Abstract: A method for forming a phase grating is disclosed. First, a substrate is provided. Second, a first dielectric layer with a tapered recess or bulge is formed on the substrate. Later, a second dielectric layer is formed to fill the tapered recess and to cover the first dielectric layer. Afterwards, the second dielectric layer is selectively etched to form the phase grating. The phase grating includes a column and multiple rings. The column and multiple rings are concentric and the multiple rings are disposed on the tapered side so that the height of each ring is different.

Abstract: A photographic optical system includes, in order from an object side to an image side, a first lens unit, a second lens unit for focusing, and a third lens unit. The first lens unit includes a first lens sub-unit having a positive refractive power and a second lens sub-unit. The first lens unit includes a diffractive optical element and an aspheric surface. A length on an optical axis from a lens surface furthest on the object side of the first lens sub-unit to an image plane, an air space between the first lens sub-unit and the second lens sub-unit, a focal length of the first lens sub-unit, a focal length of the second lens sub-unit, a focal length of the diffractive optical element by only a diffractive component, a focal length and an F-number of the entire photographic optical system are appropriately set to satisfy predetermined conditions for optimal focusing.

Abstract: The invention comprises a polymeric microarray support (1) for an optical assay arrangement (2) comprising optical means (3, 4, 6) for detection of light emitted from the support. The microarray support is provided with microfeatures comprising a surface enlarging pattern (5), i.e. grooves having a selected depth (8). The depth is selected such that the sum of the depth and of the variations in the thickness (7) of the support substantially corresponds to the depth of focus of the optical means.

Abstract: A diffractive optical system including a diffractive optical element is provided with a first lens component having a first positive lens, and a second lens component having a second positive lens and a negative lens. The diffractive optical element has a first diffractive optical member having a first diffractive optical surface, and a second diffractive optical member having a second diffractive optical surface. The first diffractive optical member and the second diffractive optical member are arranged so that the first diffractive optical surface and the second diffractive optical surface are in contact with each other. A refractive index of the first diffractive optical member and a refractive index of the second diffractive optical member at the d line are different from each other.

Abstract: A system and method for uniform light generation in projection display systems. An illumination source comprises a light source to produce colored light, and a scrolling optics unit optically coupled to the light source, the scrolling optics unit configured to create lines of colored light from the colored light, and to scroll the lines of colored light along a direction orthogonal to a light path of the illumination source. The scrolling optics unit comprises a single light shaping diffuser to transform the colored light into the lines of colored light, an optical filter positioned in the light path after the light shaping diffuser, and a scrolling optics element positioned in the light path after the optical filter. The single light shaping diffuser is capable of simultaneously transforming colored light into lines of colored light having substantially uniform intensity to provide uniform illumination.

Abstract: A diffractive optical system including a diffractive optical element has a concave lens component having a first diffractive optical surface, and an optical member having a second diffractive optical surface, the concave lens component and the optical member being arranged so that the first diffractive optical surface and the second diffractive optical surface face each other, and the conditional expression 0.003<t/f<0.3 being satisfied, where t is the thickness of the concave lens component on the optical axis, and f is the focal length of the diffractive optical system.

Abstract: Systems and methods are provided for providing wideband diffraction limited performance in an optical receiver. A first lens is constructed from a first material and has a first surface and a second surface. A second lens is constructed from a second material and having a first surface and a second surface. The second lens is positioned such that a first surface of the second lens faces a second surface of the first lens across a gap of air. A diffraction grating is applied to one of the first and second surfaces of the first and second lenses.

Abstract: To provide a compact image forming optical system in which an incident angle to an imaging plane of a solid-state imaging device is small and whose chromatic aberration, astigmatism, field curvature, and distortion are reduced. An image forming optical system of a first embodiment of the present invention comprises four lenses arranged from the object side to the imaging plane side in order, that are a first lens that is a double-convex lens, a second lens that is a double-concave lens, a third lens that is a positive meniscus lens that is convex toward an image side, and a fourth lens that is a negative meniscus lens that is convex toward an object side. An aperture is placed closer to the object than the image side surface of the first lens.

