Abstract: An optical pickup apparatus comprises: a first laser diode that generates a first laser beam having a first wavelength; a second laser diode that generates a second laser beam having a second wavelength longer than the wavelength; a third laser diode that generates a third laser beam having a third wavelength longer than the first wavelength and shorter than the second wavelength; an objective lens having an inner, outer, intermediate regions on an incident surface, the first laser beam being condensed on a signal recording layer of a first optical disc by condensing actions of the inner and outer regions, the second laser beam being condensed on a signal recording layer of a second optical disc by condensing actions of the inner and intermediate regions, the third laser beam being condensed on a signal recording layer of a third optical disc by condensing actions of the inner and intermediate regions.

Abstract: An optical pickup device includes a diffraction grating 12 for separating an emitted light beam into at least three light beams. The diffraction grating 12 is divided into three regions by dividing lines D1 and D2 extending in a first direction parallel to a tangent line of a track of an optical information recording medium. A second region 12B is divided into four sub-blocks by a dividing line D3 extending in the first direction and a dividing line D4 extending in a second direction that crosses the first direction. The sub-blocks located diagonally opposite to each other have a same phase, and the sub-blocks located adjacent to each other have a phase difference of approximately 180 degrees. The first region 12A has a phase difference of approximately 90 degrees from each sub-block of the second region 12B, and the first region 12A has a phase difference of approximately 180 degrees from the third region 12C.

Abstract: An optical pickup apparatus, which reads signals recorded on first and second signal recording layers of an optical disc, includes: a laser diode; an objective lens to condense a laser beam to the first and second signal recording layers; and a collimating lens disposed in a light path of the laser beam between the laser diode and the objective lens and configured to correct a spherical aberration by moving in a light axis direction of the laser beam, and the objective lens includes a bifocal lens and is configured such that a second focal point does not coincide in position with the second signal recording layer when a first focal point coincides in position with the first signal recording layer, and the first focal point does not coincide in position with the first signal recording layer when the second focal point coincides in position with the second signal recording layer.

Abstract: To reduce a bad influence on a tracking control signal and a data signal by reflected light from an adjacent layer on a multi-layer disc as stray light, the following device is made in the invention. Reflected light from the multi-layer optical disc including stray light from another layer is once converged by a reflected light condenser lens and is reflected on a reflector. A grating which prevents zero-order light from being generated by setting groove depth to ?/4 and which is set to pitch to prevent positive and negative first- or higher-order diffracted lights from returning to the reflected light condenser lens is arranged between the lens and the reflector including an optical axis with the grating apart from the reflector. Hereby, as reflected light from another layer is cut off though reflected light from a corresponding layer is transmitted to a detector, a detected control signal and a detected data signal are not influenced by reflected light from another layer.

Abstract: Methods and apparatus to correct a curved Petzval focusing surface to a plane using a convex lens, a concave lens, and a space arranged between the curved side of the convex lens and the curved side of the concave lens. The method and apparatus may also include a Fresnel lens arranged between the concave lens and a pixel array.

Abstract: An optical information recording/reproducing optical system, comprising a light source; an optical element converting a laser beam into a substantially collimated beam; and an objective lens, wherein a wavelength ? (unit: nm) of the laser beam falls within a range of 400<?<410, the optical element and the objective lens are made of same resin materials or different resin materials having a glass transition temperature of Tg>115° C., each of optical surfaces is configured not to have an optical thin film which contains at least one of or elements of titanium, tantalum, hafnium, zirconium, niobium, molybdenum and chromium, each of optical surfaces of the optical element is provided with an antireflection film made of one of or a mixture of at least two of silicon oxide, aluminum oxide, aluminum fluoride and magnesium fluoride, and a following condition is satisfied. ? i = 1 n - 1 ? ( 1 - R ( BL ) ? i 100 ) - ? i = 1 n - 1 ? ( 1 - R ( UV ) ? i 100 ) > 0.

