| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a 1/4 wavelength plate for optical pickup device in which it can be prohibited that a light receiving plane of a photodetector receives reflected light of a laser beam from other information recording layers when a laser beam is condensed on one information recording layer of an optical disk having a plurality of information recording layers. <P>SOLUTION: The 1/4 wavelength plate for optical pickup device is provided with a diffraction grating generating 0th order light and diffraction light, a polarization beam splitter, a 1/4 wavelength plate, an objective lens, and a photodetector having a 0th order light receiving plane receiving 0th order light from the polarization beam splitter and diffraction light, wherein the 1/4 wavelength plate has a prohibition area where it is prohibited that the diffraction light receiving plane receives 0th order light obtained being reflected from other information recording layers when the objective lens condenses 0th order light and diffraction light on one information recording layer of the optical disk having a plurality of information recording layers. <P>COPYRIGHT: (C)2008,JPO&INPIT |
