| 摘要 |
A control device for maintaining proper focus of a radiant recording beam comprised of a photo detector for detecting a reading beam used to recover the recorded information, a focusing lens movable with respect to the recording surface to focus the writing and reading beams, a dither oscillator to generate a dither signal employed to move the focusing lens in an oscillatorymanner, a duty cycle detector to provide a signal indicative of the duty cycle of the information- carrying signal recovered by the reading beam, and a multiplier for comparing the phase of the duty cycle signal and the dither oscillator signal. |
