| 摘要 |
PURPOSE:To improve the SN of a track error signal by adding a track error detecting signal based upon a single beam method to a detector and a circuit using a tracking error based upon three beams and a focus error based upon astigmatism. CONSTITUTION:Tracking error signals are extracted from a detector circuit 13 obtaining a tracking error signal from a differential output and a focus error signal and an information reproducing signal (HF) from the reproducing signal of a center beam 2 by a differential phase detecting method based upon the single beam method and these two kinds of tracking error signals are synthesized. Since the phases of noise components in both the track error signals are random and their generating states are different, an error signal T.OUT to be the synthesized signal is surely doubled and a random noise is raised by 2<1/2> times. Consequently, noises can be reduced by 1/2<1/2>-1/2 as compared with only one tracking error signal.
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