To provide a method of sintering an optical fiber porous glass base material, capable of sufficient dehydration and reducing a transmission loss caused by residual moisture by efficiently transferring heat from the heater to the base material during a process in dehydration/sintering for an optical fiber porous glass base material, a porous glass base material having a heat shield plate installed in a vicinity of a lower end is vertically inserted into a furnace core tube provided with a heater along an outer circumference, and heating using the heater is performed. The heat shield plate has an outer diameter which is 70% or larger than a diameter of the porous glass base material and smaller than an inner diameter of the furnace core 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 sintering apparatus comprising: a furnace core tube containing a porous glass base material for optical fiber whose longitudinal direction is along the axial direction; and a multi-stage heater in which two or more heaters surround the furnace core tube and are arranged in the axial direction of the furnace core tube to form a heating area in the furnace core tube, is used. The sintering method includes a step in which the base material is heated in the heating area to perform a first dehydration process; and a step in which the base material is moved so that the position in the longitudinal direction of the base material where the dehydration was identified as the most insufficient, is at the position in the axial direction of the furnace core tube where the temperature is highest in the heating area, and then a second dehydration process is performed.

An apparatus for drying and/or consolidating an at least partially porous optical fibre preform.

The invention relates to a device, system, and method for forming a core-rod for optical fibers by collapsing a tube comprising deposited layers of silica to form the core-rod. The device comprises an elongate cavity, an elongate cylindrical carbon liner bounding the cavity, the liner connecting to a frame of the device at opposing end portions, a heating element in a heating element space, surrounding the liner, the liner separating the heating element space from the cavity, a ring of a refractory material, fixated to the frame, surrounding a part of a length of the cavity, the liner being provided such that an inner surface portion at a first end portion of the liner mates with a cylindrical outer surface portion of the ring such that the liner can axially move with the first end portion thereof along the outer surface portion of the ring.

Provided is an elongating method for elongating a glass base material by heating the same while moving the same downward within an elongating apparatus, the glass base material including a transparent tapered section, wherein the transparent tapered section is located at an upper end of the glass base material and has an end face to which a suspension dummy formed from a glass pole is welded, the elongating method comprising steps for: starting to elongate the glass base material by heating the same, starting from a lower-end side thereof, by causing the glass base material to pass through a range within the elongating apparatus in which a preset elongating process temperature or higher is maintained; and after the tapered section enters the range, ending the elongating of the glass base material before the end face enters the range.

A manufacturing method of glass base material for optical fiber that can obtain glass base material for optical fiber with reduced fluctuation in optical properties in the longitudinal direction is provided. The manufacturing method includes: a first heat treatment step in which the porous glass base material inserted in a vessel of a sintering furnace is heated by a heater installed around the periphery of the vessel while being raised or lowered in the longitudinal direction in a chlorine-based gas containing atmosphere in the vessel of the sintering furnace; a second heat treatment step in which the porous glass base material is heated by the heater to obtain a transparent glass body while being raised or lowered in the longitudinal direction in an inert gas containing atmosphere in the vessel after the first heat treatment step; and a preliminary fluorine doping step prior to the second heat treatment step.

A heating apparatus includes: a furnace core tube configured to house a glass base material; a heating device installed at outer periphery of the furnace core tube; and a controller configured to control the heating device. The heating device includes a plurality of independently-controllable heaters arranged along a longitudinal direction of the glass base material. The heaters are grouped into a plurality of heating groups controllable in an independent manner by the controller. Each of the heating groups includes at least one of the heaters configured to heat the furnace core tube.

A method of preparing an optical preform, comprises the steps of: positioning an optical preform comprising silica within a cavity of a furnace; passing an etchant gas into the furnace and at least one of through an open channel defined in the optical preform and around the optical preform; and passing a neutralizing gas into the cavity of the furnace, the neutralizing gas configured to neutralize the etchant gas.

Apparatuses and methods for processing an optical fiber preform are disclosed. According to one aspect, an apparatus may generally include a muffle defining an interior volume enclosed by at least one sidewall and a handle assembly for supporting the optical fiber preform in the muffle. The handle assembly may be removably coupled to the muffle and extend into the interior volume. At least one baffle may be positioned in the interior volume and define an upper portion of the interior volume and a lower portion of the interior volume. The at least one baffle may define at least one flow channel between the upper portion of the interior volume and the lower portion of the interior volume.