Optical fiber amplifier and its amplification method

Abstract

A optical signal from the input terminal 6a is amplified and goes through the optical fiber doped with rare earth. The excitation lights from the excitation light sources 2 and 3 are synthesized at the optical coupler 4 and outputted to the optical fiber doped with rare earth 1 through the optical coupler 5. A part of the light is branched from the optical coupler 11 to optical receiver 14 through the band pass light filter 13. The optical receiver 14 converts the received optical signal to an electrical signal and outputs it to the error signal output circuit 114. The receiving current is amplified in the error signal output circuit 114 and branched to the excitation light source output control circuits 9 and 10. The excitation light source output control circuits 9 and 10 execute feedback control so as to obtain a constant excitation light level outputted to the optical fiber doped with rare earth from the excitation light sources 2 and 3, in response to the output signal of the optical receiving circuits 7 and 8, and the output signal of the error signal branching circuit 115.