Abstract: A diffractive lens 11 according to the present invention includes: a lens base 18, which has a second surface 13 with first and second groups of diffraction grating portions 20 and 21; and a protective coating 17, which is arranged on the first group of diffraction grating portions 20. The first group of diffraction grating portions 20 has a first group of diffraction steps and the second group of diffraction grating portions 21 has a second group of diffraction steps, which is lower in height than the first group of diffraction steps. One of the respective materials of the base 18 and the protective coating 17 has a higher refractive index and a greater Abbe number than the other material. And the second group of diffraction steps is not covered with the protective coating 17.

Abstract: According to the present invention, a small-sized double-lens imaging optical system whose chromatic aberration is corrected even at a super wide angle of 150° or more can be provided. The double-lens imaging optical system of the present invention includes a concave lens, and a convex lens having a diffraction grating provided thereon, and satisfies the following conditional expression (1): 4.5<P1=(1?f/fa)·?d<9.0??(1). Herein, f is an effective focal length of the double-lens imaging optical system; fa is an effective focal length of the double-lens imaging optical system excluding the diffraction grating; and ?d is an Abbe number of the material of the convex lens with respect to the d-line. As a result, chromatic aberration can be well corrected even with respect to rays entering at high angles of view.

Abstract: A concave diffraction grating device, a reflective dispersion device, and a spectral device of the invention include a diffraction grating plane having an aspherical configuration, wherein the diffraction grating plane is symmetrical in a predetermined direction, and asymmetrical in a direction orthogonal to the predetermined direction in such a manner that the curvature of one end portion of the diffraction grating plane in the direction orthogonal to the predetermined direction is gradually decreased, and the curvature of the other end portion thereof is gradually increased. The concave diffraction grating device, the reflective dispersion device, and the spectral device with the above arrangement have desirable slit image forming performance with respect to all the wavelengths in a visible region, and are suitable for mass-production.

Abstract: Microparticles 8 includes an optical substrate 10 having at least one diffraction grating 12 disposed therein. The grating 12 having a plurality of colocated pitches ? which represent a unique identification digital code that is detected when illuminated by incident light 24. The incident light 24 may be directed transversely from the side of the substrate 10 with a narrow band (single wavelength) or multiple wavelength source, in which case the code is represented by a spatial distribution of light or a wavelength spectrum, respectively. The code may be digital binary or may be other numerical bases. The micro-particles 8 can provide a large number of unique codes, e.g., greater than 67 million codes, and can withstand harsh environments. The micro-particles 8 are functionalized by coating them with a material/substance of interest, which are then used to perform multiplexed experiments involving chemical processes, e.g., DNA testing and combinatorial chemistry.

Abstract: A diffractive optical system including a diffractive optical element has a concave lens component having a first diffractive optical surface, and an optical member having a second diffractive optical surface, the concave lens component and the optical member being arranged so that the first diffractive optical surface and the second diffractive optical surface face each other, and the conditional expression 0.003<t/f<0.3 being satisfied, where t is the thickness of the concave lens component on the optical axis, and f is the focal length of the diffractive optical system.

Abstract: An antireflection film includes a multilayer film having six layers, in total, provided between an optical substrate and an adhesion layer. The respective layers of first to sixth layers are laminated in order from one side of the adhesion layer. A refractive index of the antireflection film as a whole is lower than that of the optical substrate and higher than that of the adhesion layer. The first and third layers are low refractive index layers having a refractive index of 1.35 to 1.50 at d line. The second, fourth and sixth layers are middle refractive index layers having a refractive index of 1.55 to 1.85 at the d line. The fifth layer is a high refractive index layer having a refractive index, at the d line, that is in a range of 1.70 to 2.50 and that is higher than that of the middle refractive index layer.

Abstract: A plurality of convex strip portions are formed on a front surface (or a back surface) of a light guiding plate, extending in a direction from a light incidence plane to an opposite side surface. A concave portion is formed on a side surface of each convex strip portion. An inner wall of the concave portion is formed from at least two flat planes inclined with respect to three axial directions orthogonal to each other (X, Y and Z axial directions), respectively. Thereby, damage to the surface illuminant equipment such as a light guiding plate due to the interference between a back surface and units disposed on the back surface of the light guiding plate is prevented, while preventing a linear part with relatively low luminance from being viewed from the front surface of the light guiding plate.

