Abstract: An interference-type optical pickup, an optical information detection method, and an optical information recording and reproducing apparatus, which allow easy adjustment of a path difference between two lights, have a high signal amplification effect and are suitable for size reduction of an optical system, are provided. A signal light reflected from an optical disk and a reference light branched from the same light source and guided into detectors without being projected onto the optical disk are caused to interfere with each other on detectors. Detector outputs in four interference states in which phase relationships between the reference light and the signal light are different from each other by degrees are simultaneously obtained and calculated. Accordingly, a readout signal RF that is always stable and amplified with high quality is obtained even when an optical path changes due to disk undulations.

Abstract: An optical pickup apparatus comprising: a laser light source; an objective lens; a reflection mirror; a photodetector; and a beam splitter, the beam splitter including a first reflective film configured to generate a first phase difference corresponding to a predetermined wavelength with respect to laser light, the reflection mirror including a second reflective film configured to generate a second phase difference corresponding to the predetermined wavelength with respect to the laser light, the first reflective film and the second reflective film being formed so that a combined phase difference of the first phase difference and the second phase difference becomes substantially quarter-wave with respect to the laser light.

Abstract: A near-field light generating device (10) which converts incident light into near-field light, includes: a metallic member (11) made of a metallic material; and a dielectric member (12) made of a dielectric material, the metallic member (11) having a first interface (16) and a second interface (18) that sandwich the dielectric member (12), the first interface (16) and the second interface (18) having flections (P16 and P18), respectively, an inner-interface distance, which is a distance between the first interface (16) and the second interface (18), being minimum at location of the flections (P16 and P18), and a rate of change of the inner-interface distance between the first interface (16) and the second interface (18) being asymmetrical with respect to the flections (P16 and P18). With the arrangement, it is possible to provide a minute near-field light generating device which can be easily fabricated and which can obtain high-intensity near-field light whose temporal change in intensity is small.

Abstract: In a beam applying method, recording and reproducing operations are performed on an optical recording medium, in which a signal is recorded and reproduced by applying a beam thereto and which has a recording layer on which the signal is recorded, a quarter-wavelength plate formed below the recording layer, a polarizing plate formed further below the quarter-wavelength plate, and a reflecting film formed below the quarter-wavelength plate. The beam applying method includes the steps of; emitting a beam to be applied to the optical recording medium; and driving a quarter-wavelength plate inserted into an optical system serving to guide the emitted beam to the optical recording medium so that the optical axis direction thereof has a predetermined angle difference at the time of performing a recording operation and reproduction.

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: Certain embodiments provide an optical recording/reproducing apparatus including: a slider that has a medium facing surface that faces an optical recording medium, and moves along a recording/reproducing face of the optical recording/reproducing medium; a metal nanoparticle structure that is provided in the medium facing surface of the slider; a light illumination device that illuminates the optical recording medium and the metal nanoparticle structure with light that has polarization components in a direction perpendicular to the recording/reproducing face; and a detection device that detects Rayleigh scattering light that is generated from a portion of the optical recording medium and is intensified by the metal nanoparticle structure, the portion being located close to the metal nanoparticle structure.

Abstract: An interference type optical head and an optical disk device that can easily adjust an optical path length difference of a couple of lights, ensure higher signal amplification effect, and are suitable for reduction in size are provided in order to improve a regeneration signal quality with amplification of signal in the case where reflectivity of each layer must be lowered and relative noise for the signal increases because read speed is high in a multilayer optical disk. In view of essentially improving an S/N ratio of the regeneration signal in high-speed rotation of a multilayer disk, a plurality of interference phases are generated and an optical system for differential calculation has been reduced in size with an angular selective polarization conversion element in the optical disk device for amplifying the signal with interference of the light not radiated to the disk with the reflected light from the disk.

Abstract: An object of the present invention is to provide an extraction optical system capable of separating and extracting a signal light and a stray light with a simple configuration, and an optical head device including the same. A phase plate and a phase plate are +?/4 phase plates, while a phase plate and a phase plate are ??/4 phase plates. A focal line, a focal line and a focal line represent a focal line of a stray light, a focal line of a reproduction light and a focal line of a stray light, respectively. All beams of the reproduction light enter the state in which a polarization direction is rotated by 90 degrees after passing through the phase element. In contrast to the all light bundles of the reproduction light, polarization directions of all light bundles of the stray lights and are not rotated even after passing through the phase element.

