form a first multiplexed beam. The vertical reflective multiplexer replicates the first multiplexed beam along a second dimension to form a second multiplexed beam. In one example, the horizontal reflective multiplexer includes a first beam splitter, second beam splitter, and mirror. The vertical reflective multiplexer includes a beam splitter and mirror.

Abstract: A multi-channel optical device includes a first plurality of optical structures formed simultaneously using vapor deposition on different regions of a common substrate. Each optical structure in the plurality is comprised of a plurality of thin-film layers. The thickness of each layer in a given optical structure corresponds to a wavelength associated with one of the channels. A reflector has a surface parallel to the common substrate, and a transport region is disposed between the first plurality of optical structures and the reflector. An aperture is disposed at one end of the transport region, and the first plurality of optical structures are disposed along a length of the transport region. When an input optical signal is provided to the aperture, the device functions as an optical demultiplexer and output optical signals associated with different ones of the channels are generated at separate positions along a length of the transport region.

Abstract: Disclosed is a color separation and color synthesis optical system provided between a light source portion and a projection optical system in a reflection type projection display apparatus, which color-separates a white color beam emitted from the light source portion into three primary color light beams of R (red), G (green) and B (blue), guides the three primary color light beams to a plurality of spatial light modulators corresponding to R, G and B, and color-synthesizes color light beams optically modulated by the respective spatial light modulators for the colors depending on video signals to emit a color-synthesized light beam, wherein at least one or more wavelength-selective polarization converting plates which rotate a plane of polarization of a specific color light beam by 90 degrees are located, and the wavelength-selective polarization converting plate is adhered to an incidence plane and/or an emission plane of a polarization beam splitter by adhesive with a slight gap.

Abstract: A beam splitting apparatus generates, from incident light having a specific polarization, first and second split light that has the specific polarization.

Abstract: In a reflection-type image projecting unit, being applicable into a reflection-type image display apparatus, being superior in contrast and achieving small-sizing of the apparatus, together with a light source for use therein, a light flux including three (3) color components, R, G and B, emitted from a light source portion 100, are modulated and synthesized by means of reflection-type liquid crystal panels.

Abstract: A multi-mode color filter 400 having an inner hub region 402 used to mount the color filter 400 to a motor shaft. A first track 404 and a second track 406 of color filter segments arc formed on the color filter, as is an optional clear track 406. The first and second tracks each have a different set of color filters. One set of filters is chosen to improve image brightness, another set is selected to improve color saturation. Typically, the set of filters used to improve brightness includes one or more clear segments, while the set of filters selected to improve color saturation does not. Depending on the image being projected, the user or the display controller moves the color wheel to select a particular filter set.

Abstract: A projector projects pixels to form an image in accordance with image data. The projector includes a modulator which modulates light from a light source and outputs projected pixels in a plurality of color spectral bands. The projector has a light source with a non-uniform spectral power distribution with spectral energy within each of the plurality of color spectral bands. A first notch filter removes spectral energy from a first spectral range within a first color spectral band to improve gamut.

Abstract: A spectroscopic probe includes a monolithic block (10) of transparent material and GRIN lenses (20, 22, 24). Light for illuminating a sample is delivered by an optical fiber (31), and light scattered by the sample is output by an optical fiber (33). The block (10) has opposing angled faces (12A, 12B), coated with a dichroic filter coating and a reflective coating respectively. A method for making blocks (10) is also disclosed, in which the coatings are first provided on a large sheet, and blocks (10) are then cut from the sheet using angled cuts. Since the coated block reduces the number of components required, the probe can be miniaturized, e.g. for use in an endoscope.

Abstract: A digital projection apparatus (10) for projection of a multicolor image uniformizes polychromatic light from a light source (12) and provides magnification to the uniformized illumination beam using a base condenser relay (80), providing a reduced numerical aperture for conditioning at a dichroic separator (27). For each monochromatic component color provided from the dichroic separator (27), a reducing relay (82) then demagnifies the illumination beam to provide source illumination to a spatial light modulator (30) at an increased numerical aperture. As a result, color shading across the field is minimized and brightness is optimized.

Abstract: A four port optical add/drop multiplexer (OADM) includes an optical filter reflective at a first wavelength and transmissive at a second wavelength. An input path having both first and second wavelengths is routed toward a first side of the filter. An optical DROP path is routed from a second side of the filter, to carry the transmitted second wavelength from the filter; and an optical ADD path is routed toward the second side of the filter for carrying an ADD signal, at the second wavelength. An output path carries the first and second wavelengths from the first side of the filter, including the ADD signal at the second wavelength, providing full OADM functionality, using a single filter. The device may include collimating lenses in the signal paths, and in one embodiment the filter can be a thin film filter fabricated directly on one of these lenses, thus improving optical performance.

