Abstract: The invention relates to a diffractive optical system having a two-dimensional structure, which can be used as a phase shift mask for the fabrication of an optical element having a two-dimensional fine periodic structure, and a two-dimensional light beam splitter. The diffractive optical system 10 comprises a transparent substrate surface 1 that is divided in alignment with orthogonal two directions into minuscule square cell groups 2, 3 of the same shape in a checked pattern. The square cells that give a phase 2p? and a phase {(2q+1)?±??} where 0???0.25 and p and q are each an integer with respect to reference-wavelength light striking vertically on the transparent substrate surface 1 are alternately arranged in each direction, and the phase 2p?-giving square cells and the phase {(2q+1)?±??}-giving square cells are located in such a way as to be in alignment with 45° diagonal directions of said two directions.

Abstract: The invention relates to an apparatus for shaping a light beam, having at least two optically functional boundary surfaces that are arranged one behind another in the propagation direction (z) of the light beam to be shaped, such that the light beam can pass through the at least two optically functional boundary surfaces one after another, and two groups of refractive or diffractive imaging elements that are arranged on at least one of the optically functional boundary surfaces, at least two of the imaging elements having different properties within at least one of the groups.

Abstract: An optical system includes a diffractive optical element and a refractive optical element. The diffractive optical element corrects a chromatic aberration flare component of wavelengths other than a predetermined wavelength (a design wavelength) remaining in the refractive optical element by means of an aspherical component given by the grating pitch of a diffraction grating included in a diffractive portion of the diffractive optical element. In addition, a refractive portion of the diffractive optical element is adapted to correct an aberration component as a composite of the aberration component of the design standard wavelength shifted by the correction and the aberration component of the design standard wavelength of the refractive optical element.

Abstract: An electromagnetic radiation diffuser, operative at extreme ultraviolet (EUV) wavelengths, is fabricated on a substrate. The diffuser comprises a randomized structure having a peak and valley profile over which a highly reflective coating is evaporated. The reflective coating substantially takes the form of the peak and valley profile beneath it. An absorptive grating is then fabricated over the reflective coating. The grating spaces will diffusely reflect electromagnetic radiation because of the profile of the randomized structure beneath. The absorptive grating will absorb the electromagnetic radiation. The grating thus becomes a specialized Ronchi ruling that may be used for wavefront evaluation and other optical diagnostics in extremely short wavelength reflective lithography systems, such as EUV lithography systems.

Abstract: A method of wave propagation from 100–10000 GHz. The currently disclosed method and apparatus adapts micro-opto-electro-mechanical systems (MOEMS) technologies and processes to construct Kinoform optical components from microwave to terahertz range. The method uses induced coupled plasma (ICP) and gray scale processes for upper terahertz band; LIGA-based high aspect ratio (HAR) and gray scale processes are for the mid band; and computer numerical control (CNC) for lower band. In all cases, the thickness of any processed components is about the respective wavelength and system efficiency is about 95%. A Kinoform lens element is designed at 5000 GHz. However, the method is applicable for the entire terahertz band.

Abstract: A planar optical waveguide has sets of diffractive elements, each routing between input and output optical ports diffracted portions of an input optical signal. The diffractive elements are arranged so that the impulse response function of the diffractive element set comprises a reference temporal waveform or its time-reverse. A planar optical waveguide has N×M sets of diffractive elements, each routing between corresponding input and output optical ports corresponding diffracted portions of an input optical signal. The N×M diffractive element sets, N×M input optical ports, and N 1×M optical switches enable routing of an input optical signal any of the N input optical sources to any of the M output optical ports based on the operational state of the corresponding 1×M optical switch.

Abstract: Provided is a light emitting device including a Fresnel lens and/or a holographic diffuser formed on a surface of a semiconductor light emitter for improved light extraction, and a method for forming such light emitting device. Also provided is a light emitting device including an optical element stamped on a surface for improved light extraction and the stamping method used to form such device. An optical element formed on the surface of a semiconductor light emitter reduces reflective loss and loss due to total internal reflection, thereby improving light extraction efficiency. A Fresnel lens or a holographic diffuser may be formed on a surface by wet chemical etching or dry etching techniques, such as plasma etching, reactive ion etching, and chemically-assisted ion beam etching, optionally in conjunction with a lithographic technique. In addition, a Fresnel lens or a holographic diffuser may be milled, scribed, or ablated into the surface.

