Abstract: The present invention is related to a chromatic aberration-correcting element which allows the adoption of BDs even when DVD/CD light beams are incident. The chromatic aberration-correcting element has a diffractive structure formed thereon, which can correct chromatic aberration in BD wavelength light beams in addition to adopting DVD/CD wavelength light beams. Also provided is an optical pickup device whose structure is simplified by employing the chromatic aberration-correcting element.

Abstract: When reproducing a multilayer optical disk using a high-numerical-aperture objective, the period of time required before the disk is reproduced is reduced by discriminating recording layers. A spherical aberration signal is detected as a differential signal between focus position fluctuation signals respectively in a central section and in a peripheral section of a reproduced flux of light. A recording layer is discriminated using a quantity of correction of spherical aberration at a zero-crossing point of a level or a spherical aberration signal associated with the differential signal. After adding the spherical aberration for the correction of the discriminated layer, residual spherical aberration is corrected by feedback control using a residual spherical aberration signal.

Abstract: To stably carry out recording and reproducing to and from a high density optical disk without using a double servo in the optical disk using a high NA objective lens. A detection of a spherical aberration and a detection of a coma aberration in a radial direction are simultaneously performed, and the coma aberration generated with the offset of an objective lens 109 is corrected in real time, thus enlarging an allowable offset amount of the objective lens. In order to simultaneously detect the spherical aberration and the coma aberration, focal shift and tracking shift signals in an inside region and outside region of reflected light flux are detected respectively, and the differential signals are set as spherical aberration and coma aberration signals.

Abstract: The present invention is related to a chromatic aberration-correcting element which allows the adoption of BDs even when DVD/CD light beams are incident. The chromatic aberration-correcting element has a diffractive structure formed thereon, which can correct chromatic aberration in BD wavelength light beams in addition to adopting DVD/CD wavelength light beams. Also provided is an optical pickup device whose structure is simplified by employing the chromatic aberration-correcting element.

Abstract: Disclosed is a diffractive optical element which can diffract incident light beams in such a controlled manner as to compatibly accommodate various optical discs of different thicknesses by an optical pickup device. Also, a simple optical pickup device provided with the diffractive optical element is disclosed.

Abstract: Provided is a chromatic aberration-correcting optical system which corrects chromatic aberrations in light beams for a high-density recording medium using a large numerical aperture in addition to allowing the universal adoption of light beams for high- and low-density recording media.

Abstract: To stably carry out recording and reproducing to and from a high density optical disk without using a double servo in the optical disk using a high NA objective lens. A detection of a spherical aberration and a detection of a coma aberration in a radial direction are simultaneously performed, and the coma aberration generated with the offset of an objective lens 109 is corrected in real time, thus enlarging an allowable offset amount of the objective lens. In order to simultaneously detect the spherical aberration and the coma aberration, focal shift and tracking shift signals in an inside region and outside region of reflected light flux are detected respectively, and the differential signals are set as spherical aberration and coma aberration signals.

Abstract: To stably carry out recording and reproducing to and from a high density optical disk without using a double servo in the optical disk using a high NA objective lens. A detection of a spherical aberration and a detection of a coma aberration in a radial direction are simultaneously performed, and the coma aberration generated with the offset of an objective lens 109 is corrected in real time, thus enlarging an allowable offset amount of the objective lens. In order to simultaneously detect the spherical aberration and the coma aberration, focal shift and tracking shift signals in an inside region and outside region of reflected light flux are detected respectively, and the differential signals are set as spherical aberration and coma aberration signals.

Abstract: When it is intended to realize a lens having a large NA with one lens, an adjustment precision between both surfaces of the lens is very strict. Accordingly an objective lens having an NA of 0.8 or more was usually realized by two lenses. However, a working distance is small, and collision of the objective lens with a disc is apt to occur. A coma corrector for compensating coma caused by decentering of both surfaces in realizing the high NA lens with one lens is added. However, in this case, astigmatism occurs when the objective lens decenters from the coma corrector relatively accompanied with a tracking operation. The objective lens and the coma corrector are fixed to a mirror barrel so as to be unified with each other, and driven by a two-dimensional lens actuator. With such a constitution, decentering of the objective lens and the coma corrector does not occur, and hence astigmatism does not occur.

