| 摘要 |
PURPOSE:To maintain an optical spot in an accurately focused state by a method wherein an offset voltage is applied in such a way that an AF (autofocusing) signal becomes a zero level at the peak point of a cross track signal. CONSTITUTION:The following are provided: a four-divided detector 1 by means of which an optical disk is irradiated with the light flux of a semiconductor laser and reflected light is detected; adders 3 to 7 for analog operation use; and subtractors 8 to 9. In addition, the following is provided: a means 10 to apply an offset voltage to a focusing error signal so that, when an optical spot has traversed a track, the focusing error signal obtained from the reflected light from the recording medium is set to a nearly zero level when the optical spot is situated in the track. Thereby, it is possible to follow the track in a state that the optical spot has been focused accurately. |