Abstract: A spectral filter comprises a planar optical waveguide having at least one set of diffractive elements. The waveguide confines in one transverse dimension an optical signal propagating in two other dimensions therein. The waveguide supports multiple transverse modes. Each diffractive element set routes, between input and output ports, a diffracted portion of the optical signal propagating in the planar waveguide and diffracted by the diffractive elements. The diffracted portion of the optical signal reaches the output port as a superposition of multiple transverse modes. A multimode optical source may launch the optical signal into the planar waveguide, through the corresponding input optical port, as a superposition of multiple transverse modes. A multimode output waveguide may receive, through the output port, the diffracted portion of the optical signal. Multiple diffractive element sets may route corresponding diffracted portions of optical signal between one or more corresponding input and output ports.

Abstract: An optical apparatus (spectral filter, temporal encoder, or other) comprises a planar optical waveguide having at least one set of diffractive elements. Each diffractive element set routes by diffraction therefrom a portion of the optical signal propagating in the planar waveguide. The planar waveguide includes at least one material having thermo-optic properties chosen so as to yield a designed temperature dependence of spectral and/or temporal characteristics of the diffracted portion of the optical signal. Variations of material refractive indices, physical dimensions, and/or optical mode distributions with temperature may at least partly compensate one another to yield the designed temperature dependence. Optical materials with ?n/?T of various magnitudes and signs may be variously incorporated into the waveguide core and/or cladding.

Abstract: A three-dimensional imaging system is described which exploits the defocusing of non-zero diffraction order images caused by the quadratic distortion of a diffraction grating (4). An optical system (1) is used such that objects (5, 6 and 7), located at different distances from grating (4), are imaged simultaneously and spatially separated on a single plane B.

Abstract: A distributed optical structure comprises a set of diffractive elements. Individual diffractive element transfer functions collectively yield an overall transfer function between entrance and exit ports. Diffractive elements are defined relative to virtual contours and include diffracting region(s) altered to diffract, reflect, and/or scatter incident optical fields (altered index, surface, etc). Element and/or overall set transfer functions (amplitude and/or phase) are determined by: longitudinal and/or angular displacement of diffracting region(s) relative to a virtual contour (facet-displacement grayscale); longitudinal displacement of diffractive elements relative to a virtual contour (element-displacement grayscale); and/or virtual contour(s) lacking a diffractive element (proportional-line-density gray scale).

Abstract: The present invention has for its object to provide an optical device whose size is made small. In order to achieve this, according to the present invention there is provided an optical device in which a clad and a core whose refractive index is relatively higher than that of the clad are formed on a substrate and light can be transmitted through the core, wherein the core is provided with an input light transmitting pattern section, a diffraction pattern section, and a phase difference generating pattern section. Further, at least in the phase difference generating pattern section, a part, where refractive indexes are different respectively in the direction parallel to the substrate and in the direction perpendicular to the substrate, is provided.

Abstract: A diffractive optical element includes a first diffractive optical part having a phase type diffractive grating, and a second diffractive optical part having a phase type diffractive grating formed of a material differing from that of the first diffractive optical part. The first diffractive optical part and the second diffractive optical part are disposed in proximity to each other with an air layer. Each of the first diffractive optical part and the second diffractive optical part has a mark for aligning them with the optical effective areas thereof.

Abstract: The device of the present invention includes an electrochromic element having a transmittance that varies in response to an electrical signal, a base substrate disposed in spaced relation to the electrochromic element, a seal disposed between the base substrate and the electrochromic element, and an optical sensor. The seal, base substrate, and electrochromic element form a sealed cavity therebetween, in which the optical sensor is disposed. According to another embodiment, an electrochromic device is provided that includes a first substrate, an electrochromic medium disposed on the first substrate, a pair of electrodes in contact with the electrochromic medium, a pair of conductive clips, each in electrical contact with a respective one of the electrodes, and two pairs of electrical lead posts for mounting the first substrate to the circuit board. Each pair of lead posts is attached to, and extends from, a respective one of the conductive clips.

Abstract: In order to achieve highly dispersive spectrometry in wide wavelength with the use of a single grism, but not a plurality of grisms, the grism is composed of a prism the vertex angle of which can be varied and a volume phase holographic (VPH) grating. More specifically, the grism comprises a prism the vertex angle of which can be varied; and a VPH grating being a diffraction grating and disposed substantially orthogonal with respect to a side including the vertex angle of the prism; the VPH grating being rotated around an axis being substantially orthogonal to the side of the prism, whereby a slope angle defined by the VPH grating and a predetermined plane is varied.

