We propose and demonstrate experimentally a direct-detection single-end Brillouin temperature sensing system based on single-photon detector to evaluate the ambient temperature along the sensing link, which is an excellent candidate for the demodulation of frequency shift from Brillouin gain spectrum in traditional Brillouin configurations. In the proposed method, the ratio of the Rayleigh backscattering component and the Brillouin anti-Stokes component is used to demodulate the temperature information along the measured optical fiber link. Proof-of-concept experiment proves that a spatial resolution of 1.2m over 4.2km sensing range with a 1.24°C temperature error can be obtained. Additionally, the proposed direct-detection Brillouin sensor maintains large dynamic range, which boosts its practicability.
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.
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