Abstract
Fiber-optic distributed sensors are candidates for sensing elements of structural health monitoring that improves reliability and safety of composite structures. Among fiber-optic sensors, Brillouin Optical Time Domain Reflectometer (BOTDR) can measure strain at an arbitrary position of a sensing fiber by detecting the variation in Brillouin frequency shift. In the case of the measurement based on the Brillouin frequency shift, however, it is difficult to detect the damage leading to nonuniform strain distributed within the length of the spatial resolution of BOTDR along a fiber. In this paper, we propose a new technique to detect the nonuniform strain changing sharply within the length of the spatial resolution. This technique is based on the fact that the profile of Brillouin gain spectrum changes depending on the strain distribution. We confirmed the fact theoretically and experimentally. The applicability of BOTDR to detecting the damage in composite structures was improved.