Abstract: An optical information recording/reproducing optical system where resin material has Tg>115° C., first, second and third films are on an optical disc side of an objective lens and surfaces of an optical element, respectively, a light source side of the objective lens has a fourth film having four or more layers not containing Ti, each of the first, second and third films includes a non-high refractive index layer made of one of silicon oxide, aluminum oxide, aluminum fluoride and magnesium fluoride or a mixture of at least two of them, each of the first, second and third films is not made of one of Ti, Ta, Hf, Zr, Nb, Mo and Cr, a layer of the fourth film closest to a base material is the non-high refractive index layer. The fourth film satisfies 350<?max(2)<420 and 600<?min(2)<750, and reflectivity thereof decreases monotonously.

Abstract: An optical pickup apparatus includes an astigmatic element, an angle adjusting element for contradicting propagation directions of luminous fluxes within four different luminous flux regions out of a reflected light, a polarization adjusting element. Two of the luminous flux regions are placed in a direction in which aligned are a set of opposite angles made by the two mutually crossing straight lines respectively parallel to a first convergence direction and a second convergence direction vertical to the first convergence direction by the astigmatic element, and the remaining two luminous flux regions are placed in a direction in which an alternate set of opposite angles are aligned. The polarization adjusting element differentiates polarization directions of luminous fluxes which are selected out of the luminous fluxes within the four luminous flux regions and which are adjacent in a peripheral direction in which the optical axis of reflected light serves as an axis.

Abstract: An optical pickup for irradiating an information recording medium, such as a DVD, with a laser beam when an information signal is recorded or reproduced, and information equipment provided with the optical pickup.

Abstract: A complex objective lens composed of a hologram and an objective lens, capable of realizing stable and high-precision compatible reproducing/recording of a BD with a base thickness of about 0.1 mm for a blue light beam (wavelength ?1) and a DVD with a base thickness of about 0.6 mm for a red light beam (wavelength ?2). In an inner circumferential portion of the hologram, a grating is formed, which has a cross-sectional shape including as one period a step of heights in the order of 0 time, twice, once, and three times a unit level difference that gives a difference in optical path of about one wavelength with respect to a blue light beam, from an outer peripheral side to an optical axis side. The hologram transmits a blue light beam as 0th-order diffracted light without diffracting it, and disperses a red light beam passing through an inner circumferential portion as +1st-order diffracted light and allows it to be condensed by an objective lens.

Abstract: A diffraction optical element is provided to reduce harmful lights and also suppress deterioration in the optical characteristics of the element. The diffraction optical element 22 is formed with a plurality of diffraction gratings 17?, 18?, 19? and 20?. From these diffraction gratings, there are selected the diffraction gratings 18?, 19? and 20? whose groove apex angles are less than a predetermined angle. The diffraction gratings 18?, 19? and 20? has chamfer surfaces 18c?, 19c? and 20c? formed on the lower side of respective slanted surfaces 18a?, 19a? and 20a?. The chamfer surfaces 18c?, 19c? and 20c? are slanted to the slanted surfaces 18a?, 19a? and 20a?, respectively.

Abstract: A diffractive optical element having a diffraction region for diffracting a part of a luminous flux is mounted and an unwanted luminous flux generated in a multi-layer optical disc is suppressed from entering a photodetector surface. Using the above-described structure, fluctuation of a tracking error signal can be suppressed from being caused by the unwanted luminous flux and preferable recording or reproduction quality can be obtained also in the multi-layer optical disc.

Abstract: An optical pickup device includes a polarization diffraction grating to diverge an optical beam reflected from an optical disc and an optical detector to receive the optical beam diverged by the polarization diffraction grating, a polarization of 0 order diffracted light diffracted through the polarization diffraction grating is substantially perpendicular to that of a +1 order diffracted light diffracted therethrough, and a polarization filter having a plurality of domains is mounted between the polarization diffraction grating and the optical detector.

Abstract: An optical system for spatially controlling light polarization, and method for manufacturing the same, includes a light source for generating a light beam of a designated wavelength, a beam shaper for splitting the light beam generated from the light source into a plurality of partial beams, and a polarization controller controlling the polarization states of the partial beams. The polarization controller may be formed on the beam shaper or separate from the beam shaper.

