Patent ID: 7724634

Claim:
An optical pickup apparatus, comprising: a first light source to emit a light flux with a first wavelength λH; a light converging system including an objective lens to converge the light flux emitted from said first light source onto an information recording surface of an optical information recording medium through a protective substrate of the optical information recording medium, wherein a thickness of the protective substrate is t 1 ; a first diffraction element placed within an optical path from said first light source up to the optical information recording medium; a light flux splitting element that is placed within the optical path from said first light source up to the optical information recording medium and that splits an incident light flux emitted by the first light source; a monitor element that receives a light flux that is split by said light flux splitting element and outputs a signal according to a received light amount; a second diffraction element placed between said light flux splitting element and said monitor element; and a control section that controls the drive of said first light source according to the signal from said monitor element; wherein a diffraction structure of said first diffraction element and a diffraction structure of said second diffraction element are formed in such a manner that, when a fluctuation occurs in the wavelength of the light flux emitted from said first light source, if a diffraction efficiency of the light flux passing through the diffraction structure of said first diffraction element increases, the diffraction efficiency of the light flux passing through the diffraction structure of said second diffraction element increases, and if the diffraction efficiency of the light flux passing through the diffraction structure of said first diffraction element decreases, the diffraction efficiency of the light flux passing through the diffraction structure of said second diffraction element decreases.