Non-linear temperature dependence of Bragg gratings written in different fibres, optimised for sensor applications over a wide range of temperatures

Abstract

Temperature measurements have been made by using fibre Bragg gratings (FBGs) written in a range of fibres and detailed data on their characteristics are presented. The data are fitted to polynomials that may be used in the calibration of temperature measurements with these types of gratings in automated systems. Issues of precision in such measurements from room temperature to 500 °C have been considered using several gratings of type I and IIA written in three different photosensitive fibres, taking into account the non-linear temperature response of the fibre Bragg gratings. Comparisons between the linear and the higher order polynomial regression showed a better performance in calibrated temperature measurement applications when the non-linear temperature coefficients are included, yielding an acceptable rms error of less than or comparable to 1.9 °C, compared to linear regression, with the rms error range of 3.3–7.5 °C for the various gratings studied, over the whole measurement range.