Research on PFN suppression methods in φ-OTDR systems based on the MSI-VPFN algorithm

The phase-sensitive optical time-domain reflectometry (φ-OTDR) system can monitor the distribution of the acoustic field along the sensing fiber through single-ended access, making it applicable in various fields. However, phase fluctuation noise (PFN) suppression remains a significant challenge. This paper aims to clarify the complex relationship between the signal-to-noise ratio (SNR) of the intermediate frequency (IF) signal and PFN in φ-OTDR systems by quantitatively establishing the nonlinear relationship between the carrier-to-noise ratio (CNR) of the IF signal and the variance of the PFN (VPFN). Accordingly, we propose the MSI-VPFN algorithm, which effectively suppresses PFN by dynamically adjusting spatial weighting according to the standard deviation of VPFN. Compared to the original signal, applying the MSI-VPFN algorithm reduces the PFN standard deviation from 0.386 rad to 0.068 rad and decreases the probability of fading noise from 6.23% to 0.19%. The MSI-VPFN algorithm outperforms traditional methods, providing a scientific basis for evaluating system performance and establishing a solid foundation for the broader application of φ-OTDR technology.