High spatial resolution multiplexing of fiber Bragg gratings using single-arm frequency-shifted interferometry

We demonstrate a high spatial resolution multiplexing scheme for fiber Bragg grating (FBG) sensors based on single-arm frequency-shifted interferometry (SA-FSI). The SA-FSI system uses an incoherent broadband source, a slow detector, and an electro-optic modulator (EOM). By sweeping the frequency of EOM and taking the fast Fourier transform (FFT) of the interference signal, we resolved the locations of FBGs distributed both in parallel and in series along fiber links despite their reflection spectral overlap. Eighteen weak FBGs (~5% reflectivity) separated by ~0.1 m were clearly resolved experimentally, sweeping EOM modulation frequency in the range of 2-11 GHz.