Experimental study of mode instability in high power all-fiber amplifier under different pumping power distribution

Abstract

Detailed experimental investigations are presented on suppressing mode instability and stimulated Raman scattering by varying the pumping power distribution in a large mode area all-fiber amplifier with fiber core diameter of 20μm using bi-directional configuration. Results reveal that compared to employing co-directional pumping scheme, the fiber amplifier employing counter-directional pumping scheme can enhance the MI threshold power from 1250W to 1447W. Optimizing the pumping power distribution can further strength the mitigation of mode instability, such as the ratio of 57% and 66%, the threshold power is 2176W (highest output power) and 2150W respectively. For the ratio of 49%, which means almost identical scale of co-pumped light and counter-pumped light, the threshold power is 1934W. On the other hand, raising the proportion of backward pumping power can also mitigate the stimulated Raman scattering. 66% of backward pumping power can acquire 2150W output power and 20dB signal-to-noise ratio of the Raman peak, which indicates that optimizing the pumping power ratio can suppress mode instability and stimulated Raman scattering simultaneously.