Characteristics of carbon coatings on optical fibers prepared by plasma enhanced chemical vapor deposition using different argon/methane ratios

The effect of argon/methane ratios on the characteristics of carbon coatings on optical fibers prepared by plasma enhanced chemical vapor deposition is investigated. The argon/methane ratios are selected at 0, 1, 2, 4, 6, and 8. Results show that if the argon/methane ratio increases from 0 to 4, the deposition process is mainly sustained by the Penning effect. The Penning effect enhances the dissociation of the hydrocarbon gas molecules. The carbon coating shifts to the graphite-like carbon and the surface of the carbon coating becomes smoother. As the argon/methane ratio increases from 4 to 8, etching becomes more important. The sp2 CC bonding in the carbon coating transforms from order into disorder. Because the disordered sp2 CC bonding increases, the surface of the carbon coating becomes rougher. When the argon/methane ratio is 4, the surface roughness of the carbon coating is a minimum, while the water contact angle of carbon coating is a maximum. At this argon/methane ratio, the carbon coating has the best ability to minimize low temperature induced delamination or microcracks, so is the best for the production of a hermetically sealed optical fiber coating.