Patent ID: 7738347

Claim:
An optical pickup device, comprising: a laser source for emitting, to an optical disk, a laser beam having a wavelength λ 1 and a laser beam having a wavelength λ 2 , which is longer than the wavelength λ 1 ; a light receiver, for receiving laser beams having the wavelength λ 1 and the wavelength λ 2 that are reflected by the optical disk; a beam splitter, for directing, to the light receiver, the laser beams having the wavelength λ 1 and the wavelength λ 2 that are reflected by the optical disk; and an astigmatism generation element, located between the beam splitter and the light receiver, for generating the laser beams having the wavelength λ 1 and the wavelength λ 2 , which are to be used for focusing control, by designating as the front of the light receiver a focal point on one of the intersecting cross sections that include the light axes of the laser beams, and by designating as the rear of the light receiver, a focal point on the other cross section, wherein the astigmatism generation element is an optical element, which is like a Fresnel lens, whose step depth is substantially a natural number times either the wavelength λ 1 or the wavelength λ 2 .