从掺镱(Yb)光纤放大器的功率传输方程出发,利用有限差分法对小模场面积(SMA)和大模场面积(LMA)掺镱双包层光纤放大器的放大特性进行了分析比较。采用模场直径(MFD)6.5 μm和20 μm的双包层掺镱光纤作为放大器增益介质进行窄线宽连续信号的放大,在915 nm激光抽运下模拟计算了大、小模场面积输出功率随输入信号功率、抽运光功率和光纤长度的变化特性,特别是对于大模场面积光纤放大器,最优光纤长度的选择至关重要;讨论了模场直径不同时的最优抽运功率和光纤长度的选择,得出4 m光纤放大时的临界抽运功率为4 W,理论与实验结果基本一致。为实际应用中根据信号光、抽运光、增益和模式等要求而选择光纤长度和类型等优化设计提供了理论依据。

Based on the rate equation, the amplification performance of small-mode-area (SMA) and large-mode-area (LMA) ytterbium-doped double-clad fiber amplifiers was studied using the finite-difference method. The Yb-doped double-clad fibers with the mode diameter 6.5 μm and 20 μm were used as the gain media for the amplification of narrow-band signals. Under the pump laser at the center wavelength of 915 nm, the relationships between output power and input signal power, pump power as well as fiber length, were discussed for SMA and LMA. Especially for LMA fiber amplifiers, it is important to choose the optimal fiber length. For the fiber amplifier with different mode diameters, the optimal pump power and fiber length were also analyzed. It is obtained that the critical pump power is about 4 W with the fiber length of 4 m, which is in accord with the experimental results. The results provide a theoretical guide to optimize fiber type and fiber length considering available signal and pump power, desired gain and mode requirement of fiber amplifiers.