Temperature and strain sensing properties of the zinc coated FBG

Fiber Bragg grating (FBG) was metal coated and the associated sensing properties were tested. In the metal coating, FBG was firstly coated with a thinner nickel conductive layer by chemical plating, and then electroplated with a thicker zinc coating. Surfaces of the metal coated FBGs are smooth, uniform and compact, without any obvious defects. Temperature and strain sensing results show that temperature sensitivity of the zinc coated FBG can be enhanced about 5 times than the bare FBG, and the wavelength shift under the applied load shows a linear trend as well. In order to further study the thermal sensing properties, three zinc coated FBGs and a bare FBG were compared in subjecting to the transiently changed temperature. Results indicate that the response tendency of the zinc coated FBG to a transient temperature change is similar to that of bare FBG, which could be attributed to the small thermal capacity and thickness of the metal coating. In addition, the central wavelength stability of the metal coated FBG is lower than that of the bare FBG due to the high temperature sensitivity.