Patent ID: 6958856

Claim:
A Raman amplifier comprising: an optical fiber for Raman-amplifying a plurality of signal channels of signal light having respective center optical frequencies different from each other; a pumping light supply section for supplying N (N being an integer of 2 or more) pumping channels of pumping light having respective center optical frequencies different from each other to said optical fiber; and a feedback section for detecting a part of said signal light Raman-amplified within said optical fiber when said pumping light is supplied thereto, and controlling said pumping light supply section such that said Raman-amplified signal light has a substantially flat power spectrum with respect to an optical frequency direction according to a result of said detection; said feedback section dividing said detected Raman-amplified signal light into N optical frequency ranges defined so as to include respective Raman amplification peaks as optical frequencies lower than respective center optical frequencies of said pumping channels of pumping light by an optical frequency shift of 13.5 to 15.7 THz, and controlling said pumping light supply section such that said Raman-amplified signal light has a power fluctuation of 2 dB or less in each of thus divided N optical frequency ranges.