Patent ID: 7995433
Filing Date: 2011-08-09
Classification: G11B

Abstract:
1. An optical head apparatus irradiating a multi-layer optical disc having a plurality of information recording surfaces with laser light and detecting reflected light of the laser light, the optical head apparatus comprising: a laser light source; a diffraction means splitting laser light which is emitted from the laser light source into zero-order diffracted light, positive-first-order diffracted light, and negative-first-order diffracted light; a photodetector; and an optical system means collecting the zero-order diffracted light, the positive-first-order diffracted light, and the negative-first-order diffracted light, on an access-target information recording surface out of the plurality of information recording surfaces, and guiding on the photodetector, reflected light of the zero-order diffracted light, reflected light of the positive-first-order diffracted light, and reflected light of the negative-first-order diffracted light by the access-target information recording surface; wherein: the optical system means includes an adjusting means moving a light-collected position of the zero-order diffracted light, the positive-first-order diffracted light, and the negative-first-order diffracted light, in a focus direction and a tracking direction; the photodetector includes a main-beam light-receiving unit which is disposed at a position where the reflected light of the zero-order diffracted light by the access-target information recording surface is received, a first sub-beam light-receiving unit which is disposed at a position where the reflected light of the positive-first-order diffracted light by the access-target information recording surface is received, and a second sub-beam light-receiving unit which is disposed at a position where the reflected light of the negative-first-order diffracted light by the access-target information recording surface is received; the first sub-beam light-receiving unit is divided by a first division line in an x-direction being a direction on the photodetector corresponding to a tangential direction of a recording track on the optical disc, and includes a first divisional light-receiving element and a second divisional light-receiving element which are arranged in a y-direction being orthogonal to the x-direction; the second sub-beam light-receiving unit is divided by a second division line in the x-direction, and includes a third divisional light-receiving element and a fourth divisional light-receiving element which are arranged in the y-direction; where T N U