Patent ID: 6807139
Filing Date: 2004-10-19
Classification: G11B

Abstract:
An objective lens for use in an optical pickup apparatus which comprises a first light source to emit a first light flux having a wavelength &lgr;1 for recording or reproducing information of a first optical information recording medium including a transparent substrate having a thickness t1, a second light source to emit a second light flux having a wavelength &lgr;2 for recording or reproducing information of a second optical information recording medium including a transparent substrate having a thickness t2 (t12), a converging optical system having the objective lens to converge the first or second light flux through the transparent substrate onto an information recording plane of the first or second information recording medium, and a photo detector,the objective lens having a magnification m satisfying the following formula: âˆ’0.33the objective lens comprising at least two optically functional regions arranged in a direction perpendicular to an optical axis and each of the two optically functional regions having a diffractive structure; wherein the diffractive structure of an inner optically functional region arranged closer to the optical axis among the two optically functional regions corrects aspherical aberration of the first or second light flux when the first or second light flux passes through the inner optically functional region for recording or reproducing information of the first or second information recording medium; wherein the diffractive structure of an outer optically functional region arranged far from the optical axis among the two optically functional regions corrects aspherical aberration of the first light flux when the first light flux passes through the outer optically functional region for recording or reproducing information of the first information recording medium; wherein the diffractive structure of the outer optically functional region makes the second light flux flared when the second light flux passes through the outer optically functional region; and the objective lens comprising a light amount reducing structure to reduce an amount of the second light flux passing through a region of the objective lens other than the inner optically functional region.