A high sensitivity temperature sensor exploiting indium fluoride optical fibers is designed and characterized. It is based on a non-adiabatic tapered optical fiber, acting as a Mach-Zender interferometer. The sensitivity of the sensor is predicted via mode analysis, performed with Finite Element Method, and then computing the phase delay between the LP01 mode and the LP02 mode. By considering the effect of the thermal expansion and of the thermo-optical properties of the glass, respectively on the waist length and on the core and the cladding refractive indices, the sensing mechanism is explained. The non-adiabatic tapered optical fiber (Le Verre Fluoré IFG SM [2.95] 7.5/125) sensor is fabricated with Vytran GPX-2400 glass processing system, addressing the difficulties of indium fluoride glass, including its inclination to crystallize, its limited temperature range for fabrication, and its low glass transition temperature. The sensor is characterized in the mid-infrared spectral range with an interband cascade laser, emitting at the wavelength λ = 3.34 µm.
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