| 摘要 |
PURPOSE:To reduce noise returned to a semiconductor laser sufficiently and to reproduce a data without being affected by noise by varying a pulse lighting frequency of a laser beam so as to control returned optical noise to be a reference quantity or below. CONSTITUTION:A pulse lighting frequency of a laser beam is varied at reproduction so that returned optical noise is controlled to be a reference quantity or below. That is, when the noise is much more than the reference quantity as the result of comparison at a comparator 15, a signal representing it is outputted to a control circuit 12. Upon the receipt of the signal, the control circuit 12 varies a voltage of a power supply voltage variable device 16 in a high frequency superimposing module 6 to vary the oscillating frequency of an oscillator 17. Then the noise corresponding to a frequency at each occasion is detected by varying the frequency of the oscillator to find out a frequency at which the noise is a reference quantity or below. Thus, the return optical noise is sufficiently reduced and a data is reproduced without being affected by noise. |