Abstract: An optical beam forming apparatus capable of forming a polarization of laser beam into an elliptic polarization includes a beam source to emit a semiconductor laser beam, a wave plate to receive the beam emitted from the beam source and to form an elliptic polarization, and a lens to focus the beam passed through the wave plate to form a beam spot on a disc.

Abstract: An optical head device having a broadband phase plate of transforming at least three linearly polarized light beams having different wavelengths into circularly polarized light beams, is obtained. A broadband phase plate comprising two phase plates 9A and 9B laminated with e.g. an adhesive agent so that their optical axes are crossed, wherein provided that wavelengths of linearly polarized incident light beams are ?1, ?2 and ?3 (?1<?2<?3), at least one or both of the two phase plates has such a phase difference characteristics that a ratio R(?1)/R(?3) and a ratio R(?2)/R(?3) between retardation values of the wavelengths are smaller than 1 and R(?1)/R(?3) is smaller than R(?2)/R(?3), is integrated in the optical head device.

Abstract: An optical pickup includes a wave plate on an optical path to be followed by every light beam emitted from three light sources (with wavelengths ?1, ?2 and ?3, respectively) both on their way toward an optical disc and back from the disc toward a photodetector. The wave plate has two layers with different retardations and different optic axis directions. The sum of the retardations of the first and second layers is defined to be approximately 5/4?1, 3/4?2 and 1/2?3 to the light beams with the wavelengths ?1, ?2 and ?3.

Abstract: An optical pickup apparatus comprising: a laser light source configured to emit a laser beam; an objective lens configured to apply the laser beam to an optical recording medium; and a beam splitter including a first reflective film configured to reflect the laser beam so as to be directed to the objective lens, the beam splitter interposed in an optical path between the laser light source and the objective lens, an incidence polarization angle of the laser beam relative to the first reflective film being set such that a P-polarization component is greater than an S-polarization component in linear polarization components of the laser beam incident on the first reflective film.

Abstract: A laser converging apparatus comprising: a nonpolarizing hologram element having a first area defined by a numerical aperture corresponding to a thickness of a first protective layer of a first disk medium and a second area inside the first area, the second area defined by a numerical aperture corresponding to a thickness of a second protective layer (>the thickness of the first protective layer) of a second disk medium, the second area having a hologram pattern for diffracting laser light into zero order light and high-order diffracted light having the order of primary or higher; an objective lens having the numerical aperture corresponding to the thickness of the first protective layer, the objective lens converging the laser light having passed through a part of the first area other than the second area and the zero order light having passed through the second area onto an information surface on one side of the first protective layer, the objective lens converging the high-order diffracted light having

Abstract: In an optical pickup capable of removing inter-layer crosstalk, a dark line that may appear in a central portion of a beam is removed. Thereby, an error in a data signal is reduced. Reflected light from a multi-layer disc is split into two parallel bundles with a splitting optical system in a way that the light is split at a central line. Thereby, when reflected light from a target layer is focused, the reflected light is not influenced from an attenuation element provided on an optical axis.

Abstract: A multiple wavelength-adaptive optical pickup according to the present invention enables to obtain stable signals by suppressing displacement of optical intensity distribution at a light receiving section. When an incident angle of a central beam of a zero-dimensional beam of a beam reflected at an optical disc into a half mirror is taken as ?, if variation in transmittance of the mirror become a maximum with respect to change in the incident angle from ? to a plus side in any one of the wavelengths corresponding to the respective optical discs, a ?1 dimensional beam generated on the minus side with respect to the zero-dimensional beam is received by the light receiving section, and if the variation in the transmittance of the mirror become the maximum with respect to change in the incident angle from ? to the minus side, a +1 dimensional beam generated on the plus side with respect to the zero-dimensional beam is received by the light receiving section.

Abstract: The present invention uses a stationary medium and a stationary optical pickup unit. The stationary optical pickup unit has a laser, which sends a beam of light through an objective lens, which focuses the beam on a point on the track of the stationary medium. The beam is then reflected toward a re-directing surface (e.g., prism) which diverts it to a photodiode array. Instead of the entire optical pickup moving to follow the track as in conventional systems, only the objective lens inside of the optical pickup moves. The position of the objective lens determines where on the information track the laser will reach. Depending upon where the laser beam reaches, the reflected light beam received by the photodetector array changes. This, in turn, affects the amount of light sensed by each photodetector in the array, thereby causing the output of each of the four photodetectors to change each time the objective lens moves.

