Modeling analysis and experimental study on epoxy packaged FBG sensor for cryogenic temperature measurement

The Fiber Bragg grating (FBG) is a kind of temperature-sensitive optical device that has irreplaceable advantages for cryogenic measurement. In this work, a model-driven FBG temperature sensor packaging method was proposed to improve the sensor's sensitivity and linearity and predict the sensor's response time in cryogenic. The numerical model explores the relationship between the sensor's size and performance. The packaging method can prepare high-precision samples of multiple sizes and provide experimental support for this study. The accuracy of the model is verified by comparing the calculated results with the results of a warming-up experiment and a liquid nitrogen experiment. The results show an improvement in sensitivity and linearity, and the model can also be used to predict the characteristics of FBG coated with epoxy resins at cryogenic temperature. The sensor with a thickness of 0.2 mm has a sensitivity and linearity of 26.6 pm/K and 0.997, respectively, in the range of 80 K-270 K.