Highly accurate slope-assisted distributed fiber strain and temperature sensor based on pseudo-Voigt profile and quartic function.

• Slope-assisted distributed fiber strain or temperature sensor is investigated. • Brillouin frequency shift estimated by different models is compared. • Slope-assisted method based on pseudo-Voigt model has highest accuracy. • A closed-form analytical solution for BFS is presented. • Proposed method can ensure high accuracy and enhance the dynamic range. To improve accuracy in temperature and strain measured by the slope-assisted distributed optical fiber sensor based on Brillouin scattering, the Lorentzian, Gaussian, pseudo-Voigt and Voigt models are used to approximate the measured Brillouin spectra. The results reveal that the pseudo-Voigt and Voigt profiles can give the better approximation than the other two profiles. In view of computational burden, a slope-assisted Brillouin frequency shift (BFS) estimation method based on the pseudo-Voigt model is proposed. To simplify BFS estimation in the slope-assisted method, by fitting the quartic function to the pseudo-Voigt profiles, a slope-assisted method based on the quartic function is proposed and a closed-form analytical solution for BFS is obtained in the method. The computer programs for the slope-assisted methods based on the line, Lorentzian, Gaussian, pseudo-Voigt models and quartic function are written and are used to estimate BFS for the measured Brillouin spectra with different pulse widths and average times along an optical fiber. The results reveal that the line model-based slope-assisted method has a narrow dynamic range. The Lorentzian, Gaussian models-based methods cannot always ensure its accuracy for Brillouin spectra measured in different situations. The method based on the pseudo-Voigt model possesses higher accuracy and wider dynamic range than the line, Lorentzian, Gaussian models-based ones. The quartic function-based slope-assisted method has almost the same accuracy as the pseudo-Voigt model-based one. [ABSTRACT FROM AUTHOR]