基于内调制啁啾脉冲的高信噪比低成本直接探测型φ-OTDR系统

Internally Modulated Chirped Pulse Based Direct Detection Type φ-OTDR System with High Signal-to-Noise Ratio and Low Cost

提出一种新型的基于内调制啁啾脉冲的高信噪比(SNR)直接探测型相位敏感光时域反射计(φ-OTDR)。通过理论分析可得,利用啁啾脉冲的方法并通过提高受激布里渊阈值可提高注入光能量,提高探测信号中的直流分量可使信号与噪声分离,进而提升SNR。提出一种φ-OTDR系统信噪比的综合评判方法,对SNR的统计特性进行分析。同时,开展了基于分布式反馈激光器的内调制直接探测型φ-OTDR系统实验研究,利用可调谐滤波器对内调制产生的频率啁啾范围进行控制,经对比实验验证,可得所提系统与传统φ-OTDR系统的信噪比期望相当,分布方差更小,测量可靠度更高的结论。此外,该系统还具有成本低、结构简单等优点,实际应用时可以利用光纤布拉格光栅代替可调谐滤波器,提升其应用的灵活性,为工程应用提供新的解决方案。

This paper proposes an internally modulated chirped pulse based direct detection type phase sensitive time domain reflectometer(φ-OTDR) system with high signal-to-noise ratio(SNR). Based on theoretical analysis, we find that the stimulated Brillouin threshold increases with the increasing injection pulse energy, the high direct current component of the detection signal keeps the signal and noise separate, and the SNR can be enhanced. Then a statistical evaluation method is proposed to calculate the SNR of the sensing system. Meanwhile, an internally modulated direct detection type φ-OTDR system based on the distributed feedback laser is experimentally studied. The frequency chirp range introduced by internal modulation is controlled by the tunable filter. Compared with the traditional φ-OTDR system, the proposed system can obtain similar SNR and smaller distribution variance and realize higher measurement reliability. Additionally, The proposed system has the advantages of low cost and small volume, and the tunable filter can be replaced by fiber Bragg grating in practical application. It can improve the flexibility of application and provide a new idea for engineering.