British Telecommunications Corporation

The Post Office

Sally Partington

Keith J Beales

Paul W France

Steven F Carter

Anthony G Dunn

Steve F Carter

A glass suitable for use in optical fibre cores has a refractive index of 1.540-1.610, Na.sub.2 O and B.sub.2 O.sub.3 in a molar ratio of 1.05-2:1, 2-12 mole percent BaO, 40-63 mole percent SiO.sub.2, and 1.5-15 mole percent ZrO.sub.2, the proportion of SiO.sub.2 and ZrO.sub.2 together not exceeding 65 mole percent. The glass can be prepared in a highly reduced state by the use of CO and a redox buffering agent. The glass is especially suitable for the production of high numerical aperture wide cored fibres.

Glasses and methods for making them

An oxide glass is dried by passing through a melt of the glass fluorine or another perhalogenated compound including fluorine atoms. For example, C.sub.3 F.sub.8 (e.g. after pre-cracking) can be used to reduce the OH content of a borosilicate glass, and the loss of an optical fibre drawn from such a glass, to low levels.

Method for drying oxide glasses

A glass suitable for use as the core glass in a high numerical aperture optical fibre has a composition selected from the range of glasses which comprise

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Bradfield, Nr. Manningtree, United Kingdom

Sally Partington