Patent ID: 7463570

Claim:
A multi-focal objective lens for use in an optical pickup apparatus for recording and/or reproducing information using a first light flux with a wavelength λ 1 , wherein λ 1 ≦450 nm, on a first optical disc with a protective layer with a thickness t 1 and a second optical disc with a protective layer with a thickness t 2 , wherein t 1 <t 2 , the multi-focal objective lens comprising: a first optical surface including a first diffractive structure which has a plurality of ring-shaped zones and generates a m-th diffracted light flux and a n-th diffracted light flux, wherein m≠n, from the first light flux entering into the first diffractive structure, wherein each of the plurality of ring-shaped zones is divided by steps, the multi-focal objective lens converges a diffracted light flux with one of a m-th diffraction order and a n-th diffraction order on an information recording surface of the first optical disc for recording and/or reproducing information of the first optical disc, and the multi-focal objective lens converges a diffracted light flux with another of the m-th diffraction order and the n-th diffraction order on an information recording surface of the second optical disc for recording and/or reproducing information of the second optical disc.