| 摘要 |
Before tracking control, tilt control is performed using an offset value of a differential phase tracking error signal obtained by performing signal process of the outputs from, e.g., a 4-split photodetector. A direction in which the tilting angle of the tilt control is to be corrected is determined based on information indicating whether the center value of the differential phase tracking error signal is "offset to plus or minus". Hence, tilt servo that aims at an optimal point is made while observing the amplitude of the differential phase tracking error signal using this offset polarity information.
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