Abstract: The invention relates to an electronic display arrangement comprising a light pipe (1) for transmitting light signals emitted by a miniature screen (2) from one of its ends, referred to as its entry surface (1A), to its other end, referred to as its exit surface (1B), and thence towards the eye (0) of a user for viewing a virtual image, the arrangement further comprising a field lens (3) interposed between said screen (2) and said entry surface (1A), the field lens having both a plane working surface (3A) of rectilinear section that is placed facing the screen (2) centered on the optical axis (L3) of said field lens, and an aspherical working surface (3B). According to the invention, said aspherical surface is placed facing said entry surface (1A), with the optical axis of the field lens and the optical axis of the light pipe coinciding, and said plane working surface (3A) is adhesively bonded to the screen (2).

Abstract: To provide a compact image forming optical system in which an incident angle to an imaging plane of a solid-state imaging device is small and whose chromatic aberration, astigmatism, field curvature, and distortion are reduced. An image forming optical system of a first embodiment of the present invention comprises four lenses arranged from the object side to the imaging plane side in order, that are a first lens that is a double-convex lens, a second lens that is a double-concave lens, a third lens that is a positive meniscus lens that is convex toward an image side, and a fourth lens that is a negative meniscus lens that is convex toward an object side. An aperture is placed closer to the object than the image side surface of the first lens.

Abstract: A second region (12) composed of a plane is formed around a first region (11) having a lens function, and a third region (13) is formed between the first region and the second region. A protection film (24) is formed on the surface of the first region 1. The first region is protruded relative to the second region, the third region is formed throughout the rim of the first region 1, and the surface of the third region is recessed relative to a virtual curved surface (11a) that is a curved surface along the surface shape of the first region being extended to the second region. Consequently, it is possible to form throughout the first region a protection film having a surface shape that substantially matches the surface shape of the first region.

Abstract: A color dividing optical device has an integrated structure of dual surfaces, each has a micro/nano structure. The optical device can perform beam splitting and color dividing on an incident light source, which has a constitution from multiple different wavelengths. In a space, the original incident light source is equally split into multiple light beams in an array, according to light intensity. At the same time, the light beam constituted from different wavelengths is divided into multiple sub-light sources, according to the wavelength, so as to have the function to propagate a color array with color dividing. The optical device with capability of modulating the color wavelengths can transform the wide-band incident light source into sub-light beams in array with color dividing (wavelength dividing) and beam splitting.

Abstract: An element includes a first resin layer and a second resin layer disposed between a first glass lens substrate and a second glass lens substrate, a boundary surface between the first resin layer and the second resin layer having a diffraction grating shape including a plurality of inclined surfaces and wall surfaces. The second resin layer is composed of a fluororesin in which fine metal oxide particles are dispersed. Since a refractive index distribution easily occurs in this material during curing by application of ultraviolet light, by applying ultraviolet light substantially perpendicular to the inclined surfaces of the diffraction grating shape, a refractive index distribution is formed in the thickness direction perpendicularly to the inclined surfaces.

Abstract: In a refraction lens having an aspheric shape formed thereon and having a positive power, a diffraction grating is formed on at least one of the faces of the refraction lens. In order to reduce the curvature of field and the chromatic aberration in a well-balanced manner, the zonal pitch of the diffraction grating is constituted so as to satisfy the following conditional expression. [ eq . ? 19 ] 0.21 ? ? m 2 ? v d ? ? ? f h max < ? min < 0.30 ? ? m 2 ? v d ? ? ? f h max ( 1 ) Herein, ?min is a minimum zonal pitch 12; m is an order of diffraction; ?d is an Abbe number of the lens substrate material with respect to the d-line; ? is a wavelength; f is an effective focal length; and hmax is an effective radius 13 of the face on which the diffraction grating is formed.

Abstract: Aspheric diffractive lenses are disclosed for ophthalmic applications. For example, multifocal intraocular lens (IOLs) are disclosed that include an optic having an anterior surface and a posterior surface, at least one of which surfaces includes an aspherical base profile on a portion of which a plurality of diffractive zones are disposed so as to generate a far focus and a near focus. The aspherical base profile enhances image contrast at the far focus of the lens relative to that obtained by a substantially identical IOL in which the respective base profile is spherical.

Abstract: A lens according to the present invention includes at least one first area (11) including a lens portion (11a) with a convex shape, and a second area (12) surrounding the first area (11). A groove (13) surrounding the first area (11) is formed between the first area (11) and the second area (12). A coating layer (14) is formed on the lens portion (11a).

