Ultra-Low Frequency Vibration Sensing in Long-Distance Phase-Sensitive OTDR Using CEEMDAN

The multi-pump laser amplification in long-distance phase-sensitive optical time domain reflectometer (Φ-OTDR) leads to laser frequency drift (LFD) superposition, and limits the low frequency vibration sensing. Firstly, the influence of multi-pump laser amplification on LFD is theoretically analyzed. A phase curve multiple iterative decomposition scheme based on complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) is then designed. A bidirectional Raman and relay erbium-doped fiber hybrid amplification structure is used to realize long-distance vibration detection, and a structure of Mach-Zehnder interference is combined to simultaneously provide the LFD information in Φ-OTDR. Experimental results show that the LFD can cause the low-frequency drift of phase curve, and multi-pump laser amplification can further exacerbate the LFD of system. Ultra-low frequency vibration signal as low as 0.08 Hz is accurately detected and recovered at the long sensing distance of 190.7 km. The signal-to-noise ratio of vibration phase is improved, and the influence of LFD on Φ-OTDR is effectively suppressed. This paper provides an effective solution for the low-frequency and long-distance vibration monitoring application scenarios.