Abstract: An optical recording medium improves the quality of servo signals and readout signals by preventing light convergence on the back of the surface of the optical recording medium and reducing interference of light reflected from recording surfaces of the optical recording medium. An optical recording medium 40 includes at least three information recording surfaces, and satisfies d1<(d4?d1), where d1 is a distance from a surface 40z of the optical recording medium 40 to a first information recording surface 40a that is nearest to the surface 40z and d4 is a distance from the surface 40z to a fourth information recording surface 40d that is most distant from the surface 40z, and satisfies dmin?8 ?m, where dmin is a minimum interlayer thickness between the at least three information recording surfaces.

Abstract: An optical head device is provided with a semiconductor laser, an aberration correcting element for transmitting a beam from the semiconductor laser, a light guiding portion for introducing the beam from the semiconductor laser to the aberration correcting element, and an objective lens for focusing the beam having passed through the aberration correcting element on an optical disc. The aberration correcting element corrects a longitudinal chromatic aberration occurring in the objective lens and a longitudinal chromatic aberration occurring in the light guiding portion excluding the objective lens and the aberration correcting element based on a longitudinal chromatic aberration occurring in the aberration correcting element when the semiconductor laser emits a beam having a wavelength different by a specified wavelength difference.

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

Abstract: Fifth order spherical aberration in addition to third order spherical aberration for an optical information recording medium of which thickness of a light transmission layer changes greatly is corrected. An objective lens collects a laser beam emitted from a semiconductor laser on an optical information recording medium. A spherical aberration correcting portion corrects spherical aberration generated according to a thickness of the light transmission layer of the optical information recording medium, in which the spherical aberration correcting portion includes a collimator lens, a lens holder and a stepping motor for correcting the third order spherical aberration and a liquid crystal element and an applied voltage control portion for correcting the fifth order spherical aberration.

Abstract: Stable tracking control is achieved for an optical recording medium having a plurality of information recording planes. To achieve this, an optical information device comprises a light source for emitting a light beam, a focusing unit for converging the light beam emitted from the light source onto a predetermined information recording plane of an optical recording medium having a plurality of information recording planes, a beam splitting unit for splitting the light beam reflected by the optical recording medium, and a light detection unit having a light receiver that receives the light beam split by the beam splitting unit, for outputting a signal corresponding to the light intensity of the light beams received by the light receiver.

Abstract: An optical head is provided which can be restrained from becoming larger, even if it is used for an optical-information recording medium that includes a plurality of information recording layers. In this optical head, a collimating lens is formed by a concave lens disposed on the side of a light source and a convex lens disposed on the side of an objective lens. A collimating-lens actuator moves the convex lens in a direction where a spherical aberration is cancelled which is generated according to the thickness of a light transmission layer up to an information recording layer of the optical-information recording medium. An aperture stop is provided on the side of the collimating lens with respect to the objective lens, and the aperture stop is located near the focal position of the convex lens on the side of the objective lens.

Abstract: In a optical head, a beam is emitted from a light emitting element in which a plurality of light sources are integrally formed, the light sources being able to emit beams having different wave lengths from one another. An optical system converges the beam coming from any one of the light sources onto an optical information storage medium. An optical separator separates a reflected beam coming from the optical information storage medium from the beam coming from the light source. A light receiving element detects light quantities of the reflected beam separated by the optical separator.

Abstract: In a optical head, a beam is emitted from a light emitting element in which a plurality of light sources are integrally formed, the light sources being able to emit beams having different wave lengths to one another. An optical system converges the beam coming from any one of the light sources onto an optical information storage medium. An optical separator separates a reflected beam coming from the optical information storage medium from the beam coming from the light source. A light receiving element detects light quantities of the reflected beam separated by the optical separator.

Abstract: An objective lens driving apparatus includes an objective lens opposed to an optical disk, the objective lens having an optical axis in a vertical direction which is perpendicular to the optical disk, a holder for holding the objective lens; a supporting member for supporting the holder to be movable in at least the vertical direction and a radial direction of the optical disk; a focusing coil provided on the holder and wound around the vertical direction; and a magnetic field generation section for generating a magnetic flux crossing the focusing coil in a direction perpendicular to the vertical direction, the magnetic flux being generated to be substantially linear.