A simple algorithm for gain spectrum adjustment of backward-pumped distributed fiber Raman amplifiers

In this letter, a simple algorithm for the gain spectrum adjustment of backward-pumped distributed fiber Raman amplifier (B-DFRA) is demonstrated both theoretically and experimentally. It is shown that the change in pump power and corresponding change in gain spectrum are approximately related through a linear matrix, while the elements of the matrix can be easily measured. Feasibility of this algorithm is approved by experiment: a gain ripple of less than 1.2 dB across the C + L band is achieved during net gain adjustment from -15 dB to -9 dB of a 160-channel B-DFRA by varying the launched power of four pumping LDs.