| 摘要 |
PURPOSE:To reduce influence when spot light crosses a recording track and to improve an SN ratio by widening the range of focusing control by providing a six-divided photodetector to receive reflected light from a recording medium and then by arranging partitioning lines of the photodetector in parallel to or at right angles to a signal track. CONSTITUTION:A rectangular beam emitted from semiconductor laser 1 is reflected by tracking mirror 5 by way of the optical system including cylindrical lenses 3 and 4 to irradiate recording medium 7. The reflected light is led onto photodetector 15 via beam splitter 10. Photodetector 15 is divided into six photodetectors E-J and the partitioning lines are in parallel to or at right angles to signal track 14. To photodetectors E-J, amplifiers 16-21 are connected; a reproduced signal appears at terminal K of amplifier 26 coupling their outputs, a focusing control error signal at terminal L of amplifier 27, and a tracking error signal at terminal M of amplifier 28. Thus, the control range is widened and the SN ratio can be improved. |