Abstract: The liquid crystal element includes a pair of transparent substrates, a liquid crystal arranged between the substrates, a diffraction pattern including concentric diffraction electrodes formed on one substrate, and a phase shift pattern including concentric phase shift electrodes formed on the other substrate. The diffraction pattern includes a first region being of a constant range in a radial direction from a center and having a wide electrode interval, a second region being arranged on the outer side of the first region and having a narrow electrode interval, and a third region being arranged on the outer side of the second region and including a single diffraction electrode. An additional electrode facing the phase shift electrode is arranged in a gap between the diffraction electrodes in the first region.

Abstract: To provide an objective lens and an optical pickup device which can thin the objective lens and a device on which the objective lens is mounted, and which can prevent that the pitch of the diffraction grating at the outer periphery of the objective lens becomes too small in the manufacturing procedure and so it becomes difficult to manufacture the Fresnel lens or which does not require a high-grade fine processing technique in order to minimize the pitch of the diffraction grating, in an objective lens which condenses a laser light emitted from a light source to irradiate on an optical disk, the outer periphery on the side surface of the objective lens in which the laser light is incident is formed by a refractive lens portion 7a and the inner periphery thereof is formed by a Fresnel lens portion 7b.

Abstract: An optical pickup includes a light source emitting a light beam, a diffraction element diffracting the light beam to separate it into a main beam and a sub beam, an objective lens focusing the main and sub beams onto a desired recording layer of an optical disc, a lens moving section moving the objective lens in focusing and tracking directions, a light-separating element separating a reflected light beam, formed by reflecting each of the main and sub beams at the recording layer, into multiple beam components and allowing the reflected light beam to travel without rotating an image thereof, and a light-receiving element having multiple light-receiving regions that optically receive the reflected light beam and generating a light reception signal based on the amount of received light to allow a signal processing section to generate a focus error signal and a tracking error signal based on the light reception signal.

Abstract: A diffractive optical element includes a first optical part and a second optical part bonded to each other with a bonded surface therebetween configured as a diffraction surface. In this diffractive optical element, the diffraction order of diffracted light with the largest quantity of light out of diffracted light for one of a plurality of kinds of laser beams obtained on the diffraction surface is different from the diffraction order for at least another laser beam.

Abstract: An optical pickup device according to an embodiment of the present invention comprises a light source for projecting a beam of light to record and reproduce information with respect to an optical recording medium. A collimating lens is disposed on a path of the light to converge and convert the light into a parallel beam. An object lens condenses the parallel beam from the collimating lens and projects the parallel beam onto the optical recording medium. An optical element is disposed between the collimating lens and the object lens. A first actuator moves the collimating lens along the optical axis to thereby control a distance between the collimating lens and the optical element. A first controller drives the first actuator to find a position for the collimating lens, for reducing aberration generated in the light being projected to the optical recording medium. Accordingly, the aberration can be effectively prevented, thereby improving recording and reproducing performance of the optical pickup device.

Abstract: An optical pickup device includes an astigmatism element which sets focal line positions to be defined by convergence of laser light away from each other, a diffraction element which diffracts four light fluxes obtained by a light flux of the laser light to disperse the four light fluxes from each other, and a photodetector having a first sensing section and a second sensing section which respectively receive m-th order diffraction light and n-th order diffraction light of the four light fluxes. In this arrangement, the first sensing section receives eight light fluxes obtained by dividing the four light fluxes of the m-th order diffraction light by two straight lines to output detection signals of the number less than eight.

Abstract: An optical pickup apparatus includes: a first light source for emitting a first light flux; a light-converging optical system including an objective lens and a diffractive structure. When the first light flux from an optical information recording medium enters into the diffractive structure, the diffractive structure emits a main light flux and a secondary light flux. The optical pickup apparatus further includes: a first optical element including a first optical area and a second optical area; a second optical element including a third optical area and a fourth optical area; a light-converging element for converging the main light flux at a position between the first optical element and second optical element; a polarization splitting optical member for splitting the main light flux and the secondary light flux each emitted from the first optical element and second optical element; and a photodetector for receiving the main light flux.

