Abstract: An optical illumination apparatus has a polarization conversion device for converting light from a light source into light polarized uniformly in a predetermined manner and an optical integrator system for illuminating a display panel with the light polarized in the predetermined manner. The polarization conversion device splits the light from the light source into a first light beam and a second light beam in such a way that the first and second light beams are polarized in different manners, and then converts one of the first and second light beams into light polarized in the identical manner as the other light beam. Moreover, the first and second light beams pass through an identical lens cell of a first lens array of the optical integrator system and are imaged on an identical lens cell of a second lens array of the optical integrator system.

Abstract: Disclosed herein is an optical pickup device and method of adjusting the same. The optical pickup device and method of adjusting the same of the present invention can correct aberrations due to variation of thickness of an optical disc and dispersion of the emission wavelength by a semiconductor laser, which are generated in manufacturing processes of the optical disc and the optical pickup device, correct aberrations generated in recording/reproducing of the optical disc, due to variation of the emission wavelength and secular changes in the environment of the semiconductor laser, simplify and miniaturize the construction of the optical pickup device, and easily reduce manufacturing cost thereof. The optical pickup device of the present invention has a semiconductor laser (1) and a photo diode (13) for narrowing light emitted from the semiconductor laser (1) to a predetermined diameter and for detecting light reflected and returned from an optical disc (14).

Abstract: An information storage apparatus includes an optical element, a detector, an adjustment mechanism, a memory and a controller. The optical element emits and/or receives a radiation beam along an optical axis. The detector produces a first signal representing a tilt angle of the storage medium with respect to the detector. The adjustment mechanism compensates a tilt angle between the optical axis of the radiation beam and a direction normal to the optical storage medium in response to a second signal. The memory stores calibration data obtained based on relationship information between the first and second signals and tilt-angle information about the deleted tilt angle. The controller generates the second signal referring to the calibration data such that the tilt angle is substantially canceled. The relationship information reflects a deviation of a property of at least one of the detector and the adjustment mechanism measured by an individual test.

Abstract: A polarizing optical element is used in an optical pickup apparatus. A diffraction grating (hologram) is formed on the polarizing optical element. The diffraction efficiency of the diffraction grating varies in accordance with the polarization direction of an incident optical beam. When the duty ratio of the diffraction grating is defined as the ratio of the width of a protrusion of the diffraction grating to the grating period, the duty ratio of the diffraction grating is within the range of 0.4-0.5.

Abstract: A beam shaping device shapes a light beam from a light source to have a circular cross section, and changes the refractive index thereof by causing an electric field to be produced by a voltage applied to electrodes thereof. In this way, the light beam from the light source is deflected, and an objective lens gather the shaped and deflected light beam to expose an optical disk.

Abstract: A variable optical unit is provided with at least two phase-shift regions for providing light with phase differences. Phase-shift amount of the phase-shift region is adjusted by the applied voltage in accordance with birefringence of an information medium. A light beam emitted from a light source is incident on the variable optical unit through a collimator lens and a beam splitter. The light beam is polarized in accordance with the aforementioned phase-shift amount of the variable optical unit and converged by an objective lens to radiate the information medium. The reflected light polarized due to the effect of the birefringence of the information medium is polarized again according to the phase-shift amount of the variable optical unit. The reflected light is thereby polarized in the direction in which the beam splitter can reflect the reflected light and then the reflected light reflected by the beam splitter is detected by the condenser lens and an optical detector.

Abstract: An optical pick-up composed of an objective lens and a liquid crystal element, for recording and reproduction of optical discs having different recording densities, the liquid crystal element having nine zones, including: zones 2, 4 located in center parts of half circles of a small diameter beam for a low density optical disc, zones 3, 5 laid along the outer peripheries of zones 2, 4 within the half circles so as to surround zones 2, 4, zones 6, 7 along the outer peripheries of zones 3, 5, between the outer periphery of the small diameter beam and a large diameter beam, extending along substantially half circumferential parts of the small diameter beam, zones 8, 9 extending along substantially half circumferential parts of the large diameter beam, a remainder first zone and including a diameter whose the direction is the same as a tilt direction to be corrected.

