Abstract: An optical pickup with a simplified structure in which, according to the type of optical disc, diffracted light from three types of laser light can be directed efficiently onto a photodetector and appropriate focus control can be performed based on the signals detected by the photodetector, and a diffractive optical element that can be used in the optical pickup, which has a semiconductor laser 10 that can emit three types of laser light, a diffractive optical element 42 that diffracts the laser light reflected from the optical disc 31, and a single photodetector 43 that detects the diffracted light exiting the diffractive optical element 42.

Abstract: An optical head device 201 includes a light source 1, an objective lens group 13, a two-dimensional actuator 15, spherical aberration adding means 9, 10, and 16, a hologram element 17 for splitting the light beam from the optical disk 14 into a plurality of split light beams, and a photodetector 22 which includes at least one photoreceptor including a plurality of split light receiving areas and outputs an electric signal corresponding to the light amount of a split light beam entering each of the plurality of split light receiving areas or an electric signal corresponding to a combination of the light amount of split light beams entering the corresponding split light receiving areas, and the plurality of split light beams split by the hologram element 17 include one circular ray U1 and at least two annular rays U2 and U3.

Abstract: When using an optical disc medium that includes pit trains having their widths narrower than a diffraction limit, it is difficult to detect a tracking error signal and take a tracking-servo control while increasing pit density in a direction orthogonal to a pit-train extension direction. Information pit trains are arranged spirally or concentrically and formed in a structure in which their depths are changed periodically at a pitch radially along the optical disc medium, so that the tracking error signal can be obtained by push-pull detection of diffraction light from the structure.

Abstract: An optical head device 201 includes a light source 1, an objective lens group 13, a two-dimensional actuator 15, spherical aberration adding means 9, 10, and 16, a hologram element 17 for splitting the light beam from the optical disk 14 into a plurality of split light beams, and a photodetector 22 which includes at least one photoreceptor including a plurality of split light receiving areas and outputs an electric signal corresponding to the light amount of a split light beam entering each of the plurality of split light receiving areas or an electric signal corresponding to a combination of the light amount of split light beams entering the corresponding split light receiving areas, and the plurality of split light beams split by the hologram element 17 include one circular ray U1 and at least two annular rays U2 and U3.

Abstract: An optical-pickup-adjustment optical disk used for adjusting or producing an optical pickup device, includes a transparent protective substrate; and an optical-pickup-adjustment middle-depth information recording layer formed on a side of an inside surface of the transparent protective substrate, wherein the optical-pickup-adjustment middle-depth information recording layer is formed to have a middle depth which is a center of the maximum depth of the maximum-depth information recording layer prescribed by the optical disk standard and the minimum depth of the minimum-depth information recording layer prescribed by the optical disk standard.

Abstract: [Problem to be Solved] It has been a problem that, with focusing servo control based on a focus error signal according to a conventional astigmatism method, due to a positional deviation of a received light beam on the light-receiving plane of a photodetector or an offset caused by asymmetry in the intensity distribution of reflected light, an error occurs in the focus error signal, whereby the focusing servo cannot correctly be performed.

Abstract: A semiconductor laser unit includes a plurality of semiconductor laser elements arranged parallel with one another in a laser beam-emitting direction, and a base for positioning and fixing the plurality of semiconductor laser elements. The plurality of semiconductor laser elements are arranged such that a laser beam emitted from the semiconductor laser element greatest in astigmatism, of the plurality of semiconductor laser elements, is coincident in its axis with a reference axis of the base. In the case that the semiconductor laser unit is arranged on an optical head device, the focusing characteristic on the plurality of laser beams can be improved.

Abstract: A semiconductor laser unit includes a plurality of semiconductor laser elements arranged parallel with one another in a laser beam-emitting direction, and a base for positioning and fixing the plurality of semiconductor laser elements. The plurality of semiconductor laser elements are arranged such that a laser beam emitted from the semiconductor laser element greatest in astigmatism, of the plurality of semiconductor laser elements, is coincident in its axis with a reference axis of the base. In the case that the semiconductor laser unit is arranged on an optical head device, the focusing characteristic on the plurality of laser beams can be improved.

Abstract: A semiconductor laser unit includes a plurality of semiconductor laser elements arranged parallel with one another in a laser beam-emitting direction, and a base for positioning and fixing the plurality of semiconductor laser elements. The plurality of semiconductor laser elements are arranged such that a laser beam emitted from the semiconductor laser element greatest in astigmatism, of the plurality of semiconductor laser elements, is coincident in its axis with a reference axis of the base. In the case that the semiconductor laser unit is arranged on an optical head device, the focusing characteristic on the plurality of laser beams can be improved.

Abstract: A semiconductor laser unit includes a plurality of semiconductor laser elements arranged parallel with one another in a laser beam-emitting direction, and a base for positioning and fixing the plurality of semiconductor laser elements. The plurality of semiconductor laser elements are arranged such that a laser beam emitted from the semiconductor laser element greatest in astigmatism, of the plurality of semiconductor laser elements, is coincident in its axis with a reference axis of the base. In the case that the semiconductor laser unit is arranged on an optical head device, the focusing characteristic on the plurality of laser beams can be improved.