| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide an optical pickup which can record or reproduce information for a plurality of recording media of which the thickness of light transmissive layers and optimum light beam wavelength are different, while in which loss of light quantity made incident on respective recording media is reduced. <P>SOLUTION: An optical pickup 20 is provided with a diffraction optical element 11 which has a diffraction plane and a refraction plane, and in which first, second and third light beams having wavelengths 405 nm, 650 nm, 780 nm are converged/diverged in accordance with wavelength of each light beam, while they are made incident on an objective lens 12 as first order diffraction light for the first light beam, as diffraction light having the same diffraction order as the first light beam or being lower diffraction order than it. depth of a diffraction grating 11a in the diffraction plane of the diffraction optical element 11 is so set that diffraction efficiency of the diffraction light of each optical beam made incident on the objective lens 12 become higher than diffraction efficiency of diffraction light of the other diffraction order. <P>COPYRIGHT: (C)2008,JPO&INPIT |
