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Brillouin frequency shift (BFS) and Brillouin power change (BPC) and the core refractive index of the sensing fiber vary linearly with thermal formations in the medium. In this study, a novel Brillouin Coherent detection based distributed temperature and thermal strain sensing model depending on the core refractive index dependencies of BFS and BPC has been proposed. Using this model, core refractive index dependencies of BFS and BPC have been theoretically analyzed and corresponding simulations have been performed, accordingly. In this research, for 20 °C – 39.44 °C temperature range of the sensing fiber, refractive index of the fiber core changes from 1.44183 to 1.44202. Moreover, BFS and BPC values along the sensing fiber have been obtained as 43.80 MHz, 62.05 MHz and 66.92 MHz and 10.44 %, 13.04 % and 13.73 % versus core refractive index values of 1.44193, 1.44200 and 1.44202, respectively. Nevertheless, RMS error values of BFS and BPC have been computed for specific fiber regions along the sensing fiber and then using the interpolation method, linear and quadratic equations of the RMS curves have been derived. According to the results of the simulations and the equations, average values of the frequency and power RMS have been attained as ~ 1.60 MHz and ~ 0.26 %, respectively. Furthermore, quadratic equations related to the core refractive index dependencies of Brillouin parameters and the cubic equations relative to the temperature and thermal strain resolutions of the system have been produced by utilizing interpolation and curve fitting methods. Consequently, temperature and thermal strain resolutions of the system have been calculated as ~ 0.76 °C and ~ 46.80 μɛ for the entire length of the sensing fiber, respectively..
Brillouin Coherent detection, Distributed sensing, Core refractive index of optical fiber, Brillouin frequency shift RMS, Brillouin power change RMS, RMS error value.
ABDURRAHMAN GÜNDAY, Computational analysis of the core refractive index dependencies of Brillouin frequency shift and Brillouin power change in Brillouin coherent detection based distributed sensing systems, Optoelectronics and Advanced Materials - Rapid Communications, 12, 9-10, September-October 2018, pp.502-511 (2018).
Submitted at: March 21, 2018
Accepted at: Oct. 10, 2018