Patent ID: 7522508
Filing Date: 2009-04-21
Classification: G02B,G11B

Abstract:
1. An optical pickup comprising: a first light source that emits a first light beam of a first wavelength λ a second light source that emits a second light beam of a second wavelength λ an objective lens that focuses the first light beam on an information recording face of a first recording medium having a first light transmissive layer, and focuses the second light beam on an information recording face of a second recording medium having a second light transmissive layer thicker than the first light transmissive layer; a diffraction optical element disposed in an optical path between the first and second light sources and the objective lens, and including a diffraction grating and a lens with a refractive index n; and a collimator lens, provided between the first light source and the diffraction optical element and between the second light source and the diffraction optical element, for causing the respective first and second light beams of the first and second light sources to be incident on the diffraction optical element as parallel rays, wherein: when a distance between a diffracting face of the diffraction grating and a peak of a lens face of the lens is a, a radius of the second light beam is R, and a pitch of the diffraction grating confined by outermost rays of the second light beam passing through the diffracting grating is d, said diffraction optical element is set so that m  where f(d, m  where α