Highly sensitive Ni-Cu duplex metal coated fiber Bragg grating temperature sensor

Fiber Bragg grating (FBG) sensors have great potential for measuring temperature or strain and even detecting fractures in metal materials. The use of metal coatings is one of the most efficient methods for protecting FBG sensors. This article describes a new type of etchless duplex metal coating especially developed for FBG for sensing purposes. Copper was chosen as the conductive layer for deposition on FBG by electroless plating and nickel was then coated on top of the copper by electro deposition. Thermal shock testing confirmed that the copper coating had excellent surface adhesion to the FBG. SEM images revealed that the duplex coating has smooth boundaries. To compare the temperature sensing performance of Ni-Cu-coated FBG with the Ni-coated FBG, two samples were thermally tested from 30 to 100 degrees C in this study. The results indicate that Ni-Cu-coated FBG sensor not only has the better temperature repeatability but also has the higher temperature sensitivity.