Patent ID: 7885167

Claim:
An objective lens for an optical pickup apparatus recording or reproducing information by converging a light flux with a wavelength λ 1 in the range of 380 nm<λ 1 <420 nm emitted from a light source onto an information recording surface of an optical information recording medium, the objective lens comprising: a single lens including at least one aspheric surface, wherein the objective lens converges only the light flux with the wavelength λ 1 onto the information recording surface of the optical information recording medium; and wherein the objective lens satisfies the following expressions: 2.0≦φ≦2.8, 1.5<n<1.75, 0.9<d/f<1.092, 0.8<NA<0.9, and −1.17 n +2.8 <d/f< −0.59 n +2.0, where φ (mm) is an effective aperture at a light source side of the objective lens, d (mm) is a thickness on an optical axis of the objective lens, f (mm) is a focal length of the objective lens, NA is a numerical aperture at an image side of the objective lens, and n is a refractive index of the objective lens for the wavelength λ 1 .