Numerical study of a bi-directional in-band pumped dysprosium-doped fluoride fiber laser at 3.2 µm

Dy³⁺-doped fluoride fiber lasers have important applications in environment monitoring, real-time sensing, and polymer processing. At present, achieving a high-efficiency and high-power Dy³⁺-doped fluoride fiber laser in the mid-infrared (mid-IR) region over 3 µm is a scientific and technological frontier. Typically, Dy³⁺-doped fluoride fiber lasers use a unidirectional pumping method, which suffers from the drawback of high thermal loading density on the fiber tips, thus limiting power scalability. In this study, a bi-directional in-band pumping scheme, to address the limitations of output power scaling and to enhance the efficiency of the Dy³⁺-doped fluoride fiber laser at 3.2 µm, is investigated numerically based on rate equations and propagation equations. Detailed simulation results reveal that the optical–optical efficiency of the bi-directional in-band pumped Dy³⁺-doped fluoride fiber laser can reach 75.1%, approaching the Stokes limit of 87.3%. The potential for further improvement of the efficiency of the Dy³⁺-doped fluoride fiber laser is also discussed. The bi-directional pumping scheme offers the intrinsic advantage of mitigating the thermal load on the fiber tips, unlike unidirectional pumping, in addition to its high efficiency. As a result, it is expected to significantly scale the power output of Dy³⁺-doped fluoride fiber lasers in the mid-IR regime.