Thermal stability of carbon/polyimide coated optical fiber dried in hydrogen atmosphere

Manufacturing of polyimide-coated special optical fibers involves multiple steps of polyimide curing, including so called “drying” the fiber after draw. In this work, a fiber with carbon/polyimide coating is dried in a hydrogen atmosphere, and a complex analysis of the fiber characteristics (mechanical, optical, and thermal) is performed. Drying in hydrogen leads to an increase in strength of the carbon/polyimide coating and decreases a number of defects along the length of the fiber. The fiber strength analysis was performed in the framework of the Weibull distribution. No adverse effects of hydrogen on optical losses had been found at the operating wavelengths of the single-mode fiber at 1310 and 1550 nm. The temperature stability has been analyzed via thermogravimetry for the fiber samples taken before and after the drying in air and hydrogen environments. The activation energies were calculated by Kissinger method. Per the performance acceptance criteria, the upper use temperature of the hydrogen atmosphere dried coating reach 397 °C, while for the air-dried fiber it is just 215 °C. Thus, drying carbon/polyimide coated optical fibers in hydrogen atmosphere provides a promising improvement, which allows further use of these fibers in harsh environments.