Method of producing an optical fiber

A method of producing an optical fibre by extruding close tolerance multi-component coaxial material, comprising the sequential steps of forming a circular cylindrical body of inorganic glass sheath cladding material having a coaxial circular cylindrical bore, and placing a circular cylindrical body of inorganic glass core material in said bore, said bodies as placed together being a block of material to be extruded, said cladding and core materials having different properties, with said components arranged in relative position and geometry the same as that desired in the finished product;

• placing the block of material in a block holder in an extruding press having the block holder and an extrusion die aligned coaxially with the block of material;
• heating said block of material to a plastic state before applying said extruding pressure;
• and then extruding said material by applying extruding pressure to the extrusion die so as to move the die with respect to the block holder in a direction opposite the discharge direction of the extruded material, thereby producing an extruded rod having a constant ratio of core diameter to sheath diameter along the rod length and drawing said rod into an optical fibre.