| 摘要 |
PURPOSE:To obtain simple and accurately the lens position information in the tracking direction regardless of the operating or stopping state of a servo system by cancelling the 1st and 2nd tracking error components outputted from the 1st and 2nd photodetection region so as to detect the offset component corresponding to the position of an objective lens. CONSTITUTION:Since a reflected stop is biased to either photodetection region PDa or a PDb if the objective lens is deviated from a position 10, the offset component is added to one of frequency signals Pa, Pb and subtracted from the other. Thus, offset components Oa, Ob attended with the movement of the objective lens 13 are superimposed on the tracking error components Ta, Tb and the result is outputted. The tracking error components Ta, Tb of the voltage signals A, B are of opposite phase and the offset components Oa, Ob are in phase, a voltage signal C corresponding to the moving position of the objective lens 13 is extracted by adding the voltage signals A, B at an adder 43. |
