Method and furnace for drawing optical fibers

A method of drawing an optical fiber comprising the steps of:

• providing a structure having an inner surface defining a furnace core chamber,
• inserting a preform through an upper end of the furnace core chamber, the furnace core chamber containing an inner furnace core tube comprising a cylindrical part and a funnel-like part, the cylindrical part being in communication with a lower opening of the furnace core chamber, the funnel-like part having a diameter gradually and upwardly increased, at least a portion of an upper periphery of the funnel-like part being spaced from the inner surface of the structure;
• supplying an inert gas to the furnace core chamber to establish an inert gas atmosphere within the chamber;
• melting a lower portion of the preform by operating a heating means to obtain a molten portion of the preform, the heating means being positioned around a periphery of said structure, while arranging a lower end of the molten portion so as to be surrounded by the funnel-like part of the inner furnace core tube;
• drawing the molten portion to obtain an optical fiber;
• and
• removing the optical fiber through the lower opening.

A method for drawing an optical fiber comprising the steps of:

• providing a structure having an inner surface defining a furnace core chamber,
• inserting the preform through an upper end of the furnace core chamber, the furnace core chamber containing an inner furnace core tube comprising a cylindrical part and a funnel-like part, the cylindrical part being in communication with a lower opening of the chamber, the funnel-like part having a diameter gradually and upwardly increased, at least a portion of an upper periphery of the funnel-like part being spaced from the inner surface of the structure;
• introducing an inert gas to the furnace core chamber through a first port formed in a lower portion of the furnace core chamber;
• heating the inert gas by passing the inert gas through a first space defined between the inner surface of the structure and an outer surface of the inner furnace core tube;
• passing a first portion of the inert gas through a second space defined by an inner surface of the inner furnace core tube and discharging the first portion of the inert gas through the lower opening of the furnace core chamber;
• and
• passing a second portion of the inert gas through the furnace core chamber and discharging the second portion of the inert gas through a second port positioned at an upper portion of the furnace core chamber.