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

Dy^(3+)-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 Dy^(3+)-doped fluoride fiber laser in the mid-infrared(mid-IR)region over 3μm is a scientific and technological frontier.Typically,Dy^(3+)-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 Dy^(3+)-doped fluoride fiber laser at 3.2μm,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 Dy^(3+)-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 Dy^(3+)-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 Dy^(3+)-doped fluoride fiber lasers in the mid-IR regime.