Patent ID: 6999399
Filing Date: 2006-02-14
Classification: G11B

Abstract:
1. An objective lens for being provided in an optical pickup device for carrying out at least one of a record of information on at least two types of optical information storing media and a reproduction of information from the optical information storing media, so as to face to each information recording layer of the optical information storing media; each optical information storing medium having a transparent substrate having a different thickness from the others and each optical information storing medium having a different recording density from the others; comprising: a diffraction pattern which is provided on at least one surface of the objective lens; wherein at least one of the record of the information on a first optical information storing medium having a transparent substrate having a thickness of t at least one of the record of the information on a second optical information storing medium having a transparent substrate having a thickness of t a first numerical aperture of the objective lens on a side of the optical information storing medium is NA a second numerical aperture of the objective lens on the side of the optical information storing medium is NA a third-order spherical aberration component of the wavefront aberration caused by transmitting a light through the transparent substrate of the second optical information storing medium in a first region that a numerical aperture on the side of the optical information storing medium is approximately not more than NA wherein the objective lens includes an optical surface, which consists of a first region and a second region outside the first region, the first region corresponding to a region having a numerical aperture approximately not more than the second numerical aperture NA wherein when the second light flux emitted from the second light source enters the objective lens, the boundary between a first spherical aberration curve and a second spherical aberration curve is discontinuous, and each of the first spherical aberration curve and the second spherical aberration curve are continuous, where the first spherical aberration curve is obtained by transmitting the first or second light flux through the first region and the transparent substrate of the first or second optical information storing medium, and the second spherical aberration curve is obtained by transmitting the first or second light flux through the second region and the transparent substrate of the first or second optical information storing medium, a standard deviation value of a wavefront aberration caused by transmitting a light through the transparent substrate of the second optical information storing medium in a region that the numerical aperture on the side of the optical information storing medium is approximately not more than NA