Patent ID: 8089848

Claim:
An optical pickup for performing at least recording, reproduction, or deletion of information on multiple types of optical recording media, the multiple types of optical recording media being a first optical recording medium, a second optical recording medium, a third optical recording medium, and a fourth optical recording medium in descending order of recording density, the optical pickup comprising: a first light source configured to emit first light having a first wavelength λ 1 corresponding to the first and second optical recording media; a second light source configured to emit second light having a second wavelength λ 2 corresponding to the third optical recording medium; a third light source configured to emit third light having a third wavelength λ 3 corresponding to the fourth optical recording medium, wherein λ 1 <λ 2 <λ 3 is true; an objective lens configured to focus the first light, the second light, and the third light on corresponding recording surfaces of the first, second, third, and fourth optical recording media; and an aberration correcting unit between the objective lens and the first, second, and third light sources, the aberration correcting unit having a first diffraction plane and a second diffraction plane, each of the first and second diffraction planes having at least one diffraction structure made of concentrically arranged orbicular ridges and grooves, wherein the first diffraction plane has multiple concentric zones including a center zone and a second zone, the center zone being located in the center of the first diffraction plane and having the diffraction structure and the second zone being located second from the center of the first diffraction plane and having the diffraction structure, wherein when diffraction orders of most intense diffracted light produced from the first light, the second light, and the third light by the diffraction structure of the center zone are N 11 , N 12 , and N 13 , respectively, |N 11 |<|N 12 |<|N 13 | is true, wherein when diffraction orders of most intense diffracted light produced from the first light and the second light by the diffraction structure of the second zone are N 21 and N 22 , respectively, |N 21 |<|N 22 | is true, and wherein signs of the diffraction orders N 11 , N 12 , and N 13 are opposite to those of the diffraction orders N 21 and N 22 .