Ultra long distance Phase-sensitive OTDR using SOVMD method

In order to enhance the sensing distance of phase-sensitive optical time-domain reflectometer (Φ-OTDR), a hybrid optical amplification structure is proposed, which combines backward Brillouin amplification, bi-directional Raman amplification, and relay erbium-doped fiber (EDF) amplification. Unconsumed Raman pump light is used for the relay EDF amplification, and partial intrinsic light is modulated as Brillouin pump light. Due to the large amount of background noise imported by the hybrid optical amplification, a sparrow optimization variational mode decomposition (SOVMD) algorithm is designed to demodulate the vibration phase. The sparrow optimization processing aims to optimize the decomposition parameters corresponding to different sample entropy values of amplification stages. Experimental results show that a sensing distance up to 211.90 km is achieved without any relay power supply. Multi-points vibration signals are localized at 171.34 km and 211.75 km, with a positioning signal-to-noise ratio of above 11 dB. Different vibration signals are decomposed and recovered through the SOVMD algorithm. The SOVMD algorithm has a significant effect on the recovery of low-frequency vibration signals, and it can recover the vibration frequency as low as 0.01 Hz. Therefore, this system can provide a reference for ultra-long-distance detection.