Patent ID: 7596071

Claim:
An objective lens focusing any of a first optical beam having a wavelength λ 1 and a first beam diameter φ 1 , a second optical beam having a wavelength λ 2 and a second beam diameter φ 2 and a third optical beam having a wavelength λ 3 and a third beam diameter φ 3 incident to an incident side of said objective lens to an optical recording medium provided at an exit side of said objective lens, where λ 1 <λ 2 <λ 3 , said objective lens having a single-lens construction and defined by a non-spherical convex surface at said incident side and said exit side, wherein the objective lens satisfies a condition: νd>35 (1) 1.58>nd (2) 0.58 nd− 0.29 ≦R 1 /f (3) where nd and νd represent respectively the refractive index and Abbe number for a D-line, R 1 represents the paraxial radius of curvature and f represents the focal distance of the objective lens, said objective lens having a first effective numerical aperture value NA(λ1) for said first optical beam, a second effective numerical aperture value NA(λ2) for said second optical beam and a third effective numerical aperture value NA(λ3) for said third optical beam, wherein the first, second and third effective numerical aperture values NA(λ1), NA(λ2) and NA(λ3) satisfy a condition: NA (λ1)> NA (λ2)> NA (λ3) (4), and wherein the first, second and third beam diameters φ 1 , φ 2 and φ 3 satisfy a condition: φ1=φ2>φ3 (5).