| 摘要 |
PURPOSE:To accurately detect a tracking error signal despite the spot shift caused by a change in the lapse of time by outputting the tracking error signal through a combination where the inner and outer circumferential areas of a spot are approximately equal to each other. CONSTITUTION:A light spot SP is formed via the signal bit of a disk to a photodetector 89 which is divided into >=3 detecting parts in the diameter direction of the disk. A selection means 73 selects a combination of those detecting parts so that the inner and outer circumferential areas of the SP are approximately equal to each other. then, a tracking error signal of an optical pickup is obtained based on the detected value of a detecting part selected as the outer circumferential side and the detected value of a detecting art selected as the inner circumferential side of the SP respectively. Thus, the inner and outer circumferential spot areas are approximately equal to each other at all times even in case where the SP moves by a tracking servo action. As a result, the accuracy of the tracking error signal is improved.
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