| 摘要 |
PURPOSE:To form an accurate recording bit by controlling a sample holding circuit by the timing of a recording signal and driving a focus control system only by a focus detecting signal obtained at the time of high laser emitting power. CONSTITUTION:A pulse synchronizing with a recording signal 22 is generated from a timing circuit 21 and the sample holding circuit 20 outputs an input signal as it is at the time of high laser power and holds the immediately preceding signal at the time of low laser power based on the pulse generated from the circuit 21. Since a focus control circuit closes a loop only by a focus detecting signal obtained at the time of low laser power, the influence of a focus detecting error is not exerted even if the laser power is reduced and laser oscillation wavelength is changed, and optimum bit formation can be attained because focusing is attained at the time of forming a recording bit. Thereby, servo band frequency f1, the cut-off frequency f2 of an input filter 4 and the sampling frequency f3 of the circuit 20 are set up so that f3>f2>f1 is formed. Consequently, defocusing is not generated at the time of forming a recording bit and optimum bit formation is attained. |
