Effect of Seed Power on the Inter-Modal Four-Wave-Mixing Effect in Distributed Side-Pumped Fiber Amplifiers

The effect of seed power on the inter-modal four-wave mixing (IM-FWM) effect in a distributed side-pumped fiber amplifier is investigated for the first time, to the best of our knowledge. By using a seed source smaller than 70 W, the effect of seed power on the IM-FWM is studied experimentally. Surprisingly, it is found that the IM-FWM effect becomes stronger with the weaker seed. To analyze the physics behind this result, a numerical model is introduced, and the numerical results are in good agreement with the experimental observations. It is revealed that the IM-FWM enhancement is induced by the gain competition between the signal light and the anti-Stokes light of the IM-FWM. It is also found that there is an optimized seed power for suppressing the IM-FWM effect. The experimental and numerical results which are presented in this work can provide significant guidance for understanding the IM-FWM in fiber lasers and amplifiers.