Abstract: In an optical disk medium, land recording tracks (1) are coupled by first and second coupling portions (3 and 4) at a particular radial position to form a tilt detecting mark SM.

Abstract: In an optical disk apparatus for focusing a light beam on a track of an optical disk by using a tracking control loop to perform at least one of recording and reproducing operations upon the optical disk, a loop level calculating unit calculates loop levels of the tracking control loop. A control unit calculates a loop gain of the tracking control loop in accordance with the loop levels of the tracking control loop and compensates for a radial tilt of the optical disk in accordance with the calculated loop gain of the tracking control loop.

Abstract: An optical head apparatus includes a light source section having a plurality of light sources configured to output a plurality of light beams whose wavelengths are different from each other. A plurality of output light beams from the light source section are collected onto an optical recording medium by an objective lens. Reflection light beams corresponding to the output light beams reflected by the optical recording medium, and having different wavelengths are detected by a light detecting section. The output light beams outputted from the plurality of light sources and having the different wavelengths and the reflection light beams reflected by the optical recording medium and having the different wavelengths are separated by an optical separating section. An optical diffracting section is provided between the optical separating section and the light detecting section to generate a plurality of diffraction light beams from the reflection light beam reflected by the optical recording medium.

Abstract: Four types of optical systems, a polarization optical system including an objective lens having a high numerical aperture, a polarization optical system including an objective lens having a low numerical aperture, a non-polarization optical system including an objective lens having a high numerical aperture and a non-polarization optical system including an objective lens having a low numerical aperture, are selectively used at the time of irradiating light from a semiconductor laser on a target disk for measurement, and the in-plane birefringence characteristic and perpendicular birefringence characteristic of the target disk are separately acquired based on the amounts of received light obtained by measuring reflected light from the target disk by a photosensor.

Abstract: Four types of optical systems, a polarization optical system including an objective lens having a high numerical aperture, a polarization optical system including an objective lens having a low numerical aperture, a non-polarization optical system including an objective lens having a high numerical aperture and a non-polarization optical system including an objective lens having a low numerical aperture, are selectively used at the time of irradiating light from a semiconductor laser on a target disk for measurement, and the in-plane birefringence characteristic and perpendicular birefringence characteristic of the target disk are separately acquired based on the amounts of received light obtained by measuring reflected light from the target disk by a photosensor.

Abstract: An optical head unit is provided including a first light source emitting a light with a first wavelength, a second light source emitting a light with a second wavelength, and a third light source emitting a light with a third wavelength. The optical head unit also includes a first objective lens irradiating the light emitted from the first light source onto an optical recording medium, a second objective lens irradiating the light emitted from the second light source or the light emitted from the third light source onto an optical recording medium, and a photodetector receiving a reflected light from the optical recording medium.

Abstract: In an optical head apparatus for an optical recording medium, including a light source for emitting a light beam, an objective lens for focusing the light beam at the optical recording medium and receiving a reflected light beam from the optical recording medium, and a photodetector for receiving the reflected light beam from the objective lens, a unit is provided between the light source and the objective lens to generate a main beam and a sub beam from the light beam. The intensity distributions of the main beam and the sub beam are different from each other, and the sub beam is divided into a plurality of portions having different phase distributions from each other. The photodetector includes photodetecting portions for each of the main beam and the sub beam, thus obtaining a push-pull signal from each of the main beam and the sub beam.

Abstract: In an optical head device and an optical information recording/reproducing device using the optical head device, by driving a liquid crystal panel 4a, the liquid crystal panel 4a produces wave aberration for light on a going path and light on a returning path likewise. Accordingly, when the substrate-thickness deviation or tilt of the disc 7 is corrected, the wave aberration due to the substrate-thickness deviation or tilt of the disc 7 and the wave aberration produced by the liquid crystal panel 4a are canceled by each other for both of the light on the going path and the light on the returning path, so that no wave aberration remains for the light on the returning path and the phase distribution is not varied.

Abstract: Light emitted from a semiconductor laser (1) is split by a diffractive optical element (3a) into a main beam and sub-beams. The diffractive optical element (3a) is divided into four regions by a straight line parallel to a tangential direction of a disc (7) and a straight line parallel to a radial direction of the disc (7). A phase of grating in two regions arranged diagonally and a phase of grating in the other two regions arranged diagonally are different from each other by ?. A focused spot of the main beam and focused spots of the sub-beams are located on the same track. A focusing error signal is detected by a differential astigmatism method, using the main beam and the sub-beams.

Abstract: In an optical head device and an optical information recording/reproducing device using the optical head device, by driving a liquid crystal panel 4a, the liquid crystal panel 4a produces wave aberration for light on a going path and light on a returning path likewise. Accordingly, when the substrate-thickness deviation or tilt of the disc 7 is corrected, the wave aberration due to the substrate-thickness deviation or tilt of the disc 7 and the wave aberration produced by the liquid crystal panel 4a are canceled by each other for both of the light on the going path and the light on the returning path, so that no wave aberration remains for the light on the returning path and the phase distribution is not varied.

