Phase Demodulation under Ultra-low sampling rate in heterodyne coherent Φ-OTDR

Heterodyne coherent phase-sensitive optical time-domain reflectometry($\Phi$-OTDR) requires a higher data sampling rate to demodulate phase in the “distance” direction effectively. Aiming at the problem of large amount of demodulated data, we propose a phase demodulation method that can effectively recover disturbance information from ultra-low sampling data. This method demodulates the phase of the two-dimensional reconstructed signal in the “time” direction. Thus, the influence of spectrum aliasing in the “distance” direction caused by undersampling is avoided. The undersampling rate is not limited by the spectrum aliasing effect of the detected signal when using this method to demodulate phase. Therefore, accurate phase information can be retrieved under ultra-low sampling rates, significantly reducing the data for phase demodulation in heterodyne coherent $\Phi$-OTDR. In the experiment, three sampling rates (100 MSa/s, 10 MSa/s, 1 MSa/s) within the restricted area of the traditional undersampling demodulation method were selected to acquire data, and the proposed method can also accurately demodulate phase information.