Abstract: An optical pickup includes: a first emitting unit to emit an optical beam of a first wavelength; a second emitting unit to emit an optical beam of a second wavelength; a third emitting unit to emit an optical beam of a third wavelength; an object lens to condense optical beams emitted from the first through third emitting units onto a signal recording face of an optical disc; and a diffraction unit provided on one face of an optical element or the object lens positioned on the optical path of the optical beams of the first through third wavelengths; wherein the diffraction unit includes a generally circular first diffraction region provided on the innermost perimeter, a ring zone shaped second diffraction region provided on the outer side of the first diffraction region, and a ring zone shaped third diffraction region provided on the outer side of the second diffraction region.

Abstract: A beam applying method includes the steps of: rotationally driving an optical recording medium, in which a signal is recorded and reproduced by applying a beam thereto and which has a recording layer on which the signal is recorded, a polarization element formed below the recording layer, and a reflecting film formed below the polarization element; and applying a beam to the rotating optical recording medium through a half-wavelength plate that is rotationally driven with the rotation of the optical recording medium.

Abstract: A polarization detection system structured for optical read-out of disc-shaped optical data/information storage and retrieval media with surfaces comprised of pits or marks configured as multilevel oriented nano-structures (ONS) with varying pit or mark orientations and widths. The polarization detection system comprises: an optical beam source; a stage for mounting and rotating an optical disc medium about a central axis; at least one photodetector; a beam splitter positioned in an optical path between the source and stage, for directing an incident beam from the source onto an optical disc mounted on the stage and a return beam from the disc onto the photodetector; and an optical polarizer positioned in an optical path between the beam splitter and the at least one photodetector, for detection and analysis of changes in polarization of the return beam effected by variation of the orientation of the walls and/or widths of the pits or marks of the disc.

Abstract: A hologram recording/reproducing apparatus records data as a hologram by applying signal and reference light beams to a hologram-recording medium, obtains a diffracted light beam by applying a reproduction light beam to the hologram, and reproduces the data using the diffracted light beam. The hologram recording/reproducing apparatus includes an external-cavity light source, a polarization-control element that changes a polarization angle of a light beam emitted from the external-cavity light source, a polarizing-beam-splitting element that splits the light beam to obtain two light beams and that changes a ratio between amounts of the two light beams, a photoreceptor that receives one of the two light beams, a spatial light modulator that receives the other beam and that generates signal, reference, and reproduction light beams, and a control unit that changes the polarization angle or polarization state of the light beam.

Abstract: An optical unit is provided with a light source; a light dividing means for dividing light emerging from the light source into a first light and a second light; a light converging means for converging the first and second lights at the same position in the recording layer in the manner that they face each other; a polarization state switching means for switching the polarization states of the first and second lights at the convergence point in the recording layer; and a light irradiation state switching means for switching between the state in which the optical cording medium is irradiated with both the first light and the second light and the state in which the optical recording medium is irradiated with only one of the first and second lights.

Abstract: The present invention provides an optical pickup apparatus to for recording and/or reproducing information on an optical information recording medium including multilayered information recording surfaces. The optical pickup apparatus includes: a light source; an objective lens; 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. The optical pickup apparatus further includes a light-converging element for receiving a main light flux from one information recording surface and a secondary light flux from another information recording surface and converging the main light flux at a position between the first optical element and the second optical element. The optical pickup apparatus further includes a polarization splitting optical member for splitting the main light flux and the secondary light flux; and a photodetector for receiving the main light flux.

Abstract: An optical element is disposed on an optical path between a beam branching element and a photodetector. The optical element is disposed at a focal position of a stray light beam reflected by a recording layer except a target recording layer, and shields or attenuates the light beam in a region where the stray light beam converges.

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 pickup device is disclosed. In the optical pickup device, S-polarized light is input to a polarization filter from a DVD light source or a CD light source. Since the polarization filter transmits through the S-polarized light and diffracts P-polarized light, the S-polarized light is transmitted through the polarization filter. The S-polarized light is converted into three beams by being diffracted by a diffraction element. The three beams reflected at a polarization beam splitter are converted into circularly polarized light by a ¼ wavelength plate via a collimate lens, and the circularly polarized light is condensed on an optical recording medium via an objective lens. Light reflected from the optical recording medium is converted into linear P-polarized light by the ¼ wavelength plate via the objective lens. Substantially almost all P-polarized light is transmitted through the polarization beam splitter. A slight amount of the returning light travels to the side of the light source.

