Liquid refractive index sensors using resonant optical tunneling effect for ultra-high sensitivity

This paper reports the design and analysis of a liquid refractive index (RI) fiber sensor based on resonant optical tunneling effect (ROTE). The device utilizes an optical cavity formed between two angled silver-coated optical fibers to detect the RI changes by measuring the intensity variation of transmission intensity or the wavelength shift of transmission peak. The simulation results show that the intensity-based method could reach a sensitivity of 10−7 RIU (refractive index unit) and the spectrum-based method promises a sensitivity of 81,000 nm/RIU, which are much larger than those of Fabry–Pérot etalons and surface plasmon resonance sensors. With ultrahigh sensitivity, pico-litre sample volume and fiber integration, this sensor may find potential applications in biochemical analysis.