Patent ID: 7411883

Claim:
An optical pickup apparatus comprising: a first light source for emitting a first light flux with a first wavelength λ 1 of 450 nm or less; a second light source for emitting a second light flux with a second wavelength λ 2 which is in the range of 600 nm-700 nm; a third light source for emitting a third wavelength λ 3 which is in the range of 730 nm-830 nm; an objective lens unit to converge the first light flux emitted by the first light source onto a first information recording surface of a first optical disk, to converge the second light flux emitted by the second light source onto a second information recording surface of a second optical disk with a different recording density from that of the first optical disk, and to converge the third light flux emitted by the third light source onto a third information recording surface of a third optical disk with a different recording density from those of the first and the second optical disks; a spherical aberration correcting optical unit which is arranged between both of the first light source and the second light source and the objective lens unit and is arranged in a common optical path of the first light flux and the second light flux; and a chromatic aberration correcting optical element which is arranged in the common optical path of the first light flux, the second light flux and the third light flux and includes a diffractive surface on at least one optical surface of the chromatic aberration correcting optical element such that a diffractive structure which is constructed by a plurality of ring-shaped zones separated by fine steps is formed on the diffractive surface, wherein the depth of steps along an optical axis is designed so that n 2 , which is a diffraction order of a diffracted ray having a largest diffraction efficiency among diffracted rays caused when the second light flux enters into the diffractive structure, is a lower order than n 1 , which is a diffraction order of a diffracted ray having a largest diffraction efficiency among diffracted light rays caused when the first light flux enters into the diffractive structure, and wherein the chromatic aberration correcting optical element satisfies one of the following combinations: (n 1 , n 2 , n 3 ,)=(2, 1, 1), (4, 2, 2), (6, 4, 3), (8, 5, 4), (10, 6, 5) where n 1 , n 2 , and n 3 are diffraction orders of diffracted rays with the largest diffraction efficiencies in the diffracted rays when the first, second and third light fluxes enter into the chromatic aberration correcting optical element, respectively.