Optical glass fibres and method of forming such fibres

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.