Patent ID: 7525879

Claim:
An objective optical element for use in an optical pickup apparatus including a first light source emitting a first light flux with a first wavelength λ1for recording and/or reproducing information on an information recording surface of a first optical information recording medium having a protective layer with a thickness t1, a second light source emitting a second light flux with a second wavelength λ2 (λ1 <λ2) for recording and/or reproducing information on an information recording surface of a second optical information recording medium having a protective layer with a thickness t2 (t1≦t2), a third light source emitting a third light flux with a third wavelength λ3 (λ2 <λ3) for recording and/or reproducing information on an information recording surface of a third optical information recording medium having a protective layer with a thickness t3 (t2 <t3), and a light converging optical system including an objective optical element, the objective optical element comprising: a first optical path difference providing structure for providing an optical path difference which provides a substantial phase change to the third light flux and does not provide a substantial phase change to the first and second light fluxes; and a second optical path difference providing structure for providing an optical path difference to the first light flux, the second light flux and the third light flux, wherein the objective optical element converges the first - third light fluxes through the protective layers with the thicknesses t1-t3 onto an information recording surface of the first - third optical information media respectively, and wherein the second optical path difference providing structure has a serrated cross sectional shape and generates a L-th order diffracted light flux for being formed into a converged spot on the first optical information recording medium, a M-th order diffracted light flux for being formed into a converged spot on the second optical information recording medium, a N-th order diffracted light flux for being formed into a converged spot on the third optical information recording medium, where N is an integer number, L is 2N, and M is an integer number.