Patent ID: 7282684

Claim:
An optical pickup apparatus, comprising: (1) a light source device to emit selectively an ordinary polarized light ray and an extraordinary polarized light ray by controlling a polarization condition of a light flux having a wavelength of λ1; (2) a light converging optical system having an objective lens and for converging a light flux having the wavelength of λ1 onto an information recording surface of a first optical information recording medium through a protective layer having a thickness of t 1 or onto an information recording surface of a second optical information recording medium through a protective layer having a thickness of t 2 different from t 1 (t 1 ≠t 2 ); and (3) an optical detector for receiving a reflected light from the information recording surface of the first optical information recording medium and the second information recording medium and for outputting a signal; wherein the objective lens has a phase structure on one of optical surfaces through which a parallel light flux is transmitted, the phase structure is made of a doubly refracting medium in which an ordinary ray refractive index n o for the ordinary polarized light ray is different from an extraordinary ray refractive index n e (n e ≠n o ) for the extraordinary polarized light ray and an optical axis of a refractive index ellipsoid is aligned in a single direction so that the phase structure has a function for not changing a transmitted wavefront of an incident light ray being one of the ordinary polarized light ray and the extraordinary polarized light ray and for changing a transmitted wavefront of an incident light ray being the other one of the ordinary polarized light ray and the extraordinary polarized light ray.