Interference Fading Suppression for Multi-frequency φ-OTDR

In phase-sensitive optical time domain reflectometer (Phi-OTDR), due to interference fading, the intensity of Rayleigh backward scattering (RBS) signals may be close to zero at the fading position and submerged in noise, resulting in the abnormal demodulated phase of vibration signal. In this paper, a multi-frequency phi-OTDR is proposed for the interference fading suppression. Three acousto-optical modulators (AOMs) are used to generate multi-frequency probe pulses. Data alignment processing is carried to ensure the consistency of multi-frequency beat signals. Rotated-vector-sum method is adopted to aggregate multi-frequency signals. Experimental results show that with the help of data alignment processing, the fading probability of aligned curve can be reduced to 1.90%, and the SNR of positioning curve can reach 16.03dB.