OS09W0194 Detection of strain variation based on Brillouin spectrum shape changing

Abstract

Fiber-optic distributed sensors, which can measure physical variables as a function of position along an optical fiber, are regarded as attractive sensors for structural health monitoring (SHM). Brillouin optical time domain reflectometry (BOTDR) can be used for measurements of strain distributions on structures, such as aircrafts, ships and bridges. In the BOTDR system for strain measurements, a pulsed light is launched into an optical fiber and the Brillouin backscattered light is measured. A short pulse is required to improve the spatial resolution. However, the measurement accuracy of BOTDR extremely becomes worse when the pulse width is less than 10 ns. When using 10 ns pulse, the accuracy and the spatial resolution are about ±30με and 1 m, respectively. This fact puts limitations on its applicability to SHM, because it is difficult to detect strain perturbation within the length of the spatial resolution. In this study, we developed a new technique with BOTDR to detect inhomogeneous strain fluctuating sharply within the spatial resolution. This technique is based on the fact that the profile of the Brillouin spectrum changes depending on strain distributions. We confirmed the dependency of the Brillouin spectrum on the strain distributions theoretically and experimentally.