Abstract: Even in the case where there is used technique such as “high NA”, “multi-layer recording”, etc., in order to carry out optimum correction of wave front aberration produced thereby with a simple technique, such an aberration correcting element to vary variable A and variable B(A≠B) of phase distribution formula A(−r4)−B(−r2) as phase correction pattern by aberration correcting element is realized by using a liquid crystal element (30). The liquid crystal element (30) forms such an electrode pattern to generate phase distribution corresponding to spherical aberration at one transparent electrode (31A), and forms such an electrode pattern to generate defocus pattern at the other transparent electrode (31B). In addition, by controlling applied voltages with respect to these electrodes, it becomes possible to independently carry out variable control of the above-described variables A and B.

Abstract: An aberration correcting unit is provided for correcting an aberration of a light beam radiated onto an object to be detected and then reflected from the object. This unit comprises an aberration correcting device comprising a first corrector configured to correct the aberration of the light beam radiated onto the object; and a second corrector configured to correct the aberration of the light beam reflected from the object and to divide the reflected light beam into a plurality of light beams. The aberration correcting unit further comprises a first driver configured to drive the first corrector and a second driver configured to drive the second corrector.

Abstract: A high density optical disc that can be driven changeably with the existent optical disc by the same driving apparatus. On the recording surface of the optical disc, a light transmissive layer with a thickness of about 0.2 to 0.4 mm is formed. The recording face is accessed by allowing a light beam with a wavelength of 395 to 425 nm in a spot shape to be irradiated onto it. Also, the light beam is converged in a spot shape by an objective lens having the numerical aperture of about 0.62 to 0.68.

Abstract: There are disclosed an optical storage device for accessing an optical recording medium such as a phase change type of optical disk and an optical magnetic disk, and a liquid crystal device preferably applicable to such a optical storage device. The liquid crystal device has a structure that two liquid crystal layers, each of which has stripe-like shaped electrodes arranged in a direction perpendicularly intersecting one another, are superposed. This structure makes it possible to effectively correct an aberration caused by a change in a depth from a surface of an optical recording medium to a condensing point, for example, in cases of unevenness in thickness of a protective layer and a multi-layer recording.

Abstract: Disclosed herein is an optical pick-up apparatus. The apparatus for recording and reproducing information by radiating first or second laser lights onto first and second discs, respectively, the first disc for recording and reproducing information using the first laser light, the second disc for recording and reproducing information using the second laser light having a band of wavelengths different from that of the first laser light, includes a first liquid crystal display for correcting spherical aberration by acting on the first laser light, a second liquid crystal display for correcting coma aberration by acting on the second laser light having a polarization direction perpendicular to that of the first laser light, and an object lens. The first and second liquid crystal displays and the object lens are movably supported. Accordingly, a BD can be compatible with a DVD or CD in the optical pick-up apparatus.

Abstract: A holographic recording method for recording information as phase information of light by projecting a signal beam and a reference beam onto a recording medium, wherein an X direction is defined as the direction of a line of intersection between a plane including the optical axes of the signal beam and reference beam (incidence plane) and the recording plane of the recording medium, and the Y direction is defined as the direction of a line lying normal to the incidence plane and intersecting said line of intersection, comprises steps of using the reference beam modulated with a first phase code to record a first hologram at a predetermined position and using the reference beam modulated with a second phase code whose pattern is different from that of the first phase code to record at a position shifted in the Y direction a second hologram that partially overlaps the first hologram.

Abstract: An actuator for an optical pickup includes a base, a holder fixed to the base, a moving portion on which an objective lens for focusing incident light onto a disc and a liquid crystal panel for correcting spherical aberration are mounted, a magnetic driving portion which drives the moving portion in a radial direction and in a focusing direction relative to the disc, and a connection section which includes a first connection part which serves as an electrical connection path of a signal used to drive the magnetic driving portion and has at least four wires, and a second connection part electrically independent of the first connection part, which serves as an electrical connection path of a signal used to drive the liquid crystal panel, and has wires, and which supports the moving portion to be movable with respect to the holder.

Abstract: An optical pickup in an optical disk reproducing device is operable to switch operations between a low-power operation mode and a high-power operation mode, and includes a liquid crystal element and a polarization beam splitter, which together attenuate, only in the low-power operation mode, a laser beam emitted by a laser diode onto an optical disk. The liquid crystal element is turned ON only in the low-power operation mode to serve as a polarization rotating element. Working with the polarization beam splitter, the polarization rotating element attenuates a polarized component of the incident light on the optical disk.

Abstract: In an optical pickup apparatus which includes at least a laser light source and an object lens and can apply a laser beam to different types of optical discs, an aberration correction liquid crystal device is placed on the optical axis of the laser beam emitted from the laser light source. The aberration correction liquid crystal device includes a first electrode section being placed on the side of the laser light source and having a first electrode pattern for correcting aberration concerning a first optical disc, a second electrode section being placed on the side of the optical disc and having a second electrode pattern for correcting aberration concerning a second optical disc different from the first optical disc in type, and liquid crystal being sandwiched between the first and second electrode sections.

