Fully Distributed Strain Sensor Based on a Dual-Loop Optoelectronic Oscillator

A high spatial resolution fully distributed linearly chirped fiber Bragg grating (LCFBG) sensing method based on a dual-loop optoelectronic oscillator (OEO) is proposed. Compared with the traditional distributed grating interrogation system, this work achieves fully distributed strain sensing based on the sensing principle of OEO and the wavelength-position one-to-one mapping mechanism in LCFBG. The interrogation method is simple and fast by processing the sensing information in the RF domain. With the help of the dual-loop OEO, the frequency fluctuation of the signal is only 1.8% of that of the single-loop OEO, which enhances the stability of the system and thus improves the measurement accuracy. To verify the feasibility of the proposed method, a non-uniform distributed strain sensing experiment was performed. The results show that a high spatial resolution of 0.29 mm and a sensing resolution of $0.6~\mu \varepsilon $ were achieved over a length of 53 mm. The system provides a feasible solution for structural health monitoring (SHM).