| 摘要 |
PROBLEM TO BE SOLVED: To reduce the transmission power consumption and to obtain a stable synchronization output. SOLUTION: A video signal received by an input terminal 11 is frequency-modulated by a frequency of a carrier with a sufficiently higher than a video signal frequency at an FM modulator 12, current-amplified by a light emission drive circuit 14, converted into an optical element by a light emitting element 15 and the signal is sent to a reception section. The video signal is led to a synchronizing signal detection circuit 13, in which the synchronizing signal only is separated from the received signal and the resulting signal is given to a light emission control circuit 16, where the operation of the light emission drive circuit is stopped for the synchronizing signal period to stop the light emission of the light emitting element. The optical signal received from a light receiving element 21 is given to an FM demodulator 23 of the reception section, where the video signal is obtained by demodulating the received signal with the carrier frequency used by the FM modulator. The optical signal is led also to a carrier detection circuit 24 and when its output changes when no carrier component is detected and the circuit 24 allows a synchronizing signal generating circuit 27 to generate a synchronizing signal depending on a period of the change. A changeover switch 25 selects the synchronizing signal or the demodulation signal depending on an output from the synchronizing signal generating circuit 27 and the synchronizing signal appears at an output terminal 26 for a period when no carrier in existence. |
