Optimizing the Demodulation Method for DAS System Based on Point-Backscattering-Enhanced Fiber

The signal-to-noise ratio (SNR) of fiber-optic distributed acoustic sensing (DAS) systems based on Rayleigh backscattered (RBS) signals can be improved using point-backscattering-enhanced fiber (PBSEF). It is necessary to explore the methods to achieve stable and low noise demodulation for PBSEF-based DAS system. Driven by this, this work theoretically analyzes the effect of the phase and intensity noises on the PBSEF-based demodulated signal during averaging process. The results show that the phase noise has a weaker impact on the demodulated phase than the intensity noise. Based on this analysis, two methods, direct averaging and weighted averaging, for suppressing the noise level of DAS have been investigated and the optimal parameters are investigated. For both methods, simulation and experiments show the noise level suppression of 1.5 and 4.4 times, corresponding to the noise level reduction of 0.45 and 3.78 $\text{p}\varepsilon /\surd $ Hz, respectively. The relationship between the system noise level and the number of sampling points used in the demodulation is different for the two methods. The weighted-averaging method demonstrates superior performance for its higher stability. These conclusions provide significant theoretical basis and guidance for the development of practical high-performance DAS systems for field applications.