Abstract: In an optical disc device of the present invention, time differences among the focus error signal corresponding to the surface of the optical disc, the focus error signal corresponding to the first reflection layer, and the focus error signal corresponding to the second reflection layer, all of which are obtained through the light receiving element when a relative distance between the objective lens and the optical disc is linearly changed in a focus search of the optical disc are measured. The thickness of the cover layer from the surface of the optical disc to the first reflection layer and the thickness of a cover layer from the surface of the optical disc to the second reflection layer are detected on the basis of these time differences.

Abstract: An optical pickup device is applied to DVD recorders and includes a beam expander unit. A drive coil wound around a lens holder within the beam expander unit, is located in a magnetic field formed by a magnet. When an electric current is passed through the drive coil, the drive coil moves an expander second lens in a direction of an optical axis, receiving a force based on interaction between the electric current and the magnetic field. This changes a distance between an expander first lens and the expander second lens, and thus light emitted from the beam expander unit toward an object lens becomes diffused light or converged light. Consequently, the objective lens generates a spherical aberration in a reverse direction of a spherical aberration that has occurred owing to a deviation of a cover layer in film thickness from a reference value, which cancels the latter spherical aberration.

Abstract: An optical pickup device is applied to DVD recorders and includes a beam expander unit. A drive coil wound around a lens holder within the beam expander unit, is located in a magnetic field formed by a magnet. When an electric current is passed through the drive coil, the drive coil moves an expander second lens in a direction of an optical axis, receiving a force based on interaction between the electric current and the magnetic field. This changes a distance between an expander first lens and the expander second lens, and thus light emitted from the beam expander unit toward an object lens becomes diffused light or converged light. Consequently, the objective lens generates a spherical aberration in a reverse direction of a spherical aberration that has occurred owing to a deviation of a cover layer in film thickness from a reference value, which cancels the latter spherical aberration.

Abstract: In an optical disc device of the present invention, time differences among the focus error signal corresponding to the surface of the optical disc, the focus error signal corresponding to the first reflection layer, and the focus error signal corresponding to the second reflection layer, all of which are obtained through the light receiving element when a relative distance between the objective lens and the optical disc is linearly changed in a focus search of the optical disc are measured. The thickness of the cover layer from the surface of the optical disc to the first reflection layer and the thickness of a cover layer from the surface of the optical disc to the second reflection layer are detected on the basis of these time differences.

Abstract: In an optical pickup device (10) including a laser light source (1) and an objective lens (7), an optical device (6) is provided that transmits a laser beam of 635 nm in wavelength emitted from a first semiconductor laser (1A) straightforwardly into the objective lens (7) while maintaining its incident intensity, and that selectively diffracts a laser beam of 780 nm in wavelength emitted from a second semiconductor laser (1B) to a desired direction while maintaining its incident intensity and directs only the predetermined center portion of the laser beam into the objective lens (7). The optical pickup device (10) records or reproduces a signal onto or from a plurality of types of optical disks differing in substrate thickness while directing a laser beam of sufficient intensity onto a signal recording plane.

Abstract: An optical pickup device which includes a semiconductor laser selectively generating a laser beam with a wavelength of 635 nm, a laser beam with a wavelength of 780 nm, and an optical device having a central region in which a hologram is formed and a peripheral region in which a diffraction grating is formed. In particular, the optical device is arranged immediately below an objective lens, and the central region allows transmission of the laser beam with the wavelength of 635 nm without any diffraction but increases the diameter of the teaser beam to the wavelength of 780 nm by diffraction. On the other hand, peripheral region allows transmission of the laser beam with the wavelength of 635 nm without any diffraction, but substantially shields the laser beam with the wavelength of 780 nm by diffraction. Thus, each laser beam with the wavelength 635 nm is transmitted through objective lens and focused on a signal recording surface of a DVD.

