High sensitivity Mach–Zehnder interferometer sensors based on concatenated ultra-abrupt tapers on thinned fibers

This study proposes a simple, cost-effective method to fabricate fiber-based Mach–Zehnder interferometer (MZI) sensors by concatenating two ultra-abrupt fiber tapers together using a fusion splicer. By concatenating, the taper diameter and length ratio is 1:1 that is much greater than that (1:10) by stretching. The refractive index sensitivity is comparable to the MZI sensors based on long-period fiber grating pairs or stretched fiber taper pairs. The MZI fiber claddings are etched to improve the sensitivity of refractive index measurements. The sensitivity is 664.57 nm/RIU (refractive index unit) for the refractive index ranging from 1.3348 to 1.3558, which is 2–6 times greater than those measured by long period fiber gratings (LPFGs) after sensitivity enhancement.