Abstract: An achromatic Fresnel optic that combines a Fresnel zone plate and a refractive Fresnel lens. The zone plate provides high resolution for imaging and focusing, while the refractive lens takes advantage of the refraction index change properties of appropriate elements near absorption edges to recombine the electromagnetic radiation of different energies dispersed by the zone plate. This compound lens effectively solves the high chromatic aberration problem of zone plates. The AFO has a wide range of potential applications in lithography, microimaging with various contrast mechanisms and measurement techniques.

Abstract: A mask blank inspection tool includes an AFO having a diffractive lens and a refractive lens formed on a common substrate. The diffractive lens is a Fresnel zone plate and the refractive lens is a refractive Fresnel lens. The AFO is used to image light from a defect particle on a multilayer mask blank or the surface of the multilayer mask blank to a detector.

Abstract: When a Gaussian power distribution laser beam is converted into a uniform power density beam by a converging homogenizing DOE and is divided into a plurality of homogenized beams by a diverging DOE, the power of the separated beam spatially fluctuates. For alleviating the power fluctuation of the beams, an aperture mask having a window wider than a section of the homogenized beam but narrower than a noise region at a focus of the converging homogenizer DOE. Since a homogenized beam can pass the aperture mask as a whole, the power fluctuation, in particular, near edges is reduced.

Abstract: A lithography apparatus having achromatic Fresnel objective (AFO) that combines a Fresnel zone plate and a refractive Fresnel lens. The zone plate provides high resolution for imaging and focusing, while the refractive lens takes advantage of the refraction index change properties of appropriate elements near absorption edges to recombine the electromagnetic radiation of different energies dispersed by the zone plate. This compound lens effectively solves the high chromatic aberration problem of zone plates. The lithography apparatus allows the use of short wavelength radiation in the 1-15 nm spectral range to print high resolution features as small as 20 nm.

Abstract: A liquid-crystal lens includes a hologram liquid-crystal element having a liquid crystal which provides a light beam transmitting therethrough with a phase change so as to have a wavefront of a blaze-hologram shape; and a segment liquid-crystal element including a first electrode divided correspondingly to the blaze-hologram shape, a second electrode opposed to the first electrode and a liquid crystal for providing the transmitting light beam with a phase change by voltage application to the first and second electrodes, the segment liquid-crystal element being arranged coaxial to the hologram liquid-crystal element.

Abstract: Disclosed is a diffractive optical element which is made of at least two materials of different dispersions and which includes at least two diffraction gratings being accumulated one upon another, wherein each diffraction grating is formed on a curved surface of a substrate, and wherein a diffraction grating, of the at least two diffraction gratings, in which a curvature radius of the curved surface and a curvature radius of a grating surface in a portion where a grating pitch is largest, have different signs, is one of the at least two diffraction gratings which has a smallest grating thickness.

Abstract: An optical element having a diffraction shape uses an optical material comprising at least N-vinylcarbazole, polyvinylcarbazole, and the light polymerization initiator. By using such optical material, it is possible to suppress crystallization of the optical material during molding even at room temperature and appropriately control the dropping amount suited for replica molding. It is possible to provide the optical material also suited for replica molding at room temperature by setting a ratio of N-vinylcarbazole to polyvinylcarbazole, i.e. N-vinylcarbazole/polyvinylcarbazole, to a range between 90/10 and 70/30.

Abstract: An aberration compensating optical element includes: a diffractive structure having a plurality of ring-shaped zone steps formed into substantially concentric circles on at least one surface of the aberration compensating optical element; wherein the aberration compensating optical element is adapted for being disposed on an optical path between a light source for emitting a light having a wavelength of not more than 550 nm, and an objective lens made of a material having an Abbe constant of not more than 95.

Abstract: A light transmission system includes a laser, an optical fiber, and a transfer lens. The transfer lens transfers light emitted by the laser into the optical fiber. The transfer lens includes a diffractive surface for receiving and collimating the light originating form the laser. The diffractive surface is defined by a surface function that includes a first phase function having angular symmetry and a second phase function having radial symmetry. The second phase function includes a cusp region with a discontinuous slope therein. The transfer lens provides reflection management so that light reflected from the end of the optical fiber is not focused at a location at which light is emitted by the laser and also favorable launch conditions so that light launched into the optical fiber avoids index anomalies along the axis of the optical fiber.

