Simultaneous temperature and strain sensing using few-mode fiber in a single-ended BOTDA system

Few-mode fibers contain a limited number of orthogonal modes, and the Brillouin frequency shift of different modes has different sensitivities to temperature and strain, which provides the possibility of realizing multi-parameter sensing. This paper proposes a novel single-ended Brillouin optical time domain analysis (BOTDA) sensing system that uses Rayleigh backscattered light in the fiber as the probe light, and uses a four-mode graded-index few-mode fiber (4GI-FMF) and a photonic lantern to realize two-parameter sensing. The mechanism of single-ended BOTDA based on FMF is investigated, the modes of 4GI-FMF and the principle of two-parameter measurement are analyzed, and an experimental setup utilizing single-ended BOTDA system with 4GI-FMF is constructed. The performance of the sensing system is analyzed by characterizing and evaluating the Brillouin scattering spectral of different modes and the sensitivity of Brillouin frequency shift to temperature and strain. The proposed sensing system realized reliable temperature and strain discrimination on a 1 km long 4GI-FMF, with temperature and strain accuracies of 1.9 degrees C and 43.7 mu epsilon, respectively.