Patent ID: 8208361
Filing Date: 2012-06-26
Classification: G11B

Abstract:
1. 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 forms a convergent spot on an information-recording surface of a second optical disk having a t forms a convergent spot on an information-recording surface of a third optical disk having a t 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; the L and N are opposite in positive/negative signs.