Abstract: An optical pickup includes: a first light source that emits a first linearly polarized light beam; a second light source that emits a second linearly polarized light beam different from the first wavelength; a drive unit configured to selectively drive the light sources; a first light path along which the first light beam travels to an optical disk; a second light path along which the second light beam travels to the optical disk, the first and second light paths intersecting in the middle of the light paths and are combined into a third light path; a light path-combining optical element provided at the intersection of the first and second light paths; a light path-separating optical element provided along the third light path; a phase difference-imparting optical element provided along the third light path; and a light receiving element that receives the first and second light beams reflected off the optical disk.

Abstract: An optical pick-up including a fold mirror having an achromatic quarter-wave plate coating is provided. To allow the thin film coating to efficiently provide the quarter-wave retardation, the optical pick-up is configured such that the polarization of light incident on the fold mirror is at a predetermined angle. According to one embodiment, the predetermined angle is provided by rotating the light sources. According to another embodiment, the predetermined angle is provided by rotating a plane containing the light sources and the beam combiners. In each embodiment, the beam combiners and the fold mirror are arranged along the same axis to further improve efficiency.

Abstract: An optical pickup apparatus for performing recording, reproduction and deletion of information onto each of three types of optical recording mediums including light sources of a blue wavelength zone, light sources of a red wavelength zone and light sources of an infrared wavelength zone. The optical pickup apparatus also has a single object lens which condenses a light from any of the light sources and a single aberration correction device disposed in a common light path between each of the light sources and the object lens.

Abstract: An optical head includes: a first optical element having an optical characteristic of reflecting a light of a first wavelength and transmitting lights of second and third wavelengths, on the first optical element the light of the first wavelength from a first light source being incident; and a second optical element having an optical characteristic of transmitting the light of the first wavelength, reflecting the light of the second or the third wavelength in a first polarization state and transmitting the light of the second or the third wavelength in a second polarization state, a first surface on which the light reflected by the first optical element is incident, a second surface on which the lights of the second and the third wavelengths from second and third light sources are incident, and a third surface emitting the first, the second and the third lights incident from the first and the second surfaces.

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: An optical pickup device has a first light source and a second light source each adapted for outputting a laser beam of a predetermined wavelength, a photodetector for detecting an intensity of the laser beam outputted from the first light source or the second light source to control the power of the laser beam to be outputted from the first light source or the second light source, a wideband quarter wavelength plate for converting the laser beam outputted from the first light source or the second light source into a circularly polarized laser beam, and a first rise-up mirror and a second rise-up mirror for guiding a P-polarized component in the laser beam converted by the wideband quarter wavelength plate to the photodetector, and guiding an S-polarized component in the laser beam different from the P-polarized component to an optical recording medium.

Abstract: An optical pickup unit includes a light source emitting a light beam, an objective lens focusing the light beam onto an information recording medium, a light detection part receiving the light beam reflected from the information recording medium, and a light blocking part selectively blocking a part of the light beam with respect to a radial direction. The light blocking part is provided in an optical path of the light beam centered on an optical axis.

Abstract: A half-wave plate is attached to a lens holder to integrally drive a collimator lens and the half-wave plate. When the lens holder is moved to a servo position, the half-wave plate is inserted in and retracted from an optical path of a laser beam. Therefore, the laser beam is formed in S-polarized light or P-polarized light with respect to a polarization beam splitter, and the laser beam is guided to a first objective lens or a second objective lens.

Abstract: Polarization direction switching elements do not change the polarization direction of incoming light, in the case where a disc is an optical recording medium conforming to the HD DVD standards. At this time, light outputted from a semiconducted laser is collected on the disc by an objective lens, and reflection light from the disc is received by a light detector. In the case where the disc is an optical recording medium conforming to the BD standards, the polarization direction switching elements change the polarization directed of the incoming light by ninety degrees. At this time, light outputted from the semiconductor laser is collected on the disc by the objective lens, and reflection light from the disc is received by the light detector. Liquid crystal lenses correct spherical aberrations on an outgoing path and a returning path.

Abstract: An optical pickup which is compatible with different types of media is disclosed. A plurality of light sources emit light with different wavelengths. Light path changers change the path of light emitted by the plurality of light sources so that the light is incident upon an objective lens. The objective lens focuses the incident light onto a recording medium. A collimating lens is disposed in front of the objective lens to collimate the incident lights. The collimating lens is movable to correct a spherical aberration. A diffractive optical element is disposed in a path of a light with a short wavelength and has a diffractive surface to correct a chromatic aberration.

