3~5 μm 中红外激光在**、医疗、自由空间光通信及材料加工等领域具有重要的应用价值。本文提出利用发展较成熟的2.7~2.9 μm 掺Er 激光作为拉曼抽运源，ZBLAN 光纤作为拉曼增益介质，为获得激射波长灵活、结构紧凑的3~5 μm 中红外激光提供一种可行方法。依据光纤拉曼激光器的非线性耦合方程组，数值分析并优化设计了3~5 μm 中红外ZBLAN 光纤一级/二级拉曼激光器。主要研究了ZBLAN 光纤长度和输出镜反射率等参数对拉曼激光阈值及输出功率的影响。数值结果表明：1) 拉曼阈值随着输出镜反射率的增大而明显下降，且存在最优的ZBLAN光纤长度使一级拉曼阈值最低(4.15 W)；2) 为获得最高拉曼激光输出功率，最优输出镜反射率分别为84%~98%(一级)和42%~60%(二级)，最优ZBLAN 光纤长度分别为6.7~8.9 m(一级)和1.5~2.4 m(二级)，最优斜率效率分别高达72.36%(一级)和34.06%(二级)。研究工作在一定程度上可为实验研究此类中红外拉曼激光器提供理论指导。

3~5 μm mid-infrared lasers have attracted much attentions due to their wide applications in defences, medicine, free-space optical communication and materials processing. A new scheme for obtaining a 3~5 μm flexible-wavelength, compact mid-infrared Raman fiber laser is proposed, using a 2.7~2.9 μm Erdoped fiber laser as Raman pump source and a ZBLAN fluoride fiber as Raman gain medium. Based on the nonlinear coupling equations of Raman fiber lasers, the 3~5 μm mid-infrared ZBLAN fiber 1st/2nd-order Raman lasers are numerically analyzed and optimized. The theoretical optimization is mainly focused on the effects of ZBLAN fiber length and output-mirror reflectivity on the Raman laser threshold and output power. The numerical results show: 1) the Raman laser threshold significantly reduces with the increase of the outputmirror reflectivity, and there always exists the optimized ZBLAN fiber length for the lowest Raman threshold (4.15 W); 2) in order to obtain the high-power Raman laser output, the optimized reflectivities of output mirror are 84~98% (1st-order) and 42~60% (2nd-order), the optimized ZBLAN fiber lengths are 6.7~8.9 m(1st-order) and 1.5~2.4 m (2nd-order), respectively. The optimized slope conversion efficiencies can be as high as 72.36% (1st-order) and 34.06% (2nd-order). These results could provide a theoretical guidance for such mid-infrared fiber Raman lasers.