Segmented Fiber Optic Sensors Based on Hybrid Microwave-Photonic Interrogation

In this paper, we propose and demonstrate a novel concept of segmented fiber optic sensors by integrating the fiber Bragg grating (FBG) reflector modality and a hybrid interrogation technique enabled by microwave photonics. As a proof of concept, a radiofrequency Fabry-Perot interferometer (FPI) based on an optical fiber with two FBGs as the two reflectors of the Fabry-Perot (FP) cavity is constructed. By measuring the frequency response of the FPI device followed by a joint-time-frequency-domain analysis, the interferogram of the FPI in the microwave domain and the time-domain signal of the FBGs can be unambiguously reconstructed. Thus, the two elements of the FPI, i.e., the optical fiber connecting the two FBGs (the FP cavity) and the two FBGs (the reflectors), can both be used as sensors, forming a three-segmented sensor device. Experimental results match well with theoretical predictions. Another heterogeneous FPI device with an FBG reflector and the cleaved end facet reflector is shown for measuring salinity and temperature to further demonstrate the proposed technique. The novel concept of segmented fiber optic sensors might find applications in multi-parameter sensing and spatially distributed sensing.