Patent ID: 7706220
Filing Date: 2010-04-27
Classification: G11B

Abstract:
1. A photodetector comprising: a first light receiving area to receive one light beam as 0-order diffracted light out of at least three light beams resulting from splitting of a light beam emitted from a laser light source of a first wavelength and subsequent reflection by a first optical information recording medium; a second light receiving area to receive one of two light beams as first-order diffracted light out of the light beams reflected by said first optical information recording medium; a third light receiving area to receive another of two light beams as first-order diffracted light out of the light beams reflected by said first optical information recording medium; a fourth light receiving area to receive one light beam as 0-order diffracted light beam out of at least three light beams resulting from splitting of a light beam emitted from a laser light source of a second wavelength longer than said first wavelength and subsequent reflection by a second optical information recording medium; a fifth light receiving area to receive one of two light beams as first-order diffracted light out of the light beams reflected by said second optical information recording medium; and a sixth light receiving area to receive another of two light beams as first-order diffracted light out of the light beams reflected by said second optical information recording medium; wherein a distance from said second light receiving area to said third light receiving area is longer than a distance from said fifth light receiving area to said sixth light receiving area.