British Telecommunications Public Limited Company

British Telecommunications Corporation

Steven F Carter

Paul W France

John R Williams

Sally Partington

Martin W Moore

Halide glass articles, e.g. rods, tubes and preforms for making fluoride glass fibres, are prepared by melting and/or casting the articles under a low pressure, e.g. 0.01 to 500 mbars and, during the low pressure regime, a gas flow rate of between 0.01 to 100 liters/min (measured at NTP) is maintained. It has been found that subjecting the melts to a low pressure reduces the attenuation of the fibre which eventually results from the melts.

Method of making halide fibers including casting under a reduced pressure

Method for the preparation of halide glass articles

An optical fibre cable for radiation monitoring, e.g. remote spectroscopy, has the fibres immersed in a water miscible liquid such as ethylene glycol or isopropanol. It has been found that water miscible liquids protect even fluoride fibre against attack by water, e.g. water which diffuses into the bore of a cable during its useful life.

Cables comprising optical fibres of halide glass

A process for treating a halide, e.g. fluoride, glass composition, characterized by contacting a melt of the composition (3) with dry oxygen (6). Oxygen, simply on contact with a fluoride glass melt, converts transition metals, e.g. from Fe(II) to Fe(III), from one stable state to another and thereby reduces loss at transmission wavelengths in optical fibre, e.g. the loss at 2.6 .mu.m attributabel to Fe(II).

Method of preparing a halide optical fibre

A process for treating a halide, e.g. fluoride, glass composition, characterized by contacting a melt of the composition with dry oxygen. Oxygen, simply on contact with a fluoride glass melt, converts transition metals, e.g. from Fe(II) to Fe(III), from one stable state to another and thereby reduces loss at transmission wavelengths in optical fiber, e.g. the loss at 2.7 .mu.m attributable to Fe(II).

Treating glass compositions

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.

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Ipswich, United Kingdom

Steven F Carter