Raman gain flattening by using pump sources with different linewidths

Broadband Raman fibre amplifiers backward-pumped by sources with different linewidths are numerically studied for the first time. The approximation of the preliminary determined optimal continuous pump spectrum by four pump sources allowed the expansion of the spectral range of a 100-km Raman amplifier up to 1522–1596 nm with the gain ripple less than 0.2 dB. The pump scheme proposed in the paper is compared with schemes using pump sources with the same linewidths.