Patent ID: 7551539

Claim:
An optical system for use in an optical pickup apparatus in which reproducing and/or recording information is conducted for a first optical information recording medium equipped with a protective layer having a thickness t 1 by using a light flux having a first wavelength λ 1 emitted from a first light source and reproducing and/or recording information is conducted for a second optical information recording medium equipped with a protective layer having a thickness t 2 (t 2 ≧t 1 ) by using a light flux having a second wavelength λ 2 (λ 2 >λ 1 ) emitted from a second light source, comprising: a correcting optical system; a light converging element to converge a light flux having a wavelength λ 1 emitted from the correcting optical system on an information recording plane of the first optical information recording medium and to converge a light flux having a wavelength λ 2 emitted from the correcting optical system on an information recording plane of the second optical information recording medium; wherein an optical surface of the correcting optical system has a plurality of optical functional zones, and a superposition type diffractive structure is formed within one of the plurality of optical functional zones such that a plurality of ring-shaped zones are formed concentrically around the optical axis and plural stepped sections shaped stepwise are formed within each ring-shaped zone.