Effects of metal coating on the fiber Bragg grating temperature sensing characteristics

Effects of the metal coatings on the fiber Bragg grating (FBG) temperature sensing characteristics were simulated and experimentally investigated. Temperature sensitivity of the coated FBG as a function of the coating material properties was simulated using MATLAB software based on the temperature sensing model. The simulation results show that the elastic modulus, Poisson's ratio, thermal expansion coefficient and coating thickness of the coatings have noticeable impacts on the sensing characteristics of the coated FBG. It is noted that (i) there is an extreme value for the influence of the elastic modulus on temperature sensitivity; (ii) temperature sensitivity increases with the increase of Poisson's ratio and thermal expansion coefficient; (iii) with the increase of the coating thickness, the temperature sensitivity increases first then reaches a plateau asymptotically. To validate the simulation results, several FBGs were coated with copper, nickel, cobalt, copper-zinc, and Ni-ZrO2, and subsequently the associated temperature sensitivities were measured using a network analyzer as well as a water bath. The results show that the simulation results agree well with that of the experiments, with the errors up to 5.49%.