Objective lens and optical pickup device

An optical element for use in an optical pickup device for conducting reproducing and/or recording information for an optical information recording medium equipped with a protective substrate having a thickness of 0.6 mm and to converge a light flux having a working reference wavelength λ0 (380 nm≦λ0≦450 nm) onto an information recording plane of the optical information recording medium, comprising:

• a diffractive structure provided on at least one optical surface of the optical element and including plural ring-shaped zones having a center on an optical axis,
• wherein the optical element satisfies the following formula:
• 90≦Lk (f1/2)≦300
• where L is the number of ring-shaped zones, k is an order of a diffracted light ray having the maximum diffraction efficiency among diffracted light rays generated by the diffractive structural section when recording and/or reproducing information is conducted for an optical information recording medium, and f is a focal length (mm).

An optical pickup device for conducting reproducing and/or recording information for an optical information recording medium equipped with a protective substrate having a thickness of 0.6 mm and to converge a light flux having a working reference wavelength λ0 (380 nm≦λ0≦450 nm) onto an information recording plane of the optical information recording medium, comprising:

• an optical element to converge the light flux and including a diffractive structure provided on at least one optical surface of the optical element and including plural ring-shaped zones having a center on an optical axis,
• wherein the following formula is satisfied:
• 90≦Lk (f1/2)≦300
• where L is the number of ring-shaped zones, k is an order of a diffracted light ray having the maximum diffraction efficiency among diffracted light rays generated by the diffractive structural section when recording and/or reproducing information is conducted for an optical information recording medium, and f is a focal length (mm).