Thin-Core Fiber Taper-Based Multi-Mode Interferometer for Refractive Index Sensing

We demonstrate a thin-core fiber (TCF)-based hybrid modal interferometer for high-sensitivity refractive index (RI) sensing. It mainly consists of a tapered TCF with an air bubble fabricated by the arc discharge technique using a fusion splicer machine. Due to mode mismatch and the tapering of the TCF, high-order cladding modes are excited, which can be used for high-sensitivity index sensing. The selected two interference dips of the sensor can obtain the index sensitivities of 370.37 and -72.22 dB/RIU in the RI range from 1.333 to 1.3799. Using the differential intensity demodulation method, a total index sensitivity as high as 442.59 dB/RIU can be achieved. Featured with high sensitivity, linear response, small size, ease of fabrication, and low cost, the proposed sensor may have various applications in biochemical sensing field.