| 摘要 |
PURPOSE:To detect a track error signal where an offset component is eliminated by forming a projecting part and recessed part alternately in the lengthwise direction of track and obtaining a difference signal between the first and the second track error signals obtained from the reflected light. CONSTITUTION:The projecting parts 11a and recessed parts 11b are formed alternately in the lengthwise direction on each track, and pits P are formed on these parts. The detecting elements of a two-divided detector 14 are provided in accordance with the breadthwise direction of the track. The difference signal of the output of a differential amplifier 15 is the track error signal, and this signal has an opposite polarity to the deviation direction as shown in Fig. (a) and (b). A changeover switch 16 switches the signals from the projecting parts and recessed parts. Both signals are sample-held, and the difference between signals shown in Fig. (a) and (b) is outputted as the final track error signal from a differential amplifier 22. Since the offset is shown by broken lines in Fig. (a) and (b), the offset components are cancelled in said output. Signal levels are maximum and have opposite polarities because of the reflected light from the projecting parts and recessed parts having the height and the depth of + or -lambda/8, and therefore, the S/N ratio is high.
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