High-Sensitivity Distributed Temperature Sensor Based on Brillouin Scattering with Double-Coated Single-Mode Fibers

A high-sensitivity distributed temperature sensor based on Brillouin scattering is theoretically proposed and experimentally demonstrated. Double-coated single-mode fibers (SMF) are used as sensing fibers to improve the temperature sensitivity of Brillouin frequency shift (BFS). The thermomechanical model of double-coated fiber based on Lame formula is established, and the reasons for improving the BFS temperature sensitivity are analyzed. In the simulation, the BFS temperature sensitivity is improved with increasing of outer coating thermal expansion coefficient, Young's modulus, and radius, but the effect of Poisson's ratio can be ignored. In the experiment, four kinds of optical fibers are designed to verify the theoretical results, including a single-coated fiber and three double-coated fibers. The outer coating radii of double-coated fibers are 450 μm , 1000μm and 1500μm , respectively. The BFS temperature sensitivity of these fibers are calculated to be 1.07 MHz/°C, 3.28 MHz/°C, 4.57 MHz/°C and 6.04 MHz/°C within the temperature range of -30 to 40 °C, respectively. With a spatial resolution of 1.5 m, the maximum BFS temperature sensitivity of the double-coated SMFs is measured, which is about 6 times higher than that of single-coated SMF, achieving a maximum measurement error less than 0.05 °C.