Fig. 1. Φ-OTDR system based on heterodyne coherent detection

Fig. 2. I/Q demodulation process

Fig. 3. Flow chart of denoising algorithm based on VMD-MI

Fig. 4. Waveform of original beat signal

Fig. 5. Vibration positioning results

Fig. 6. Time domain diagram and spectrum diagram of phase signal of 500 Hz vibration demodulated by I/Q

Fig. 7. MI values of components processed by VMD of single-frequency vibration signal

Fig. 8. Denoising effects of different methods on 500 Hz single-frequency vibration signal. (a1) (b1) Wavelet; (a2) (b2) EMD; (a3) (b3) CEEMDAN; (a4) (b4) VMD-MI

Fig. 9. MI values of components processed by VMD of multi-frequency vibration signal

Fig. 10. Denoising effects of different methods on multi-frequency vibration signal. (a1) (b1) Original signal; (a2) (b2) Wavelet; (a3) (b3) EMD; (a4) (b4) CEEMDAN; (a5) (b5) VMD-MI