Dominguez-Lopez Alejandro, Yang Zhisheng, Soto Marcelo A, Angulo-Vinuesa Xabier, Martin-Lopez Sonia, Thevenaz Luc, Gonzalez-Herraez Miguel
Opt Express. 2016 May 16;24(10):10188-204. doi: 10.1364/OE.24.010188.
Systematic errors induced by distortions in the pump pulse of conventional Brillouin distributed fiber sensors are thoroughly investigated. Experimental results, supported by a theoretical analysis, demonstrate that the two probe sidebands in standard Brillouin optical time-domain analyzers provide a non-zero net gain on the pump pulse, inducing severe distortions of the pump when scanning the pump-probe frequency offset, especially at high probe power levels. Compared to the impact of non-local effects reported in the state-of-the-art, measurements here indicate that for probe powers in the mW range (below the onset of amplified spontaneous Brillouin scattering), the obtained gain and loss spectra show two strong side-lobes that lead to significant strain/temperature errors. This phenomenon is not related to the well-known spectral hole burning resulting from pump depletion, but it is strictly related to the temporal and spectral distortions that the pump pulse experiences when scanning the Brillouin gain/loss spectrum. As a solution to this problem, a novel scanning scheme for Brillouin sensing is proposed. The method relies on a fixed frequency separation between the two probe sidebands, so that a flat zero net gain is achieved on the pump pulse when scanning the pump-probe frequency offset. The proposed technique is experimentally validated, demonstrating its ability to completely cancel out non-local effects up to a probe power ultimately limited by the onset of amplified spontaneous Brillouin scattering. The method allows for one order of magnitude improvement in the figure-of-merit of optimized long-range Brillouin distributed fiber sensors, enabling measurements along a 100 km-long sensing fiber with 2 m spatial resolution and with no need of added features for performance enhancement.
对传统布里渊分布式光纤传感器泵浦脉冲失真所引起的系统误差进行了深入研究。理论分析支持下的实验结果表明，标准布里渊光时域分析仪中的两个探测边带在泵浦脉冲上提供了非零净增益，在扫描泵浦 - 探测频率偏移时会导致泵浦严重失真，尤其是在高探测功率水平下。与现有技术中报道的非局部效应的影响相比，此处的测量表明，对于毫瓦范围内的探测功率（低于受激布里渊散射开始时），所获得的增益和损耗光谱显示出两个强烈的旁瓣，这会导致显著的应变/温度误差。这种现象与由泵浦耗尽引起的众所周知的光谱烧孔无关，而是与扫描布里渊增益/损耗光谱时泵浦脉冲所经历的时间和光谱失真密切相关。作为解决该问题的方案，提出了一种用于布里渊传感的新型扫描方案。该方法依赖于两个探测边带之间固定的频率间隔，以便在扫描泵浦 - 探测频率偏移时在泵浦脉冲上实现平坦的零净增益。所提出的技术经过了实验验证，证明了其能够完全消除非局部效应，直至探测功率最终受激布里渊散射开始的限制。该方法使优化后的远程布里渊分布式光纤传感器的品质因数提高了一个数量级，能够沿着100公里长的传感光纤进行测量，空间分辨率为2米，且无需添加用于性能增强的附加功能。
