Pilkington Brothers P.l.c.

James Robert Mellor

Colin Billington

Charles R Bamford

Bernard Parker

In optical glass fibres formed of high-silica glass which is susceptible to the production of color centers on drawing into fibres, the attenuation due to such drawing-induced color centers is suppressed or reduced by incorporating from 1 to 100 (preferably 3 to 50) parts per million of cerium oxide in the glass from which the fibre is drawn, under oxidizing conditions such that a significant proportion of the cerium is in the form of ceric ions and the total attenuation is not more than 20 dB/Km in the wavelength range from 800 to 900 nm. The invention is applicable to the known process in which a batch of glass-forming materials is melted to form a phase-separable silicate glass and a rod is drawn or cast from the glass, which is then phase-separated and leached to form a porous rod; the rod is stuffed with a dopant which increases the refractive index; the dopant is dissolved out from an outer region of the rod, which is collapsed by heating to produce a pre-form of a high silica glass with an inner region of higher refractive index; and optical fibre is drawn from the pre-form. In this process, a cerium compound may be introduced into the batch, the melting and the drawing or casting of the rod then being carried out under oxidizing conditions, or a cerium compound may be introduced with the dopant into the porous rod.

Optical glass fibres and method of forming such fibres

A method of producing clad glass rod of uniform diameter from which an optical fibre is drawn. The rate of drawing of the rod from a glass melt and the diameter of the drawn rod are sensed and the sensed values are fed to a coarse open loop control and a high gain closed loop control which regulate the draw speed of the rod and the movement of a cooling jacket which cools the rod as it is drawn.

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Ormskirk, United Kingdom

James Robert Mellor