Patent ID: 7379233

Claim:
A Raman amplifier comprising: a transmission medium propagating a WDM signal; a pump light source generating a plurality of pump lights having different frequencies; a modulation unit modulating the pump lights into a plurality of coordinating pairs of pump lights, wherein each pair includes a first pump light and a second pump light, and for each pair, a frequency difference between the first pump light and the second pump light is equal to a Raman frequency shift, the first pump light within the pair alternates between a first optical level and a second optical level lower than the first optical level, the second pump light within the pair alternates between the second optical level and the first optical level, and the modulation unit modulates the first and second pump lights within the pair so that the first pump light and the second pump light within the pair are not simultaneously at the first optical level; and an optical guide device guiding the pump lights modulated by said modulation unit to said transmission medium so that the modulated pump lights thereby cause Raman amplification of the WDM signal propagating in the transmission medium.