Provided is a method for manufacturing an optical fiber glass preform in which a refractive index distribution is stable in a longitudinal direction of the glass preform. A method for manufacturing an optical fiber glass preform includes: depositing a porous glass preform by a vapor phase method; and sintering the porous glass preform in a heating region, when sintering the porous glass preform, the porous glass preform being inserted into a vessel of a sintering furnace, and an inside of the vessel being heated with a heater installed on an outer periphery of the vessel to form the heating region. The sintering is started after a surface temperature difference of the porous glass preform in a longitudinal direction is made 50° C. or lower.

In known methods for producing a glass component, a void-containing intermediate product containing doped or non-doped SiO.sub.2 is inserted into a sheath tube composed of glass, which has a longitudinal axis and an inner bore, and is thermally treated therein. In order to subject the intermediate product to a thermal and/or reactive treatment that is reproducible and uniform in its effect from this starting point, it is proposed in one embodiment that into the sheath tube's inner bore a first gas-permeable gas diffuser is inserted which is displaceable along the sheath tube's longitudinal axis and is pressed against the intermediate product during the thermal treatment.

An optical fiber draw system and method of operating thereof. The method includes positioning a downfeed handle for supporting an optical fiber preform within a furnace such that the downfeed handle is movable within the furnace. The method further includes operating one or more heating elements to thermally heat at least a portion of an upper muffle extension disposed within the furnace, the one or more heating elements being moveable with the downfeed handle.

An optical fiber draw system and method of operating thereof. The method includes positioning a downfeed handle for supporting an optical fiber preform within a furnace such that the downfeed handle is movable within the furnace. The method further includes operating one or more heating elements to thermally heat at least a portion of an upper muffle extension disposed within the furnace, the one or more heating elements being moveable with the downfeed handle.

An optical fiber forming apparatus comprises: a draw furnace comprising: (i) a muffle with an inner surface, (ii) an axial opening below the muffle, the inner surface of the muffle defining a passageway extending through the axial opening, and (iii) an upper inlet into the passageway; and a tube that extends into the passageway of the draw furnace above the axial opening, the tube having (i) an outer surface and the inner surface of the muffle surrounds the outer surface of the tube with a space separating the outer surface of the tube from the inner surface of the muffle, (ii) an inner surface that defines a second passageway extending through the tube, (iii) an inlet into the second passageway of the tube, (iii) an outlet out of the second passageway of the tube.

A system and method for nitridizing a glass article includes supplying a source of a nitridizing gas including gaseous NH.sub.3 to a glass article supported within a furnace assembly and heating the glass article. In some embodiments, the system includes a handle assembly configured to support the glass article within the furnace assembly and a gas supply conduit carried by the handle and configured to supply the nitridizing gas to the glass article. In some embodiments, a method of nitridizing a glass article includes supplying the nitridizing gas such that a residence time of the nitridizing gas at temperatures greater than 500° C. corresponds to a predetermined time period. In some embodiments, a method of nitridizing a glass article includes supplying the nitridizing gas such that the glass articles is exposed to the nitridizing gas within a contact time t.sub.c.

A wire-drawing optical fiber base material manufacturing method of heating an optical fiber base material by a heater and forming a drawing shape portion at an end portion. The manufacturing method includes: forming, by a flow-regulating member disposed adjacent to the heater, a gas flow such that formation, along a surface of the optical fiber base material, of a flow of a gas containing a Si compound generated from the optical fiber base material heated by the heater is inhibited; and forming, while maintaining the gas flow, the drawing shape portion by pulling part of the optical fiber base material softened by being heated by the heater.

A wire-drawing optical fiber base material manufacturing method of heating an optical fiber base material by a heater and forming a drawing shape portion at an end portion. The manufacturing method includes: forming, by a flow-regulating member disposed adjacent to the heater, a gas flow such that formation, along a surface of the optical fiber base material, of a flow of a gas containing a Si compound generated from the optical fiber base material heated by the heater is inhibited; and forming, while maintaining the gas flow, the drawing shape portion by pulling part of the optical fiber base material softened by being heated by the heater.

An optical fiber draw system and method of operating thereof. The method includes positioning a downfeed handle for supporting an optical fiber preform within a furnace such that the downfeed handle is movable within the furnace. The method further includes operating one or more heating elements to thermally heat at least a portion of an upper muffle extension disposed within the furnace, the one or more heating elements being moveable with the downfeed handle.

An optical fiber drawing furnace heating element includes a heat generator including: a tubular resistance heating element in which at least a part of an optical fiber preform is disposed in a through-hole; a first portion extending, from a first end portion, over a predetermined section along a longitudinal direction; and a second portion disposed closer to a second end portion than the first portion. The second portion has a wall thickness on a side of the first end portion being equal to or larger than a wall thickness of the first portion. The wall thickness of the second portion increases toward a side of the second end portion from the side of the first end portion.