Method of manufacturing preform for nonoxide glass fiber

A method of manufacturing a preform for a nonoxide glass fiber, comprising the steps of:

• preparing an extrusion apparatus comprising a cylinder, a molding section mounted to a forward end of said cylinder, said molding section having a molding nozzle, an extrusion punch inserted in said cylinder for sliding movement, and a liner connected to said molding nozzle in said molding section;
• preparing a cladding glass preform having end faces extending substantially in parallel relation to each other, and at least one of said end faces being polished to such an extent that it is in optical contact with a core glass preform;
• preparing the core glass preform having end faces extending substantially in parallel relation to each other, and at least one of said end faces of said core glass material being polished to such an extent that it is in optical contact with a cladding glass preform;
• preparing an over-cladding glass preform having end faces extending substantially in parallel relation to each other, at least one of said end faces of said over-cladding glass material being polished;
• placing said over-cladding glass preform, said cladding glass preform and said core glass preform in said cylinder of said extrusion apparatus such that the polished end face of said over-cladding glass preform, both the polished end faces of said cladding glass preform and the polished end face of said core glass preform are in contact with each other and such that said over-cladding glass preform is located adjacent said molding section of said extrusion apparatus, said core glass preform is located adjacent said extrusion punch of said extrusion apparatus, and said cladding glass preform is located between said over-cladding glass preform and said core glass preform;
• heating said over-cladding glass preform, said cladding glass preform, and said core glass preform to a temperature between a high sag temperature and a low crystalline start temperature of respective preforms;
• pushing said extrusion punch to extrude said over-cladding glass preform, said cladding glass preform and said core glass preform through said molding nozzle in said molding section while said over-cladding glass preform, said cladding glass preform and said core glass preform are in fusible contact with each other, thereby forming said preform with a concentric three-layer structure;
• and
• cooling said preform gradually within said liner connected to said molding section.

A method of manufacturing a nonoxide glass fiber, comprising the steps of:

• providing at least first and second preforms, each of which has at least one polished face which is in optical contact with each other;
• positioning the first preform adjacent the second preform so that the polished faces thereof are in contact with one another, and so that the polished faces provide a high quality optical interface between the first and second preforms;
• heating the first and second preforms;
• extruding the first and second preforms into an elongated tubular configuration;
• and
• cooling the tubular configuration.