Abstract: A color separation method and system wherein an optical spectrum is separated into optical wavelength ranges and wherein the optical signals of the separated wavelength ranges are further separated temporally. The optical spectrum can be spatially dispersed and the optical signals can be temporally dispersed, with three optical signals representing primary colors, such as red, green and blue.

Abstract: A color display apparatus for forming, on a display surface, a color image of superimposed color images, the display apparatus having a first color modulation channel for forming a first color two-dimensional image using a laser light source for providing a first color source beam, a linear spatial light modulator for modulating the first color source beam, and a scanning element for scanning the modulated light beam to form a first color two-dimensional image. A second color modulation channel forms a second color two-dimensional image using an incoherent light source for providing a second color source beam to an area spatial light modulator for modulating the second color source beam to form a second color two-dimensional image. A projection lens then projects a superimposed color image of the first color two-dimensional image and the second color two-dimensional image and any third color two-dimensional image.

Abstract: The invention provides an optical device including a polarization diversity unit for receiving an input optical signal and producing two beams of light having a same polarization state therefrom, a beam swapping element disposed for receiving the first and second beams of light and for redirecting the two beams of light to a same overlapping area of a modulator, and a reflective surface for reflecting the two beams of light back to the polarization diversity unit where they are combined to form an output optical signal. The beam swapping element is designed and positioned such that the first and second beams of light swap positions upon reflection from the reflective surface and trace out the other's optical path. Advantageously, this optical arrangement essentially eliminates all PDL and PMD.

Abstract: The invention is an on-axis optical projection system that displays an image on a projection surface. The optical projection system includes a light source and a reflective LCD microdisplay that modifies light from the light source to form a desired image. The LCD microdisplay reflects light toward the projection surface. A mirror reflects light from the light source in a first optical path toward the LCD microdisplay. The mirror does not affect the polarization orientation of the light reflected thereupon. A plurality of lenses are positioned within the system to focus and direct light along the first optical path and along a second optical path from the microdisplay to the projection surface. The first optical path is substantially opposite in direction to the second optical path. The plurality of lenses includes a dual-purpose lens that simultaneously transmits light along both the first optical path and the second optical path.

Abstract: A projection type image display apparatus includes a light axis moving unit for moving a direction of a light from a light source substantially in parallel periodically at a predetermined rate, a light separating unit for separating the light from the light axis moving unit into a plurality of color light components of predetermined wavelength bands, and a radiation unit for radiating the color light components from the light separating unit on an image display device, projecting an optical image corresponding to the image signal in enlarge form.

Abstract: A projection type display apparatus including an illumination optical system for emitting a light flux, a decomposition optical system for decomposing the light flux into color lights of red, green and blue, liquid crystal light valves for the colors for receiving the decomposed color lights, a synthesis optical system for synthesizing the image lights of the colors from the liquid crystal light valves, and a projection optical system for projecting the synthesized image lights to a screen. A filter is disposed at one of positions opposing to each other across the center of the light flux between the white light source and the decomposition optical system and attenuates or cuts off light of a wavelength region different from that of light which passes the other of the positions.

Abstract: The present invention relates to an image display apparatus, e.g. a head-mounted image display apparatus, in which an image from a single image display device is led to two eyes without using a half-mirror, thereby allowing observation of a bright image. The image display apparatus has an optical path distributing mirror 1 for distributing the image of a single display device 10 to an optical path for a right eye and an optical path for a left eye, and an ocular prism 2R for the right eye and an ocular prism 2L for the left eye, which are placed on the right- and left-hand sides, respectively, of the optical path distributing mirror 1.

Abstract: Removal of unnecessary reflected light in an image display apparatus employing reflective spatial light modulators to enable display of a high-quality image, having good contrast and no occurrence of the ghosting phenomena. Modulated light of each color synthesized by a fourth modulated light beam splitter 16 is injected into a projection lens 19 as circularly polarized light by a &lgr;/4 plate 18, reflected light (R′, G′, B′) reflected from the projection lens 19 does not return to the respective spatial light modulating elements 7, 11 and 12 for each color.

Abstract: A wavelength controller includes a wavelength locker module, having a prism for dividing incident light into first and second branched light beams, a first light quantity detector for receiving the first branched light beam through a wavelength selective filter and a second light quantity detector for directly receiving the second branched light beam, and detects and suppresses a wavelength variation in incident light entering the module based on outputs of the light quantity detectors.

