Patent ID: 8275269

Claim:
A distributed Raman amplifier for supplying a pumping light to a transmission path to Raman amplify a WDM light being propagated through the transmission path, comprising: a pumping light supplying section configured to supply a pumping light output from at least one pumping light source to the transmission path; an OSNR monitoring section configured to monitor an OSNR representing a ratio between a signal light level of each channel contained in the WDM light which has been propagated through the transmission path to be Raman amplified and thereafter is amplified by an optical amplifier in an optical repeating node connected to a signal output end of the transmission path, and a noise light level of each channel contained in the WDM light; a judging section configured to judge whether a monitor value of the OSNR of each channel in the OSNR monitoring section is larger or smaller than a previously set target value thereof; and a control section configured to control a driving state of the pumping light source based on the judgment result in the judging section, wherein the pumping light supplying section includes: a plurality of pumping light sources of different wavelengths; and a multiplexer configured to multiplex pumping lights output from the respective pumping light sources to supply the multiplexed light to the transmission path, and the control section is configured to select only the pumping light source which corresponds to a pumping wavelength of which gain efficiency of Raman amplification is largest, among the plurality of pumping light sources, based on the judgment result in the judging section, and then to increase or decrease the output power of the selected pumping light source.