Patent ID: 8767285

Claim:
A method of compensating for channel power depletion induced by Raman amplification noise in a hybrid distributed Raman amplifier-Erbium doped fibre amplifier, the method comprising: determining an equivalent noise figure for a virtual amplifier equivalent to the hybrid distributed Raman amplifier-Erbium doped fibre amplifier, and having an input power equal to the input power of the Erbium doped fibre amplifier when the distributed Raman amplifier is off and an output power equal to the Erbium doped fibre amplifier output power; determining a compensation power dependent at least in part upon the equivalent noise figure; and providing a control signal for controlling the hybrid amplifier such that an optical signal amplified by the hybrid amplifier has a total output power equal to a predetermined nominal output power plus the compensation power, wherein the distributed Raman amplifier has a noise figure and the equivalent noise figure comprises the noise figure of the distributed Raman amplifier, and wherein the noise figure of the distributed Raman amplifier is estimated from a Raman gain value using a pre-determined relationship between only Raman gain and the noise figure of the distributed Raman amplifier.