GLASS FIBRES FOR OPTICAL COMMUNICATIONS

In an optical fibre having a core and a cladding region, the core comprises silica doped with a refractiveindex-increasing substance, and the cladding has an outer region comprising substantially undoped silica, with the remainder of the cladding including regions of silica doped with both refractive-index-increasing and refractive-index-decreasing substances, and wherein the concentration of said dopants in said remainder of the cladding is less towards the core of the fibre so that there exists at least an intermediate region of the cladding where the concentration of said dopants is greater than the remaining inner region of the cladding.