| 摘要 |
PURPOSE:To form plural beams on a disk without using a diffraction grating as an independent optical part by giving the function of a diffraction grating to the reflecting face of a beam splitter so that the emitted light of a semiconductor laser LD is reflected on the reflecting face and is diffracted and separated into plural beams. CONSTITUTION:A luminous flux 2 emitted from an LD 1 is reflected and diffracted on a face 30, where a diffraction grating of a plane plate optical element 40 is formed, and is separated to the 0-th order light and the + or - 1st order light and is condensed as three spots on an optical disc 6 by a condenser lens 5. The light beams reflected from the disk are transmitted through the condenser lens 5 again and is transmitted through the plane plate optical element 40, and astigmatism is given, and this light beams are made incident on a photodetector 10. The other parts are operated similarly to a conventional device, and a focus error signal is obtained by the astigatism, method, and a tracking error signal is obtained by differential detection of the + or - 1st order light. |
