Patent ID: 7414948
Filing Date: 2008-08-19
Classification: G11B

Abstract:
1. An objective lens used for recording data to and/or reproducing data from a plurality of types of optical discs having different thicknesses of cover layers, the plurality of types of optical discs including a first optical disc and a second optical disc having a cover layer thicker than that of the first optical disc, the objective lens comprising: a front surface located on a light source side; and a rear surface located on an optical disc side, wherein each of the front and rear surface includes: an inner region for attaining a numerical aperture required to record data to and/or to reproduce data from the second optical disc; and an outer region for attaining a numerical aperture required to record data to and/or to reproduce data from the first optical disc, the outer region being located outside the inner region, wherein the outer region of each of the front and rear surfaces has a surface shape which suppresses a coma caused when a beam used for the first optical disc is incident thereon obliquely with respect to an optical axis of the objective lens, wherein the inner region of each of the front and rear surfaces is configured such that, at a boundary position between the inner region and the outer region, the coma caused when a beam used for the second optical disc is incident on the inner region obliquely at a first angle with respect to the optical axis is less than the coma caused when the beam used for the second optical disc is incident on the outer region obliquely at the first angle with respect to the optical axis, wherein the rear surface is configured to satisfy a condition: where θ