单频大功率光纤放大器中抑制受激布里渊散射的理论分析

Study of Stimulated Brillouin Scattering Effect in High-Power Single-Frequency Fiber Amplifiers

对单频大功率光纤放大器中的受激布里渊散射(SBS)抑制问题进行了分析和模拟。建立了双包层光纤放大器的含有受激布里渊散射效应的传输方程组,并考虑了温度差对受激布里渊增益系数的影响。通过数值求解方程组研究了前向、后向和双向抽运方式下,抽运功率、对流系数、光纤长度和斯托克斯频率偏移对受激布里渊散射增益的影响。在抽运功率、对流系数和光纤长度均相同的条件下,后向抽运方式的受激布里渊增益最小;对流系数或光纤长度的减少会降低受激布里渊增益。计算了总抽运功率为1kW,三段抽运方式下的受激布里渊增益,其结果远远大于增益阈值。因此,设计单频大功率光纤放大器宜采用后向抽运方式,尽量减小光纤外表面空气的对流速度以增加温度差,同时应该尽量缩短光纤长度。

Suppression condition of stimulated Brillouin scattering （SBS） in high-power single-frequency fiber amplifier is analyzed and simulated in this paper. The set of differential equations for an fiber amplifier with pump, signal and the first-order Stokes, taking into account effects of thermal gradients caused by heat generation, is presented. The influence of pump powers, convective coefficient, fiber lengths, and detuning of the Stokes frequency from exact SBS resonance on SBS gain （G） is studied under unidirectional and bi-directional end pumps. Compared to forward pump and bi-directional pump schemes, backward pump scheme offers the least gain （G）, which can be further reduced through decreasing convective coefficient and fiber lengths. When total pump power is 1 kW, gain （G） of three-segment distributed pumping scheme is higher than the SBS gain threshold value. The results show that the backward pump scheme has advantage over other pump schemes in suppression of SBS, and the SBS is not a limiting factor to single-frequency power extraction from fiber amplifiers for a properly temperature variation and sufficiently short amplifier length.