Process for producing chalcogenide glass fiber

A process for producing a chalcogenide glass fiber which comprises placing:

• a cylindrical chalcogenide glass preform vertically in a cylindrical crucible furnished with a nozzle in its bottom portion, said glass preform including a core glass in a rod shape that is inserted into a tube of a cladding glass having a lower refractive index than said core glass, the cladding tube adhering to the core rod thereby to form a unitary assembly, said assembly being inserted in a closed vessel in which an inert atmosphere is maintained;
• and softening the cladding tube locally and continuously from one end to the other with the pressure of the inert gas in the gap between the cladding tube and the core rod being held no higher than 10.sup.-1 Torr and with the pressure of the inert gas around the cladding tube being held no lower than 0.2 kg/cm.sup.2 ;
• heating the crucible only at the vicinity of the nozzle;
• and
• continuously drawing the glass into a fiber with the temperature of the crucible at the vicinity of the nozzle being maintained at such a level that the viscosity of the glass is within the range of 10.sup.3 to 10.sup.7.5 poises.