Novel Interrogation Method for Fully Distributed LCFBG Sensor Based on Microwave Photonic Filtering

A novel interrogation method for linearly chirped fiber Bragg grating (LCFBG) based fully distributed strain sensor which can simultaneously determine strain value and recognize position is proposed and experimentally demonstrated. Compared with the traditional distributed grating interrogation systems by analyzing the reflection spectrum of the LCFBG, the system is mainly based on frequency domain measurement from a microwave photonic filter (MPF) configuration, which has the features of fast responding and high resolution. By using this structure, when distributed strain is applied to the LCFBG, the reflective point on the LCFBG for a certain wavelength as well as the frequency response of the MPF will change. By detecting the resonance frequency shift of the MPF, the strain value can be achieved. Combined with the one-to-one correspondence between the wavelength and the spatial position of the LCFBG, the distributed strain profile along the LCFBG can be reconstructed. In a proof of concept experiment, interrogation of fully distributed grating sensors with ununiform strain distributions is experimentally demonstrated. A spatial resolution of ~0.2 mm over a gauge length of 27mm and a strain resolution of $ < 1\text{u}\varepsilon $ have been achieved.