Abstract: An optical disk device has an aperture of an objective lens in an incoming path of a beam from a semiconductor laser to an optical disk formed larger than an aperture in a return path from the optical disk or an aperture is varied in recording and in reproduction. This configuration improves recording/reproducing ability since light is focused on an optical disk with high numerical aperture. In addition, since reflected light from the optical disk is detected with low numerical aperture, margins for tilt and defocus are not reduced. Furthermore, since unnecessary signal components contained in the reflected light can be eliminated, a S/N (signal-to-noise ratio) of an information signal also increases. Thus, a high-performance optical disk device can be obtained. Alternatively, by varying the aperture of an objective lens in recording and in reproduction, an optical disk device in which recording density and recording quality are increased without deteriorating reproduction quality can be obtained.

Abstract: Light emitted from a laser is divided into two light waves so that the ratio of the power of one light wave to the power of the other will be appropriate. The resultant light waves are irradiated to the same track on a medium. The preceding spot is used for erasure, and modulated so that the same pattern as the one formed with a recording pulse will be formed. The high-power component of the modulated light of the erasing spot causes the temperature of a recording layer to be equal to or higher than the melting point. The medium-power component of the modulated light forms a crystallizing temperature area on the recording layer. A liquid crystal diffraction grating is used to divide power, and a power division ratio is variable and controllable.

Abstract: An optical pickup is provided for recording and reproduction of information onto and from an optical disk. In the optical disk, in a forward optical path, a single polarized optical beam is converted to plural polarized optical beams. Polarization modes of the plural polarized optical beams are then converted to a polarization mode suitable for one of the recording and the reproduction to produce polarization-converted optical beams and to radiate the polarization-converted optical beams to the disk. In the backward optical path, polarization modes of the polarization-converted optical beams reflected from the disk are returned to the same polarization mode as that of the plural polarized optical beams, so that plural polarized reflected optical beams are produced. Polarization modes of the plural polarized reflected optical beams are then returned to the same polarization mode as the single polarized optical mode.

Abstract: An aberration correction apparatus includes a first aberration correction element having aberration correction portions, a second aberration correction element which causes the wave front of the transmitted light beam to have a blaze hologram shape, a discriminator which discriminates the aberration of the reflected light beam, a coarse phase adjuster which drives the second aberration correction element on the basis of the magnitude of the aberration of the reflected light beam, and a fine phase adjuster which corrects aberration remained after the aberration correction by the coarse phase adjuster.

Abstract: An optical information recording and reproducing apparatus capable of recording and reproducing information data accurately with respect to an optical recording medium. The optical information recording and reproducing apparatus includes an aberration correction part which corrects aberration of the optical system. The apparatus determines whether or not an aberration correction by the aberration correction part is completed based on the signal level read from the optical recording medium, while changing a spherical aberration correction amount of the aberration correction part. The apparatus commences a recording operation or a reproducing operation of the optical information recording and reproducing apparatus if it is determined that the aberration correction was completed.

Abstract: A returning light beam emitted by a light source and reflected by an optical disk is separated by a half mirror, and partitioned and deflected at a hologram into a light beam passing a first region and a light beam passing a second region. The light beam passing the first region is received by a plurality of photo-detectors, and the aberration is detected by comparing the resulting signals. Based on the aberration detection, the aberration of an optical system can be reduced by driving an aberration correction element in real-time.

Abstract: Provided are an optical pickup device, which is capable of detecting and correcting spherical aberration while suppressing an increase in the number of construction elements and without increasing outer dimensions of a pickup device main body, and a recording and/or reproducing device having the optical pickup device built therein. A lens is designed such that when the thickness of a disk protective layer is greater than an optimum value, returning light (reflection light) from a disk is condensed on a sensor. The sensor is arranged at a condensing point and has a shape with which around 50% of the returning light is received when the thickness of the protective layer assumes the optimum value. With this construction, the quantity of light received by the sensor is increased when the thickness of the protective layer is greater than the optimum value, and is conversely reduced when the thickness of the protective layer is smaller than the optimum value.

