Mitigating transverse mode instability in Yb-doped active fibers via multicomponent regulation

Under high-power operation, the transverse mode instability (TMI) effect has become a primary limitation to further power scaling of Yb-doped fiber (YDF) lasers while maintaining high beam quality. Existing mitigation strategies, such as optimizing fiber coiling or pump configurations, fail to address the material-level origin of TMI. In this study, we effectively suppressed TMI by constructing a phosphorus-rich environment of Yb³⁺ and precisely tuning the P/Al doping ratio and fluorine content in YDF. Using an all-fiber MOPA system incorporating our four custom-designed 30/400 μm double-cladded YDFs, the optical-to-optical efficiency was improved from 64.7% to 77.9%, and the TMI threshold increased from 1.9 kW to 3.3 kW. The results further indicate that optimizing the dopant composition plays a significant role in stabilizing the Yb³⁺ valence state and mitigating the TMI effect, underscoring the central role of multicomponent regulation in enhancing fiber performance. This study not only offers a theoretical basis for material optimization of high-power YDF lasers, but also lays the groundwork for their deployment in high-brightness-demanding applications such as aerospace, precision manufacturing and laser therapy.