Silica glass doping is widely used in the fiber-optic technology. Fluorine, decreasing the silica refractive index, is one of the widespread dopants. Fluorine-doped silica is, therefore, a material for the cladding in optical fibers. Fluorine is introduced into silica during the glass synthesis by different techniques, the most flexible and promising technique being reduced - pressure plasmachemical deposition. Despite the widespread practical implementation of the silica fluorination, the mechanism of fluorine incorporation into the glass network is so far poorly understood. We report a model for silica fluorination for the case of reduced - pressure plasmachemical deposition. It is known that under these conditions the glass layers synthesised on the inner surface of the substrate tube are transparent and subsequent fusion is not required.
