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Strain-insensitive optical fiber Mach-Zehnder interferometric temperature sensor

A fiber Mach-Zehnder interferometer (MZI) constructed by concatenating a micro cavity in the fiber core and a taper is proposed and applied for temperature sensing. Femtosecond laser micro-machining technique and fusion splicing technique are utilized to fabricate the micro cavity in a single mode optical fiber core. The fiber taper is fabricated by electric arc-discharge with a conventional fusion splicer. A sensitivity of 68 pm/°C is obtained at the temperature range of 200-400°C. The interferometer is also characterized by different strain.It exhibits very low strain sensitivity because only low order cladding modes are excited by the micro cavity, which is a desirable merit for temperature sensor to eliminate cross sensitivity to strain.