| 摘要 |
PROBLEM TO BE SOLVED: To converge turbulence in switching laser power in a short period of time, when amplitude of a light reception signal is normalized by a sum signal. SOLUTION: A servo error signal S1 which is obtained by calculating detection signals of a plurality of split photodetectors are normalized by a normalization signal S3 in a division circuit 103. The normalization signal is a signal made by adding a plurality of detection signals of split photodetectors and smoothing with a low pass filter 104. A cut off frequency of the low pass filter 104 is switched to a high frequency side by a control signal S4 only in a transition period before and after the switching timing of the laser power. A normalized signal S5 is supplied to a hold circuit 106 and held in the transition period. Switching of the cut off frequency is carried out in the period when the hold operation is performed. After the lapse of the transition period, the cut-off frequency is switched to a low frequency side. COPYRIGHT: (C)2005,JPO&NCIPI
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