| 摘要 |
PURPOSE:To attain accurate focus control by detecting a middle value between positive ad negative peak values, correcting a focus error signal so as to take the value as the center of control and applying focus control of an optical beam via an error detection circuit. CONSTITUTION:An optical beam is irradiated to an information track 3 comprising pits formed intermittently via a condenser lens 6, the optical spot is moved relatively to the information track, the reflected beam from the information track is irradiated to photoelectric converting elements 9, 10 and the focus control of the optical beam is conducted by using a phase difference between output signals of the photoelectric converting element as a focus error signal. When the optical spot is converged into a proper diameter, the output signal is made in-phase by shifting the phase of the signal from the photoelectric converting elements 9, 10 and the condenser lens 6 is moved to an information medium 1 so as to zero the phase difference at all times based on the phase difference of both the output signals. Thus, accurate focus control is attained. |