Abstract: An optical head device and an optical recording and reproducing apparatus using this optical head device, which can record information and reproduce the recorded information at any of optical recording media, such as a next generation optical recording medium, in which the wavelength of the light source is made to be shorter, the numerical aperture of the objective lens is made to be higher, and the thickness of the recording medium is made to be thinner, and conventional recording media of DVD and CD standards, are provided. A light having wavelength of 405 nm, emitted from one of optics, is inputted to an objective lens as a collimated light, and is focused on a disk having thickness of 0.1 mm. A light having wavelength of 650 nm, emitted from the other of optics, is inputted to the objective lens as a diverged light, and is focused on a disk having thickness of 0.6 nm.

Abstract: In order to correct specific aberration that occurs within an optical system, a plurality of aberration correction optical elements (4) with differing amounts and/or signs of aberration correction are prepared. The amount and sign of the aberration that is generated within the optical system, except the aberration correction optical elements (4), between a semiconductor laser (1) and an objective lens 6, is then measured using an interferometer or the like. Based on the measured amount and sign of the aberration, where necessary, the aberration correction optical element (4) which, following correction, is most capable of minimizing the residual RMS wave-front aberration is selected from amongst the plurality of different aberration correction optical elements (4), and is then inserted into the optical system between the semiconductor laser (1) and the objective lens (6).

Abstract: In an optical head apparatus including a first light source for emitting a first light beam having a first wavelength, a second light source for emitting a second light beam having a second wavelength different from the first wavelength, an objective lens, a photodetector, and first and second optical combining/splitting elements, the first optical combining/splitting element receives the first light beam from the first light source to outgo most of the first light beam therefrom to the second optical combining/splitting element and receives the first and second light beams from the second optical combining/splitting element to outgo most of the first and second light beams therefrom to the photodetector.

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: A diffractive optical element for dividing a light emitted from a light source into a main beam and at least one sub-beam, an objective lens for focusing the beams on a disk-shaped optical recording medium with spiral tracks, and a photodetector for receiving the beams reflected from the optical recording medium are provided.

Abstract: In an optical head device, a birefringence correcting element 5a containing a material showing mono-axial refractive index anisotropy is located before an objective lens. The birefringence correcting element 5a is circumferentially divided into four regions by two straight lines passing through an optical axis and intersecting each other at right angle. Each of the four regions is radially divided into four sub-regions by three circles centered at the optical axis. The direction of optic axes of the sub-regions 11a to 14a and 11c to 14c is a direction of x-axis, while the direction of optic axes of the sub-regions 11b to 14b and 11d to 14d is a direction of y-axis. A phase difference of sub-regions between a polarized light component polarized in a direction parallel to the optic axis and another polarized light component polarized in a direction vertical to the optic axis increases in order of the sub-regions 11a to 11d, sub-regions 12a to 12d, sub-regions 13a to 13d and the sub-regions 14a to 14d.

Abstract: Light emitted from a laser is separated into a main beam, first sub beams, and second sub beams. The distribution intensity of each first sub beams is the same as that of the main beam. The distribution intensity of each second sub beam is different from that of the main beam. The sum of the focusing error signals relating to the main beam and first sub beams is a final focusing error signal. The difference between the tracking error signal relating to the main beam and the tracking error signal of each first sub beam is a final tracking error signal. The deviation of the thickness of the substrate of the disk and the radial tilt thereof are detected on the basis of the deviation of the zero crossing points of the focusing error signal and the tracking error signal relating to the main beam and each second sub beam.

Abstract: In an optical system, reflected light from the disk is diffracted by a hologram optical element, and received by an optical detector. A focusing error signal is detected from ?1st-order diffracted light of the hologram optical element. A tracking error signal by the differential phase method, a tracking error signal by a push-pull method and the data signal recorded on the disk are detected from +1st-order diffracted light of the hologram optical element. A diffraction efficiency of the +1st-order diffracted light is higher than a diffraction efficiency of the ?1st-order diffracted light.

Abstract: There is disclosed an optical head apparatus and an optical information recording or reproducing apparatus capable of obtaining a high light output at a recording time, and a high S/N at a reproducing time with respect to any of disks of next-generation, DVD, and CD standards. Light having a wavelength of 400 nm emitted from a semiconductor laser is almost all reflected by a beam splitter, and condensed on a disk of the next-generation standard. Light having a wavelength of 660 nm emitted from a semiconductor laser is almost all reflected by a beam splitter, almost all transmitted through the beam splitter, and condensed on the disk of the DVD standard. Light having a wavelength of 780 nm emitted from a semiconductor laser is almost all reflected by a beam splitter, almost all transmitted through the beam splitters and condensed on the disk of the CD standard. Reflected light from the disk is almost all transmitted through the beam splitters and received by a photodetector.

Abstract: Light emitted from a semiconductor laser (1) is split by a diffractive optical element (3a) into a main beam and sub-beams. The diffractive optical element (3a) is divided into four regions by a straight line parallel to a tangential direction of a disc (7) and a straight line parallel to a radial direction of the disc (7). A phase of grating in two regions arranged diagonally and a phase of grating in the other two regions arranged diagonally are different from each other by ?. A focused spot of the main beam and focused spots of the sub-beams are located on the same track. A focusing error signal is detected by a differential astigmatism method, using the main beam and the sub-beams.