Fiber optic refractive index sensors through spectral detection of Rayleigh backscattering in a chemically etched MgO-based nanoparticle-doped fiber.

We demonstrate and experimentally validate a fiber optic refractive index (RI) sensor obtained by simply etching a high-scattering MgO-based nanoparticle-doped single-mode fiber in hydrofluoric acid (HF). The fiber has 32.3 dB stronger Rayleigh scattering than a standard fiber, allowing a detection of scattering spectral signatures with an optical backscatter reflectometer, even when the core is exposed to the outer RI. The obtained sensitivity is 1.53 nm/RIU (RI units), measured by correlating the scattering spectra. We prove the possibility of implementing a distributed RI detection (seven locations spaced by 1 mm). The fabrication method for this RI sensor is simplified, since it simply requires etching in an HF bath, without the need of inscribing reflective elements or fabricating microstructures in the fiber.