Distributed Optical Fiber Low-Frequency Vibration Detecting Using Cross-Correlation Spectrum Analysis

Based upon a phase-sensitive optical time-domain reflectometer (φ-OTDR) using a probe light with a pulse width of 200 ns, we propose and experimentally validate a cross-correlation spectrum analysis method for distributed optical fiber low frequency vibration detecting, for the first time to our knowledge. Experimental results show that it can detect and locate vibrations with a low-frequency of 0.0001 Hz. Besides, two vibrations at different positions with a 3 m interval can be successfully located, which suggests the proposed method is capable of locating low-frequency vibrations in high spatial resolution (SR) although the theoretical SR of the φ-OTDR is 20 m using conventional methods. There is no fundamental limit in achieving higher spatial resolution as long as the frequencies of vibrations to be located are different.