Raman-noise enhanced stimulated Raman scattering in high-power continuous-wave fiber amplifier

The stimulated Raman scattering (SRS) in high-power continuous-wave (CW) fiber amplifier is investigated with the seeded Raman noise taken into account. It is revealed that the seeded Raman noise, as a portion of seed light, should enhance SRS in high-power CW fiber amplifier even when it is much weaker than the seeded signal light. The analytic formula for predicting the Raman threshold of bi-directional pumping fiber amplifier is given with the seeded Raman noise taken into account, and the predictions agree well with the numerical results. It is also revealed that the co-pumping amplifier suffer from the lowest Raman threshold, and the counter-pumping one is more beneficial to the SRS suppression than the bi-directional pumping one when the pump absorption of active fiber is larger than 8.7 dB. These results will provide guidance for the design of high-power CW fiber amplifier.