| 摘要 |
PURPOSE:To prevent deterioration in S/N ratio and improve transmission performance by making signal light and local oscillation light coincident in electric field direction through polarization, demultiplexing, and multiplexing, performing photodetection and summing up voltages, and changing local oscillation in polarization state. CONSTITUTION:A polarizing demultiplexer and multiplexer 7 separates signal light 11 and local oscillation light 12 into linear polarized light beams 11p, 12s and 11s, 12p which cross each other at right angles, and they are multiplexed into projection light beams 13 and 14. Further, polarizers 9 and 9' make two kinds of linear polarized light beams of the projection light beams 13 and 14 coincident in electric field direction, and a couple of photodetectors 5 and 5' detect individually the projection light beams 13 and 14 which are coincident in electric field direction. Then, a signal processing circuit 10 sums up the voltages of the detectors 5 and 5', and a polarizing modulator 8 is interposed between a local oscillation power source 3 and the multiplexer 7 to change the polarization state of the local oscillation light 12 so that the output of the circuit 10 is maximum. |
