Fabrication and thermal characteristics of multilayer metal-coated regenerated grating sensors for high-temperature sensing

Health monitoring of components operating at high temperatures requires the development of new sensors to measure temperature and deformation. A regenerated grating (RG) sensor with titanium (Ti)-silver (Ag)-nickel (Ni) multilayer coatings is fabricated by magnetron sputtering and electroplating processes. Optical and thermal tests are performed to evaluate the characteristics of the Ti-Ag-Ni-coated RG sensor. The shapes of the reflection spectra for the RG are slightly affected by the metallization process. The Ti-Ag-Ni-coated RG sensor exhibits a higher sensitivity than that of the bare RG for temperatures up to 600 degrees C, with good repeatability and stability. It is verified that the titanium coating can achieve good adhesion to the optical fiber and that the silver coating is suitable as a conductive layer for electroplating. An analytical model for the axial strain and radial strain in a multilayer metal-coated optical fiber is proposed. Comparisons of the experimental results and the theoretical predictions show a good agreement below 250 degrees C. These results indicate that multilayer metal-coated RG sensors can be successfully fabricated by combining magnetron sputtering with electroplating and provide great potential for high-temperature sensing.