| 摘要 |
PURPOSE:To realize a stable and sufficient eccentric follow-up property by providing the first photodetector for obtaining a track shift signal and the second photodetector for detecting a moving portion of a reflected light beam, in accordance with a prescribed arrangement, and correcting a signal of the first photodetector by a signal from the second photodetector. CONSTITUTION:A track follow follows up the eccentricity of a recording medium 20, therefore, it is executed by moving an objective lens 4 in the left and right directions in the figure, but in that case, a reflected light beam moves in the direction vertical to the paper surface in the figure, on the first and the second photodetectors 5, 6, and especially, it moves in a centralized state on the second photodetector 6. Accordingly, a moving portion of the beam is mixed in a track shift signal (A-B) from the first photodetector 5. On the other hand, a signal (C-E/C+E) corresponding to the moving portion of the beam is obtained by the second photodetector 6, therefore, a correct track shift signal can be obtained by compensating the signal (A-B) from the first photodetector 5 by use of this signal. |
