Interference Fading Suppression Using Active Frequency Transformation Method With Auxiliary Interferometer Feedback

In order to eliminate the distortion of demodulated signal caused by the incomplete suppression of interference fading, an active frequency transformation (AFT) method is proposed for phase-sensitive optical time domain reflectometry (Φ-OTDR). An auxiliary interferometer feedback structure combined with Φ-OTDR is firstly used for the identification of signal distortion caused by the fading state at demodulation positions. The correlation coefficient of vibration signals detected by auxiliary interferometer and Φ-OTDR system can be considered as the feedback variable. The feedback process is then realized by the modulation frequency transformation of phase modulator. Experimental results show that the fading probability can be reduced to 1.58% by means of multi-frequency detection. With the AFT from 25 MHz to 30 MHz, the distortion of demodulated signal can be eliminated with an improved correlation coefficient up to 0.9898.