Abstract: Methods for measuring and automatically controlling the light distribution and overall brightness in electronic-based spatial light modulator projection display systems. One method takes a small fraction of the projected light from a partial turning mirror 407 in the projector's optics path and focuses this light on to a detector 420 for use in controlling the light distribution and brightness of the system. Another method uses an array of embedded light sensors 518-522 at chosen locations on the surface of a display screen 517 to control the light distribution and brightness parameters of the projection system. Both methods use a micro-controller, servomotors, and an adjustable power supply, controlled by the detector/sensor outputs, to maintain the desired light distribution and brightness in the projected image.

Abstract: An optical apparatus for producing chromatic dispersion. The apparatus includes a virtually imaged phased array (VIPA) generator, a mirror and a lens. The VIPA generator receives an input light at a respective wavelength and produces a corresponding collimated output light traveling from the VIPA generator in a direction determined by the wavelength of the input light, the output light thereby being spatially distinguishable from an output light produced for an input light at a different wavelength. The mirror has a cone shape, or a modified cone shape. The lens focuses the output light traveling from the VIPA generator onto the mirror so that the mirror reflects the output light. The reflected light is directed by the lens back to the VIPA generator. In this manner, the apparatus provides chromatic dispersion to the input light.

Abstract: A projector arrangement has a light-splitting and recombining device that divides white light into red, green and blue light output at respective surfaces, and recombines red, green and blue light input to these respective. A transparent base body of the arrangement contains a layer of a material with lower refractive index and at least one layer of a material with higher refractive index. The lower refractive index is selected so that 1.7≦NLS≦2.1 and the refractive index of the transparent base body is selected so that 1.52≧NK≧1.

Abstract: The present invention provides a technique for improving the optical characteristics of a light-selective prism. By cutting a block along a plane perpendicular to a first direction, a plurality of first small blocks are obtained. A first selective film is formed on the cut face of the first small block, and the plurality of first small blocks are stuck together so as to obtain a first processed block in which the first selective film is located at the interface of adjacent two first small blocks. Next, by cutting the first processed block along a plane perpendicular to a second direction that is substantially perpendicular to the first direction, a plurality of second small blocks are obtained. A second selective film is formed on the cut face of the second small block, and the plurality of second small blocks are stuck together to obtain a second processed block in which the second selective film is located at the interface of adjacent two second small blocks.

Abstract: Optical engines using a reduced number of components offer advantages over more complex optical systems. Three panel optical engines have offered the advantage of relatively high throughput but at the cost of complexity and increased components on the bill of materials. Conventional two-panel engines have required the use of complex retarder structures to achieve the dual polarizations state for the three primary colors. The present invention achieves this goal while using simpler optical retarders.

Abstract: A system capable of tuning the wavelength and intensity of an output light includes an input end, a first output end, a second output end, a first rotatable optical device, a second rotatable optical device, and a third optical device. The input end is used to receive a first optical signal and a second optical signal. When the angle of the first rotatable optical device is adjusted, the first optical signal is able to pass through and the second optical signal is reflected. The second rotatable optical device allows the first optical signal to be outputted from the first output end. When the angle of the second rotatable optical device is adjusted, the intensity of the first optical signal outputted from the first output end changes. The angle of the third rotatable optical device is adjusted with respect to the angle of the first rotatable optical device, so that the second optical signal can be outputted from the second output end.

Abstract: A sequential color display system using a white light source (202) to create a full color image projected onto an image plane (214). A dynamic filter (206), typically a series of moving dichroic filters, generates a series of primary colored light beams that are swept across the surface of a spatial light modulator (210). Light rejected by the dynamic filter (206) enters a light recycler (204) and is reapplied to the dynamic filter (206). The light recycler is typically one or more reflective surfaces, including mirrors, baffles, enclosures, lamp reflectors, TIR surfaces, or specially coated material arranged in such a way as to encourage light toward an aperture separating the light recycler (204) and the dynamic filter (206). Typically all three primary colors are produced simultaneously by the dynamic filter (206).

Abstract: An optical device adapted for handling plane polarised light comprising a beamsplitter cube formed of two prisms having a polarising beamsplitter (PBS) arrangement located between the hypoteneuse faces of the prisms, the cube having a first pair of opposing faces forming an illumination input face and an illumination output face, and a second pair of opposing faces at which reflection means are located, wherein image-forming light is output from the output face, the image being derived from a display source located at one of the other faces of the cube and the arrangement of the reflection means being such that the cube does not support an intermediate image of the display source.

