Ultra-Sensitive Optical Fiber Glucose Sensor Based on In-Fiber MZI With Vernier Effect

In this article, an ultra-sensitive optical sensor based on vernier effect for glucose concentration measurement is reported. First of all, the structure of lateral offset single side-hole optical fiber (SSHF) is designed, which can ingeniously excite two integrated parallel Mach-Zehnder interferometers (MZIs) with significantly different free spectral ranges (FSRs). Then, according to the optical path difference (OPD) theory, a novel FSR regulation scheme is proposed to solve the problem that the FSRs of two parallel MZIs are quite different. Finally, two integrated parallel MZIs with similar FSRs are constructed, which are respectively used as reference MZI and sensing MZI, and then vernier effect is formed in this in-fiber structure. An ultra-high refractive index (RI) sensitivity of more than 10, 0000 nm/RIU has been confirmed theoretically and experimentally. In addition, this ultra-sensitive configuration is used for direct measurement of clinically relevant glucose concentration. In the linear range of 0–30 mM, the glucose sensitivity is up to −2.47 nm/mM. The sensing configuration behaves the merits of simple preparation, high sensitivity and compact structure, and has great application potential in biochemical analysis, clinical diagnosis, dynamic process monitoring and other fields.