Patent ID: 8004954

Claim:
An optical pickup comprising: a first light source that emits light of wavelength λ 1 ; a second light source that emits light of wavelength λ 2 ; a third light source that emits light of wavelength λ 3 ; an objective lens that focuses light of wavelength λ 1 onto a first optical disk having a protective layer of thickness t 1 , focuses light of wavelength λ 2 onto a second optical disk having a protective layer of thickness t 2 and focuses light of wavelength λ 3 onto a third optical disk having a protective layer of thickness t 3 ; a detector that detects light reflected by the optical disk; and a diffraction aperture element that transmits or diffracts the light emitted by the light sources and the light reflected by the optical disk, wherein the diffraction aperture element has a first diffraction region of annular configuration whose an inner radius is R 1 and an outer radius is R 2 (R 2 >R 1 ) or more with respect to an optical axis as a center and a second diffraction region of annular configuration whose an inner radius is R 2 with respect to the optical axis as the center, the first diffraction region being constituted such that the light of wavelength λ 1 and the light of wavelength λ 2 are transmitted and the light of wavelength λ 3 is diffracted asymmetrically with respect to the optical axis, and the second diffraction region being constituted such that the light of wavelength λ 1 is transmitted and the light of wavelength λ 2 is diffracted asymmetrically with respect to the optical axis, the first diffraction region is divided into a plurality of first regions by the direction of diffraction, while the direction of diffraction of the divided first region is different from the direction of diffraction of the first region that is located at a position disposed symmetrically thereto with respect to the optical axis, and the second diffraction region is divided into a plurality of second regions by the direction of diffraction, while the direction of diffraction of the divided second region is different from the direction of diffraction of the second region that is located at a position disposed symmetrically thereto with respect to the optical axis.