Mitigation of interference fading in coherent Φ-OTDR utilizing positive and negative frequency bands with intradyne detection

Abstract

The performance of the phase-sensitive optical time-domain reflectometry (Φ-OTDR) system can be significantly enhanced by detecting larger bandwidth of Rayleigh backscattered signal. However, the detection bandwidth is often constrained by the limitations of electronic components when only single-sideband probe signal is used. To address these challenges, we proposed to use intradyne detection that combines positive and negative frequency bands to eliminate the interference fading and improve the signal-to-noise ratio (SNR) of the recovered disturbance signal. In this study, we employ a Mach-Zehnder modulator (MZM) to generate double-sideband probe signal and intradyne detection to double the available bandwidth of the Φ-OTDR system. By combining the positive and negative frequency bands, we experimentally demonstrate that the interference fading can be effectively mitigated at a sampling rate of 250 MSa/s after intradyne detection. The strain sensitivities of 47.5 $p\epsilon /\sqrt{Hz}$ is achieved in 5 km fiber length with 2.5 m spatial resolution.