Characteristics of carbon coatings on optical fibers prepared by radio-frequency plasma enhanced chemical vapor deposition with different H_2/C_2H_2 ratios

摘要

Characteristics of carbon coatings on optical fibers prepared by radio-frequency plasma enhanced chemical vapor deposition with different H_2/C_2H_2 ratios are investigated. Five kinds of carbon coatings are prepared with H_2/C_2H_2 ratios of 2,4,6,8, and 10. Experimental results show that the deposition rate and surface roughness of carbon coatings decrease as the H_2/C_2H_2 ratio increases. When the H_2/C_2H_2 ratio changes from 2 to 8, the increase of H_2/C_2H_2 ratios detrimentally yields sp3 carbon atoms and sp~3-CH_3 bonds in the carbon coatings. However, when the H_2/C_2H_2 ratio exceeds 8, the hydrogen retards the growth of the graphite structure. Moreover, the redundant hydrogen radicals favor bonding with the dangling bonds in the coating surface. Therefore, when the H_2/C_2H_2 ratio increases from 8 to 10, the amounts of sp3 carbon atoms and sp~3-CH_3 bonds in the carbon coatings increase. At an H_2/C_2H_2 ratio of 8, the carbon coating exhibits excellent water-repellency and thermal-loading resistance, and so this ratio is the best for producing a hermetically sealed optical fiber coating.