Glass manufacturing – Processes of manufacturing fibers – filaments – or preforms – Process of manufacturing optical fibers – waveguides – or...
Patent
1995-07-13
1997-06-10
Hoffmann, John
Glass manufacturing
Processes of manufacturing fibers, filaments, or preforms
Process of manufacturing optical fibers, waveguides, or...
65513, 65533, 65510, C03B 37027
Patent
active
056371306
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a furnace and method for drawing an optical fiber and in particular to a furnace and method capable of drawing an optical fiber having only a slight variation in the outer diameter.
BACKGROUND ART
An optical fiber is in general formed by drawing while heating and melting a transparent glass mass or tube called an optical fiber preform (preform) in an optical fiber-drawing furnace.
FIG. 1 shows an embodiment of an optical fiber-drawing furnace according to the conventional technique. Drawing furnaces as shown in FIG. 1 are disclosed in, for instance, Japanese Patent Application Publication No. 3-24421.
As seen from FIG. 1, a furnace body 11 made of stainless steel is in general provided therein with a heater 13 for heating and melting an optical fiber preform 12. A furnace core tube 14 in which the foregoing preform 12 is inserted through the top thereof is positioned inside the heater 13.
The furnace core tube 14 is in general composed of a carbon material and fixed to the furnace body 11 at both upper and lower ends of the latter. The furnace core tube 14 comprises an upper cylindrical part 14a, a funnel-like part 14b, and a lower cylindrical part 14c. The upper cylindrical part 14a is composed of a cylinder having a diameter slightly greater than that of the preform 12. The lower cylindrical part 14c, has a diameter which is smaller than that of the preform 12 and permits the passage of a drawn optical fiber 15. The funnel-like part 14b, is positioned between the upper and lower cylindrical parts 14a and 14c, and thus serves to connect the upper cylindrical part 14a to the lower cylindrical part 14c. The funnel like part 14b has a shape whose diameter is gradually reduced in a direction from the upper portion to the lower portion thereof along the molten portion at the lower end of the preform 12 which is drawn into the optical fiber 15.
An annular thermal insulating material 16 comprising, for instance, a carbon felt material is disposed between the furnace body 11 and the heater 13 so as to prevent any external diffusion of the heat radiated from the heater 13.
Moreover, an upper cylindrical member 17 which is communicated with the upper end of the furnace core tube 14 is disposed on the top of the furnace body 11. This upper cylindrical member 17 is usually made of stainless steel and the upper opening thereof is covered with a cap member 18. Further the upper cylindrical member 17 is provided with a gas introduction port 17a at an upper portion thereof. On the other hand, a lower cylindrical member 19 is positioned at the bottom of the furnace body 11 and is communicated with the lower end of the furnace core tube 14. The lower cylindrical member 19 is commonly formed from stainless steel and is provided, at the lower end thereof, with an opening 19a through which the drawn optical fiber 15 can pass.
An inert gas 20 such as N.sub.2 and He is supplied to the upper cylindrical member 17 through the gas introduction port 17a. The inert gas 20 establishes an inert gas atmosphere within the furnace core tube 14 and is discharged through the opening 19a of the lower cylindrical member 19. The inert gas 20 serves to protect the furnace core tube 14 and the preform from oxidation and to thus keep the internal space of the furnace core tube 14 clean.
Incidentally, the aforementioned furnace core tube 14 is not a cylinder having a uniform diameter over the entire length thereof, but is provided with, at the lower part thereof, the funnel-like part 14b, and the lower cylindrical part 14c. These funnel-like and lower cylindrical parts 14b, and 14c, are incorporated into the drawing furnace for the purpose of preventing any variation in the outer diameter of the optical fiber 15 during drawing the optical fiber. More specifically, the space formed between the inner wall of the furnace core tube 14 and the preform 12 is almost identical to that formed between the inner wall of the furnace core tube and the optical fiber 15 drawn therefrom, along the fiber-drawin
REFERENCES:
patent: 4309201 (1982-01-01), Klop
patent: 4547644 (1985-10-01), Bair
patent: 4578098 (1986-03-01), Paek
patent: 4673427 (1987-06-01), Van Der Giessen et al.
Kobayashi Kohei
Nagayama Katsuya
Ohta Hiroaki
Tsuchiya Ichiro
Hoffmann John
Sumitomo Electric Industries Inc.
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