| 摘要 |
PURPOSE:To photodetect, without omission, a reflected beam reflected by a reflecting film, which is provided with light-intensity dependence, on an optical disk. CONSTITUTION:A collimating lens 23, a polarization beam splitter 24, a quarter- wave plate 25 and an object lens 26 from the laser side are arranged in a light path between a laser 22 and an optical disk 21. A photodetector 27 is arranged in a light path branched from the polarization beam splitter 24. An effective aperture diameter 2a0 for the object lens 26 on which a beam for readout use is incident is made smaller than an aperture diameter 2a for the object lens 26. By this constitution, the cutoff spatial frequency of a playback optical system is extended to the side of a high frequency. |
