| 摘要 |
PROBLEM TO BE SOLVED: To improve the code error rate characteristic of the optical receiver of the polarized wave diversity type optical heterodyne system. SOLUTION: A signal light 117 is separated by a polarized wave separation coupler 101, given to optical detection circuits 102, 103 in which the signal is converted into an intermediate frequency signal. It is amplified by variable gain amplifiers 105, 106 and demodulated by demodulation circuits 107, 108. A synthesizer 109 synthesizes signals from the two demodulation circuits to obtain a demodulation signal 119. A gain control circuit 114 outputs a gain control signal, based on outputs of detectors 110, 111 so as to make an amplitude of the demodulation signal 119 constant. The gain control signal is branched into two and they are respectively given to adders 115, 116. The adder 115, 116, based on the output of the detector 113, 112, adds a detection signal to the gain control signal so that the gain is smaller when the detected level is higher and the gain is higher when the detected level is smaller and provides a resulting new gain control signal to the variable gain amplifier 105, 106. |