Abstract: The present application discloses a system comprising a compact curved grating (CCG) and its associated compact curved grating spectrometer (CCGS) or compact curved grating wavelength multiplexer/demultiplexer (WMDM) module and a method for making the same. The system is capable of achieving a very small (resolution vs. size) RS factor. In the invention, the location of the entrance slit and detector can be adjusted in order to have the best performance for a particular design goal. The initial groove spacing is calculated using a prescribed formula dependent on operation wavelength. The location of the grooves is calculated based on two conditions. The first one being that the path-difference between adjacent grooves should be an integral multiple of the wavelength in the medium to achieve aberration-free grating focusing at the detector or output slit (or output waveguide) even with large beam diffraction angle from the entrance slit or input slit (or input waveguide).

Abstract: A diffractive optical element includes a plurality of diffraction gratings. A diffraction grating within the plurality of diffraction gratings includes a plurality of grating parts having a curved grating surface and grating tips which connect to define a curved envelope face. The grating surface has a radius of curvature larger than a radius of curvature of the envelope face. In addition, two diffraction gratings within the plurality of diffraction gratings are composed of different materials having different dispersions. Therefore, even when the radius of curvature of the envelope face is small, the degradation of the diffraction efficiency is suppressed.

Abstract: A spill light removing device includes a first blocker which is located perpendicularly to a stream route of light being irradiated from a light source and blocks a stream of light that is incident to the surface of the first blocker, except on a hole formed on the first blocker; a pass-through tunnel which is connected to the hole and is formed in the same direction to the stream route of light and allows the stream of the light to pass through; and a second blocker which has a irregularity pattern that is formed on a inner wall of the pass-through tunnel and reflects the light that is incident in the deviated direction of the stream route of light.

Abstract: A diffractive optical element includes a plurality of diffraction gratings. A diffraction grating within the plurality of diffraction gratings includes a plurality of grating parts having a curved grating surface and grating tips which connect to define a curved envelope face. The grating surface has a radius of curvature larger than a radius of curvature of the envelope face. In addition, two diffraction gratings within the plurality of diffraction gratings are composed of different materials having different dispersions. Therefore, even when the radius of curvature of the envelope face is small, the degradation of the diffraction efficiency is suppressed.

Abstract: A light diffusion arrangement, for a photographic device having a flashlight, includes a diffuser housing, a plurality of diffracting mesh members, and a plurality of light diffusing elements. The diffuser housing has a light-admissible surrounding sidewall radially extended from a base portion to define a light diffraction cavity. The diffracting mesh members are integrally formed on an inner side surface of the surrounding sidewall of the diffuser housing, while the light diffusing elements are integrally formed on an outer side surface of the surrounding sidewall of the diffuser housing, wherein the diffracted light is arranged to impinge on the light diffusing elements from the light diffraction cavity, in such a manner that each of the light diffusing elements is adapted to diverge the diffracted light for diffusing the diffracted light, so as to provide a uniform light diffusion effect as an optimal lighting effect for the photographic device.

Abstract: A multi-spectrum, multi-channel imaging spectrometer includes two or more input slits or other light input devices, one for each of two or more input channels. The input slits are vertically and horizontally displaced, with respect to each other. The vertical displacements cause spectra from the two channels to be vertically displaced, with respect to each other, on a single image sensor on a stationary image plane. The horizontal displacements cause incident light beams from the respective input channels to strike a convex grating at different respective incidence angles and produce separate spectra having different respective spectral ranges. A retroflective spectrometer includes a convex grating that, by diffraction, disperses wavelengths of light at different angles and orders approximately back along an incident light beam. A single concave mirror reflects both the input channel and the dispersed spectrum.

Abstract: Negative refraction in photonic crystals and diffraction grating is used to design plano-concave lenses to focus plane waves. Microwave experiments are carried out to demonstrate negative refraction and the performance of these lenses. Demonstration of negative refraction of visible light is also performed for the grism. These lenses can be used in optical circuits, astronomical applications, etc.

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: This invention provides a mold with which a two-dimensional subwavelength grating can be produced with a higher percentage transfer by injection molding and a two-dimensional subwavelength grating having a high aspect ratio produced with such a mold. The mold for a fine grating according to the present invention has protrusion parts (107) arranged at an interval on the bottom face (103) of a cavity, wherein the interval is a distance between centers of the protrusion parts and a period of the fine grating smaller than wavelengths of visible lights. In one embodiment, a cross-section of the protrusion parts, parallel to the bottom face of the cavity decreases with height along the protrusion parts and a decreasing rate of the cross-section increases with height along the protrusions.

