Patent ID: 7283451

Claim:
An objective lens for converging a light beam emitted from a first light source on a recording surface of a first optical information recording medium covered with a transparent substrate, and for converging a light beam that is emitted from a second light source and different in the wavelength from the light beam emitted from the first light source on a recording surface of a second optical information recording medium covered with a transparent substrate thicker than the transparent substrate on the first optical information recording medium, wherein the objective lens comprises, on any of an incident plane or an emission plane for the two light beams, a center region where center axes of the two light beams pass through, an intermediate region formed to surround the center region, and a peripheral region formed to surround the intermediate region, the intermediate region has a diffraction structure on its lens surface and stepped portions at boundaries with the center region and the peripheral region, and the stepped portions causes an advance or a delay of a phase of a light beam passing through the intermediate region with respect to the light beams passing through the center region and the peripheral region, the stepped portions are formed so that a value of a tertiary spherical aberration on a recording surface of the second optical information recording medium is more than −30 mλ and less than −30 mλ, such that a jitter value of a reproduction signal from the second optical information recording medium not more than 15%.