Hitachi, Ltd.

Other

Tetsuo Ariyoshi

Takeshi Shimano

Harukazu Miyamoto

Toshimichi Shintani

Mariko Umeda

Takeshi Maeda

Motoyasu Terao

Koichi Maruyama

Hirofumi Sukeda

Takahiro Kurokawa

Shuichi Takeuchi

Kazuo Shigematsu

Shigeharu Kimura

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.

Information reproducing method and information reproducing apparatus of multilayer optical disk

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 lensis 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.

Optical head and optical disk apparatus

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 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.

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.

Objective lens optical system, optical head and optical information reproduction apparatus

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.

Optical disk having a plurality of information recording units

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 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.

Optical information recording/reproducing apparatus, and optical head apparatus

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.

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Kokubunji, Japan

Tetsuo Ariyoshi