The signal characteristics of reflected spectra of fiber Bragg grating sensors with strain gradients and grating lengths

Among the numerous types of fiber optic sensors, FBG sensors are currently the most actively studied sensors due to their good multiplexing capabilities. The demodulation method of FBG sensors is based on detecting the wavelength shift of their sensor peaks. Properties such as strain, temperature, etc. can be measured simply by detecting them. However, the signal stability of FBG sensors can be influenced by strain gradients induced by structural geometry or cracks on the surface when FBG sensors are embedded into or attached on the structure. In this study, the signal characteristics of reflected spectra of FBG sensors were verified under strain gradients and the correlation between the grating length of FBG sensors and strain gradients were investigated quantitatively. From the experimental results, the optimum working range of the FBG sensors, where FBG sensors could be used without split of the sensor peak, was shown when they were under strain gradients.