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.
A unique multi-parameter sensor for distributed measurement of temperature and strain based on spontaneous Brillouin scattering in communication optical fiber is proposed, which is an excellent candidate for the crosstalk effects in conventional Brillouin sensing network. In experimental section, the discrimination of strain and temperature is successfully demonstrated by analyzing the unequal sensing coefficients of the Brillouin frequency shifts generated by different acoustic modes. The Brillouin frequency shifts of first two three peaks are successfully measured to discriminate the strain and temperature with an accuracy 19.48με and 0.93°C in 10km sensing range. The proposed distributed Brillouin optical fiber sensor allows simultaneously temperature and strain measurement, thus opening a door for practical application such as smart grid.
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