AUTHOR=Lu Yao , Jiang Zongfu , Xiao Hu , Chen Zilun , Jiang Man , Chai Junyu , Yang Hao , Ding Lianchuang , Zhang Dan , Zhang Jiangbin , Zhou Qiong , Liu Wenguang 

TITLE=Mitigating mode instabilities by controllable mode beating excitation with a photonic lantern

JOURNAL=Frontiers in Physics

VOLUME=Volume 11 - 2023

YEAR=2023

URL=https://www.frontiersin.org/journals/physics/articles/10.3389/fphy.2023.1198092

DOI=10.3389/fphy.2023.1198092

ISSN=2296-424X

ABSTRACT=We demonstrate a method of stabilizing the output beam of a large mode area fiber amplifier operating above the mode instability threshold. A mode control system based on the photonic lantern is used to excite dynamic mode beatings as the seeding stage of a 42/250 µm Yb-doped fiber amplifier. We propose a theoretical explanation for the validity of this method: provided that the mode interference patterns generated by input mode beatings are antisymmetric to those in the main amplifier caused by thermally-induced nonlinear effect, the refractive index grating will not be formed to indicate the onset of mode instability. Experimentally, a significant mode stability and beam quality improvement has been achieved in this system at power levels of up to nearly four times the mode instabilities threshold.