| 摘要 |
PURPOSE:To obtain a tracking error signal by a difference signal between outputs of the first signal and the second signal, by sampling an output difference between the first detector and the second detector, and holding the second signal which has been brought to sampling. CONSTITUTION:The first pre-group g2 for tracking, having depth of lambda/8 with respect to the wavelength lambda of a recording or reproducing laser source 1 in the track direction is provided as a disk 5. Also, in a signal recording area which has been formed by being separated by a prescribed interval in the track direction from this tracking pre-group g2, the second pre-group g1 having depth of lambda/8 is provided, and an interval in the radial direction of the first pre-group g2 and the second pre-group g1 is set to half of a track pitch which has been determined in advance. In this state, when a beam scans the second pre-group g1, an output difference between the first detector 6A and the second detector 6B is brought to sampling, the second signal which has been brought to sampling is held, and a tracking error signal is obtained by an output difference signal between the first signal and the second signal.
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