Patent ID: 7369481

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 first optical surface having a superposition type diffractive structure including a plurality of ring-shaped zones which are formed concentrically around an optical axis, wherein each ring-shaped zone is composed of a plurality of stepped sections stepwise, and a second optical surface having an optical path difference providing structure including a plurality of ring-shaped zones which are formed concentrically around an optical axis, wherein each of the plurality of ring-shaped zones is divided by a stepped section so as to provide a predetermined optical path difference, and wherein an optical path length of each of the plurality of ring-shaped zones changes in response to a height from the optical axis.