Mechanical strength and thermally induced stress voids of carbon-coated optical fibers prepared by plasma enhanced chemical vapor deposition method with different hydrogen/methane ratio

Carbon coatings are deposited on the outer surface of the glass fiber using the plasma enhanced chemical vapor deposition method with six different hydrogen/methane (H2/CH4) ratios. As a result, the carbon coating structure exhibits a graphitic phase incorporated with a disordered phase, and the amount of the disordered phase increases with increasing H2/CH4 ratio. On the other hand, the roughness of carbon coatings decreases with increasing H2/CH4 ratio. If the H2/CH4 ratio is not larger than 2, the tensile strength of carbon-coated optical fibers increases with increasing H2/CH4 ratio, while the linear density of thermally induced stress voids decreases. Nevertheless, when the H2/CH4 ratio ranges from 2 to 3.33, the tensile strength of carbon-coated optical fibers slightly decreases with the H2/CH4 ratio, and the thermally induced stress voids are less found on the carbon coating. The method to acquire the high tensile strength of carbon-coated optical fibers and/or to minimize the thermally induced stress voids on the carbon coating is proposed.