AUTHOR=Shu Qiang , Zhang Chun , Li Fang , Chu Qiuhui , Guo Chao , Li Fengyun , Zhang Haoyu , Tao Rumao , Lin Honghuan , Wang Jianjun 

TITLE=Impact of mode instability on polarization extinction ratio in backward pumped fiber amplifiers

JOURNAL=Frontiers in Physics

VOLUME=Volume 13 - 2025

YEAR=2025

URL=https://www.frontiersin.org/journals/physics/articles/10.3389/fphy.2025.1612074

DOI=10.3389/fphy.2025.1612074

ISSN=2296-424X

ABSTRACT=The influence of mode instability (MI) on polarization extinction ratio (PER) has been investigated in a 2 kW level polarization-maintained (PM) fiber laser system with backward pumping configuration, and the phenomena is different from the existing observations in forward-pumped PM fiber amplifiers. No decrease in PER was noted with the onset of MI, revealing that the MI effect has little impact on PER in backward-pumped PM fiber amplifiers. The discrepancy induced by the pump configuration has been theoretically analyzed, which is attributed to the longitudinal-distribution difference of high order modes induced by the MI effect.