Patent ID: 7969834

Claim:
An optical pickup device which performs at least one of writing and reading information in an optical information storage medium, said optical pickup device comprising: a light source which emits light at first, second and third wavelengths, the first wavelength being shorter than the second wavelength, and the second wavelength being shorter than the third wavelength; an optical path combining unit which combines vectors of the light at the first, second and third wavelengths which is emitted by said light source, and matches optical axes of the light at the first wavelength and the light at the third wavelength; a light condensing unit which condenses the light from said optical path combining unit onto the optical information storage medium; a diffraction element which diffracts light at the first, second and third wavelength that is reflected from the optical information storage medium, in a first direction and a second direction respectively; a first photo detector which receives light at the first, second and third wavelength that is diffracted in the first direction by said diffraction element; a second photo detector which receives light at the first and third wavelength that is diffracted in the second direction by said diffraction element; and a third photo detector which receives light at the second wavelength that is diffracted in the second direction by said diffraction element, wherein said first photo detector receives positive secondary diffracted light at the first wavelength, positive primary diffracted light at the second wavelength and positive primary diffracted light at the third wavelength from said diffraction element; said second photo detector receives negative secondary diffracted light at the first wavelength, and negative primary diffracted light at the third wavelength from said diffraction element; said third photo detector receives negative primary diffracted light at the second wavelength from said diffraction element, and a cross section shape of said diffraction element is a serrated shape.