Patent ID: 7508745

Claim:
An optical element for use in an optical pickup apparatus in which information recording and/or reproducing can be conducted by converging a light flux having a wavelength λ 1 from a first light source through a protective substrate having a thickness t 1 on an information recording medium of a first optical information recording medium or can be conducted by converging a light flux having a wavelength λ 2 (λ 1 <λ 2 ) from a second light source through a protective substrate having a thickness t 2 (t 1 <t 2 ) on an information recording medium of a second optical information recording medium, the optical element comprising: an optical functional surface including a common area used for conducting information recording and/or reproducing for both of the first optical information recording medium and the second optical information recording medium, and the common area comprising an aspheric surface to cause a refractive function such that a spherical aberration becomes under corrected on the first information medium and a spherical aberration becomes over corrected on the second information medium, wherein the aspheric surface is separated around the center of an optical axis to form plural ring-shaped zones and wherein each aspheric surface of neighboring ring-shaped zones of the plural ring-shaped zones is displaced to each other in a direction of an optical axis so as to cause an optical path difference obtained by multiplying a predetermined wavelength λs (λ 1 <λs<λ 2 ) with almost an integer.