High-power single-frequency fiber lasers (SFFLs) have widely been applied in various fundamental research areas. However, the increase of intensity-noise with scaling power has prevented the applications that require a high detection sensitivity. Thus, the intensity-noise would be affected by many optical factors in power amplification, such as pumping stability and nonlinear effect. To this end, here we study the influence of stimulated Brillouin scattering (SBS) on the relative intensity-noise (RIN) in SFFL-based master-oscillator power amplifier (MOPA) system. By correlating the power ratio η of the Stokes scattering power to the output signal power to the SBS-induced RIN, we find that, with scaling output power and lengthening the total fiber, an increasing η results in the enhancement as well as the extending effective frequency range of the RIN. Moreover, with the same η, different fiber lengths lead to the same amplitude level of the output RIN. Importantly, the resultant SBS-induced RIN has the same trend whether the resonant relaxation oscillation of the seed laser is suppressed. We also perform numerical studies to verify our conclusions. This study can provide the criterion for optimizing the noise-performance of MOPAs and useful insights into the development of high-power SFFLs for coherent detection application.

高功率单频光纤激光器（SFFL）已广泛应用于各种基础研究领域。但是，强度噪声随缩放功率的增加阻止了需要高检测灵敏度的应用。因此，强度噪声将受到功率放大中许多光学因素的影响，例如泵浦稳定性和非线性效应。为此，我们在基于SFFL的主振荡器功率放大器（MOPA）系统中研究受激布里渊散射（SBS）对相对强度噪声（RIN）的影响。通过将斯托克斯散射功率的功率比η与SBS诱导的RIN的输出信号功率相关联，我们发现，随着输出功率的缩放和总光纤的加长，η的增加导致RIN的增强和扩展有效频率范围。此外，在η相同的情况下，不同的光纤长度会导致输出RIN的振幅水平相同。重要的是，无论是否抑制了种子激光器的共振弛豫振荡，所得的SBS诱导的RIN都具有相同的趋势。我们还进行数值研究以验证我们的结论。这项研究可以为优化MOPA的噪声性能提供标准，并为开发用于相干检测应用的大功率SFFL提供有用的见解。