We demonstrate a sensing network with 5000 identical ultraweak fiber Bragg gratings (uwFBGs) at equal separations of 100 mm based on optical frequency domain reflectometry. The fiber is 510-m long and includes 5000 uwFBGs with a reflectivity of 0.02% and with identical peak reflection wavelengths of ∼1553.9 nm. With an applied strain from 0 to 600 μϵ on the uwFBGs, this system can unambiguously distinguish the shifts in the wavelengths and the locations of the uwFBGs. Compared with a traditional FBG interrogation method, this technique achieves a high-spatial resolution and a large number of multiplexed uwFBGs. The distinct advantages of the proposed sensor network make it an excellent candidate for distributed strain sensing measurements.
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.
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