Patent ID: 7120108

Claim:
An objective lens for use in an optical pickup device for conducting reproducing and/or recording information for an optical information recording medium equipped with a protective substrate having a thickness of 0.6 mm and to converge a light flux having a working reference wavelength λ 0 (380 nm≦λ 0 ≦450 nm) emitted from a laser light source under a working reference temperature T 0 onto an information recording plane of the optical information recording medium with almost no aberration, comprising: a lens main body; and a diffractive structural section provided on at least one optical functional surface of the lens body; wherein the diffractive structural section has a first compensating function to compensate a change amount δSA 1 of the third-order spherical aberration component of wavefront aberration caused by a fluctuation of a working wavelength λ (|λ–λ 0 |≦10 nm) on the lens main body and the diffractive structural section to be less than a predetermined value, a second compensating function to compensate a deviation δWD of a converged-light spot in an optical axis direction caused by a fluctuation of a working wavelength to be less than a predetermined value, and a third compensating function to compensate a change amount δSA 2 of the third-order spherical aberration component of wavefront aberration caused by a change of a refractive index of the lens body due to a fluctuation of a working temperature T (|T–T 0 |≦40° C.) on the lens main body and the diffractive structural section to be less than a predetermined value.