OPTICAL FREQUENCY AUTOMATICALLY FOLLOWING SYSTEM, OPTICAL PHASE SYNCHRONIZATION FOLLOWING SYSTEM, POLARIZED WAVE FOLLOWING SYSTEM AND OPTICAL SIGNAL DETECTING CIRCUIT USING THE SYSTEMS

摘要

PROBLEM TO BE SOLVED: To prevent the deterioration of a signal quality due to the deterioration of the S/N by matching a local optical source frequency on a receiving side to a carrier optical source frequency on a transmitting side so as to generate a frequency fluctuation difference. SOLUTION: Local light emitted from a local light source 14 on the receiving side is reflected at a right angle at a partial reflecting mirror 2 and enters a partial reflecting mirror 3 with carrier light on the transmission side with an optical frequency coming through the mirror 2. Light obtained by overlapping the wave surfaces of the light of the local light and the carrier light on the transmission side by these mirrors 2 and 3 enters the part 5. A current/voltage transformer 6 transforms an output current from the photoelectric converter 5 to a voltage. The optical frequency of the light source 14 is controlled by a frequency (phase) control drive circuit 13 so that the output of a differential amplifier 12 approaches 0. In this case, in light passing through the mirror 3, namely output light 4, the frequency of light to the carrier light on the transmitting side is kept always coincident.