Characterization of metallic-packaging fiber Bragg grating sensors with coated and bare fibers

Metallic packaging of fiber Bragg grating (FBG) sensors is developed using the ultrasonic welding method. Both polyimide-coated fiber and bare fiber could be bonded well to aluminum alloy substrate using Sn-Bi alloy. Two kinds of metal-packaged FBG sensors, coated FBG and bare FBG, are characterized for studying the thermal sensitivity, strain response, short-term creep, and temporal temperature response. Both FBG sensors showed increasing sensitivity with temperature from −40°C to 80°C. The metal-packaged coated FBG sensor displayed relative strengths in strain stability, repeatability, creep, spectra shape, and temperature response when compared with the bare one. Moreover, the boundaries between optical fiber and metal alloy are intact, and cross-sectional scanning electron microscope micrographs clearly illustrated that metal alloy coated well with the coated and bare fiber.