Abstract: A system and method to chromomodally generate dispersion in light waves. The system and method may be used to control dispersive effects of an optical element such as a single-mode fiber. A light beam from the optical element is first collimated and then directed on to a spatially diffractive element where it is spatially dispersed into various chromatic frequency components. This frequency-separated light is then imparted onto a dispersion slope equalizer, and then passed into a highly multimode waveguide, where it is further dispersed. The light is then collected and focused back into an outgoing fiber-optic or other optical device.

Abstract: A diffraction element having concave/convex-like diffraction gratings in its two surfaces from which at least two separated light beams can be taken in the same direction without changing largely the propagating direction of diffracted light even if the temperature of the operating environment changes. A diffraction grating having a concave/convex shape in cross-section is formed in the incoming-side surface of the transparent substrate and two diffraction gratings of concave/convex shape in cross-section are formed in the outgoing-side surface wherein the grating pitch of the first one is made equal to the grating pitch of one of the second ones. In addition, a reflection type diffraction element exhibiting a good wavelength dependence of diffraction efficiency without being dependent largely on the direction of polarization of an incoming light is provided.

Abstract: Various embodiments include spectrometers comprising diffraction gratings monolithically integrated with other optical elements. These optical elements may include slits and mirrors. The mirrors and gratings may be curved. In one embodiment, the mirrors are concave and the grating is convex. The mirrors and grating may be concentric or nearly concentric.

Abstract: The invention concerns an optical system. The optical system comprises an input for receiving an optical signal, a predetermined output plane, and a diffraction grating for separating the optical signal received at the input into spectral elements thereof. The grating has a diffraction surface with a first predetermined profile. The first profile is formed by a plurality of points each conducted by different equations. Consequently, each spectral component is focused on the predetermined plane.

Abstract: A concave diffraction grating device, a reflective dispersion device, and a spectral device of the invention include a diffraction grating plane having an aspherical configuration, wherein the diffraction grating plane is symmetrical in a predetermined direction, and asymmetrical in a direction orthogonal to the predetermined direction in such a manner that the curvature of one end portion of the diffraction grating plane in the direction orthogonal to the predetermined direction is gradually decreased, and the curvature of the other end portion thereof is gradually increased. The concave diffraction grating device, the reflective dispersion device, and the spectral device with the above arrangement have desirable slit image forming performance with respect to all the wavelengths in a visible region, and are suitable for mass-production.

Abstract: A method for determining a set of grating parameters for producing a diffraction grating for a vacuum-ultraviolet spectrometer, the parameters used being the small and large radius of the toroidal grating substrate, the two distances between the two holographic illumination points and the grating origin, the angular position of the holographic illumination points in relation to the grating normal, and the laser wavelength for the holographic illumination. The method determines respective optimum grating parameters on numeric iterative paths for a specific problem definition. The method thus advantageously enables the production of a VUV spectrometer having a diffraction grating that for a predetermined wavelength range produces a minimum line width on the detector with a large range.

Abstract: An image pick-up lens system from an object side to an image side includes an aperture stop (10), and a meniscus-shaped lens (20) having a concave surface on the object side and a convex surface on the image side. The lens has at least one aspheric surface and a diffraction grating provided on the convex surface thereof. The lens system satisfies the following condition: (1) 0.1<R2/R1<0.5, wherein, R1 is an absolute value of a radius of curvature of the concave surface of the lens, and R2 is an absolute value of a radius of curvature of the convex surface of the lens. Condition (1) governs a distribution of refracting power for the lens, in order to correct monochromatic aberrations. The lens system also satisfies other conditions (2)-(4) as disclosed, in order to provide compactness, cost-effectiveness and improved optical performance.

Abstract: An image display apparatus includes an indicating element which modulates or emits light as a pixel in accordance with image information. A displacement unit optically displaces a position of the pixel for each of two or more sub-fields constituting an image field corresponding to the image information. A projection unit enlarges the pixel and projects an enlarged pixel on a screen. A pixel-profile deformation unit changes an optical intensity profile of the pixel.

