Characterization of vibration relative amplitude in direct detection Phi-OTDR using variable gain method

摘要

Vibration relative amplitude characterization has always been a tough problem in direct detection phase-sensitive optical time-domain reflectometry (Phi-OTDR) system due to the nonlinear relationship between the optical intensity and vibration amplitude. In this paper, a novel variable gain method is proposed to characterize the relative amplitude of external vibration. The mathematical model of Phi-OTDR is established, and the influence of external vibration on detected coherent Rayleigh back-scattering light in a single-mode fiber is simulated. Then, the vibration signals of different amplitudes imposed on the sensing fiber are further investigated, and the relationship between the interference amplitude peak power and vibration amplitude is derived. On the basis of the theoretical analysis, the variable gain method is carried out and implemented in Phi-OTDR system. The experimental results demonstrate that the calibrated interference peak power increases linearly with the applied vibration amplitude, and a high correlation coefficient (R-2 = 0.93071) for linear fitting is obtained. (C) 2019 Elsevier Ltd. All rights reserved.