Patent ID: 8208361

Claim:
An objective lens for use in an optical pickup apparatus which forms a convergent spot on an information-recording surface of a first optical disk having a t 1 -thick protective layer, using a first light flux having a wavelength λ 1 emitted from a first light source, forms a convergent spot on an information-recording surface of a second optical disk having a t 2 -thick protective layer (t 1 ≦t 2 ), using a second light flux having a wavelength λ 2 (λ 1 <λ 2 ) emitted from a second light source, and forms a convergent spot on an information-recording surface of a third optical disk having a t 3 -thick protective layer (t 2 <t 3 ), using a third light flux having a wavelength λ 3 (λ 2 <λ 3 ) emitted from a third light source; the objective lens comprising an optical surface provided with a first optical path difference giving structure, wherein the first optical path difference giving structure emits a L-th order diffracted light with a larger light amount than any diffracted light fluxes with the other diffraction order (including 0-th order), when the first light flux passes through the first optical path difference giving structure , emits a M-th order diffracted light with a larger light amount than any diffracted light fluxes with the other diffraction order, when the second light flux passes through the first optical path difference giving structure, and emits a N-th order diffracted light with a larger light amount than any diffracted light fluxes with the other diffraction order (including 0-th order), when the third light flux passes through the first optical path difference giving structure; and, the following formula is satisfied; | L|= 2 , M= 0 , |N|= 1, and the L and N are opposite in positive/negative signs.