| 摘要 |
PURPOSE:To reduce number of required optical directional couplers by providing an optical directional coupler for coherent light to each end of one optical fiber transmission line so as to attain 2-way communication. CONSTITUTION:A transmission signal at an incoming transmission input terminal W1 is converted into a drive signal for a light emitting element 133 by an incoming signal interface section 132 to drive the light emitting element 133, by which the signal is converted into an optical signal and it is fed to a 2nd port P2 of an optical directional coupler 15. The incoming optical signal is sent to an optical fiber transmission line 3 from a 1st port P1. Moreover, a local oscillation light source control circuit 116 controls the oscillating frequency of a local oscillation light source 111, and the controlled local oscillation light is inputted to a 4th port P4 of the optical coupler 15. Thus, the optical signal inputted from a 3rd port P3 is inputted to a photodetector 112 and fed to a preamplifier 113. The signal amplified by the amplifier 113 is outputted from an output terminal W0. Furthermore, part of the output signal from a main amplifier 114 controls the circuit 116. |
