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A novel Mach–Zehnder Interferometer (MZI) formed by cascading two vase-shaped tapers in a single mode fiber (SMF) is proposed in this work. The vase-shaped taper is fabricated by fusion splicing a fiber sphere with a fiber tip by applying strong arc discharge. The curvature sensing characteristic of the proposed vase-shaped taper-based MZI is experimentally investigated, displaying that the interference spectrum has a blue shift with the increase of applied curvature. The sensor realizes a large range measurement of curvature from 0.9284 m −1 to 4.0470 m −1 with sensitivities of −8.41 nm/m −1 and −16.72 nm/ m −1 in the curvature range of 0.9284 m −1 to 2.4564 m −1 and 2.6025 m −1 to 4.0470 m −1 , respectively. Its temperature-curvature cross-sensitivities are −0.0021 m −1 / °C and −0.0011 m −1 / °C in the two measurement ranges, which are lower than the corresponding curvature resolutions which are 0.0024 m −1 and 0.0012 m −1 . The proposed sensor exhibits the advantages of low cost, negligible temperature cross-sensitivity, fine curvature sensitivity and large measurement scale. [ABSTRACT FROM AUTHOR]

All-fiber Mach-Zehnder interferometers (MZIs) working as curvature sensors have been attracting increasing attention. However, previously reported MZI-based curvature sensors with offset or abrupt-taper structures suffer from weak mechanical strength and low curvature sensitivity. In this letter, a robust and highly-sensitive MZI-based curvature sensor formed by cascading two up-tapers in a single mode fiber (SMF) is proposed and experimentally demonstrated. By optimizing structural parameters of the MZI both in simulation and in experiment, a high quality interference spectrum with a maximum extinction ratio (ER) of around 20 dB is obtained, which is crucial in curvature sensing with spectrum intensity variation and interference dip identifiability being considered. Experimental results show that a high curvature sensitivity of −35.41 nm/m −1 is obtained in the range of 0.6846 m −1 – 1.0606 m −1 , which is 2.4 times higher than that of the interferometer with single-mode-multimode-single-mode (SMS) structure. The two up-tapers, featured by great mechanical strength, are fabricated by only fusion pushing together a whole SMF without cleaving procedure, contributing to excellent repeatability and consistency in the sensor fabrication process. Such an all-fiber sensor exhibits advantages of simple configuration, ease of fabrication, excellent mechanical strength, low cost, and high curvature sensitivity. [ABSTRACT FROM AUTHOR]