| 摘要 |
PURPOSE:To realize the write check due to a reflected light with high reliability, by allowing the characteristic between the optical input to a photodetector and the output of an amplifier to have a clamp characteristic by the level of the intensity of the reflected light while read. CONSTITUTION:The input/output characteristic of an amplifier 31 is a clamp characteristic as shown fig. An operating point is so set that the signal level at the read time is brought to a bending point P of this clamp characteristic or near this point. Then, the output hardly appears despite of a write pulse signal has a wide input amplitude. When normal information is recorded by a write pulse, the change of a read waveform corresponding to the change of an optical characteristic of a recording film appears as shown by 311 in fig. Since the change direction of the influence 312 of the write pulse and that of the read waveform 311 are opposite to each other and their states are different from each other, the read waveform 311 can be discriminated sufficiently. It is discriminated whether the amplitude of the waveform 311 reaches a prescribed level or not, thereby check of the write state is attained. |