Abstract: A diffractive optical element includes a plurality of diffraction gratings. A diffraction grating within the plurality of diffraction gratings includes a plurality of grating parts having a curved grating surface and grating tips which connect to define a curved envelope face. The grating surface has a radius of curvature larger than a radius of curvature of the envelope face. In addition, two diffraction gratings within the plurality of diffraction gratings are composed of different materials having different dispersions. Therefore, even when the radius of curvature of the envelope face is small, the degradation of the diffraction efficiency is suppressed.

Abstract: An antireflection structure (10) comprises a base (1), and a finely roughened antireflection part (2) formed in a surface of the base (1). The finely roughened antireflection part (2) includes a plurality of projections and depressions defined by the projections. The projections are distributed such that PMAX??MIN, where PMAX is the biggest one of distances between tips (2t) of the adjacent projections and ?MIN is the shortest one of wavelengths of visible light rays in a vacuum. The sectional area of each projection in a plane parallel to the surface of the base (1) increases continuously from the tip (2t) toward the bottom (2b) of the depression adjacent to the projection. The shape (2Mt) of a tip part (Mt) of each projection in a plane perpendicular to the surface of the base (1) is sharper than the shape (2Mb) of a bottom part (Mb) of each depression in the same plane vertical to the surface of the base (1).

Abstract: A lens optical system is provided with a cemented lens element formed by cementing two constituent lens elements made of different optical materials together, with a diffractive optical surface formed at the cementing interface between the two constituent lens elements. The two constituent lens elements have at their respective interfaces with air a radius of curvature different from the radius of curvature that they have at the cementing interface.

Abstract: The present invention provides a compact color illumination device (100) for emitting collimated light. The illumination device comprises a reflector cup (102), a blazed diffraction grating (108) formed on the inner surface of the reflector cup, and a plurality of light emitting sources (110) positioned linearly in a focal plane of the reflector cup. Each light emitting source emits a different color of light that is incident on the blazed diffraction grating. The light emitted by the light emitting sources is reflected by the blazed diffraction grating, wherein the reflected light is collimated.

Abstract: An image display apparatus includes an indicating element which modulates or emits light as a pixel in accordance with image information. A displacement unit optically displaces a position of the pixel for each of two or more sub-fields constituting an image field corresponding to the image information. A projection unit enlarges the pixel and projects an enlarged pixel on a screen. A pixel-profile deformation unit changes an optical intensity profile of the pixel.

Abstract: To provide a zoom lens system having high optical performance by using a diffractive optical element, the system includes a first group having positive power, a second group having negative power, and a third group having positive power. When zooming from a wide-angle end state to a telephoto end state, a distance between the first group and the second group and a distance between the second group and the third group vary. The third group is composed of a front group having positive power locating to the object side of the largest space in the third group and a rear group having negative power locating to an image side of the space. The front group includes an aperture stop and a diffractive optical surface. An incident angle of a principal ray reaching the maximum image height to the diffractive optical surface is ten degrees or less. Given condition is satisfied.

Abstract: Microlenses including wire-grid polarizers and methods for their manufacture are disclosed. The method involves forming wire-grid polarizer patterns on a surface of the microlens. The devices and methods provide simple and economical microlenses with polarizers.

Abstract: The present invention relates to a diffractive optical element which has chromatic aberration capable of recording and reproducing without any problem even in the case of instantaneous wavelength change in a laser beam that cannot be followed by an actuator, and can control an adverse effect caused on a spot diameter of a converged spot and on a signal read by a sensor. The diffractive optical element includes a diffractive structure, and diffraction efficiency of mth order diffracted beam satisfies prescribed conditions, and a distance between a paraxial converging position of the diffracted beam having a higher diffraction efficiency among (m+1)th order diffracted beam and (m?1)th order diffracted beam and a paraxial converging position of the mth diffracted beam satisfies prescribed conditions, when m represents a diffraction order number of the diffracted beam used for the first optical information recording medium.

Abstract: An observation optical system is disclosed with which the Fresnel reflection at the surfaces of optical members can be reduced, the transmittance can be improved, and the surface reflection ghost that occur among a plurality of optical surfaces can be suppressed. The observation optical system of the present invention comprises a plurality of optical surfaces, and a fine periodic structure, with a period smaller than the wavelength of incident light, is provided at an effective optical region of at least one surface among the aforementioned plurality of optical surfaces.

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.