Optical Phase‐Sensitive Reflectometry Based on Orthogonal Frequency‐Division Multiplexed LFM Signal in Fractional Fourier Domain

Abstract

Linear frequency modulated (LFM) phase-sensitive optical time-domain reflectometry (𝝋-OTDR) relieves the trade-off between sensing range and spatial resolution; however, it is still limited by low sidelobe suppression ratio and signal fading. Fractional Fourier transform (FrFT) is applied to LFM 𝝋-OTDR for signal generation and compression. An LFM pulse is generated using the p-order FrFT of a direct current signal and then compressed using FrFT with order 1−p to achieve a high sidelobe suppression ratio. Orthogonal frequency-division multiplexing in the fractional Fourier domain is utilized to suppress signal fading. In experiments, fading-free distributed phase measurement is realized using a multiplexed LFM probe pulse generated using a 0.4-order FrFT. Dynamic sensing is demonstrated via single-frequency or sweep-frequency vibration, thereby validating high sensing performance. This work will not only open up a route for signal processing in LFM pulse based high-performance 𝝋-OTDR, but also has significant potential for applications in other sensing systems using LFM signals.