Patent ID: 6674059
Filing Date: 2004-01-06
Classification: G11B

Abstract:
An objective lens comprising:a convex lens; and a diffractive optical element provided on at least one surface or in the vicinity of the convex lens, said convex lens having a first portion which is effectively covered by the diffractive optical element and a second portion which is not effectively covered by the diffractive optical element; wherein when the convex lens condenses an incident light beam having a first wavelength onto a condensation surface via a parallel plate with a first predetermined thickness, spherical aberration is corrected in the second portion of the convex lens, and wherein when the convex lens condenses an incident light beam having a second wavelength onto a condensation surface via a parallel plate with a second predetermined thickness, spherical aberration is corrected by the diffractive optical element for the portion of the incident light beam passing through the first portion of the convex lens.