Abstract: The present invention can simplify the configuration of a polarization adjustment plate. According to the present invention, the crystal axis of the polarization adjustment wavelength plate 32 is so arranged as to be turned up from the X-Y plane being an orthogonal plane with respect to the optical axis 40a, and the wavelength dependence which the crystal material is originally provided with is largely expressed, and further the thickness “ta” with respect to the optical axis 40a is set up such that the phase difference ? to be brought about at the beam center becomes low from 360°+180°=540° being a desired design value to irradiate the optical beam as the P-polarization by a predetermined difference value or 60°.

Abstract: Providing an objective lens with a large numerical aperture (NA), the present invention records or plays conventional optical disks such as CDs and DVDs using an optical head capable of recording or reproducing high-density optical disks. An optical element (8) is provided between a first and second laser light source and an objective lens (18) for the purpose of converting a wave front of a second optical beam 32. Furthermore, the optical element (8) and the objective lens (18) are fixed to move as a single piece.

Abstract: A servo controlling method for controlling an information processing apparatus using a hologram. The method includes a step of irradiating a holographic recording medium with light having a first wavelength and irradiating the holographic recording medium with light having a second wavelength, different from the first wavelength, a step of directing first return light by the light of the first wavelength and second return light by the light of the second wavelength to be incident on the same light receiving element, and a step of performing servo control by separating the first return light from the second return light at the light receiving element.

Abstract: A laser converging apparatus is disclosed that comprises a polarizing hologram element having a first area defined by a numerical aperture corresponding to a thickness of a first protective layer of a first disk medium and a second area inside the first area, the second area defined by a numerical aperture corresponding to a thickness of a second protective layer (> the thickness of the first protective layer) of a second disk medium, the second area having a hologram pattern for transmitting first laser light linearly polarized in a first direction without diffracting the first laser light while diffracting and transmitting second laser light that is linearly polarized in a second direction crossing the first direction at right angles, the second laser light having the same wavelength as the first laser light; an objective lens having the numerical aperture corresponding to the thickness of the first protective layer, the objective lens converging the first laser light having passed through the first area

Abstract: A polarizing diffraction element having a wavelength selectivity which functions as a polarizing diffraction element at a wavelength ?1, and which does not function as a diffraction grating not depending on incident polarization state and shows high transmittance at a wavelength ?2, and an optical head device employing the element, are provided. The polarizing diffraction element selectively diffracts or transmits incident light having two different wavelengths each containing a first circularly polarized light and a second circularly polarized light having a rotation opposite from the rotation of the first circularly polarized light, depending on wavelength and polarization state of the incident light. Then, a reflective wavelength region for at least the first circularly incident light, does not contain said two incident wavelengths.

Abstract: An optical element having an optical multi-layer coating which can function as a phase plate without using quartz crystal or an optical film. The optical multi-layer coating is deposited on a plane which is set up on the optical element by way of a perpendicularly intersecting plane located on perpendicularly intersecting X- and Y-axes in perpendicularly intersecting relation with optical axis of an incident light beam on the optical multi-layer coating, the perpendicularly intersecting plane being inclined through a predetermined angle about the X- and/or Y-axis to establish a phase differential between two linearly polarized components of the incident light beam.

Abstract: Provided is an optical head device and an optical information recording or reproducing device for performing recording or reproduction to/from a plurality of types of optical recording medium, which can obtain a stable track error signal by a small size and exhibits high efficiency. Light PD and light PC emitted from a double-wavelength light source make incidence to a diffractive optical element in the same polarization directions. Diffraction gratings have a double refractive characteristic and in these areas the polarization directions of the two light beams become orthogonal. The light of 650 nm band is divided into 0th-order light and ±1st-order diffracted light in one of the diffraction grating and transmits through the other diffraction grating. The light of 780 nm band transmits through one of the diffraction grating and is divided into 0th-order light and ±1st-order diffracted light in the other diffraction grating.

Abstract: The present invention discloses an optical system for extracting signal light components from a beam including the signal light components and stray light components. The optical system includes a condensing optical element situated on an optical path of the beam for condensing the beam, a polarization changing unit for changing the state of polarization of at least one of the signal light components and the stray light components included in the incident beam transmitted through the condensing optical element, and an extracting element for extracting the signal light components included in the beam transmitted through the polarization changing unit.

