Patent ID: 7280270

Claim:
A method for controlling a gain of cascaded Raman amplifiers through a first optical fiber facility and a second optical fiber facility of an optical fiber system and having a feed-forward configuration, the cascaded Raman amplifiers including a first Raman fiber amplifier and a second Raman fiber amplifier, the first Raman fiber amplifier being coupled to the first optical fiber facility and the second Raman fiber amplifier being coupled to the second optical fiber facility, the method comprising: (a) determining a fixed pump power for at least one fixed optical pump of the second pumped Raman fiber amplifier; (b) determining an input signal power variation for at least one wavelength region, the plurality of optical signal channels being associated with the at least one wavelength region; (c) determining a pump power adjustment for at least one adjustable optical pump of the first Raman fiber amplifier using a predetermined function that depends on the input signal power variation; the predetermined function corresponding to a linear relationship between the pump power adjustment and the input signal power variation of the at least one wavelength region; and (d) adjusting the at least one adjustable optical pump of the first Raman fiber amplifier in accordance with the pump power adjustment, the predetermined function comprising: P d ⁡ ( j , t ) ≈ P do ⁡ ( j , t ) + ∑ k = 1 K ⁢ T dL ⁡ ( j , k ) ⁡ [ S L ⁡ ( k , t - T ) - S L ⁢ ⁢ 0 ⁡ ( k ) ] , wherein k corresponds to a k th wavelength region, t corresponds to a time instant, j corresponds to a j th forward Raman pump, P d (j,t) denotes a required power of the j th pump in a logarithmic scale, P d0 (j,t) and S L0 (k) denote a pump power and a signal power at a reference operating point, T dL (j,k) corresponds to a linear coeffiecient relating the forward pump power adjustment of the j th forward Raman pump and the input signal power variation for the k th wavelength region, S L (k,t−T) denotes a detected input signal power in the k th wavelength region as linearly scaled, and T denotes a determined time delay between a required pump power adjustment and a detected input signal power variation.