A fiber refractive index (RI) sensor based on a Mach–Zehnder interferometer (MZI) formed by sandwiching a thinned
taper between two abrupt tapers. The abrupt tapers and the thinned taper are easily fabricated by a commercial fiber
fusion splicer and a homemade tapering machine, respectively. The sensor has been experimentally demonstrated for RI
sensing by monitoring its spectral shifts. The experimental results show that the sensor with a thinner taper has higher
sensitivity due to the strong evanescent field interaction. A sensitivity of 3808.4 nm/RIU (refractive index unit) is
obtained, which is about 100 times higher than that of the conventional taper-based MZI sensors.
We propose a novel refractive index (RI) sensor based on a fiber Mach-Zehnder interferometer formed by large lateral offset fusion splicing between two abrupt tapers. The cladding modes are efficiently excited by transmitted light in the large misalignment junctions. The RI sensitivity of the sensor to surrounding RI change is measured, and the sensitivity of 100 nm/RIU is obtained, which is three to six times higher than that of fiber structures with only a pair of tapers or two offset junctions. Moreover, the sensor is made by a low-cost fabrication method. Thus, the proposed structure is beneficial to the RI sensing applications.