Abstract: An optical pick-up which permits the relative position of a diffracting optical element and a photodetector to be adjusted by feedback control with signals which are generated when more than one kind of diffracted light differing in order is received, the diffracted light occurring as the reflected light from the optical disc is divided and diffracted by the diffracting optical element having multiple regions. The photodetector which detects the light beam passing through the central region of the diffracting optical element and generates RF signals is juxtaposed with sub-photodetectors, so that they receive reflected stray light from out-of-focus layers and perform computation to calculate the reflected stray light component which the RF signal detector receives, thereby detecting only the component of signals of the reflected light from a target layer.

Abstract: An optical pickup including a light source, a light focus device, a diffraction element, an optical split element, a ¼ wavelength board, a light reception device and a correction element wherein the correction element is divided into multiple areas in a surface vertical to an optical axis, each area of the multiple areas has a sub-wavelength convexo-concave structure having a pitch equal to or shorter than a wavelength of the outgoing light beam and the sub-wavelength convexo-concave structures of the multiple areas adjacent to each other have groove directions perpendicular to each other, and the filling factors of adjacent areas of the multiple areas are determined to substantially equalize effective refractive indices with regard to the polarization direction of the outgoing beam emitted from the light source and impart a phase difference of ? with regard to a polarization direction perpendicular to the polarization direction of the outgoing beam.

Abstract: Provided is an objective lens used in an optical pickup that performs recording and/or reproducing of information signals on three different types of optical discs using different wavelengths. The objective lens is configured to collect light beams with the at least three wavelengths ?1, ?2, and ?3, which satisfy a relationship of ?1<?2<?3, on signal recording surfaces of compatible optical discs corresponding to the respective wavelengths. The objective lens includes: a diffractive portion that has a predetermined diffraction structure formed on an incident side surface. The diffractive portion has a first region that is provided in an innermost peripheral portion so as to diffract the light beams, a second region that is provided outside the first region so as to diffract the light beams, and a third region that is provided outside the second region.

Abstract: Provided is an objective lens for selectively focusing each of light beams having three wavelengths ?1, ?2, and ?3 on a signal recording surface of a corresponding optical disc, the wavelengths ?1, ?2, and ?3 satisfying at least a relationship ?1<?2<?3, the objective lens including a diffraction section disposed on an entry-side surface thereof, the diffraction section including a first region disposed in an innermost radius portion, a second region disposed outside the first region, and a third region disposed outside the second region, the first to third regions being formed so that an aperture of the light beams are appropriately limited, the first region including a staircase-like diffractive structure having a certain number of levels configured so that diffracted light of a predetermined order has the highest diffraction efficiency and optical-path-difference phase amounts for the levels of the diffractive structure has a certain relationship.

Abstract: An optical pickup apparatus comprises first, second and third light sources to emit light fluxes of wavelength ?1, ?2 and ?3 for conducting recording and/or reproducing information for first, second and third optical information recording mediums having respective protective substrates of thickness t1, t2 and t3 and a diffractive optical element located on a common optical path for the first, second and third light sources. A converged-light spot is formed on the first optical information recording medium with m-th order diffracted-light ray of the wavelength ?1, on the second optical information recording medium with n-th order diffracted-light ray of the wavelength ?2, and on the third optical information recording medium with k-th order diffracted-light ray of the wavelength ?3 generated by the diffractive optical element respectively, wherein one of m, n and k is different from one of other two numbers.

Abstract: A diffraction element is disposed between a beam branching element (such as a beam splitter) and a photodetector. The diffraction element further segment an interference fringe introduced into stray light by a diffraction grating which divides a laser beam emitted from a laser beam source into a main beam and two sub-beams.

Abstract: To provide an optical head device and an optical information recording/reproducing device for recording/reproducing a signal on/from an optical recording medium having two recording layers without generating the disturbance on the track error signal detected with differential push-pull method even if the interval between the target layer and the non-target layer changes. The light beam emitted from a semiconductor laser is divided into a zeroth order main beam and a positive and a negative first order diffracted light sub-beams by a diffractive optical element. The light beams are applied onto a disk by an objective lens. The reflected light beam of the main beam and reflected light beams of the sub-beams from the disk are received by a photodetector. From the output of the photodetector, a differential push-pull signal is calculated, and used as a track error signal. The sub-beams become Laguerre-Gauss beams by the diffractive optical element.

