Curvature and Temperature Discrimination Using Multimode Interference Fiber Optic Structures—A Proof of Concept

Singlemode-multimode-singlemode fiber structures (SMS) based on distinct sections of a pure silica multimode fiber (coreless-MMF) with diameters of 125 and 55 μm, were reported for the measurement of curvature and temperature. The sensing concept relies on the multimode interference that occurs in the coreless-MMF section and, in accordance with the length of the MMF section used, two fiber devices were developed: one based on a bandpass filter (self-image effect) and the other on a band-rejection filter. Maximum sensitivities of 64.7 nm·m and 13.08 pm/^°C could be attained, for curvature and temperature, respectively, using the band-rejection filter with 55 μm-MMF diameter. A proof of concept was also explored for the simultaneous measurement of curvature and temperature by means of the matrix method.