| 摘要 |
PROBLEM TO BE SOLVED: To accurately detect a tracking error signal even in a prepit part without being affected by detection delay. SOLUTION: The output of a photodetector 11, which detects the reflected light RG+ of +1st order diffracted light that precedes the main beam in the three-beam method, is delayed for a specified time by a delay circuit 10; the output of this delay circuit 10 and the output of a photodetector 12, which detects the reflected light RG- of -1st order diffracted light in the threebeam method, are inputted in a differential amplifier 13. In addition, the output of the differential amplifier 13 is inputted in a multiplier 19.
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