Abstract: To provide a liquid crystal optical modulation element which is excellent in durability against blue laser and which can maintain the characteristics for a long period of time. A liquid crystal optical modulation element to modulate a laser beam having a wavelength of at most 500 nm, which comprises a layer of a polymer liquid crystal composition sandwiched between a pair of transparent substrates facing each other, characterized in that each of the pair of transparent substrates has an alignment film on the surface which faces the other transparent substrate, and the polymer liquid crystal composition is a polymer liquid crystal containing a hindered amine compound and a hindered phenol compound.

Abstract: A signal, which is derived from the relationship between the lens shift amount of an objective lens and the amount of the positional-deviation, of a received light beam with respect to a light-receiving plane, which occurs in the tangential direction on a photodetector, is corrected by an offset caused by asymmetry in the intensity distribution of reflected light; a multiplication value is obtained by multiplying the corrected signal by a predetermined constant; based on a focus error signal obtained by subtracting the calculated value from the calculation expression according to the conventional astigmatism method, the focusing servo control is performed.

Abstract: The present invention makes it possible to accurately and adequately adjust the position where sub beams are shone when performing tracking correction or CTC using three beams. The invention adjusts the positions where the sub beams are shone onto the surface of an optical disc DK by changing the angle of a diffraction grating 211 that is mounted inside an optical pickup. When performing adjustment, the angle of the diffraction grating 211 is performed in three stages: (i) rough adjustment, (ii) initial fine adjustment and (iii) continuous fine adjustment.

Abstract: An objective lens includes a first optical path difference providing structure in which a first basic structure and a second basic structure are overlapped together, and a second optical path difference providing structure in which a third basic structure, a fourth basic structure, and a fifth basic structure are overlapped together. The first and third basic structures emit diffracted light fluxes with the same diffraction order having the maximum light amount. The second and fourth basic structures emit diffracted light fluxes with the same diffraction order having the maximum light amount. The fifth basic structure emits 0th-order diffracted light fluxes with the maximum light amount, for the first light flux, emits 0th-order diffracted light fluxes with the maximum light amount, for the second light flux, and emits Gth-order diffracted light fluxes with the maximum light amount, for the third light flux, where G is an integer excluding zero.

Abstract: An optical head (30) comprises a blue-violet laser light source (1) for emitting a blue-violet laser beam, a mirror with a diffraction grating (5) for transmitting and reflecting the blue-violet laser beam at a predetermined ratio, and a front monitor sensor (24) for receiving transmitted light or reflected light from the mirror with a diffraction grating (5) and creating an APC signal for controlling an output of the blue-violet laser light source (1). The minor with a diffraction grating (5) includes a first surface (5a) which the blue-violet laser beam enters, and a second surface (5b) facing the first surface (5a). The first surface (5a) and the second surface (5b) are mutually parallel. A reflecting coat for transmitting and reflecting the blue-violet laser beam at a predetermined ratio is formed on the first surface (5a), and a diffraction grating is formed on the second surface (5b).

Abstract: The present invention provides an optical pickup device requiring no position adjustment of a diffraction grating at the time of assembling the optical pickup device, and capable of suppressing fluctuations in a differential push-pull signal amplitude and cancelling a push-pull offset. An optical pickup device 200 of an embodiment of the present invention has a diffraction grating 230 of a special shape including predetermined grooves and two kinds of lattice grooves arranged at a pitch determined on the basis of a pitch of grooves formed in the surface of an optical disk 50, numerical aperture, wavelength of a light beam, and effective diameter of the light beam applied on the optical disk 50.

Abstract: A transmissive or reflective diffractive optical element, comprising: a substrate having a top surface, the top surface being etched into a pattern, the pattern including a periodic surface pattern of grooves formed such that when an incoming light beam is shone onto the top surface, the incoming light beam will be split into a plurality of diffracted light beams, the plurality of diffracted light beams including a plurality of primary diffracted order beams and a plurality of secondary diffracted order beams, wherein the primary diffracted order beams have a primary aggregate efficiency above ninety percent, wherein the plurality of secondary diffracted order beams have a secondary aggregate efficiency of lower than ten percent, and wherein a maximum power of the primary diffracted order beams and a minimum power of the primary diffracted order beams differ by at least ten percent of an average power of the primary diffracted order beams.