Abstract: An optical integrated unit includes a semiconductor laser (11), a polarized light beam splitter (14), a light receiving element (12), and a polarized light diffraction element (15) for diffracting an optical beam (20) and returning light. The polarized light diffraction element (15) is so provided as to receive the light beam (20) having passed through a polarized light beam splitter surface (14a), and as to diffract the returning light such that an optical path of the returning light is changed to lead to the light receiving element (12). This makes it possible to provide (i) an optical integrated unit in which the beam diameter of light incidenting on a diffraction element is large and in which an optical path length from the diffraction element to a light receiving element is long, and (ii) an optical pickup device including such an optical integrated unit.

Abstract: An optical device having a sub-wavelength grating formed in a specified region is disclosed that is able to prevent wave front degradation accompanying a phase difference of a polarized light beam passing through the optical device. The optical device includes a circular-belt-like region where the sub-wavelength diffraction grating is formed, and a center portion where the sub-wavelength diffraction grating is not formed. A vertically polarized light beam used for operations on a blue-light optical recording medium A has a phase difference in the sub-wavelength diffraction grating to be an integral multiple of 2? and hence is transmitted through the sub-wavelength diffraction grating. A horizontally polarized light beam used for operations on a blue-light optical recording medium is diffracted by the sub-wavelength diffraction grating.

Abstract: Light outputted from a semiconductor laser (1) passes through a liquid crystal diffraction optical element (2a) as 0-order light and is collected to a disc (5). Reflection light from the disc (5) is diffracted by the liquid crystal diffraction optical element (2a) as ±primary diffracted light and received by optical detectors (6a, 6b). When information is being recorded on the disc (5), light entered the liquid crystal diffraction optical element (2a) from the side of the semiconductor laser (1) is outputted to the side of an objective lens (4) from the liquid crystal diffraction optical element (2a) at a high efficiency.

Abstract: A polarizing beam splitter for separating an upstream beam from a downstream beam according to the polarization of an incident beam is provided between first and second light sources emitting laser beams at respective wavelength and an objective lens. A phase plate for providing a phase difference to a beam incident on the polarizing beam splitter is provided between the polarizing beam splitter and the light sources. A portion of the laser beam incident on the polarizing beam splitter is reflected by the polarizing beam splitter and caused to be incident on a photo-detecting unit, so as to prevent an unnecessary portion of the laser beam is incident on the photo-detecting unit. According to the invention, the laser beam is used efficiently and the cost of fabricating an optical disk apparatus is reduced by eliminating a need for a gain controlling circuit in the photo-detecting unit.

Abstract: An optical pickup apparatus for information recording and/or reproduction on different optical information recording media with compatibility among these media, the optical surface of a first objective lens and the optical surface of a second objective lens are formed only of a refractive surface. The second objective lens is used in common for the first light flux with a wavelength of ?1 and the second light flux with a wavelength of ?2, but in the case where the protective substrate t2 of the second optical information recording medium and the protective substrate t3 of the third optical information recording medium are the same, it is not necessary to take the difference in thickness of the protective substrate into consideration. Chromatic aberration based on the difference in wavelength between the first light flux and the second light flux can be corrected by displacing the second coupling lens.

Abstract: An optical pickup for writing information to and/or for reading information from an optical disc having at least two recording layers (dual layer) provided with first and second recording layers can prevent layer crosstalk resulting from disturbing a signal reproduced from the first recording layer by a reflected light beam reflected from the second recording layer during a writing operation for writing information to the first recording layer or a reading operation for reading information from the fist recording layer. An orthogonal polarization region forming component forms an orthogonal polarization region, in which respective directions of polarization of a first light beam focused on and reflected by a first recording layer of an optical disc and a second light beam reflected by a second recording layer of the optical disc are perpendicular to each other, in a region, in which the first and the second light beam overlap each other, on a light-receiving surface of a detector.

Abstract: The optical recording medium has a recording layer sensitive for recording at a first wavelength and sensitive for reading at a second wavelength, the recording layer having a groove structure, wherein at the first wavelength the groove structure has a diffraction efficiency into a first diffraction order sufficiently large to generate a push-pull signal, and at the second wavelength it has a diffraction efficiency into a first diffraciton order close to zero. The optical pickup for recording on an optical recording medium intended to be read with a second wavelength and a second numerical aperture is characterized in that it has a light source for generating a light beam at a first wavelength and a numerical aperture given by the second numerical aperture multiplied with a ration of the first wavelength and the second wavelength.