Bend-tolerant fiber sensor based on BOTDR system

Abstract

A simple and inexpensive sensing structure, single mode fiber (SMF) alignment fusion to 62.5 µm stepped index-multimode fiber (SI-MMF), combined with Brillouin optical time domain reflectometry (BOTDR) system, is used as a distributed sensor in the field of structural safety and health monitoring (SSHM) of large infrastructures in terms of its prominent bending resistance. The bend loss principle and influencing factors of the fiber are analyzed, and the bending resistances of different fibers are discussed on the basis of theoretical and experimental comparisons. The bend-tolerant capacity and temperature sensing characteristics of the 5 km sensing structure are measured by using the self-developed frequency-shifted local heterodyne BOTDR system. The results show that the proposed sensing structure has excellent bend-tolerant capacity with a minimum bend radius and temperature measurement error of 1.25 mm and 0.69 °C, respectively, which indicates that the proposed sensing structure has huge potential in the field of SSHM of large infrastructures.