British Telecommunications Public Limited Company

British Telecommunications Corporation

The Post Office

Paul W France

John R Williams

Steven F Carter

Keith J Beales

George R Newns

Sally Partington

Steve F Carter

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

Halide fibres are protected by coatings up to 2 .mu.m thick of chalcogenide glasses, eg glasses based on compounds of S, Se or Te with Ge or As. The coatings are deposited on the fibre preform by ion deposition sputtering. Preferably the preform is ethced by directing a stream of inert ions at it. Most suitably the etching immediately precedes the coating.

Surface treatments for optical fibre preforms

Halide fibers are protected by coatings up to 2.mu.m thick of chalcogenide glasses, e.g. glasses based on compounds of S, Se or Te with Ge or As. The coatings are deposited on the fiber preform by ion deposition sputtering. Preferably the preform is etched by directing a stream of inert ions at it. Most suitably the etching immediately precedes the coating.

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 high numerical aperture optical fibre, e.g. for use in remote spectroscopy, has a cladding of a halide glass which contains Hf and a core of a halide glass which contains Pb. Preferably both glasses contain ZrF.sub.4, BaF.sub.2, LaF.sub.3, AlF.sub.3 and NaF. In addition the cladding contains HfF.sub.4 but no PbF.sub.2 and the core contains PbF.sub.2 but no HfF.sub.4.

Halide fibre with high numerical aperture

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

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

In order to provide improved resistance to attack by atmospheric water etc. a clad glass optical fibre has a plastic coating which is in turn coated with a metal coating. The metal coating may in turn be coated with a second plastic coating. The metal coating is formed by drawing the plastic coated fibre through a globule of molten metal, the surface of which is exposed to an oxygen rich atmosphere.

Optical fibres and coatings therefor

A method of proof testing an optical glass fibre by pulling it around a free roller whose radius is sufficiently small to impart the strain necessary to detect fibres whose surface or near surface flaws weaken the fibre below a required strength. Proof testers are disclosed incorporating, single rollers, a set of three parallel rollers and a jig holding four sets of three rollers. Proof testers incorporating the extra rollers whose axes are at different angles are shown to more thoroughly explore the surface of the fibre for cracks.

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Suffolk, United Kingdom

Paul W France