Patent ID: 8213805

Claim:
An optical communication system comprising: a Raman amplifier that gives a Raman gain to an optical transmission line; a transmitter that transmits to the optical transmission line, a first light being subject to receive the Raman gain through the optical transmission line and a second light not being subject to receive the Raman gain through the optical transmission line; a controller that halts the Raman amplifier and controls a transmission light power of the first light so as to increase the power according to the Raman gain; a first measuring instrument that measures a first input-output light power for the first light of the optical transmission line, the first input-output light power being used for determining a reference of loss characteristic of the optical transmission line, during the Raman amplifier being halted; and a second measuring instrument that measures a second input-output light power for the second light of the optical transmission line, the second input-output light power being used for determining a fluctuation of the reference.