Abstract: An optical disk recording/reproduction apparatus includes a semiconductor laser, an objective lens provided opposite an optical disk, an optical system for supplying a laser beam from the semiconductor laser to the objective lens, an aperture for not intercepting the laser beam in reproducing from a digital video disk and intercepting an outermost portion of the laser beam in reproducing from a compact disk, and a tracking servo mechanism for moving the objective lens in a tracking direction orthogonal to the running direction of a track of the optical disk. The aperture has an oblong opening that is longer in the tracking direction than in the track running direction.

Abstract: An optical disk recording/reproduction apparatus includes a semiconductor laser, an objective lens provided opposite an optical disk, an optical system for supplying a laser beam from the semiconductor laser to the objective lens, an aperture for not intercepting the laser beam in reproducing from a digital video disk and intercepting an outermost portion of the laser beam in reproducing from a compact disk, and a tracking servo mechanism for moving the objective lens in a tracking direction orthogonal to the running direction of a track of the optical disk. The aperture has an oblong opening that is longer in the tracking direction than in the track running direction.

Abstract: An apparatus for discriminating optical disks has an optical pickup provided with an objective lens having an effective numerical aperture of 0.55 to 0.65, which can compatibly reproduce information from a CD and an SD. The apparatus discriminates presence/absence of waveforms of two focus error signals detected when the effective numerical aperture of the objective lens is set at 0.55 to 0.65 and 0.20 to 0.45 respectively in a process of performing focus servo control, thereby discriminating various types of optical disks from each other. Thus, optical disks having different substrate thicknesses, different track pitches, different minimum pit lengths and different reflectivity can be quickly and simply discriminated from each other.

Abstract: The optical pickup device includes a two wavelength semiconductor laser (23) selectively generating a laser beam having the wavelength of 635 nm and laser beam having the wavelength of 780 nm, a collimator lens (24), a hologram (25) formed on a surface of collimator lens (24), a polarizing glass (22) having an annular polarizing region (40) and an objective lens (21). Hologram (25) does not diffract the laser beam having the wavelength of 635 nm, and diffracts outward the laser beam having the wavelength of 780 nm. Therefore, virtual light source of the laser beam having the wavelength of 780 nm comes closer to the collimator lens (24) than the light source of the laser beam having the wavelength of 635 nm. Therefore, objective lens (21) focuses the laser beam having the wavelength of 635 nm on a recording surface of a transparent substrate (31) of a DVD, and focuses the laser beam having the wavelength of 780 nm on a recording surface of a transparent substrate (32) of a CD-R.

Abstract: An optical disc reproducing apparatus includes a semiconductor laser, an objective lens converging a laser beam from the semiconductor laser on a recording surface of an optical disc, a polarization plane rotating unit selectively rotating the plane of polarization of the laser beam according to the thickness of a substrate of the optical disc, and a polarizing filter selectively shading a peripheral portion of the laser beam having the rotated plane of polarization. In one embodiment, a numerical aperture changing unit includes a non-patterned twisted nematic liquid crystal, and the polarizing filter includes a polarizing film having a polarization characteristics at its peripheral portion.

Abstract: An optical pick-up device includes an optical active element (11) which transmits an introduced laser beam (18) with its polarization direction (17) rotated by 90.degree. in playback of a DVD and also transmits an introduced laser beam (18) without rotating its polarization direction (17) in playback of a CD, and a polarizer (14) which transmits the entirety of a laser beam with its polarization direction rotated in playback of a DVD and also blocks the perimeter of a laser beam with its polarization direction not rotated in playback of a CD to reduce the effective numerical aperture of an objective lens (15). A rubbing direction (28) of an rubbing film (24) of the optical active element (11) that is positioned at the incident side of the laser beam, is adapted to be parallel to the polarization direction (17) of the introduced laser beam (18). Thus, the optical pick-up device can play back DVD as well as CD while reducing laser beam loss.

