Patent ID: 7821906
Filing Date: 2010-10-26
Classification: G11B

Abstract:
1. An objective lens for an optical pick-up which is used to record data to and/or to reproduce data from at least three types of optical discs by selectively using one of at least three light beams having different wavelengths, the at least three types of optical discs having at least two different thicknesses of cover layers, when a thickness of a first optical disc of the at least three types of optical discs to be used for recording data and/or reproducing data using a first light beam of the at least three light beams having a wavelength shortest of all the wavelengths of the at least three light beams is represented by t when a numerical aperture required for recording data to and/or reproducing data from the first optical disc is represented by NA the first, second and third light beams being incident on the objective lens as substantially collimated light beams, respectively, such that an amount of aberration caused during a tracking operation where the objective lens is shifted in a direction perpendicular to an optical axis direction of the objective lens, is corrected, wherein at least one of surfaces of the objective lens includes: a first area for attaining the numerical aperture required for recording data to and/or reproducing data from the third optical disc; and a second area located outside the first area, wherein the first area includes: an inner area including the optical axis of the objective lens; and an outer area located outside the inner area, wherein the outer area is configured to converge the third light beam on a data recording layer of the third optical disc with an amount of an aberration being substantially zero, wherein the objective lens satisfies a condition: where h