Thermal characteristics of FBG sensors at cryogenic temperatures for structural health monitoring

Generally, many previous researches conducted using FBG sensors were based on the assumption that the coefficient of thermal expansion (CTE) and the thermo-optic coefficient (TOC) of FBG sensors are constants. However, they should be considered variables for higher accuracy when FBG sensors are applied to circumstances with temperature changes. In this paper, CTE and TOC of FBG sensors were precisely investigated from ambient room temperature (293 K) to cryogenic temperature (113 K). For this purpose, a new non-linear relationship between the wavelength shift and temperature change was proposed. From the test results, it was successfully investigated that the sum of CTE and TOC had a non-linear dependency on temperature changes and varied from 5.9×10^-6 /K (293 K) to 1.6×10^-6 /K (113 K).