Highly sensitive measurement of surrounding refractive index using tapered trench-assisted multicore fiber

In this study, a surrounding refractive index (SRI) sensor based on tapered trench-assisted multicore fiber (TAMCF) is proposed and experimentally demonstrated. A segment of TAMCF was spliced between two single mode fibers (SMF28). Electric arc discharge technique was employed to fabricate a tapered sensor with a SMF28-tapered TAMCF-SMF28 structure. Numerical beam propagation was used to investigate the benefit of tapering on TAMCF. Tapering allows coupling of light in the center and outer cores, thereby enhancing the sensitivity of the sensor. Two sensors were fabricated with waist lengths of 10 and 15 mm and a waist diameter of 25 mu m. The sensitivity of sensors at different SRI ranges was investigated using a set of honey/water solutions with precisely controlled concentrations. The measured SRI sensitivity was up to 35089.28 nm/RIU (refractive index unit) in SRI range from 1.4430 to 1.4442, which is higher than previously reported studies using other kinds of MCF sensors. SRI sensitivity was enhanced with the increase in waist length of the tapered TAMCF. The fabricated sensors have demonstrated good linearity in terms of spectral wavelength shift versus SRI variations.