A study of the temperature sensitivity of fiber Bragg gratings after metallization

In order to embed fiber sensors into metal material, the fiber sensors must be protected. Experiments using electroless plating of a nickel-clad fiber Bragg grating (FBG) have been carried out four times in order to learn its temperature sensitivity and the relationship between temperature sensitivity and plating thickness. In each experiment, the plating thickness and the corresponding temperature sensitivity were measured, thus achieving the temperature sensitivities of nickel-clad FBG with different plating thickness. A technique for FBG surface electroless plating is proposed. The strains and stresses on the nickel-clad FBG under varied temperature are analysed. The theoretical model of the temperature sensitivity of nickel-clad FBG is deduced. The relationship between temperature sensitivity and plating thickness of nickel-clad FBG is analysed in theory and verified by experiment. When plating thicknesses are 1.42, 4.26, 15.625 and 38.35 µm, the temperature sensitivities of FBG, with a wavelength of 1544.06 nm, are 12.1354, 14.3092, 17.9334 and 19.6499 pm °C −1 in theory and the experimental results are 12.09, 13.83, 17.48 and 19.605 pm °C −1 . The results of theoretical analysis match those from experiments. The hysteresis of the wave-shift is discussed with hysteresis disappearing after heat treatment.