| 摘要 |
PURPOSE:To make stable position control possible by exercising control over a light beam position by detecting the position shift of a light beam corresponding to envelopes of intensity detection signals of reflected light and transmitted light. CONSTITUTION:A reflected-light intensity signal from disk 10 detected by pickup 14 wobbled horizontally by actuator 16 corresponding to a sine wave from oscillator 25 is detected by synchronous detector 21 applied with sine waves from one-side envelope detector 19, BFP20 and oscillator 25 to obtain one-side envelope signal 8 on a modulation side corresponding to a track position shift. Tracking control is exercised by this signal and a focus position is similarly controlled by a position shift signal of unmodulated-side envelope 7. Therefore, the effect of shift signal detection is doubled in comparison with the detection of the overall wobbling frequency component, a one-side envelope never exerts an influence on the other-side envelope, and position shift signals of different envelopes are not mixed mutually, so that light-beam position control will stably come into effect. |
