High alumina content optical fibres by powder methods

An improvement to the Granulated Silica Method (GSM) by using thermally densified “green compacts” is described and implemented in order to produce high alumina content fibres. High alumina fibres are suitable for harsh environments at elevated temperatures due to their mechanical and optical properties. Fibres with up to 70at.% alumina in the core and up to 35at.% in the cladding (to lower the core-cladding index step) have been produced. The cores appear to be transparent for visible light. By EDX analysis diffusion of cladding material (e.g. silica) into the core, but not in the opposite direction from the core to the cladding, have been verified and are confirmed by qualitative index measurements.