Abstract: A diffractive optical element efficiently converts an input light beam into an output light beam having a specified cross-sectional shape. The diffractive optical element includes a plurality of partial optical elements. The plurality of partial optical elements convert the input light beam to respective partial light beams, each of which has a shape that does not correspond to the specified cross-sectional shape. The sum of the partial light beams matches the shape of the output light beam (i.e., having the specified cross-sectional shape).

Abstract: A distributed optical structure comprises a set of diffractive elements. Individual diffractive element transfer functions collectively yield an overall transfer function between entrance and exit ports. Diffractive elements are defined relative to virtual contours and include diffracting region(s) altered to diffract, reflect, and/or scatter incident optical fields (altered index, surface, etc). Element and/or overall set transfer functions (amplitude and/or phase) are determined by: longitudinal and/or angular displacement of diffracting region(s) relative to a virtual contour (facet-displacement grayscale); longitudinal displacement of diffractive elements relative to a virtual contour (element-displacement grayscale); and/or virtual contour(s) lacking a diffractive element (proportional-line-density gray scale).

Abstract: Novel methods are disclosed for designing and constructing miniature optical systems and devices employing light diffractive optical elements (DOEs) for modifying the size and shape of laser beams produced from a commercial-grade laser diodes, over an extended range hitherto unachievable using conventional techniques. The systems and devices of the present invention have uses in a wide range of applications, including laser scanning, optical-based information storage, medical and analytical instrumentation, and the like. In the illustrative embodiments, various techniques are disclosed for implementing the DOEs as holographic optical elements (HOEs), computer-generated holograms (CGHs), as well as other diffractive optical elements.

Abstract: An optical system includes a diffractive optical element having a diffraction grating provided, on a lens surface having a curvature, in a concentric-circles shape rotationally-symmetrical with respect to an optical axis. The sign of the curvature of the lens surface having the diffraction grating provided thereon is the same as the sign of a focal length, at a design wavelength, of a system composed of, in the optical system, a surface disposed nearest to an object side to a surface disposed immediately before the lens surface having the diffraction grating provided thereon, and is different from the sign of the distance from the optical axis to a position where the center ray of an off-axial light flux enters the lens surface having the diffraction grating provided thereon. Further, the apex of an imaginary cone formed by extending a non-effective surface of the diffraction grating is located adjacent to the center of curvature of the lens surface having the diffraction grating provided thereon.

Abstract: A first diffractive optical element pattern with a pattern pitch that is no greater than a wavelength of incident light is formed on a first main surface of substrate such as a glass plate. Second diffractive optical element patterns are formed at positions that are respectively incident to positive first-order diffracted light and negative first-order diffracted light produced by the first diffractive optical element pattern. Negative first-order diffracted light produced by each second diffractive optical element pattern is incident upon a boundary face of the substrate at an angle that is smaller than the critical angle, and so exits the substrate.

Abstract: A light transmission system includes a laser, an optical fiber, and a transfer lens. The transfer lens transfers light emitted by the laser into the optical fiber. The transfer lens includes a diffractive surface for receiving and collimating the light originating form the laser. The diffractive surface is defined by a surface function that includes a first phase function having angular symmetry and a second phase function having radial symmetry. The second phase function includes a cusp region with a discontinuous slope therein. The transfer lens provides reflection management so that light reflected from the end of the optical fiber is not focused at a location at which light is emitted by the laser and also favorable launch conditions so that light launched into the optical fiber avoids index anomalies along the axis of the optical fiber.

Abstract: An objective lens unit for an optical pickup used for recording and/or reproducing information signals from an optical disc. The objective lens unit includes a resin layer (21) having, sequentially from an object side, a first surface S1 as an aspherical surface and a second surface S2 as an aspherical surface, at least one of the first surface and the second surface including a diffractive surface, and a lens of glass (22) having the second surface S2 as an aspherical surface and a third surface S3 as an aspherical surface. The lens unit is corrected for the chromatic aberration on an image surface on the optical axis with respect to the light of a reference wavelength not larger than 420 nm within several nm of the reference wavelength, with the numerical aperture of the lens unit being not less than 0.8. This objective lens unit is able to converge the laser light close to the limit of diffraction on the image surface.

