Highly Sensitive Bi-conically Tapered Fiber Sensor with Wavelength-dependent Sensitivity

We studied the dependence of sensitivity of a biconically tapered optical fiber sensor on the wavelength of light used, and experimentally demonstrated refractive index sensitivity of about 11000 nm/RIU near 1570 nm. We predict that tapered fiber refractive index sensors with sensitivities exceeding 50000 nm/RIU can be developed. We attribute the enhanced sensitivity mainly to the nonlinear variation of the difference in mode propagation constants with wavelength. Such high sensitivity with low cost and simplicity makes tapered fiber refractive index sensors good candidates for sensing applications in medical diagnosis, food safety, environmental monitoring, and biodefense.