Patent ID: 7719949
Filing Date: 2010-05-18
Classification: G11B

Abstract:
1. An optical head, comprising: a first laser beam source for emitting a first laser beam that supports a first optical disc; a second laser beam sources for emitting a second laser beam that supports a second optical disc; an objective lens for condensing the first or the second laser beam on a recording surface of the first or the second optical disc; a diffraction optical element for permitting the first or the second laser beam reflected by the first optical disc or the second optical disc to pass through and for separating 0 order diffraction light and 1st order diffraction light independently; a detection lens for condensing the 0 order diffraction light of the first or the second laser beam on an optical axis and for condensing the 1st order diffraction light of the first or the second laser beam at a symmetric position with respect to the condensing point of the 0 order diffraction light of the first or the second laser beam; and a photo detector element including a first photo detecting portion for detecting the 0 order diffraction light of the first or the second laser beam that passed through the detection lens and two second photo detecting portions arranged symmetrically with respect to the first photo detecting portion for detecting the 1st order diffraction light of the first or the second laser beam, the first photo detecting portion and the two second photo detecting portions being arranged on the same plane, wherein the photo detector element is arranged so that the first photo detecting portion is located between the condensing point of the 0 order diffraction light of the first laser beam and the condensing point of the 0 order diffraction light of the second laser beam that is condensed at a position closer to the detection lens than the condensing point of the first laser beam and that the optical axis of the 0 order diffraction light becomes perpendicular to the first photo detecting portion, and the diffraction optical element changes a phase of a 1st order diffraction light of the first or the second laser beam so that a 1st order diffraction light that is condensed at a position closer to the detection lens of the first laser beam is condensed on one of the second photo detecting portions of the photo detector element and that a 1st order diffraction light that is condensed at a position farther from the detection lens of the second laser beam, is condensed on the other of the second photo detecting portions.