Fiber-optic Mach–Zehnder interferometric sensor for high-sensitivity high temperature measurement

We present a novel fiber-optic Mach–Zehnder interferometeric (MZI) sensor for highly-sensitive and high temperature measurement. The fiber-optic MZI is constructed using a piece of multimode fiber (MMF) sandwiched between a single mode fiber (SMF) and a sensing tapered SMF. The MMF is used to excite the cladding modes in the sensing SMF. The core mode interferes strongly with the cladding modes in the sensing fiber at the tapered region, generating interference fringes in the transmission spectrum that are sensitive to temperature. Numerical simulation results using the finite-difference time-domain method agree well with the experimental results. Some prototype sensor probes are fabricated and characterized. We measure the wavelength shift of an interference dip as temperature change from room temperature to 850 °C. A sensor prototype with 2 cm sensing length exhibits a sensitivity of 85.8 pm/°C in the temperature range of 100–400 °C and 128.6 pm/°C in the range from 400 °C to 850 °C. This sensor can be further developed as a compact and economic high-temperature sensor for harsh environment application.