Highly-sensitive fiber Bragg grating temperature sensors with metallic coatings

Temperature monitoring is an important task in temperature engineering to ensure the safety of equipment, where high-sensitivity and high-reliability sensors are required to provide real-time and accurate temperature information. Direct-write FBG fiber optic sensors have good temperature sensitivity and good temperature resistance, but bare FBGs are fragile. Four kinds of metal coatings were prepared on the surface of the optical fiber by chemical deposition and electroplating, and the grating was directly written by femtosecond laser. The thermal characteristics of the sensors were investigated. The metal coating sensor has higher sensitivity than that of the bare FBG sensor, because it can improve the temperature sensitivity of FBG sensor is more than twice times. The reflectance spectrum of the sensor does not change significantly from room temperature to 800 °C. An analytical model of temperature sensitivity of metal coated optical fiber is proposed and four kinds of electroplated metal FBG sensors are tested respectively. The experimental results are in good agreement with the analytical model. The results show that metal coated FBG sensors have great potential for temperature measurement or temperature compensation in temperature engineering by rationally selecting metal coating with different material properties.