Proposal of coherence multiplexed optical communication system using balanced receiver and its application for space transmission

Various types of theoretical studies and experimental work are being performed on coherence multiplexed systems in which multiplexing of the signal light is done by using the time incoherence of a semiconductor laser light. In this paper, the balanced receiver that uses the balanced mixer type photodetector is proposed for coherence multiplexed communication system and signal‐to‐noise power ratio (SNR) and bit‐error rate are theoretically derived. Moreover, the application of a coherence multiplexed system for space transmission is studied and the system which transmits reference light and signal light by polarization multiplexing is proposed. Moreover, the polarization diversity balanced receiver that is presented can remove the effect of polarization mismatch between the transmitter and receiver. Since both of the proposed systems are removed, then a signal‐signal beat noise (a large problem in conventional receiver using single photodetector) creates a drastic improvement in the SNR. Moreover, theoretical analysis of the receiver using an optical amplifier is performed and it is shown that there is an optimum value of spectral linewidth for obtaining the maximum SNR.