Optimization of seed power for suppression of stimulated Raman scatting in all-fiber amplifiers

Abstract

In this paper, the influence of seed power on a few-mode all-fiber amplifier is analyzed theoretically and experimentally. Numerical simulation results gave an optimized seed power for this amplifier considering three factors which are usually important in high-power fiber lasers: optic-to-optic efficiency, Raman ratio and output power. A 3.02 kW light with a good beam quality (M2 ~ 1.7) has been obtained with an injection seed power of 300 W, and the intensity of Raman light was 20 dB below the signal light in the spectrum. In experiments with other injected seed powers, the output characteristics were degraded to different degrees, in agreement with the theoretical results.

Weak-Seed Induced Enhancement of Stimulated Raman Scattering in Distributed Side-Pumped Yb-Doped Fiber Amplifiers

“…It means that with more effective suppression of Raman seed, the weak-seed induced enhancement of SRS could be observed in a larger seed power range. When the seed power is larger than the value, the SRS is not enhanced anymore, but weakened by lowering the seed power, which is coincident to formerly reported results given in [12], [14], [18], [20]. The same variation of SRS with seed power can also be revealed by Fig.…”

“…One is the single-mode fiber oscillator and the other is the oscillator with a long passive fiber for lowering the power instability. It is unexpected to find that, with both of two seeds, the SRS is weakened by increasing the seed power, which is different from all the reported theoretical or numerical predictions [14], [18], [20]. In order to deeply understand the experiment observation, the numerical study is carried out, with the help of which, the pertinent physical mechanism of the weak-seed enhancement of SRS is discussed.…”

“…It was found that the output efficiency will be dramatically lowered when the SRS was present. Then, SRS was considered as one important physical limitation to the power up-scaling of high-power Yb-doped fiber lasers, and pertinent studies became more and more heated [11], [14]- [24]. In order to make numerical studies, the SRS effect was introduced into the rate-equation model of Yb-doped fiber lasers and amplifiers [23].…”