High-temperature resistance weak fiber Bragg grating array fabrication

Abstract

Polyimide coated weak fiber Bragg grating array (PI-wFBGA) fabricated online by drawing tower overcomes the temperature limitation of conventional acrylate coating, and has broad application prospects in high-temperature environments. However, the periodic refractive index modulation of PI-wFBG is weak and rapidly decays or even erases in high temperature, indicating poor high-temperature resistance. In this paper, we report the design of a high-temperature resistance wFBGA based on PI-wFBGA fabricated online by drawing tower, which uses post hydrogen-loading and low-temperature annealing to improve its high-temperature resistance. Activated by thermal energy, hydrogen molecules react chemically with the germanium or silicon-related defects in the glass structure of the optical fiber to produce hydroxyl groups. When two hydroxyl groups combine, they form molecular water, which is a key factor in enhancing the high-temperature resistance of PI-wFBG due to its high stability and low diffusion. After annealing the post-hydrogen-loaded PI-wFBGA at 200℃ for 180 min and then removing the residual hydrogen molecules inside the fiber, the mechanical strength of the fiber remains unchanged. The high-temperature resistance PI-wFBG can operate at 350℃ for more than 40 days and have good temperature consistency in the high and low temperature cycle at 400℃. Changing the temperature and time of annealing, the experimental results show that the annealing of post-hydrogen-loaded PI-wFBG at 200℃ for 120 min is an optimal annealing method considering both the high-temperature resistance and mechanical property of high-temperature resistance PI-wFBG, which can realize the reliable use of PI-wFBGA in the temperature resistance range of polyimide coating.