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基于脉冲抽运的布里渊光时域反射计技术具有米数量级的空间分辩力。为了分析在其空间分辨力范围内的应变梯度增加对布里渊谱测量的影响,建立了后向布里渊散射谱与应变梯度的函数关系。数值分析结果表明应变梯度增大,不仅使布里渊频移随之线性增大,也会使后向布里渊散射谱峰值非线性降低,谱峰变得平坦。空间分辨力10 m的100με/m应变梯度相对于零应变梯度,引起的布里渊频移测量误差增加2.04 倍。传感光纤固定于悬臂梁上以模拟不同应变梯度,采用对频宽小于1 MHz的激光脉冲调制和基于相干平衡检测的布里渊光时域反射计系统,实验测得了沿传感光纤的后向布里渊散射谱数据和应变分布。布里渊谱数据经最小二乘法拟合后,得到的不同应变梯度的谱曲线变化与理论分析相吻合。
Brillouin optical time-domain reflectometry based on pulsed pumping has a spatial resolution of meters. In order to analyze the influence of the increase of strain gradient on the measurement of Brillouin spectrum in the range of its spatial resolution, the function relationship between the back-propagation Brillouin scattering spectrum and the strain gradient was established. The results of numerical analysis show that the strain gradient increases not only linearly with the Brillouin frequency shift, but also decreases the nonlinear peak of Brillouin scattering spectrum and flattens the spectrum peak. The 100με / m strain gradient with spatial resolution of 10 m increases the error of Brillouin frequency shift measurement by 2.04 times with respect to zero strain gradient. The sensing fiber is fixed on the cantilever beam to simulate different strain gradients. By using the laser pulse modulation with the bandwidth less than 1 MHz and the Brillouin optical time-domain reflectometer system based on the coherence balance detection, Brillouin scattering spectrum data and strain distribution. Brillouin spectral data fitted by the least squares method, the resulting strain curve of different strain curve changes consistent with the theoretical analysis.