Patent ID: 7577077

Claim:
An optical pickup apparatus, comprising: a first light source to emit a light flux of a wavelength λ 1 for conducting recording and/or reproducing information for a first optical information recording medium having a protective substrate having a thickness t 1 ; a second light source to emit a light flux of a wavelength λ 2 (λ 1 <λ 2 ) for conducting recording and/or reproducing information for a second optical information recording medium having a protective substrate having a thickness t 2 (t 1 ≦ 2 ); a third light source to emit a light flux of a wavelength λ 3 (λ 2 <λ 3 ) for conducting recording and/or reproducing information for a third optical information recording medium having a protective substrate having a thickness t 3 (t 2 <t 3 ); and an objective optical element into which an infinite parallel light flux comes when recording and/or reproducing information is conducted for the first, second and third optical information recording mediums; wherein the objective optical element comprises a first diffractive structure; wherein a converged-light spot is formed on the first optical information recording medium with m-th order (m is a natural number) diffracted-light ray of the wavelength λ 1 generated by the first diffractive structure, a converged-light spot is formed on the second optical information recording medium with n-th order (n is a natural number) diffracted-light ray of the wavelength λ 2 generated by the first diffractive structure, and a converged-light spot is formed on the third optical information recording medium with k-th order (k is a natural number) diffracted-light ray of the wavelength λ 3 generated by the first diffractive structure, and wherein one of m, n and k is different from one of other two numbers, and wherein the light flux of the wavelength λ 3 which has passed an area of the objective optical element which is out of an area within NA 3 becomes a flare, NA 3 being a numerical aperture for the converged light spot formed on the third optical information recording medium with the light flux of the wavelength λ 3 , wherein the objective optical element comprises a different diffractive structure which is farther from the optical axis of the objective optical element than the first diffractive structure and wherein the diffraction order number of the light flux of the wavelength λ 3 having passed the different diffractive structure is different from the diffraction order number of the light flux of the wavelength λ 3 having passed the first diffractive structure.