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从受激布里渊散射耦合波导方程出发建立了多模光纤布里渊频移、泵浦波、斯托克斯波和声波场理论模型,分析对比了多模光纤与单模光纤布里渊散射谱的频移、增益、线宽和受激布里渊散射阈值,并进一步分析了光纤长度、衰减系数、数值孔径对多模光纤受激布里渊散射阈值的影响。结果表明,多模光纤多个模式布里渊散射谱叠加造成其总的布里渊散射谱展宽,不再满足洛伦兹分布,其线宽增加至原来数倍、峰值增益和频移降低;渐变折射率多模光纤SBS阈值一般在80 m W以上,远大于单模光纤;纤芯直径相同时,相比于阶跃折射率多模光纤,数值孔径对渐变折射率多模光纤SBS阈值的影响较大,后者更易发生受激布里渊散射效应。理论计算与已报道测量结果的比较验证了理论分析的正确性。文中研究为建立基于多模光纤的布里渊散射分布式传感系统奠定了理论基础。
The theory of Brillouin frequency shift, pump wave, Stokes wave and acoustic wave field of multimode fiber is established based on the SBSD equation. The effects of multimode fiber and single mode fiber Brillouin scattering Spectral frequency shift, gain, linewidth and stimulated Brillouin scattering threshold, and further analysis of the fiber length, attenuation coefficient, numerical aperture of multimode fiber stimulated Brillouin scattering threshold. The results show that the superposition of multiple mode Brillouin scattering spectra of multimode fiber causes its total Brillouin scattering spectrum to broaden, which no longer satisfies the Lorentz distribution. Its linewidth increases several times and its peak gain and frequency shift decrease. The graded index multi-mode optical fiber SBS threshold is generally above 80 mW, which is much larger than that of single mode optical fiber. Compared with step index multimode fiber, the numerical aperture of the graded index multi- The impact is greater, the latter is more susceptible to stimulated Brillouin scattering effect. The comparison between the theoretical calculation and the reported measurement proves the correctness of the theoretical analysis. The research in this paper lays a theoretical foundation for the establishment of a distributed sensing system based on multimode fiber Brillouin scattering.