Cheng Zhongdi, Shi Yi
Opt Express. 2024 Feb 12;32(4):6630-6643. doi: 10.1364/OE.515479.
This article discovers that the excessive correlation between the selected temporal sensing sequences will lead to phase demodulation failure in the demodulation process of direct detection Φ-OTDR in certain duration, which reduces the quality of demodulated phase. Besides, we also first discover a phase polarity flipping phenomenon in the demodulation process, which will introduce additional errors and further degrade the quality of demodulated phase. In order to obtain the real phase change caused by external intrusion, a high-quality phase demodulation strategy with multi-position compensation based on leveraging the information redundancy between each Rayleigh back-scattered temporal sequence is proposed. The optimal demodulation position is selected by calculating the cross-correlation between temporal sensing sequences. The phase demodulation failure is then compensated by phase demodulation results from multiple positions. At the same time, the phase polarity change is also determined and corrected. The experimental results show that this strategy can effectively suppress the waveform distortion and improve the signal-to-noise ratio of the demodulated phase. This scheme can effectively improve the demodulation effect and detection performance of direct detection Φ-OTDR and may promote its application.
本文发现，在一定时长内，直接探测Φ-OTDR解调过程中所选时间传感序列之间的过度相关性会导致相位解调失败，从而降低解调相位的质量。此外，我们还首次在解调过程中发现了相位极性翻转现象，这会引入额外误差并进一步降低解调相位的质量。为了获得由外部入侵引起的真实相位变化，提出了一种基于利用每个瑞利背向散射时间序列之间信息冗余的多位置补偿高质量相位解调策略。通过计算时间传感序列之间的互相关来选择最佳解调位置。然后用多个位置的相位解调结果补偿相位解调失败。同时，还能确定并校正相位极性变化。实验结果表明，该策略能有效抑制波形失真，提高解调相位的信噪比。该方案能有效提高直接探测Φ-OTDR的解调效果和检测性能，可能会推动其应用。
