Reflector-less refractive index sensors based on etched-tapered high-scattering single-mode optical fibers

Reflector-less refractive index (RI) sensors employ simple optical fiber strictures for the accurate detection of RI changes. They operate in absence of any reflective element such as gratings, filters, interferometers while maintaining the form factor of a reflective probe; the RI dependence is encoded in the Rayleigh backscattering signatures, and is interrogated using optical backscatter reflectometry. In this work, we present a new reflector-less fiber-optic sensor based on two-steps: (1) tapering an optical fiber, followed by (2) rapid etching of the fiber. The combination of the two steps allows obtaining significant advantages in terms of manufacturing, making the process simpler and increasing the distribution of the refractive index detection. The sensitivity obtained is up to 110.9 GHz/RIU (refractive index units), with the possibility of detection over a length of 2.1 mm, with 0.035 mm average spatial resolution over distributed RI sensing.