Patent ID: 8098562

Claim:
An optical pickup device for performing recording and/or reproduction of information on a plurality of types of optical disks having different thicknesses of protective layer from one another by using light beams of a first wavelength λ 1 , a second wavelength λ 2 and a third wavelength λ 3 which are different from one another, the optical pickup device comprising: a first light source for emitting the light beam of the first wavelength λ 1 ; a second light source for emitting the light beam of the second wavelength λ 2 ; a third light source for emitting the light beam of the third wavelength λ 3 , λ 3 being longer than λ 2 and λ 2 being longer than λ 1 ; and an objective lens comprising a diffraction structure, wherein when the light beam having the third wavelength λ 3 is incident into the objective lens, diffracted lights of the third wavelength λ 3 having various diffraction orders are generated, wherein the sum of diffraction efficiencies of two diffracted lights of the third wavelength λ 3 having the two highest diffraction efficiencies in the diffracted lights is not less than 60%, wherein the objective lens performs recording or reproduction of information on an optical disk having a thickest protective layer of the plurality of types of optical disks by converging the diffracted light of the third wavelength λ 3 having a longer focal length of the two diffracted lights onto an information recording surface through the thickest protective layer of the optical disk, and wherein a distance from the objective lens to a surface of the thickest protective layer along an optical axis is shorter than a distance between focuses of the two diffracted lights of the wavelength λ 3 along the optical axis when the diffracted light having the longer focal length is converged onto the information recording surface of the optical disk through the thickest protective layer of the optical disk.