Abstract: A light transmission system includes a laser, an optical fiber, and a transfer lens. The transfer lens transfers light emitted by the laser into the optical fiber. The transfer lens includes a diffractive surface for receiving and collimating the light originating form the laser. The diffractive surface is defined by a surface function that includes a first phase function having angular symmetry and a second phase function having radial symmetry. The second phase function includes a cusp region with a discontinuous slope therein. The transfer lens provides reflection management so that light reflected from the end of the optical fiber is not focused at a location at which light is emitted by the laser and also favorable launch conditions so that light launched into the optical fiber avoids index anomalies along the axis of the optical fiber.

Abstract: A diffractive optical element has a plurality of diffraction structures for a certain wavelength. These each have a width measured in the plane of the diffractive optical element and a height measured perpendicularly thereto. The widths and the heights of the diffraction structures vary over the area of the diffractive optical element. An optical arrangement comprising such a diffractive optical element has, in addition, a neutral filter. The efficiency of such a diffractive optical element and of such an arrangement can be optimized locally for usable light.

Abstract: An aberration compensating optical element includes: a diffractive structure having a plurality of ring-shaped zone steps formed into substantially concentric circles on at least one surface of the aberration compensating optical element; wherein the aberration compensating optical element is adapted for being disposed on an optical path between a light source for emitting a light having a wavelength of not more than 550 nm, and an objective lens made of a material having an Abbe constant of not more than 95.

Abstract: An optical device for making light converge produces a convergent light beam with a satisfactorily great numerical aperture and acceptably small aberrations. The optical device has a plurality of diffraction gratings that each make light converge. The light shone into the optical device is passed through one after another of those diffraction gratings in such a way that the light is made to converge to a higher degree every time it passes through one of the diffraction gratings. The diffraction gratings may be all transmissive, all reflective, or a combination of both. The diffraction gratings are formed on a surface of or at an interface inside the optical device, and two diffraction gratings may be formed on a single surface. The light is made to eventually converge on the exit surface of the optical device so that the optical device functions as a solid immersion device.

Abstract: An optical system includes a diffractive optical element having a diffraction grating provided, on a lens surface having a curvature, in a concentric-circles shape rotationally-symmetrical with respect to an optical axis. The sign of the curvature of the lens surface having the diffraction grating provided thereon is the same as the sign of a focal length, at a design wavelength, of a system composed of, in the optical system, a surface disposed nearest to an object side to a surface disposed immediately before the lens surface having the diffraction grating provided thereon, and is different from the sign of the distance from the optical axis to a position where the center ray of an off-axial light flux enters the lens surface having the diffraction grating provided thereon. Further, the apex of an imaginary cone formed by extending a non-effective surface of the diffraction grating is located adjacent to the center of curvature of the lens surface having the diffraction grating provided thereon.

Abstract: An optical component including: a substrate made from heat absorptive glass having a front surface and a rear surface, at least one of said surfaces being a crenulate surface having optical power.

Abstract: The use of one or more wavefront modulators in the observation beam path and/or illumination beam path of a microscope provide various advantageous results. Such modulators may be adapted to change the phase and/or the amplitude of light in such a way to carry out displacement and shaping of the focus in the object space and correction of possible aberrations. The possible areas of use include confocal microscopy, laser-assisted microscopy, conventional light microscopy and analytic microscopy.

Abstract: Methods for fabricating refractive element(s) and aligning the elements in a compound optic, typically to a zone plate element are disclosed. The techniques are used for fabricating micro refractive, such as Fresnel, optics and compound optics comprising two or more optical elements for short wavelength radiation. One application is the fabrication of the Achromatic Fresnel Optic (AFO). Techniques for fabricating the refractive element generally include: 1) ultra-high precision mechanical machining, e.g,. diamond turning; 2) lithographic techniques including. gray-scale lithography and multi-step lithographic processes; 3) high-energy beam machining, such as electron-beam, focused ion beam, laser, and plasma-beam machining; and 4) photo-induced chemical etching techniques. Also addressed are methods of aligning the two optical elements during fabrication and methods of maintaining the alignment during subsequent operation.

Abstract: A hybrid achromatic optical lens having a high numerical aperture whose chromatic aberration is removed and a method for manufacturing the same are provided. The hybrid achromatic optical lens includes a first optical member of a low index of refraction and a second optical member of a high index of refraction. The second optical member is formed on a depressed portion of the first optical member and has a diffractive surface, which is a contact surface of the second optical member with the first optical member and has a plurality of pitches formed on a refractive surface.