Abstract: A combiner (10) has a glass reflector (11) with first and second curved surfaces (12, 13) each having an optical coating. A first prism (14) has a surface (15) which complements the surface (12) of the reflector (11) and a second prism (16) has a surface (17) which complements the surface (13) of the reflector (11). The surfaces (12 and 13) and the surfaces (15 and 17) are each primed and allowed to dry before being polished. The reflector (11) and prisms (14 and 16) are arranged with respect to one another such that surface (12) forms a well (18) with surface (15) and similarly surface (13) forms a well (19) with surface (17). The wells (18, 19) are completed with a seal (20) at a lower end (21) and bonding agent (22, 23) is injected into the wells (18, 19). The combiner (10) is placed in a vacuum chamber to remove trapped air bubbles and the agent (22, 23) is allowed to cool at a temperature which does not unduly stress the reflector (11) and prisms (14 and 16).

Abstract: A single plate type optical unit and display device to utilize light with high efficiency in a simple method is configured so a dichroic mirror separates light into a plurality of colors, and the plurality of colors of light reflected by the dichroic mirror are beamed onto a rotating multisurface element, the plurality of colors of light emitted from the rotating multisurface element are each beamed onto different locations on the display element, and by rotating the rotating multisurface element, the plurality of colors of light are moved in one direction along the display element, and a color image is beamed from a projection lens.

Abstract: Polarization splitter in which reflection for the 1 polarization is locally centered on at least one emission peak of the image-emitting source of a micro-display or in which reflection for the 1 polarization is locally centered on at least one peak corresponding to a wavelength selected from red, green and blue.

Abstract: A system (S) for combining multi-spectral images of a scene includes a channel (18) for transmitting a scene image (10) in a first spectral band. A separate, second detector (22) senses the scene in a second spectral band. The second detector (22) has an image output that is representative of the scene. A display (28) displays an image (12) in the second spectral band. A beam mixer (30) combines the image output (10) in the first spectral band with the displayed image (12), and conveys the combined multi-spectral images to an output (32) for a user (U).

Abstract: LCD projection systems that use reflective LCD imager units commonly use one or more polarization beamsplitters to separate the light incident on the imager from the light reflected by one or more respective imagers. The polarizing beamsplitters can be mounted onto a color combiner using an index matching layer and optical adhesive.

Abstract: A fiber optic isolator device is used by fiber optic systems operating at more than one wavelength. The device may be inserted anywhere within the fiber network. The fiber optic device permits the separation of the wavelengths so that an optical isolator module can isolate a first wavelength without significantly affecting the second wavelength. This device is useful isolating a communications signal at 1.55 &mgr;m while avoiding significant losses for an optical time domain reflectometry signal, for example at 1.3 &mgr;m.

Abstract: A method and system for providing different magnified images of an electronic device. The vision system has a first beamsplitter for receiving an image of the device illuminated by a light source, the beamsplitter providing multiple of images of the device; optical elements for receiving the plural images of the device, each of the optical elements magnifying the image by a predetermined magnification factor to produce more than one magnified images; and a second beamsplitter for receiving the magnified images and filtering out all but one of the magnified images based on a wavelength of the light source.

Abstract: A WDM demultiplexer/multiplexer comprising a plurality of narrow band reflective filters linearly disposed along an optical axis, each narrow band reflective filter reflecting a single channel or group of channels and transmitting the remaining channels, is described. In a demultiplexing mode, an optical signal initially carrying channels at &lgr;1&lgr;2 . . . &lgr;N travels along the optical axis. Each narrow band reflective filter reflects a distinct channel and is tilted with respect to the optical axis such that it directs the reflected beam away from the optical axis to an output. Each narrow band reflective filter is substantially transparent to the remaining channels of the optical signal, such that the remainder of the optical signal proceeds along the optical axis substantially undisturbed.

Abstract: A known display device consists of a sheet-like support which is covered with liquid thermocromic crystals. The crystals are tempered by individual power supply to individual heatable elements, which lie close to the crystals and are placed between the sheet-like support and the crystals. The crystals assume different shades of color dependent on the given temperature so that hereby the color of the crystals will form a certain pattern. In order to improve the possibilities to control the tempering of the individual crystals and also protect them from being effected by the ambient temperature and from mechanical damage, the crystals have an underlying arrangement which is controlled to cool down th crystals and/or keep the sheet-like support of the crystals at a certain temperature. This temperature is lower than the temperature, at which the crystals are colored. Further the crystals are covered by a coating of lacquer over the complete sheet-like support.