Abstract: When reproducing a multilayer optical disk using a high-numerical-aperture objective, the period of time required before the disk is reproduced is reduced by discriminating recording layers. A spherical aberration signal is detected as a differential signal between focus position fluctuation signals respectively in a central section and in a peripheral section of a reproduced flux of light. A recording layer is discriminated using a quantity of correction of spherical aberration at a zero-crossing point of a level or a spherical aberration signal associated with the differential signal. After adding the spherical aberration for the correction of the discriminated layer, residual spherical aberration is corrected by feedback control using a residual spherical aberration signal.

Abstract: In the recordable type multilayer optical disk, locations of an information recording unit region and of ID or address data of adjacent plural tracks on a recording medium are configured so as to be shifted in the circumferential direction by 5 &mgr;m or more. Since an effect from a layer that is not selected can be remarkably reduced, multilayer recording/reproducing can be realized. Moreover, ID or address data do not center at the same position in reference to the circumferential direction, the effect of distortion that is generated on the disk substrate and the recording layer at the time of optical disk formation or multiple overwriting can be minimized, and design and fabrication tolerances of the optical disk are extended, and, as a result, the media can be provided with a low cost.

Abstract: To reduce an effect of reflected light from a layer (or layers) other than a layer to be read upon focus position control when reading a multilayer optical disk in an optical disk drive. In an optical system where a focus error signal is generated by the knife edge method, a photodetector 53 that is divided into four parts is used. Each of two pairs of light detecting elements on the right or left side are formed by division of a detection plane of the photodetector such that the reflected light from a neighboring layer falls half-and-half on that pair of the light detecting elements. Signals from the photodetector are given with alternating polarities in such a way that any adjacent light detecting elements have mutually different polarities and are added up together to form the focus error signal.

Abstract: When it is intended to realize a lens having a large NA with one lens, an adjustment precision between both surfaces of the lens is very strict. Accordingly an objective lens having an NA of 0.8 or more was usually realized by two lenses. However, a working distance is small, and collision of the objective lens with a disc is apt to occur. A coma corrector for compensating coma caused by decentering of both surfaces in realizing the high NA lens with one lens is added. However, in this case, astigmatism occurs when the objective lens decenters from the coma corrector relatively accompanied with a tracking operation. The objective lens and the coma corrector are fixed to a mirror barrel so as to be unified with each other, and driven by a two-dimensional lens actuator. With such a constitution, decentering of the objective lens and the coma corrector does not occur, and hence astigmatism does not occur.

Abstract: In the recordable type multilayer optical disk, interlayer crosstalk is large in an ID or address data region, a boundary region between a recorded part and an unrecorded part, etc. Locations of an information recording unit region and of ID or address data of adjacent plural tracks on a recording medium are configured so as to be shifted in the circumferential direction by 5 &mgr;m or more. Since an effect from a layer that is not selected can be remarkably reduced in the multilayer optical disk, multilayer recording/reproducing can be realized in the recordable type optical disk. Moreover, since pieces of the ID or address data do not center at the same position in reference to the circumferential direction, the effect of distortion that is generated on the disk substrate and the recording layer at the time of optical disk formation or multiple overwriting can be minimized, and design and fabrication tolerances of the optical disk are extended, and as a result the media can be provided with a low cost.

Abstract: The optical disk medium permits an increase in recording density using a complex refractive index variation of an inorganic oxide film in a super-resolution medium using an inorganic oxide film. The reflectance of the disk increases due to the complex refractive index variation of the inorganic oxide film. Specifically, in the case where the inorganic oxide film is an oxide film comprising Co, a reflect addition film is provided. The effective spot diameter used for read-out is reduced, thereby increasing recording density. By using a material for which the complex refractive index varies sharply, the recording density can be approximately doubled.

Abstract: To stably carry out recording and reproducing to and from a high density optical disk without using a double servo in the optical disk using a high NA objective lens.

Abstract: To reduce an effect of reflected light from a layer (or layers) other than a layer to be read upon focus position control when reading a multilayer optical disk in an optical disk drive. In an optical system where a focus error signal is generated by the knife edge method, a photodetector 53 that is divided into four parts is used. Each of two pairs of light detecting elements on the right or left side are formed by division of a detection plane of the photodetector such that the reflected light from a neighboring layer falls half-and-half on that pair of the light detecting elements. Signals from the photodetector are given with alternating polarities in such a way that any adjacent light detecting elements have mutually different polarities and are added up together to form the focus error signal.