Tapered multicore fiber interferometer for ultra-sensitive temperature sensing with thermo-optical materials.

An in-line interferometer based on tapered multicore embedded into a flexible thermo-optical material is proposed and investigated, theoretically and experimentally. The device consists of a tapered multicore fiber spliced between two single-mode fibers covered with PDMS, with high thermo-optic coefficient. The temperature sensitivity improvement obtained from PDMS applied on a tapered multicore fiber (TMCF) interferometer has been fundamentally and experimentally verified. The experimental results show the temperature sensitivity can be improved by reducing the tapered waist diameter of TMCF. The sensor exhibits the high sensitivity of 5-25 nm/°C within the decreasing temperature range from 50 °C down to 10 °C. A sequence of simulations and corresponding experiments are performed to clarify the evolution of the interference fading and consequently build the criteria for sensor design and reachable lower limit of temperature sensing. The proposed sensor can be employed as photonic thermometer with ultra-high sensitivity for biological and deep-sea applications, particularly based on the claimed quantitative criteria.

Tapered multicore fiber interferometer for refractive index sensing with graphene enhancement.

An in-line, highly sensitive refractive index (RI) sensor based on a tapered multicore fiber (MCF) structure sandwiched between two single-mode fibers is proposed and demonstrated. The fiber tapering technique was employed to fabricate in-line interferometers based on the multicore fiber. The waist diameter is one of the dominant factors of the intercore coupling. The tapered MCF interferometer is highly sensitive to the surrounding refractive index with a maximum sensitivity of 9194.6 nm/RIU in the RI range of 1.4264 to 1.4278 when the waist diameter is 9 µm. The enhancement of the evanescent field by graphene coating is proved to be able to improve the RI sensitivity further. A graphene-coated MCF interferometer with waist diameter of 9 µm offers the maximum sensitivity of 12617.6 nm/RIU in the RI range of 1.4144 to 1.4159. The experimental data have good agreement with the simulated results.