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 fibre draw furnace includes a hollow cylindrical structure, one or more heating elements and a sealing felt. The one or more heating elements are situated at periphery of the hollow cylindrical structure. The one or more heating elements are utilized for melting the glass preform. The sealing felt is positioned at a pre-defined distance above the optical fibre draw furnace. The sealing felt includes a first opening and a second opening. The first opening is utilized to hold the glass preform. The first opening allows passing of the glass preform inside the optical fibre draw furnace. The second opening facilitates in input of gas inside the optical fibre draw furnace.

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.

A furnace gas supply apparatus configured to supply gas into a drawing furnace, includes: a first flow channel introducing the gas from a predetermined first gas inlet to flow the gas from a predetermined first gas outlet toward a gas storage portion, and a second flow channel introducing the gas stored in the gas storage portion from a predetermined second gas inlet to flow the gas from a predetermined second gas outlet toward a furnace core tube of the drawing furnace, in which the gas storage portion is provided between the first gas outlet and the second gas inlet, and in which an opening position of the second gas inlet is provided at a position different from an opening position of the first gas outlet.

An optical fiber comprises, from a center to a periphery, a fiber core of undoped silica; a cladding layer; and a coating of polyacrylate, wherein the fiber core has a radius of 5 to 7 m and an ellipticity of less than 1.5%, the cladding layer with an ellipticity of less than 0.4% comprises inner, intermediate, and outer cladding layers, the inner cladding layer being doped with fluorine of 5 to 12 m thickness, and refractive index difference to fiber core of 0.4 to 0.2%, the outer cladding layer being undoped quartz of 25 to 45 m thickness, and the coating comprises an inner coating of 25 to 40 m thickness, and an outer coating of 25 to 35 m thickness and an ellipticity of less than 2%. The optical fiber has high durability and large effective transmission area, a method and system for preparing such optical fiber are also disclosed.

An optical fiber comprises, from a center to a periphery, a fiber core of undoped silica; a cladding layer; and a coating of polyacrylate, wherein the fiber core has a radius of 5 to 7 m and an ellipticity of less than 1.5%, the cladding layer with an ellipticity of less than 0.4% comprises inner, intermediate, and outer cladding layers, the inner cladding layer being doped with fluorine of 5 to 12 m thickness, and refractive index difference to fiber core of 0.4 to 0.2%, the outer cladding layer being undoped quartz of 25 to 45 m thickness, and the coating comprises an inner coating of 25 to 40 m thickness, and an outer coating of 25 to 35 m thickness and an ellipticity of less than 2%. The optical fiber has high durability and large effective transmission area, a method and system for preparing such optical fiber are also disclosed.

A sintering apparatus for sintering a porous glass base material, including a furnace core tube surrounded by heaters, the furnace core tube housing the porous glass base material; a lid member having an insertion hole through which a holding rod coupled with the porous glass base material is inserted, the lid member mounted at one end of the furnace core tube; a sealing chamber having a supply port that introduces seal gas and a discharging port that discharges the seal gas, the sealing chamber provided at the lid member covering the insertion hole; and a cylindrical member that causes a pressure difference between gas inside of the tube of an inside the furnace core tube and gas inside of the sealing chamber to be generated while the holding rod is inserted through the cylindrical member inside of the sealing chamber.

The invention relates to an apparatus. In order to achieve efficient sealing, the apparatus includes a sealing with a plurality of sealing elements arranged generally in a ring configuration around a center opening. Each sealing element includes a sealing surface facing the center opening. At least one chamber is included for receiving sections of the sealing elements. An inlet to a fluid source provides the at least one chamber with fluid in order to generate an overpressure acting on the sections of the sealing elements received in the at least one chamber, and for pressing and moving the sealing surfaces of the sealing elements towards the center opening.

An apparatus for drying and/or consolidating an at least partially porous optical fibre preform, including: a furnace having a muffle tube extending along a vertical axis and forming a muffle chamber configured to house a preform, the muffle tube having a muffle upper opening at its top side, which is configured to allow passage of the preform; a hollow connection member having an inner diameter configured to allow passage of the preform and extending along the vertical axis, the connecting member being removably connected to the muffle tube at the muffle opening; a hood positioned on top of the connection member, the hood being removably connected to or integral with the connection member, the hood having an interior space in vertical alignment with the connection member, in which the hood includes a hood lid closing the hood at its top, in which the hood lid includes a through-hole axially aligned with the muffle opening, the hood lid through-hole being configured for the passage of a cylindrical supporting rod of a supporting handle for the suspension of the preform, and a sealing assembly including a first sealing element housed within the interior space of the hood and a second sealing element on top of the hood lid, both the first and the second sealing element being substantially centred on the vertical axis, in which the first sealing element and second sealing element include a respective first and second ring-shaped seal and a first and second expansible member having a generally tubular shape configured to allow passage of the supporting rod and to expand, contract and bend, in which each first and second ring-shaped seal is located radially inward of the respective first and second expansible member and operatively connected thereto, the respective ring-shaped seals being sized to directly contact the supporting rod.