Patent ID: 7362499

Claim:
An optical amplifier comprising: pump light sources pumping a Raman amplifying medium with pump lights at different wavelengths, to thereby Raman amplify a wavelength division multiplexed (WDM) light, including L-band light and light in at least one other wavelength band multiplexed together, traveling through the Raman amplifying medium; a coupler dividing the L-band light out of the Raman amplified WDM light; a rare earth doped fiber amplifier amplifying the divided out L-band light, to thereby output an amplified light from the rare earth doped fiber amplifier; at least one detector detecting powers of different wavelengths in the amplified light output from the rare earth doped fiber amplifier; and a controller controlling output powers of the respective pump light sources in accordance with the powers detected by said at least one detector.