| 摘要 |
PURPOSE:To reduce the fluctuation of an offset of a tracking error signal by obtaining a tracking error signal from the phase difference of output signals from two photodetection cells at the track direction and the other side respectively. CONSTITUTION:The phase difference of photodetector cells A, B is detected by a 1st phase comparator means 11 and the phase difference of photodetector cells C, D is detected by a 2nd phase comparator means 12 respectively and a tracking error detection means 13 detects the tracking error from the sum of the phase differences. In detecting the tracking error, the phase difference of the output signals among the photodetector cells before and after the moving direction of the information track, that is, the photodetector cells A, B and C, D is not affected. Thus, the objective lens is displaced by the tracking control, resulting that the fluctuation of the offset of the tracking error signal is minimized even if the remote visual image 2 is displaced on the photodetector 1. |
