Patent ID: 7463568

Claim:
An objective optical element for use in an optical pickup apparatus which is provided with a first light source of a wavelength λ 1 , a second light source of a wavelength λ 2 (λ 1 <λ 2 ) and a light converging optical system including a magnification changing element and the objective optical element, wherein the light converging optical system converges a light flux from the first light source onto an information recording plane of a first optical information recording medium through a protective substrate having a thickness t 1 so that recording and/or reproducing information is conducted for the first optical information recording medium and the light converging optical system converges a light flux from the second light source onto an information recording plane of a second optical information recording medium through a protective substrate having a thickness t 2 (t 1 ≦t 2 ) so that recording and/or reproducing information is conducted for the second optical information recording medium, wherein the objective optical element has an optical magnification m 1 (m 1 ≠ 0 ) for a light flux having the first wavelength λ 1 and an optical magnification m 2 (m 2 ≠ 0 ) for a light flux having the second wavelength λ 2 , wherein the objective optical element comprises on at least one surface: a common region through which the light flux having the first wavelength λ 1 and the light flux having the second wavelength λ 2 pass in common so as to form a converged light spot on the information recording plane of the first optical information recording medium and on the information recording plane of the second optical information recording medium, respectively; an exclusive region through which the light flux having the first wavelength λ 1 passes so as to form a converged light spot on the information recording plane of the first optical information recording medium and the light flux having the second wavelength λ 2 passes so as not to form a converged light spot on the information recording plane of the second optical information recording medium, wherein the exclusive region includes an exclusive diffractive structure having a function to suppress an increase of spherical aberration due to a raise of atmospheric temperature in accordance with a wavelength fluctuation of the light flux having the first wavelength λ 1 when the light flux having the first wavelength λ 1 having passed through the exclusive diffractive structure is converged on the information recording plane of the first optical information recording medium, wherein the light flux having the second wavelength λ 2 having passed through the exclusive diffractive structure intersects with the optical axis at a position different from the position of the converged light spot formed on the information recording plane of the second optical information recording medium, and wherein the optical magnifications m 1 and m 2 satisfy the following formula: | m 1− m 2|<0.5.