基于外差检测和前向拉曼放大的新型长距离相敏光时域反射仪

Long distance phase-sensitive optical time-domain reflectometer based on heterodyne detection and forward Raman amplification

基于外差检测与前向拉曼放大相结合的思路,提出了一种能实现长距离传感并同时具备高空间分辨率和高信噪比(SNR)的新型相位敏感光时域反射仪(Φ-OTDR)。讨论了如何优化入纤脉冲光和拉曼泵浦光功率,尽可能降低非线性效应对系统的不良影响,并在此基础上讨论了外差检测相比直接检测对系统性能的改善。实验证明,本文提出的Φ-OTDR传感距离可达到103km,为迄今报道的最长距离,空间分辨率为15.7m,SNR为7.89dB,其应用在管道防开挖现场试验中得到较好的验证。

Phase-sensitive optical time domain reflectometer （Ф-OTDR） has great potential in many security applications, such as safety monitoring of pipelines, airports, borderlines and other long-distance perimeters. The detection range, resolution, and signal-to-noise ratio （SNR） are tightly related parameters and influence each other, so all of them should be considered together to achieve effective and reliable measurements. By combining the coherent detection and the forward Raman amplification, a novel Ф-OT- DR system is proposed and demonstrated in this paper, which offers long distance sensing ability with high spatial resolution and high SNR. By optimizing the Raman peak power and its input power,the nonlinear effects of the system performance are decreased significantly. Furthermore,the coherent detection method can further improve the SNRs of the sensing signal. Experimental results show that the proposed Ф-OTDR system＇s high performance can be achieved with a long sensing distance of up to 103 km with a spatial resolution of 15.7 m,and an SNR of 7.89 dB,which is the longest distance reported as far as we know. And the system is verified in a field pipeline trial on multi-point intrusion detection ability.