Distributed strain interrogation with a linearly chirped fiber Bragg grating based on an optoelectronic oscillator

A novel distributed strain sensor method, to the best of our knowledge, based on a linearly chirped fiber Bragg grating (LCFBG), which can simultaneously determine the strain value and ascertain the position, is proposed and experimentally demonstrated. Different from the traditional distributed grating interrogation system via analyzing the optical spectrum of an LCFBG, the system is mainly based on the frequency domain measurement by using an optoelectronic oscillator (OEO) structure, which has the characteristics of fast response and high resolution. Based on this structure, when the distributed strain is applied to the LCFBG, the frequency response of the OEO for a reflective point of a certain wavelength will change. The strain value can be obtained by detecting the frequency shift of the OEO. Combined with the one-to-one correspondence between the wavelength and the spatial position of the LCFBG, the exact position of the strain point can be determined. In a proof-of-concept experiment, interrogation of fully distributed grating sensors with nonuniform strain distributions is demonstrated experimentally. A spatial resolution of ∼3µm over a gauge length of 53 mm and a strain resolution of <1µε have been achieved.