Abstract: An optical disc reproducing apparatus includes a semiconductor laser, an objective lens converging a laser beam from the semiconductor laser on a recording surface of an optical disc, a polarization plane rotating unit selectively rotating the plane of polarization of the laser beam according to the thickness of a substrate of the optical disc, and a polarizing filter selectively shading a peripheral portion of the laser beam having the rotated plane of polarization. In one embodiment, a numerical aperture changing unit includes a non-patterned twisted nematic liquid crystal, and the polarizing filter includes a polarizing film having a polarization characteristics at its peripheral portion.

Abstract: An optical disc reproducing apparatus includes a semiconductor laser, an objective lens converging a laser beam from the semiconductor laser on a recording surface of an optical disc, a polarization plane rotating unit selectively rotating the plane of polarization of the laser beam according to the thickness of a substrate of the optical disc, and a polarizing filter selectively shading a peripheral portion of the laser beam having the rotated plane of polarization. In one embodiment, a numerical aperture changing unit includes a non-patterned twisted nematic liquid crystal, and the polarizing filter includes a polarizing film having a polarization characteristics at its peripheral portion.

Abstract: An optical disc reproducing apparatus includes a semiconductor laser, an objective lens converging a laser beam from the semiconductor laser on a recording surface of an optical disc, a polarization plane rotating unit selectively rotating the plane of polarization of the laser beam according to the thickness of a substrate of the optical disc, and a polarizing filter selectively shading a peripheral portion of the laser beam having the rotated plane of polarization. In one embodiment, a numerical aperture changing unit includes a non-patterned twisted nematic liquid crystal, and the polarizing filter includes a polarizing film having a polarization characteristics at its peripheral portion.

Abstract: An optical pickup apparatus including a polarization plane rotary unit arranged between a semiconductor laser and an objective lens, and a polarizing film arranged between the polarization plane rotary unit and the objective lens. The polarization plane rotary unit includes liquid crystal, two glass plates sandwiching the liquid crystal, and transparent electrodes patterned to a predetermined configuration on an inner face of these glass planes. The polarization plane rotary unit permits passage of the laser beam without rotating the plane of polarization of the entire laser beam at the time of recording, and permits passage of the laser beam with the plane of polarization of the center portion of the laser beam rotated and the plane of polarization of the remaining outer portion of the laser beam not rotated at the time of reproduction. Only the outer portion of the laser beam is focused on a magneto-optical disk in a reproduction mode, so that a main beam of a small spot is formed by mutual interference.

Abstract: An apparatus for discriminating optical disks has an optical pickup provided with an objective lens having an effective numerical aperture of 0.55 to 0.65, which can compatibly reproduce information from a CD and an SD. The apparatus discriminates presence/absence of waveforms of two focus error signals detected when the effective numerical aperture of the objective lens is set at 0.55 to 0.65 and 0.20 to 0.45 respectively in a process of performing focus servo control, thereby discriminating various types of optical disks from each other. Thus, optical disks having different substrate thicknesses, different track pitches, different minimum pit lengths and different reflectivity can be quickly and simply discriminated from each other.

Abstract: An optical disc readout apparatus having an optical system which guides a laser beam onto a signal recording surface of a loaded disc through an objective lens and guides a reflected laser beam onto a photo detector. An effective numerical aperture of the objective lens is adjusted according to the thickness between a substrate surface of the loaded disc and the signal recording surface, and the laser spot with a diameter suitable to a recording density of the loaded disc is focused on the signal recording surface. Therefore, the data recorded in a plurality of optical discs with different thickness or recording densities can be read out.

Abstract: An optical disc reproducing apparatus includes a semiconductor laser, an objective lens converging a laser beam from the semiconductor laser on a recording surface of an optical disc, a polarization plane rotating unit selectively rotating the plane of polarization of the laser beam according to the thickness of a substrate of the optical disc, and a polarizing filter selectively blocking a peripheral portion of the laser beam depending on the plane of polarization. In one embodiment, a numerical aperture changing unit includes a non-patterned twisted nematic liquid crystal, and the polarizing filter includes a polarizing film having a polarization characteristic at its peripheral portion.