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首页> 外文期刊>Optical engineering >Stimulated Brillouin scattering in optical fibers with end reflections excited by broadband pump waves
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Stimulated Brillouin scattering in optical fibers with end reflections excited by broadband pump waves

机译：光纤中的布里渊散射光，宽带泵浦波激发的端反射

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摘要

The transient theory of stimulated Brillouin scattering (SBS) in optical fibers is used to investigate the effects of weak feedback of incident broadband laser fields exhibiting different spectral shapes. The proper boundary conditions are given for the forward- and backward-propagating electric fields inside the fiber with a finite amount of reflectivity at the fiber ends. When the linewidth of the laser approaches the Brillouin frequency shift, a weak reflection of the laser field overlaps with the SBS gain and can be amplified in the fiber, resulting in an apparent reduction in SBS threshold. It is shown that the spectral shape of the incident field and its overlap with the SBS gain spectrum affects the SBS signal. Numerical examples are presented for incident laser fields that (1) simulate a pulsed, multilongitudinal-mode laser and (2) are a constant amplitude with a sinusoidal phase modulation. For the pulsed field with mode spacing much less than the Brillouin linewidth, calculations show that an end reflection of 0.01 % (-40 dB) of the laser field with a linewidth equal to 0.75 of the Brillouin frequency shift can reduce the effective SBS threshold by a factor of 1.5. When the incident laser field is constant amplitude and phase modulated with a sinusoid, calculations predict sharp and distinct enhancement of the reflected power when the ratio of the Brillouin frequency shift to the modulation frequency is an integer for end reflections as low as 0.001% (-50 dB). Experiments performed with a sinusoidal phase modulated signal confirm the theoretical predictions. These results have implications on the design of high-power fiber laser systems that utilize spectral broadening to suppress SBS.
机译：光纤中的布里渊散射（SBS）的瞬变理论用于研究具有不同光谱形状的入射宽带激光场的弱反馈效应。为光纤内部的正向和反向传播电场提供了适当的边界条件，并且在光纤末端具有有限的反射率。当激光器的线宽接近布里渊频移时，激光场的弱反射会与SBS增益重叠，并且可以在光纤中放大，从而导致SBS阈值明显降低。结果表明，入射场的频谱形状及其与SBS增益频谱的重叠会影响SBS信号。给出了入射激光场的数值示例，这些场（1）模拟脉冲多纵向模式激光，（2）是具有正弦相位调制的恒定振幅。对于模式间距远小于布里渊线宽的脉冲场，计算表明，线宽等于布里渊频移0.75的激光场的末端反射为0.01％（-40 dB）可以降低有效SBS阈值1.5倍当入射激光场的振幅恒定且使用正弦波进行相位调制时，当布里渊频移与调制频率之比为低至0.001％的端反射的整数时，计算将预测反射功率的急剧而明显的增强。 50分贝）。用正弦相位调制信号进行的实验证实了理论预测。这些结果对利用光谱加宽抑制SBS的高功率光纤激光器系统的设计产生了影响。

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