Growth kinetics and microstructure of carbon deposited on quartz plates and optical fibers by open-air laser-induced chemical vapor deposition

Pyrolytic carbon has been successfully deposited on fused silica optical fibers and fused quartz plates by open-air laser-induced chemical vapor deposition. Raman spectroscopy, scanning electron microscopy, ion-beam sputtering and scanning white-light interferometry were used to investigate the microstructure, composition and uniformity of the carbon film. The pyrolytic carbon was derived from methane, acetylene, propane and butane precursors. Both the axial and the lateral growth rate and threshold deposition (pyrolysis) temperature of the carbon film deposited on a quartz plate were measured. Knowledge gained from deposition on fused quartz plates was used to determine the deposition conditions on optical fibers. The experimental results indicate that among the different precursors used in this study, only acetylene and propane can be used to deposit pyrolytic carbon on moving optical fibers because their threshold deposition temperature is sufficiently low to prevent fiber softening. The effect of laser power, moving fiber speed and precursor gas on the thickness, deposition rate and microstructure of the carbon layer were studied.