Kabish Wisal, Stephen C. Warren-Smith, Chun-Wei Chen, Hui Cao, A. Douglas Stone
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引用次数: 0
摘要
受激布里渊散射(SBS)通常是有源和无源光纤中一种不必要的损耗机制。有人提出,对光纤进行高度多模激发是有效抑制 SBS 的新途径。在此,我们提出了一个详细的定量理论,证实了这一提议,并阐明了其中的物理机制。从矢量光学方程和标量声学方程出发,我们为信号和斯托克斯模态振幅推导出了适当的非线性耦合模态方程,并为 SBS(斯托克斯)增益推导出了分析公式,其中包含适用的近似值,如忽略剪切效应。这样,我们就能计算出斯托克斯功率的指数增长率与高度多模信号中功率分布的函数关系。整个激发模式的增益频谱峰值决定了 SBS 门限--光纤中可发送的最大 SBS 限制功率。理论表明,由于增益展宽和相对较弱的模式间 SBS 增益,高度多模激励会大大降低 SBS 增益峰值。在计算中加入精确的矢量光学模式对于捕捉高阶模式极化模式不匹配导致的不完全模间耦合至关重要。我们证明,对商用高多模环形阶跃指数光纤的 160 个模式进行等效激励,可将 SBS 门限提高 6.5 倍,并发现在具有 D 型横截面的类似光纤中,SBS 的抑制效果相当。
Theory of Stimulated Brillouin Scattering in Fibers for Highly Multimode Excitations
Stimulated Brillouin scattering (SBS) is often an unwanted loss mechanism in both active and passive fibers. Highly multimode excitation of fibers has been proposed as a novel route toward efficient SBS suppression. Here, we develop a detailed, quantitative theory which confirms this proposal and elucidates the physical mechanisms involved. Starting from the vector optical and scalar acoustic equations, we derive appropriate nonlinear coupled mode equations for the signal and Stokes modal amplitudes and an analytical formula for the SBS (Stokes) gain with applicable approximations, such as the neglect of shear effects. This allows us to calculate the exponential growth rate of the Stokes power as a function of the distribution of power in a highly multimode signal. The peak value of the gain spectrum across the excited modes determines the SBS threshold—the maximum SBS-limited power that can be sent through the fiber. The theory shows that the peak SBS gain is greatly reduced by highly multimode excitation due to gain broadening and relatively weaker intermodal SBS gain. The inclusion of exact vector optical modes in the calculation is crucial in order to capture the incomplete intermodal coupling due to mismatch of polarization patterns of higher-order modes. 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 -shaped cross section.
期刊介绍:
Physical Review X (PRX) stands as an exclusively online, fully open-access journal, emphasizing innovation, quality, and enduring impact in the scientific content it disseminates. Devoted to showcasing a curated selection of papers from pure, applied, and interdisciplinary physics, PRX aims to feature work with the potential to shape current and future research while leaving a lasting and profound impact in their respective fields. Encompassing the entire spectrum of physics subject areas, PRX places a special focus on groundbreaking interdisciplinary research with broad-reaching influence.