Two-mode fiber Mach-Zehnder interferometric temperature sensor in the 50 °C-650 °C range

In this work a two-mode fiber Mach Zehnder interferometer (TMF-MZI) temperature sensor in the 50 - 650 degrees C range is successfully demonstrated. The sensor design incorporated a tapered fiber with dimensions of 20 mm/20 mm/20 mm for the down-taper, waist-length, and up-taper, respectively, while the waist-diameter was set to 30 mu m. Around this taper dimensions, multiple geometric configurations were explored in this research, and it was found that devices with a spectral period around 20 nm held the most favorable spectral characteristics, avoiding the appearance of shorter spectral ripples at high temperatures. The sensor exhibited consistent and repeatable behavior, maintaining its spectral characteristics throughout multiple heating and cooling cycles. The sensor interference spectrum exhibits a consistent wavelength shift through 1350-1700 nm, such shift fits a linear function with an R-square value of similar to 0.985 and a sensitivity of 70 pm/degrees C. The simple fabrication, low cost, and stability of the optical response make this sensor relevant for high-temperature measurements.