Abstract: A spherical aberration compensator for compensating for spherical aberration resulting from a thickness deviation of a recording medium. The spherical aberration compensator includes a central compensation which provides a phase distribution that is effective for compensating for spherical aberration resulting from the thickness deviation and a peripheral compensation portion which surrounds the central compensation portion and provides a phase distribution that is effective for reducing a worsening of the spherical aberration caused by axial displacement of an objective lens from the central compensation portion. The spherical aberration compensator effectively relieves an optical pickup having an objective lens of an NA of 0.7 or greater of worsening of the spherical aberration resulting from thickness deviation of the recording medium.

Abstract: An optical scanning device comprising means for scanning optical record carriers of predetermined different formats, such as CDs and DVDs, using scanning at different numerical apertures provided by an optical diaphragm. The optical diaphragm comprises cholesteric liquid crystal material of one or more selected helical pitches which provide the diaphragm with desired wavelength- and/or polarization-selective characteristics.

Abstract: An objective lens for converging light onto an information recording medium includes a refracting interface for converging an incident light into a convergent light, and a refractive index varying member disposed between the refracting interface and the information recording medium, and having a refractive index that is varied according to an externally applied voltage.

Abstract: A pickup device has various controlled elements such as a light source and a sensor which need to be electrically controlled. The controlled elements are connected with an in-pickup control element via internal signal lines and are controlled by control signals supplied from the in-pickup control element. The in-pickup control element is connected with an external microcomputer via a connector and an external signal line and receives a control signal or the like from the microcomputer. With this structure, the controlled elements in the pickup device are basically controlled, not by the external microcomputer, but by the in-pickup control element. Therefore, the signal lines for supplying the control signals to the controlled elements can be short signal lines only in the pickup.

Abstract: A tilt servo apparatus which can correct a tilt error at a high speed and with high precision irrespective of a magnitude of the tilt error even if a response speed of a liquid crystal device decreases is provided. An amount of change and an increase/decrease of a signal intensity are detected by changing a correction value of a tilt error correcting arrangement by a first correction width, and a correction width of the correction value and a correcting direction are determined on the basis of the detection result. When the amount of change of the signal intensity is smaller than a predetermined amount of change, the correction width is changed to a second correction width which is smaller than a first correction width. When it is larger than the predetermined amount of change, the correction width is changed to a third correction width larger than the first correction width. The correction width is also determined in accordance with a change in environmental temperature.

Abstract: An information recording/reproducing apparatus of the present invention includes: a light source for emitting a first light beam having a predetermined light power Ppre; a determination section for determining the number of recording layers included in the information recording medium; a light beam transmission adjustment section for adjusting the quantity of the first light beam transmitted therethrough; and a light condensing section for condensing the first light beam on the information recording medium. When the information recording medium has one recording layer, the adjustment section adjusts the predetermined light power Ppre so as to be a first light power P1. When the information recording medium has two recording layers, the adjustment section adjusts the predetermined light power Ppre so as to be a second light power P2. The predetermined light power Ppre, the first light power P1, and the second light power P2 satisfy the relationship of P1<P2≦Ppre.

Abstract: An information recording/reproducing apparatus of the invention is equipped with an objective lens, a light source find a variable optical element having a grating which demonstrates a piezo-electric effect by means of an electric field. The light source emits and irradiates a laser beam onto the grating to generate a 0th order diffraction beam and +/− 1st order diffraction beams in accordance with first order diffraction efficiency, and the objective lens converges the 0th diffraction beam and +/− 1st order diffraction beams which are irradiated onto an information recording medium for the purpose of information recording or information reproducing. By controlling an electric field applied to the grating, the first order diffraction efficiency of the grating is adjusted, whereby light beams are generated which have power levels appropriate for various kinds of information recording media.

Abstract: An optical storage device capable of at least reproducing information recorded on first and second optical storage media different in distance from a medium surface on which a light beam is incident to a recording surface and in operating wavelength. The optical storage device includes a first light emitting element for emitting a light beam having a first wavelength, a second light emitting element for emitting a light beam having a second wavelength, a first photodetector for detecting a reproduction signal from a light beam reflected on the first optical storage medium, a second photodetector for detecting a reproduction signal from a light beam reflected on the second optical storage medium, and a beam splitter for combining optical paths of the light beams emitted from the first and second light emitting elements.

Abstract: An aberration correcting element includes a first electrode layer including a plurality of electrode portions; a second electrode layer opposed to the first electrode layer; and a liquid crystal sandwiched between the first and second electrode layers for producing a phase change corresponding to voltages applied to the first and second electrode layers in a light beam passing therethrough. The first electrode layer includes a plurality of position markers.

