Patent ID: 7042636

Claim:
An apparatus comprising: optical amplifier for amplifying a wavelength division multiplexed (WDM) light including signal lights wavelength division multiplexed together, the amplifier comprising an optical fiber through which the WDM light travels and is thereby amplified via Raman amplification in accordance with multiplexed pump lights of different wavelengths traveling through the optical fiber; an optical device dividing the amplified WDM light into first and second divided lights in first and second wavelength bands, respectively; a first optical amplifier amplifying the first divided light, the first optical amplifier having a gain band including the first wavelength band; a second optical amplifier amplifying the second divided light, the second optical amplifier having a gain band including the second wavelength band; and means for controlling power of each pump light based on a power of the first divided light amplified by the first optical amplifier and a power of the second divided light amplified by the second optical amplifier to maintain a substantially flat gain over the first and second wavelength bands.