A Fast Dynamic Mode Analyzer for Few-Mode Fiber Lasers

A fast dynamic mode analyzer (FDMA), based on the matrix operation mode decomposition technique, holds significant potential for characterizing the comprehensive spatial features of few-mode fiber lasers and elucidating multi-mode nonlinear physical phenomena. In this study, the FDMA was first validated within a system where mode dynamic frequencies reached kilohertz, featuring coexistent gain dynamics and mode dynamic coupling. Utilizing the FDMA, the dynamic evolution process of modes on a sub-millisecond timescale was comprehensively characterized, with a mode decomposition (MD) speed exceeding 1500 Hz, 2.5 times swifter than the previously reported theoretical speed of the neural network MD technique—the fastest MD method besides the matrix operation MD approach—and an MD accuracy surpassing 0.98. Additionally, based on MD reconstruction of the beam field, the calculation speed of beam quality exceeded 600 Hz, which is four orders of magnitude faster than the speed of commercial equipment. As a typical application of the FDMA, the thermal-induced dynamic mode coupling threshold power was first determined through the analysis of mode components and rapid beam quality evaluations, offering a novel perspective and efficient supplement, markedly distinct from traditional evaluation methods.