Patent ID: 7929401
Filing Date: 2011-04-19
Classification: G11B

Abstract:
1. An objective lens used for an optical information recording/reproducing apparatus for recording information to and/or reproducing information from an optical disc based on a predetermined standard, wherein: the objective lens is made of resin and has a numerical aperture larger than or equal to 0.75; when f (unit: mm) represents a focal length of the objective lens with respect to a wavelength λ (unit: nm) used for recording information to and/or reproducing information from the optical disc, d (unit: mm) represents a thickness of the objective lens along an optical axis of the objective lens, and n represents a refractive index of the objective lens with respect to the wavelength λ, the objective lens satisfies following conditions (1) and (2): at least a light source side surface of the objective lens is an aspherical surface; when h (unit: mm) represents a height from the optical axis, r (unit: mm) represents a curvature radius of the aspherical surface on the optical axis, κ represents a conical coefficient, and A a gradient (SAG)′ of the aspherical surface is represented by a following equation: and the objective lens satisfies a following condition (3): where (SAG1)′