Abstract: A liquid-crystal panel is placed in an optical path of an optical beam from a light source to a recording surface of a recording medium for compensating wavefront aberration of the optical beam by giving a phase difference to the optical beam. The liquid-crystal panel comprises a layer of a liquid crystal material having an index of birefringence, wherein the product of the index of birefringence and thickness of the layer of the liquid crystal material is 0.4 &mgr;m or more.

Abstract: An electro-optic modulator is driven between discrete operating points such that a reversal of applied field polarity reduces harmful charge screening effects and the voltage swing between the operating points is reduced from previously used voltage swings.

Abstract: A land/groove discriminating method and an optical recording and/or reproducing apparatus employing the method are provided. The land/groove discriminating method emits a light beam onto an optical disc having lands and grooves through an optical element capable of causing and varying an effect of thickness variation of the optical disc, detects a light beam reflected/diffracted from the optical disc by dividing the reflected/diffracted light beam into inner and outer light beam portions, and discriminates between a land and a groove of the optical disc by detecting variation in a difference signal between detection signals from the inner and outer light beam portions while varying the degree of the effect of thickness variation of the optical disc by driving the optical element.

Abstract: An optical pickup performing recording, reproduction and deletion of information onto an optical recording medium, said optical pickup includes light sources of blue wavelength zone, red wavelength zone and infrared wavelength zone; 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: Tilt which is inclination of a normal of optical disk relative to optical axis of optical head is corrected with a liquid crystal element. In a driver for the liquid crystal element, a periodic waveform generator generates periodic waveform and an inverting element inverts the periodic waveform. The periodic waveform and the inverted waveform are connected to two ends of a potential divider which provides partial voltages. The periodic waveform is connected to a common electrode of the liquid crystal element, and the partial voltages of the potential divider are connected to electrodes opposing the common electrode. A structure of a driver circuit for each direction is simple. Tilt in a plurality of directions can be performed independently of each other. Spherical aberration is also corrected. When the liquid crystal element is mounted to a fixed component, deterioration due to jitters is reduced.

Abstract: The light emitted from a semiconductor laser is divided by a diffractive optical element into three light beams which are 0th-order light as the main beam and ±1st-order diffracted lights as the sub-beams, and the track error signals by the main beam and the sub-beams are detected, respectively, by a differential phase detection method. By the effect of the diffractive optical element, the light intensity distributions of the main beam and the sub-beams become different when making incidence on an objective lens. Therefore, when there is radial tilt in a disk, the phases of the track error signals by the main beam and the sub-beams are shifted with each other. Based on the shift in the phases of the track error signals, radial tilt of the disk is detected.

Abstract: An optical information reproducing device enables enhancement of information reading accuracy by correcting spherical aberration even if the spherical aberration occurs due to a thickness error in the transparent substrate of an optical disk. The correction amount of the spherical aberration is always changed such that the tracking servo gain in the tracking servo becomes maximum.

Abstract: An apparatus and a method are provided for compensating an aberration occurring in a reflected light beam from a recording medium. The apparatus includes a liquid crystal unit including a first electrode layer having divisional electrodes and a second electrode layer, and a liquid crystal element which provides a light beam with a phase change when an electric field is applied; a detector for receiving the reflected light beam through the liquid crystal unit to generate a detection signal; a voltage generator for generating voltages to be applied to the divisional electrodes; and a controller for performing aberration compensation control by changing the applied voltages to each of the divisional electrodes with reference to an applied reference voltage to a predetermined divisional electrode. The controller determines the applied reference voltage based on an amplitude change of the detection signal when the applied voltages to the divisional electrodes are changed.

Abstract: An information recording/reproducing apparatus of the invention is equipped with an objective lens, a light source and a variable optical element having a grating which demonstrates a piezo-electric effect by means of an electric field. The light source emits and irradiates a laser beam onto the grating to generate a 0th order diffraction beam and +/− 1st order diffraction beams in accordance with first order diffraction efficiency, and the objective lens converges the 0th diffraction beam and +/− 1st order diffraction beams which are irradiated onto an information recording medium for the purpose of information recording or information reproducing. By controlling an electric field applied to the grating, the first order diffraction efficiency of the grating is adjusted, whereby light beams are generated which have power levels appropriate for various kinds of information recording media.

