Patent attributes
An optical pickup device includes:a laser source for emitting, to an optical disk, a laser beam having a wavelength λ1 and a laser beam having a wavelength λ2, which is longer than the wavelength λ1; a light receiver, for receiving laser beams that are reflected by the optical disk;a beam splitter, for directing, to the light receiver, the laser beams reflected by the optical disk; andan astigmatism generation element, located between the beam splitter and the light receiver, for generating the laser beams 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 λ1 or the wavelength λ2.
