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arXiv 2304.09342physics.optics
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光纤中高度多模激发下的受激布里渊散射理论

Theory of Stimulated Brillouin Scattering in Fibers for Highly Multimode Excitations

Kabish Wisal, Stephen C. Warren-Smith, Chun-Wei Chen, Hui Cao, A. Douglas Stone

AI总结:

本文建立了适用于任意输入和光纤结构的受激布里渊散射理论,证明高度多模激发可通过增益展宽和较弱模间增益显著提高SBS阈值,并在160模式光纤中实现6.5倍提升。

摘要:

受激布里渊散射(SBS)是一种重要的非线性光学效应,在导波系统中既能促进也能阻碍光学过程。光纤的高度多模激发已被提出作为一种在主动和被动光纤中高效抑制SBS的新途径。为一般性地研究多模激发的影响,我们针对任意输入激发、光纤截面几何形状和折射率分布建立了SBS理论。我们从矢量光学方程和张量声学方程出发,推导了信号光与斯托克斯光模式振幅的适当非线性耦合模方程。利用适用近似,我们得到了SBS(斯托克斯)增益敏感度的解析公式,该公式精确考虑了光学模式和声学模式的矢量特性。我们证明,在多模激发下,每个斯托克斯模式中的SBS功率以指数形式增长,其增长率参数化地依赖于信号模式中的功率分布。针对各向同性光纤,我们能够定义并计算任意多模激发选择下的有效SBS增益谱。该增益谱的峰值决定了SBS阈值,即能够通过光纤传输的最大SBS限制功率。我们从理论上证明,由于增益展宽和相对较弱的模间SBS增益,高度多模激发可大幅降低峰值SBS增益。我们证明,对一种市售的高度多模圆形阶跃折射率光纤的160个模式进行等功率激发,可将SBS阈值提高6.5倍,并在具有D形截面的类似光纤中发现了相当的SBS抑制效果。

英文摘要:

Stimulated Brillouin scattering (SBS) is an important nonlinear optical effect which can both enable and impede optical processes in guided wave systems. Highly multi-mode excitation of fibers has been proposed as a novel route towards efficient suppression of SBS in both active and passive fibers. To study the effects of multimode excitation generally, we develop a theory of SBS for arbitrary input excitations, fiber cross section geometries and refractive index profiles. We derive appropriate nonlinear coupled mode equations for the signal and Stokes modal amplitudes starting from vector optical and tensor acoustic equations. Using applicable approximations, we find an analytical formula for the SBS (Stokes) gain susceptibility, which takes into account the vector nature of both optical and acoustic modes exactly. We show that upon multimode excitation, the SBS power in each Stokes mode grows exponentially with a growth rate that depends parametrically on the distribution of power in the signal modes. Specializing to isotropic fibers we are able to define and calculate an effective SBS gain spectrum for any choice of multimode excitation. The peak value of this gain spectrum determines the SBS threshold, the maximum SBS-limited power that can be sent through the fiber. We show theoretically that peak SBS gain is greatly reduced by highly multimode excitation due to gain broadening and relatively weaker intermodal SBS gain. We demonstrate that equal excitation of the 160 modes of a commercially available, highly multimode circular step index fiber raises the SBS threshold by a factor of 6.5, and find comparable suppression of SBS in similar fibers with a D-shaped cross-section.

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