| 摘要 |
PURPOSE:To attain a low cost by adjusting a light-emitting power at a transmission side so as to unify a light-receiving level without depending on an optical fiber length. CONSTITUTION:The output of a photoelectric converting circuit 181 of the receiving part of a first channel is branched, and added to a detecting comparing means 240. Here, the mean value of a light-receiving power is obtained, compared with a reference value and the voltage of the difference is outputted. When the difference voltage is inputted to a modulating means 250, a modulating signal corresponding to the voltage of the difference is outputted. The output is inputted to a front step hybrid means 140 of a light-emitting source driving circuit 152 and overlapped to the input signal of a second channel. The synthesizing signal is converted through a light-emitting source driving circuit 152 of the transmission part of the second channel, a light emitting source 162 and a light transmission line 172 to an electric signal by the photoelectric converting circuit 182 of the receiving part. The output is branched, demodulated 270, converted to the voltage, the voltage is inputted to a control means 200, a light- emitting source driving circuit 151 is controlled, the light output of a light-emitting source 160 of the first channel is adjusted, and the light receiving power in the circuit 181 of the receiving part is constantly kept.
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