Patent ID: 7385906

Claim:
An optical pickup comprising: a first optical source producing a first optical beam having a first wavelength λ 1 ; a second optical source producing a second optical beam having a second wavelength λ 2 ; a third optical source producing a third optical beam having a third wavelength λ 3 ; and an objective lens focusing any of said first, second and third optical beams on an optical recording medium, said objective lens having a single-lens construction and defined by a non-spherical convex surface at an incident side and an exit side, wherein the objective lens satisfies a condition: νd>35 (1) 1.58>nd (2) 0.58 nd −0.29 ≦R 1 /f≦ 0.62 nd− 0.31 (3) where nd and νd represent respectively the refractive index and Abbe number for a D-line, R 1 represent 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(λ 1 ) for said first optical beam, a second effective numerical aperture value NA(λ 2 ) for said second optical beam, and a third effective numerical aperture value NA(λ 3 ) for said third optical beam, said first optical beam incident to said objective lens having a first beam diameter φ 1 , said second optical beam incident to said objective lens having a second beam diameter φ 2 , said third optical beam incident to said objective lens having a third beam diameter φ 3 , said first, second and third effective numerical aperture values NA(λ 1 ), NA(λ 2 ), NA(λ 3 ) and said first, second and third beam diameters φ 2 , φ 1 , φ 3 satisfying a relationship NA (λ1)= NA (λ2)> NA (λ3) (4) φ2>φ1>φ3. (5)