Abstract: To provide a liquid crystal optical modulation element which is excellent in durability against blue laser and which can maintain the characteristics for a long period of time. A liquid crystal optical modulation element to modulate a laser beam having a wavelength of at most 500 nm, which comprises a layer of a polymer liquid crystal composition sandwiched between a pair of transparent substrates facing each other, characterized in that each of the pair of transparent substrates has an alignment film on the surface which faces the other transparent substrate, and the polymer liquid crystal composition is a polymer liquid crystal containing a hindered amine compound and a hindered phenol compound.

Abstract: Provided is an optical pickup device capable of stabilizing a tracking signal and a focusing signal and of preventing quality deterioration of a data signal by eliminating a multi-layer crosstalk. Of reflected lights from a multi-layer disc, a reflected light from a target layer is split into two by a light flux splitting optical system so that the reflected light is spread out toward two directions with respect to a central line, and then the split lights are condensed. In this case, a reflected light from another layer does not reach a condensing position of the reflected light from the target layer, and only the reflected light from the target layer can be detected by a detector. Accordingly, a crosstalk from the another layer is eliminated.

Abstract: An optical pickup apparatus and a drive apparatus having the same are provided. Second light-receiving elements or third light-receiving elements for receiving ±first-order diffraction light beams from a polarization hologram are arranged outwardly of a circular region having the optical axis of a zero-order diffraction light beam on a light detector as its center, a radius of which is expressed by (2×t/n)×(f2/f1), where f1 denotes a focal length of an objective lens, f2 denotes a focal length of a coupling lens, t denotes a maximum value of a light transmitting layer thickness, n denotes a refractive index of a light transmitting layer.

Abstract: A diffractive optical element includes a first optical part and a second optical part bonded to each other with a bonded surface therebetween configured as a diffraction surface. In this diffractive optical element, the diffraction order of diffracted light with the largest quantity of light out of diffracted light for one of a plurality of kinds of laser beams obtained on the diffraction surface is different from the diffraction order for at least another laser beam.

Abstract: An optical recording head includes: a light source; a slider comprising a wave guide which irradiates light from the light source to a recording medium, wherein a grating coupler is formed on an end portion at an opposite side of the waveguide relative to the light source; and an optical element which comprises a diffraction grating and introduces the light from the light source to the grating coupler through the diffraction grating. The optical element deflects the light from the light source so that the light is incident into the grating coupler with a deflection angle larger than 90 degrees with respect to a direction in which the light proceeds when the light is incident into the optical element.

Abstract: An optical pickup device radiates laser light to a disc having a plurality of recording layers in a direction of lamination. The optical pickup device includes an astigmatic element and a spectral element. The astigmatic element allows reflected light from the disc to converge in a first direction and form a first focal line at a first position, and allows reflected light to converge in a second direction and form a second focal line at a second position closer to the disc than the first position. The spectral element splits a reflected light flux in two along a straight line parallel to the first direction and turns traveling directions of the split two light fluxes into directions separated from each other. Here, the spectral element is interposed between the second focal line of the reflected light from a target recording layer and the second focal line of the reflected light from a deeper recording layer than the target recording layer.

Abstract: An optical pickup performing recording, reproduction and deletion of information on or from an optical recording medium. The pickup includes light sources for information recording media using a blue wavelength beam, information recording media of DVD family and information recording media of CD family. A single object lens may be used to condense light from any of the light sources. A single aberration correction device may be disposed in a common light path between each of the light sources and the object lens.

Abstract: To provide an optical head device, which can detect an excellent focus error signal for a dual layer optical recording medium, and optical information recording/reproducing device. Reflected light from a dual layer optical recording medium is diffracted by a diffractive optical element divided into four regions, and is received by a photodetector. Optical spots are equivalent to negative first order diffracted light from the four regions of the diffractive optical element, and are received by four dual-divided light receiving sections, respectively, to be used for detection a focus error signal by a Foucault's method. The four dual-divided light receiving sections are provided with positive component light receiving sections for outputting the received light as a positive component of the focus error signal and negative component light receiving sections for outputting the received light as a negative component of the focus error signal, respectively.

