Quartz glass optical fibre with high tensile strength - obtd. by coating rod blank with boric oxide, or boric oxide and silica, prior to drawing of fibre

摘要

The fibre is made by drawing a quartz glass blank; and the bank is first coated with a layer (I) preventing the crystallisation of silica to tridymite and/or cristobalite on its surface. Boric oxide, or boric oxide and silica, are pref. used as layer (I). When a conventional blank is heated in a drawing furnace tridymite and cristobalite small crystals form on its surface and do not completely me on cooling, these crystals peel off, leaving microfissures which reduce the tensile strength of waveguide fibres. The invention minimises the formation of such crystals.