Effect of Taper Waist Diameter on the Sensitivity of Multicore Fiber Coupler-Based Temperature and Strain Sensors

This paper analyses the effect of the waist diameter on the sensitivity of different sensors based on non-adiabatic multicore fiber couplers. The sensors have been evaluated for high-temperature and strain measurements. A homogeneous 7-core multicore fiber has been used to fabricate three different coupler sensors based on the tapering technique, using a special CO
₂
laser splicer. The waist length for all cases is 60 mm, while the studied waist diameters are 20 μm, 40 μm, and 60 μm. We report that the central core exhibits sensitivities of 62.1 pm/°C and −5.2 pm/
${\rm{\mu \varepsilon }}$
for temperature and strain, respectively. The evaluated high-temperature range is from 100 °C to 600 °C, and the strain range is from 0
${\rm{\mu \varepsilon }}$
to 3333
${\rm{\mu \varepsilon }}$
. Based on our findings regarding the evaluated waist diameters, we observed that the multicore fiber coupler with a waist diameter of 20 μm exhibits a large sensitivity to strain variations. Conversely, the sensor with a waist diameter of 60 μm demonstrates better sensitivity for temperature measurements. Additionally, we have used fan-in/fan-out optical devices to enable individual access to each core. This allowed us to extend our study and conduct sensitivity analysis in the outer cores.