Objective lens for optical pick-up device and optical pick-up device

An objective lens for use in an optical pickup apparatus which comprises a first light source to emit a light flux having a wavelength λ1 for conducting recording and/or reproducing information for a first optical information recording medium with a transparent substrate having a thickness t1, a second light source to emit a light flux having a wavelength λ2 (λ1<λ2) for conducting recording and/or reproducing information for a second optical information recording medium with a transparent substrate having a thickness t2 (t1<t2), a light converging optical system including a objective lens to converge a light flux emitted from the first and second light sources onto an information recording plane through a respective transparent substrate of the first and second optical information recording media, and a photodetector, the objective lens comprising:

• plural optical functional regions arranged in a direction perpendicular to an optical axis, the plural optical functional regions including an inside optical functional region closer to the optical axis, an outside optical functional region farther from the optical axis and an intermediate optical functional region provided between the inside and outside optical functional regions;
• and
• diffractive structures provided on the inside and outside optical functional regions respectively;
• wherein a spherical aberration of a light flux having passed through the inside optical functional region is corrected when recording and/or reproducing information is conducted for the first and second optical information recording media,
• wherein a spherical aberration of a light flux having passed through the outside optical functional region is corrected when recording and/or reproducing information is conducted for the first optical information recording medium and a light flux having passed through the outside optical functional region is made to be flare when recording and/or reproducing information is conducted for the second optical information recording medium,
• wherein a spherical aberration of a light flux having passed through the intermediate optical functional region is made to be discontinuous to a spherical aberration of a light flux having passed through the outside optical functional region when recording and/or reproducing information is conducted for the second optical information recording medium,
• wherein the absolute value of an amount of a spherical aberration of a light flux coming to the second optical information recording medium after having passed through the intermediate optical functional region is made larger than that of an amount of a spherical aberration of a light flux coming to the second optical information recording medium after having passed through the inside optical functional region when recording and/or reproducing information is conducted for the second optical information recording medium, and
• wherein the following formula is satisfied:
• −0.1<m1<0.1
• where m1 is a magnification of the objective lens when recording and/or reproducing information is conducted for the first optical information recording medium.