Numerical Modeling and Optimization of Mid-Infrared Fluoride Glass Raman Fiber Lasers Pumped by $\hbox {Tm}^{3+}$ -Doped Fiber Laser

Numerical modeling of multiorder cascaded fluoride glass Raman fiber laser (RFL) employing fiber Bragg gratings (FBGs) is presented. Calculations were compared with the recently reported results, and good agreement was achieved. The model was also used to optimize a fourth-order fluoride glass RFL pumped at 1.9 , which can generate a mid-infrared emission up to 3.36. The influences of launched pump power, fiber length, output coupling, fiber background loss, and insertion loss of FBG on laser performance were investigated. The fiber length of 53.1-85.5 m and reflectivity of output coupler of 0.34-0.51 were recommended to obtain a relative large output power. The calculated maximum output power of 2.96 W with slope efficiency of 19.2% and threshold of 24.7 W was obtained at launched pump power of 40 W. In addition, the strong effects of fiber background loss and insertion losses of FBGs on laser output performance emphasized the importance of development of high quality fiber and fluoride FBG writing technique.