Patent ID: 7440382

Claim:
An objective optical element for use in an optical pickup apparatus for conducting, reproducing, and/or recording information by converging a light flux of a first wavelength λ 1 emitted from a first light source onto a first optical information recording medium having a protective substrate thickness t 1 and by converging a light flux of a second wavelength λ 2 emitted from a second light source onto a second optical information recording medium having a protective substrate thickness t 2 , wherein λ 2 is greater than λ 1 and t 2 is greater than or equal to t 1 , comprising: a first optical surface including a first diffractive structure which comprises a plurality of concentric ring-shaped diffractive zones having stepped surfaces arranged to be almost parallel to the optical axis and connecting respective neighboring ring-shaped diffractive zones; and a second optical surface including a second diffractive structure which comprises a plurality of concentric ring-shaped diffractive zones having stepped surfaces arranged to be almost parallel to the optical axis and connecting respective neighboring ring-shaped diffractive zones; wherein each of the first and second optical surfaces has a center located on an optical axis and a periphery located far from the optical axis, wherein exterior surfaces of the stepped surfaces of the first diffractive structure are arranged to face the center, and exterior surfaces of the stepped surfaces of the second diffractive structure are arranged to face the periphery, wherein the first diffractive structure applies diffracting actions for the light flux of the first wavelength λ 1 and the light flux of the second wavelength λ 2 , respectively, when the light flux of the first wavelength λ 1 and the light flux of the second wavelength λ 2 pass through the first diffractive structure, wherein the second diffractive structure applies diffracting actions for the light flux of the first wavelength λ 1 and the light flux of the second wavelength λ 2 , respectively, when the light flux of the first wavelength λ 1 and the light flux of the second wavelength λ 2 pass through the second diffractive structure, the diffractive actions applied to one of the light flux of the first wavelength λ 1 and the light flux of the second wavelength λ 2 by the second diffractive structure are opposite to the diffractive actions applied to the one of the light flux of the first wavelength λ 1 and the light flux of the second wavelength λ 2 by the first diffractive structure.