多模布里渊光时域反射系统的建模分析与计算

提出了一种基于多模法布里-珀罗激光器外调制的移频本地外差检测布里渊光时域反射系统，分析了系统提高光纤受激布里渊散射阈值和移频本地外差检测的原理；推导了系统信噪比的数学表达式，研究了布里渊叠加谱峰功率和谱宽、系统信噪比和频移测量精度与纵模数的关系，以及实现最优测量精度时纵模数与脉冲宽度的关系，得到了相应的拟合公式。结果表明，选用纵模间隔0.141 nm的多模激光器和单纵模峰值功率100 mW、脉冲宽度50 ns的入纤脉冲时，随着纵模数的增加，25 km光纤末端的系统信噪比、温度和应变测量精度均得到了明显提高，且纵模数为20时，系统信噪比相对于单纵模增加11.73 dB，温度和应变测量精度分别达到最佳值3.2 ℃和70.8 με；最佳频移测量精度随脉冲宽度的增大先快速提高，后趋近于恒定值2.9 MHz。

Abstract

A Brillouin optical time domain reflectometer sensing system is proposed based on external modulation of the multi-longitudinal mode Fabry-Perot laser and frequency-shifted local optical heterodyne detection. The principles of stimulated Brillouin scattering threshold improvement and heterodyne detection of frequency-shifted local light from the same laser and Brillouin scattering from the sensing fiber are analyzed, and the mathematical expression of signal-to-noise ratio of the system is deduced. The dependence of the peak power and bandwidth of superposed Brillouin spectrum, the signal-to-noise ratio and the measurement accuracy of Brillouin frequency shift on the longitudinal mode number, and the relationship between the longitudinal mode number and the optimal measurement accuracy for different pulse widths are theoretically studied. The corresponding fitting formulas are obtained by calculation. The results show that with the increase of longitudinal mode number, the signal-to-noise ratio, temperature and strain measurement accuracies of the system at the end of 25 km long fiber are improved significantly for a multi-longitudinal mode Fabry-Perot laser with a mode interval of 0.141 nm and a pulse with a peak power of 100 mW and a width of 50 ns for single-longitudinal mode. Especially, compared with single longitudinal mode, the signal-to-noise ratio increases by 11.73 dB, and the optimal temperature and strain measurement accuracies of 3.2 ℃ and 70.8 με are achieved, respectively, when the longitudinal mode number is 20. The optimal measurement accuracy of Brillouin frequency shift rises rapidly with the increasing pulse width, and the optimal measurement accuracy tends to a constant of 2.9 MHz for pulse width larger than 100 ns.

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李永倩, 李晓娟, 张淑娥, 曹翠新. 多模布里渊光时域反射系统的建模分析与计算[J]. 光学学报, 2016, 36(10): 1006001. Li Yongqian, Li Xiaojuan, Zhang Shu′e, Cao Cuixin. Modeling Analysis and Calculation of Multi-Mode Brillouin Optical Time Domain Reflectometer System[J]. Acta Optica Sinica, 2016, 36(10): 1006001.

多模布里渊光时域反射系统的建模分析与计算

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