We investigate the origin of line-shape induced enhancement of stimulated Brillouin scattering (SBS) in narrow linewidth, noise broadened, high-power fiber lasers. A polarization-maintaining seed laser with continuously tunable linewidth (single frequency to >10 GHz), based on white noise modulation was developed for this study. With increasing linewidths, a substantial difference in SBS thresholds was observed depending on the end termination utilized. This observation can be explained by the line-broadened source, having significant power in the Stokes frequency at larger linewidths, seeding the SBS process. Here, SBS threshold for the system terminated with an anti-reflection coated delivery cable is compared with a simple angle cleaved end termination. The influence of end termination on SBS threshold becomes significant with increased linewidths, showing >20% difference in output power between the two cases at ∼10 GHz linewidth. The experiments are complemented by simulations, analyzing relative contributions of Rayleigh scattering and fiber end-facet reflections to SBS. At larger linewidths, due to substantial overlap between laser line-shape and SBS Stokes, with low end-facet reflectivity, Rayleigh is the dominant mechanism, which gives way to end-facet reflections with increasing reflectivity. The Rayleigh contribution is negligible at smaller linewidths, and end-facet reflectivity has a weaker influence than with larger linewidths.

中文翻译：

---

线形诱导的布里渊散射增强，宽噪声，窄线宽，高功率光纤激光器中线形引起的增强的确定和分析

我们研究了在窄线宽，噪声加宽，高功率光纤激光器中线形引起的受激布里渊散射（SBS）增强的起源。本研究开发了一种基于白噪声调制的，具有连续可调线宽（单频至> 10 GHz）的偏振保持种子激光器。随着线宽的增加，观察到的SBS阈值存在很大差异，具体取决于所使用的终端匹配。这种观察结果可以用线宽源来解释，它在较大的线宽处在斯托克斯频率中具有显着的功率，从而为SBS工艺注入了种子。在此，将使用抗反射涂层的传输电缆端接的系统的SBS阈值与简单的角度切割端接进行比较。端接对SBS阈值的影响随着线宽的增加而变得显着，表明在〜10 GHz线宽下，两种情况之间的输出功率差异> 20％。实验得到了仿真的补充，分析了瑞利散射和光纤端面反射对SBS的相对贡献。在较大的线宽处，由于激光线形和SBS斯托克斯之间存在大量重叠，端面反射率低，所以瑞利（Rayleigh）是主要的机制，它随着反射率的提高而让端面反射。在较小的线宽下，瑞利的贡献可以忽略不计，并且端面反射率的影响比较大的线宽要弱。分析瑞利散射和光纤端面反射对SBS的相对贡献。在较大的线宽处，由于激光线形和SBS斯托克斯之间存在大量重叠，端面反射率低，所以瑞利（Rayleigh）是主要的机理，它随着反射率的提高而让端面反射。在较小的线宽下，瑞利的贡献可以忽略不计，并且端面反射率的影响比较大的线宽要弱。分析瑞利散射和光纤端面反射对SBS的相对贡献。在较大的线宽处，由于激光线形和SBS斯托克斯之间存在大量重叠，端面反射率低，所以瑞利（Rayleigh）是主要的机制，它随着反射率的提高而让端面反射。在较小的线宽下，瑞利的贡献可以忽略不计，并且端面反射率的影响比较大的线宽要弱。