Measurement of distributed refractive index through Rayleigh backscattering spectra detection using a U-bent common fiber

We propose and experimentally validate a distributed refractive index (RI) sensor obtained by simply bending a piece of standard single mode fiber (SMF) to a radius of curvature in several millimeters with intact buffer coating. The RI of the external medium surrounding the U-bent optical fibers is measured by the wavelength shifts of the local Rayleigh backscattered spectra when the RI ranges from 1.3330 to 1.3773. To demonstrate the ability of distributed RI sensing based on the proposed method, this presented sensing element is employed to measure multipoint RI variations at the same time. The sensitivities are about 19.61nm/RIU (RI units), 27.59nm/RIU and 39.08nm/RIU in the proposed structure, respectively.