Patent ID: 7869331

Claim:
An optical head comprising: a light source; a condensing unit which collects light from the light source and directs the light onto an optical disk which has a plurality of optical information recording medium layers; a luminous flux extracting unit which extracts, from a luminous flux of reflected light from the optical disk, at least a first luminous flux branch which does not include the optical axis of the luminous flux; and a photodetection unit which receives the reflected light from the optical disk and produces signal output, wherein the photodetection unit has a-first and second photodetection areas which receive the first luminous flux branch of reflected light from an optical information recording medium layer targeted for recording or playback out of the plurality of optical information recording medium layers of the optical disk, and the first and second photodetection areas are divided by a boundary line which includes an intersecting point of the optical axis of the luminous flux of the reflected light from the optical disk and are located in such a position that a light spot formed by the first luminous flux branch of the reflected light from the optical information recording medium layer targeted for recording or playback will be focused on the boundary line, and the boundary line used to extract the first luminous flux branch in the luminous flux extracting unit is located at a distance d from a diametrical axis which includes the optical axis of the luminous flux in the luminous flux extracting unit so that the first luminous flux branch of reflected light from the layers other than the optical information recording medium layer targeted for recording or playback forms a light spot in such a position on the photodetection unit as not to overlap the first light spot.