Suppression of Transient Gain Response in Bi-Directionally Pumped Raman Amplifiers

In this paper, transient gain response in Raman fiber amplifiers (RFA) was simulated in details using an accurate dynamic numerical model. Firstly, bi-directionally pumped RFAs were designed for 80nm gain bandwidth, and less than 0.6 dB flatness of both gain and OSNR were derived by optimizing pump wavelengths and pump powers. When 50 channels were dropped from total 100 channels, Raman gain fluctuations on the surviving channels ranged from 1.1 to 1.2 dB. Then, backward pump powers were adjusted automatically to suppress inter-channel cross gain modulation by using PID negative feedback control, the maximum fluctuation of output-signal power was less than 0.16 dB on all surviving channels.