Abstract: A zoom lens includes a first lens unit having a positive optical power, a second lens unit having a negative optical power, a third lens unit having a positive optical power, and a fourth lens unit having a negative optical power in sequence from an object side. The zoom lens executes zooming by moving all the four lens units on an optical axis. At least one of the four lens units has at least one diffractive optical surface. By this arrangement, the size of the zoom lens can be easily reduced while securing a desired variable power ratio and correcting lateral chromatic aberration that is varied by zooming.

Abstract: The present invention provides a scanning device with the following features: the system is capable of writing data to record carriers of a first format because it is corrected for chromatic aberration resulting from fast wavelength variations during write operation; it has a diffractive element with a generally sawtooth-like pattern, such that it may for example be manufactured in a single-step replication process; the system has high efficiency for scanning first optical record carriers (e.g. DVDs) and acceptable efficiency for scanning second optical record carriers (e.g. CDs); and the lens provides limited spherochromatism and the system is thus able to cope with wavelength variations.

Abstract: A hybrid lens with a high numerical aperture is described.

Abstract: A lithography apparatus having achromatic Fresnel objective (AFO) that combines a Fresnel zone plate and a refractive Fresnel lens. The zone plate provides high resolution for imaging and focusing, while the refractive lens takes advantage of the refraction index change properties of appropriate elements near absorption edges to recombine the electromagnetic radiation of different energies dispersed by the zone plate. This compound lens effectively solves the high chromatic aberration problem of zone plates. The lithography apparatus allows the use of short wavelength radiation in the 1-15 nm spectral range to print high resolution features as small as 20 nm.

Abstract: An optical unit includes a first optical element and a second optical element, wherein the first optical element has a protrusion while the second optical element has a recess. The relative alignment between the first and second optical elements is accomplished by engagement of the protrusion and the recess.

Abstract: An aberration compensating optical element includes: a diffractive structure having a plurality of ring-shaped zone steps formed into substantially concentric circles on at least one surface of the aberration compensating optical element; wherein the aberration compensating optical element is adapted for being disposed on an optical path between a light source for emitting a light having a wavelength of not more than 550 nm, and an objective lens made of a material having an Abbe constant of not more than 95.

Abstract: In one embodiment of the invention, a grating structure etched on a mirror substrate has a grating period causing diffracting, out of an optical path, a first incident radiation within a first band around a first wavelength. A multi-layer coating deposited on the grating structure reflects the first incident radiation, in the optical path, within the first band and a second incident radiation within a second band around a second wavelength. In another embodiment, a first multi-layer coating deposited on a mirror substrate reflects a first incident radiation within a first band around a first wavelength and a second incident radiation, in an optical path, within a second band around a second wavelength. A grating structure is deposited on the first multi-layer coating. The grating structure is etched to have a grating period causing diffracting, out of the optical path, the second incident radiation within the second band.

Abstract: An optical scanning device for scanning optical record carriers with radiation of a selected wavelength, the device including an objective lens, having an axial direction and a radial direction, and a phase structure which is non-periodic with respect to the radial direction, the non-periodic phase structure being arranged to compensate for comatic aberrations generated in the objective lens when an optical record carrier is read in a direction which is non-axial with respect to said objective lens, whereby an improved field of view is provided for said objective lens.

Abstract: In one embodiment of the invention, a grating structure etched on a mirror substrate has a grating period causing diffracting, out of an optical path, a first incident radiation within a first band around a first wavelength. A multi-layer coating deposited on the grating structure reflects the first incident radiation, in the optical path, within the first band and a second incident radiation within a second band around a second wavelength. In another embodiment, a first multi-layer coating deposited on a mirror substrate reflects a first incident radiation within a first band around a first wavelength and a second incident radiation, in an optical path, within a second band around a second wavelength. A grating structure is deposited on the first multi-layer coating. The grating structure is etched to have a grating period causing diffracting, out of the optical path, the second incident radiation within the second band.

Abstract: A compound objective lens is composed of a hologram lens or transmitting a part of incident light without any diffraction to form a beam of transmitted light and diffracting a remaining part of the incident light to form a beam of first-order diffracted light, and an objective lens for converging the transmitted light to form a first converging spot on a front surface of a thin type of first information medium and converging the diffracted light to form a second converging spot on a front surface of a thick type of second information medium. Because the hologram selectively functions as a concave lens for the diffracted light, a curvature of the transmitted light differs from that of the diffracted light.