Improvement on refractive index sensing by exploiting the tapered two-mode fibers
Micro fibers are known as optical waveguides with diameters close to the wavelength of transmitted light. Owing to its large fractional evanescent fields, a micro fiber can guide light with enhanced light-material interaction, which makes it a versatile platform for optical sensing on micro/nanometer scale with special advantages including small footprint, fast response, and high spectral sensitivity. Refractive index (RI) sensing with micro fibers has been engaged in a wide range of applications especially in biochemical analysis, environmental monitoring, and industry process monitoring. In fact, the sensitivity to the surrounding refractive index in such fields often falls in the range of 10-4-10-5 refractive index unit (RIU) for instruments, which is a challenge to the conventional micro fibers.