Thermally induced stress voids in hermetically carbon-coated optical fibers with different coating thickness

Abstract

The thermally induced stress voids in carbon-coated optical fibers are investigated. Ten samples of carbon-coated optical fibers with different coating thickness are prepared using the plasma-enhanced chemical vapor deposition method. The carbon structure exhibits a larger amount of graphite-like phase and a smaller amount of disordered diamond-like phase. After these fibers are immersed in the liquid nitrogen for 1 day, thermally induced stress voids propagated along the fiber axial direction are found. It is believed that stress voids are caused by the thermally induced maximum tangential stresses. The stress voids slightly decrease with increasing the coating thickness in the beginning, and then increase. The carbon-coated optical fiber with a coating thickness of approximately 255 nm induces the minimum number of stress voids. Nevertheless, the stress voids become larger and even in-line cracks when the coating thickness is equal to or larger than 800 nm.