Low Refractive-Index and Temperature Crosstalk Fiber-Optic Liquid Level Sensor Based on Cascaded Quasi-Microfiber and Double-Cladding Fiber Structure

In this paper, a novel in-fiber modal interferometer for liquid level sensing is proposed and experimentally demonstrated based on the cascaded quasi-microfiber and double-cladding fiber (QM-DCF) structure. The QM is utilized to monitor the change of liquid level with intensity modulation and the part of DCF is always immersed into the liquid and serves to sense the variation of ambient temperature. Then the comprehensive tests are performed and the experimental results show that, due to the massive loss of evanescent field in the area of taper waist, a competitive liquid-level response up to -0.972 dB/mm with high linearity is gained and the calculated detection limit reaches ~ 10μm. Moreover, this cascaded structure is almost immune to the varied refractive index (RI) of liquid especially in the range of 1.33-1.357 RIU and its temperature sensitivity is 0.164 nm/°C but with a fluctuation of <; 0.1 dB. Thus, high intensity-sensitive liquid-level measurement is achieved with near-zero crosstalk in terms of RI and temperature. Besides our sensor with the merits of practicality, low-cost, ease of fabrication is very promising and potential for simultaneous high-discrimination measurement of multi-parameter.