Patent ID: 7710848

Claim:
An optical pickup apparatus comprising: a first light source for emitting a first light flux with a wavelength λ 1 (nm); a second light source for emitting a second light flux with a wavelength λ 2 (nm) satisfying λ 1 <λ 2 ; and a light-converging optical system comprising a coupling lens and an objective lens, the light-converging optical system being adopted to converge the first light flux onto an information recording surface of a first optical information recording medium through a protective layer with a thickness t 1 so that information can be recorded and/or reproduced for the first optical information recording medium, and adopted to converge the second light flux onto an information recording surface of a second optical information recording medium through a protective layer with a thickness t 2 (t 1 ≦t 2 ) so that information can be recorded and/or reproduced for the second optical information recording medium, wherein the coupling lens comprises a first diffractive structure arranged on an area on the coupling lens where the first light flux and the second light flux respectively used for recording or reproducing information on the first information recording medium and the second optical information recording medium, pass through, and the first diffractive structure includes a plurality of ring-shaped zones which are concentrically arranged around the optical axis and which have steps extending along the optical axis, and wherein the optical pickup apparatus satisfies following expressions: −4.0×10 −8 (nm −1 ·μm −1 )≦(Δ fB OBL /f OBL 2 )+(Δ fB CPL /f CPL 2 )≦−1.5×10 −8 (nm −1 ·μm −1 ), 5.2×10 −8 (nm −1 ·μm −1 )≦Δ fB OBL /f OBL 2 ≦1.0×10 −7 (nm −1 ·μm −1 ), 50≦νd OBL ≦65, and 50≦νd CPL ≦65, where ΔfB OBL is a chromatic aberration (μm/nm) of the objective lens for a light flux with the wavelength λ 1 , f OBL is a focal length (μm) of the objective lens for a light flux with the wavelength λ 1 , ΔfB CPL is a chromatic aberration (μm/nm) of the coupling lens for a light flux with the wavelength λ 1 , f CPL is a focal length (μm) of the coupling lens for the first light flux, νd OBL is a dispersion of the material of the coupling lens for line d, and νd CPL is a dispersion of the material of the coupling lens for line d.