Patent ID: 7778138

Claim:
An objective optical element for use in an optical pickup device for recording and/or reproducing information on a first optical information recording medium having a protective layer with a thickness t 1 by converging a light flux with a wavelength λ 1 through an objective optical element onto an information recording surface of the first optical information recording medium when information is recorded and/or reproduced on the first optical information recording medium, and for recording and/or reproducing information on a third optical information recording medium having a protective layer with a thickness t 3 (t 1 <t 3 ) by converging a light flux with a wavelength λ 3 (λ 1 <λ 3 ) through the objective optical element onto an information recording surface of the third optical information recording medium when information is recorded and/or reproduced on the third optical information recording medium, the objective optical element comprising: a first optical path difference providing structure providing an optical path difference so as to provide a substantial phase change with the light flux with the wavelength λ 3 and not to provide a substantial phase change with the light flux with the wavelength λ 1 , wherein the first optical path difference providing structure comprises a step portion comprising a step difference whose height in an optical axis direction is smaller than the wavelength λ 1 .