Patent ID: 7969854
Filing Date: 2011-06-28
Classification: G11B

Abstract:
1. 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 region 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 region comprising an aspheric surface to cause a refractive function such that a spherical aberration on the first optical information recording medium becomes over corrected or have no aberration and a spherical aberration on the second optical information recording medium becomes over corrected on the second optical information recording medium, wherein the aspheric surface is separated around the center of an optical axis to form plural ring-shaped zones and 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 (λs=λ