Patent ID: 6819504
Filing Date: 2004-11-16
Classification: G11B

Abstract:
A single-element objective lens for an optical pick-up, said objective lens directing an incident light beam to a data recording surface of an optical disc through a cover layer to form a beam spot, a numerical aperture of said objective lens being 0.7 or more, said objective lens being configured to compensate for coma such that a characteristic of a change of spherical aberration due to a degree of divergence/convergence of the incident beam is substantially comparable with respect to a characteristic of a change of spherical aberration due to variation of the cover layer, thereby the change of spherical aberration due to variation of the cover layer can be cancelled by the change of spherical aberration due to a degree of divergence/convergence of the incident beam,wherein an amount of an offence against a sine condition has a positive maximum value at a position within a range of 60% to 90% of an effective radius of said objective lens, the difference with respect to the sine condition monotonously decreasing on a peripheral side with respect to the position at which the difference has the maximum value.