Patent ID: 7518976
Filing Date: 2009-04-14
Classification: G11B

Abstract:
1. An optical head comprising: a first light source that emits light of a first wavelength for at least either one of recording and reproducing information of a first information recording medium; a second light source that emits light of a second wavelength for at least either one of recording and reproducing information of a second information recording medium; an optical element for diffracting light of the first and the second wavelength; and a photodetector that is provided with a detection region for detecting light that is reflected by the first information recording medium or the second information recording medium, and that passes through the optical element; wherein the first information recording medium and the second information recording medium are multi-layer disks having at least two recording layers; wherein the detection region includes a first diffracted light detection region for detecting one of first and higher order diffracted light of the first wavelength that is diffracted by the optical element, and a second diffracted light detection region for detecting one of first and higher order diffracted light of the second wavelength that is diffracted by the optical element; wherein the first diffracted light detection region is arranged such that it does not overlap an outline of a spot on the photodetector of zero order light coming from the first information recording medium that comes from a recording layer that differs from the recording layer that is to be recorded or reproduced; wherein the second diffracted light detection region is arranged such that it does not overlap an outline of a spot on the photodetector of zero order light coming from the second information recording medium that comes from a recording layer that differs from the recording layer that is to be recorded or reproduced; wherein the spot on the photodetector changes from a minimum range to a maximum range; wherein each of the first diffracted light detection region and the second diffracted light detection region includes a plurality of diffracted light detection regions; wherein both of all the first diffracted light detection regions and all the second diffracted light detection regions are arranged inside the smaller range of a first minimum range, which is the minimum range of the spot on the photodetector of zero order light coming from the first information recording medium that comes from a recording layer that differs from the recording layer that is to be recorded or reproduced, and a second minimum range, which is the minimum range of the spot on the photodetector of zero order light coming from the second information recording medium that comes from a recording layer that differs from the recording layer that is to be recorded or reproduced.