Patent ID: 7126902

Claim:
An objective lens for use in an optical pickup apparatus which conducts recording and/or reproducing information for a first optical information recording medium by converging a first light flux having a first wavelength of λ 1 from a first light source through a protective substrate having a thickness of t 1 onto an information recording plane of the first optical information recording medium and conducts recording and/or reproducing information for a second optical information recording medium by converging a second light flux having a second wavelength of λ 2 (λ 1 <λ 2 ) from a second light source through a protective substrate having a thickness of t 2 (t 1 <t 2 ) onto an information recording plane of the second optical information recording medium, comprising: an optical element provided in an optical path; and a diffractive optical surface formed on at least one surface of the optical element; wherein the first light flux is converged as a first number diffraction order diffracted-ray other than the zero-th order diffracted-ray onto the information recording plane of the first optical information recording medium having the protective substrate by the diffractive optical surface and the second light flux is converged as a second number diffraction order diffracted-ray other than the zero-th order diffracted-ray onto the information recording plane of the second optical information recording medium having the protective substrate by the diffractive optical surface; wherein the second number diffraction order is lower than the first number diffraction order; and wherein the diffractive optical surface has a diffractive characteristic to make a second focal length with regard to the second light flux to be larger than a first focal length with regard to the first light flux.