Research on the Durability of Metal-Packaged Fiber Bragg Grating Sensors

Compared to conventional adhesive packaging for fiber Bragg grating (FBG) sensors, metal packaging is considered a new and robust method with excellent advantages such as stability and resistance to high and low temperatures. Current research mainly focuses on metal coating methods, the enhancement of temperature sensing characteristics, and the method of welding onto the substrate. However, the durability of the metal packaging, which determines the measurement accuracy and lifetime of a metal-coated FBG sensor, has been ignored. This letter introduces our long-term investigation of the durability of three metal-packaged FBG sensors over the past four years. The metal packaging process for the bare FBGs and sensor substrates, the experimental design, and the test methods are presented. The research results show that the central wavelength of a prestretched metallized FBG decreases due to natural aging after 10 months and that its sensing capabilities, such as its negative strain detection capacity, sensitivity, linearity, and repeatability, significantly degrade after 48 months, revealing a deficiency in our current understanding.