| 摘要 |
PURPOSE:To follow against a fast fluctuation by transmitting an optical signal corresponding to a transmission signal and, therewith, the continuous light of a constant wavelength corresponding to the direct current electric signal of a constant level, converting the continuous light to an electric signal and executing an automatic gain control action as a control signal. CONSTITUTION:First and second optical signals L1 and L2 from photoelectric converters 11 and 31 are superimposed by a multiplexer 32 and sent to an optical fiber 1. Next, a demultiplexer 42 extracts the optical signal components of wavelengths equal to wavelengths lambda1 and lambda2 of the optical signals L1 and L2, and gives it to photoelectric converters 21 and 41. An electric signal E1R converted by the photoelectric converter 21 is given to an AGC (automatic gain control) circuit 43 as a controlled signal, an electric signal E2R converted by the photoelectric converter 41 is given to the AGC circuit 43 as a control signal, an AGC action is executed, and the level of the controlled signal E1R is fixedly controlled and outputted. Thus, even at the time of speedily transmitting through a transmission system whose loss is changed, the AGC action can be sufficiently followed. |