Abstract: The present invention makes possible a compact optical pickup device that eliminates effects due to the position where a sub beam is projected during tracking compensation, and provides for stable tracking compensation. A diffraction grating 12 in the optical pickup device PU gives an astigmatism to a sub beam (either of ±1-dimensional light), and shines that sub beam onto an optical disc DK. Also, a tracking error signal Ste is obtained by subtracting a push-pull signal PPsub that corresponds to a sub beam from a push-pull signal PPmain that corresponds to a main beam (0-dimensional light), and tracking compensation is performed based on that tracking error signal Ste.

Abstract: An optical pickup includes: a light source outputting a light beam; an objective lens collecting the light beam on a target recording layer as a target of plural recording layers provided in an optical disc; a lens moving unit moving the objective lens in a tracking direction nearly orthogonal to track grooves helically or coaxially formed in the target recording layer; a collective lens collecting a reflected light beam formed when the light beam is reflected by the optical disc; a diffraction optical element diffracting part of the reflected first-order light beam in predetermined directions as first, second, third and fourth beams; and a photodetector receiving the first and second beams using first and second light receiving areas, and generating light reception signals, and receiving the third and fourth beams using third and fourth light receiving areas, and generates light reception signals.

Abstract: An optical head device includes a diffraction grating which diffracts a part of the light beam which is selectively emitted from a semiconductor laser having two luminous points and is divided along a tangential direction of the track of the optical disk, a relationship of arrangement of the second and third regions corresponds to a relationship of the optical axes of the first and second light beams on the diffraction grating, the second region is located at a position crossing an optical axis of the first light beam, a phase difference between phases of the first and third regions is 180°, a phase difference between phases of the third and fourth regions is 180°, and the third region has a width which is not larger than amount of a position deviation of ±first-order diffracted light of the second light beam from zeroth-order diffracted light.

Abstract: An optical pickup device has an astigmatism element, a polarization setting element, and a polarizer. The astigmatism element converges laser light reflected on a disc in a first direction and a second direction to form a first focal line and a second focal line. The polarization setting element makes polarization directions of light fluxes different from each other, the light fluxes being obtained by dividing a light flux of the laser light transmitted through the astigmatism element into two by a straight line parallel to the first direction. The polarizer transmits light having polarization directions obtained by inverting the polarization directions set by the polarization setting element with respect to the straight line parallel to the first direction, respectively.

Abstract: An objective lens for an optical pickup apparatus is disclosed that can record and/or reproduce information compatibly for different optical discs with stability regardless of an environmental temperature change, in spite of its simple structure, and provides an optical pickup apparatus employing the objective lens. The objective lens includes: an optical surface which at least includes a central area, a peripheral area, and a most peripheral area. The objective lens is a single lens formed of plastic. The central area includes a first optical path difference providing structure. The peripheral area includes a second optical path difference providing structure. The objective lens further includes an optical path difference providing structure for correcting a temperature characteristic, where the optical path difference providing structure corrects an aberration caused by a temperature change of the objective lens.

Abstract: An optical element for optical pickup device is provided with an optical path difference providing structure which provides a substantial phase change to a light flux having a predefined wavelength. The optical path difference providing structure is provided with a step portion having a smaller step difference than the predefined wavelength in an optical axis direction.

Abstract: An offset-free tracking signal enables stable tracking control even if an optical disc is a multi-layer disc having three or more layers. Light receiving portions of a main region light receiving portion group are arranged between a projection line of a third dividing line on a photodetector and a projection line of a fourth dividing line on the photodetector by stray lights from information layers adjacent to the one, on which a light beam is focused, out of a plurality of information layers. Further, light receiving portions of a subregion light receiving portion group is arranged between a projection line of a first dividing line on a photodetector and a projection line of a second dividing line on the photodetector by the stray lights from the information layers adjacent to the one, on which a light beam is focused, out of the plurality of information layers.