Rod in tube process for preparing optical fibre preform, by heating rod and mantle separated by cavity containing deuterium

摘要

Gas mixture containing deuterium is present inside the annular cavity between the rod and tube during heating. A method for preparing a pre-form for optical fibres comprises: (a) providing a rod-shaped forming piece; (b) placing a tubular mantle around the rod; and (c) heating the rod and mantle whilst providing a deuterium-containing gas mixture in the annular cavity between the rod and mantle, so that the deuterium atoms replace any hydrogen atoms present in the rod and mantle.