A multi-tone narrow-linewidth fiber amplifier is demonstrated. In this kind of amplifier the seed laser is attained by combining several single frequency seed lasers which all have nearly the same wavelength (wavelength separation less than 1 nm) and with frequency difference larger than twice the Brillouin shift. An integrated theoretical model of this kind of amplifier is set up. Relationship between stimulated Brillouin scattering(SBS) and the number of the seeds is analyzed using this model. Two-tone and three-tone amplifiers are set up to study SBS threshold output power experimentally. The experimental results are in good agreement with theoretical results, revealing rationality of the theoretical model. Two-tone and three-tone amplifications can suppress SBS effectively and enhance output powers of narrow-linewidth fiber amplifiers greatly.%提出了一种多波长窄线宽光纤放大器,其种子光由多个单频激光耦合而成,所有单频激光波长几乎相等(波长间隔小于1 nm),频率间隔大于两倍布里渊频移.建立了此类多波长窄线宽光纤放大器的完整理论模型,分析了放大器中受激布里渊散射(SBS)与种子数目的关系.搭建了双波长和三波长窄线宽光纤放大器,进行SBS阈值输出功率测定实验.实验结果与理论模拟结果基本一致,验证了理论模型的合理性；双波长和三波长放大可以有效抑制SBS效应,大幅提高放大器输出功率.
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