Ultra-sensitive fiber optic sensor for glucose concentration measurement based on Vernier effect in cascaded Mach–Zehnder interferometers

Abstract In this paper, a fiber optic glucose concentration sensor based on cascaded Mach–Zehnder interferometers (CMZIs) was proposed and experimentally verified. Two single-mode fibers (SMFs) with slightly different tapering lengths and as well free spectral ranges (FSRs) were obtained through the melt-drawn cones technique and then were cascaded together to achieve the Vernier effect (VE). Experimental results showed that the measurement sensitivity of glucose concentration based on a single tapered SMF was 0.0494 nm (mmol l −1 ) −1 . Furthermore, the measurement sensitivity based on the cascaded tapered SMFs was enhanced by 4.86 times to an ultra-high level of 0.2402 nm (mmol l −l ) −1 . The resolution reached 0.083 mmol l −1 . The refractive index sensitivity reached 9066 nm/RIU. The resolution reached 2.21 × 10 −6 RIU. In addition, the proposed glucose concentration sensor based on CMZIs shows good hysteresis. In conclusion, the designed sensor, showing the merits of easy to fabricate, high sensitivity, and high detection resolution, could be used to monitor the tiny variation in glucose concentration.