| 摘要 |
PURPOSE:To read an RF signal and to increase the adjustable range of a relative position between an objective lens and a recording medium, by using a photodetector where the 2nd photodetecting surface is arranged closely so as to surround the 1st photodetecting plane having a small area located at the center. CONSTITUTION:A photodetector 91 where photodetecting sections B1-B4 splitting the 2nd photodetecting plane into four is arranged around photodetection sections A1-A4 splitting the 1st photodetecting plane into four, and the photodetector 91 is used as a photodetector 9 of an optical pickup optical system comprising a light source 1, a beam splitter 3, a 1/4 wavelength plate 4, an objective lens 5, and cylindrical lenses 7, 8. Since the photodetection sections A1-A4 are formed sufficiently small, the reading of the RF signal is realized with the photodetection sections surely. Further, the photodetection sections B1-B4 forming the 2nd photodetector plane are made into a large area so as to contribute the reading of a focusing signal and a tracking signal. |