Abstract: An optical information reproduction apparatus is provided that, even when spherical aberration has occurred because of a thickness error in a transmissive substrate of an optical disk, is capable of improving the information reading accuracy by correcting the spherical aberration. The spherical aberration of an optical system is corrected while changing the amount of correction in a state where an objective lens is retained at a position on a focus adjusting orbit where the amplitude level of a reading signal read from an optical recording medium reaches a maximum. The spherical aberration is then corrected by using the amount of correction, which is defined as the final amount of spherical aberration correction, where the amplitude level of a tracking error signal obtained during this time reaches the maximum.

Abstract: A method and an apparatus for driving an optical recording medium for recording and/or reproducing various information for the optical recording medium, in which the output power ratio of the light source may be reduced for recording and reproduction, for optical recording media of different sorts, or for respective recording surfaces of a multi-layered optical recording medium, so that optimum characteristics may be realized even with use of an easy-to-fabricate light source or a light source with a smaller light output rating.

Abstract: A pickup includes a light source for emitting a light beam that travels to an information recording medium along a first optical path, a first light receiving element group for detecting an error signal, a second light receiving element group for detecting a magneto-optical signal, a diffraction grating for diffracting light returned along the first optical path, a polarization beam splitter for separating a part of the return light such that a beam of the return light travels to the second light receiving element group along a second optical path, a mirror for bending the second optical path so that a light beam reflected thereby is directed toward the second light receiving element group, and an anisotropic crystal member that has an optic axis inclined between 30° and 60° and that includes a substantially parallel flat plate portion between the mirror and the first light receiving element group.

Abstract: The light intensity of a light beam emitted from a light source is appropriately controlled when the light beam is transmitted through a variable optical coupling efficiency device in an optical head. During a read mode, the light beam from the light source is incident on an optical disk at an intensity relatively weaker than that of the light source. By switching the optical coupling efficiency of the variable optical coupling efficiency device between a write mode and a read mode, the light intensity directed to an optical recording medium is substantially varied from the write mode to the read mode. This arrangement eliminates the need for substantially increasing the optical output power ratio of the light source of write power to read power.

Abstract: An optical disk device has an aperture of an objective lens in an incoming path of a beam from a semiconductor laser to an optical disk formed larger than an aperture in a return path from the optical disk or an aperture is varied in recording and in reproduction. This configuration improves recording/reproducing ability since light is focused on an optical disk with high numerical aperture. In addition, since reflected light from the optical disk is detected with low numerical aperture, margins for tilt and defocus are not reduced. Furthermore, since unnecessary signal components contained in the reflected light can be eliminated, a S/N (signal-to-noise ratio) of an information signal also increases. Thus, a high-performance optical disk device can be obtained. Alternatively, by varying the aperture of an objective lens in recording and in reproduction, an optical disk device in which recording density and recording quality are increased without deteriorating reproduction quality can be obtained.

Abstract: A laser beam for reproduction emitted from an LD (41) at the time of reproduction passes through an As correction board (42) and a grating (43) and becomes incident on a beam splitter (44). The beam splitter (44) transmits the laser beam and causes the laser beam to be incident on a liquid crystal unit (45). Then, at the time of reproduction, a light spot shaping device provides aberration to the laser beam transmitted through the liquid crystal unit (45) in accordance with the type of a magneto-optical disc and thus shapes a light spot on the magneto-optical disc. Therefore, optimum light spots for different media can be shaped.

Abstract: A liquid-crystal panel is placed in an optical path of an optical beam from a light source to a recording surface of a recording medium for compensating wavefront aberration of the optical beam by giving a phase difference to the optical beam. The liquid-crystal panel comprises a layer of a liquid crystal material having an index of birefringence, wherein the product of the index of birefringence and thickness of the layer of the liquid crystal material is 0.4 &mgr;m or more.

Abstract: An information recording and reproducing apparatus in accordance with the present invention has a radiation light source, a collimator turning a light beam emitted from the radiation light source into substantially parallel light, a light beam convergence member focusing the light beam on an information carrier, a light beam polarization-branching member branching the light beam by polarization, a variable wave plate located between the collimator and the light beam convergence member, photo detectors receiving the light beam branched by the light beam polarization-branching member and outputting a current according to an incident light quantity, and an output level judging member judging whether an output of the photo detectors is larger or smaller than a predetermined value.

Abstract: An optical pickup system includes a light source, an objective lens, a beam splitter for splitting light received from the light source and reflected light from an optical disc, a detector for receiving the reflected light, a liquid crystal panel for providing passing light with a phase difference in accordance with a control signal and a control means for providing the control signal to the liquid crystal panel to eliminate an influence of birefringence of the optical disc.