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

Abstract

AbstractLinear 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.