Glass manufacturing – Processes of manufacturing fibers – filaments – or preforms – Process of manufacturing optical fibers – waveguides – or...
Reexamination Certificate
1999-12-30
2001-08-28
Vincent, Sean (Department: 1731)
Glass manufacturing
Processes of manufacturing fibers, filaments, or preforms
Process of manufacturing optical fibers, waveguides, or...
C065S481000, C065S502000, C065S510000, C065S512000, C219S552000, C219S553000, C373S027000, C373S117000, C373S119000, C373S134000
Reexamination Certificate
active
06279352
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to multiple crucible methods of drawing fiber, and particularly to a heating element for a draw furnace for heating a plurality raw materials to be drawn through a multiple crucible into an optical fiber.
2. Technical Background
One common multiple crucible method of drawing an optical fiber is the double crucible method. The double crucible method of forming an optical fiber is disclosed in
Optical Fibers for Transmission
, New York, John Wiley, pp. 166-178 (Midwinter, 1979), which is hereby incorporated by reference. Inner and outer crucibles are charged with core and cladding glass raw materials. The core and cladding glass raw materials are heated into a molten state. The molten glass may be drawn into a fiber. For additional background on a double crucible apparatus and this method of drawing an optical fiber, reference is made to U.S. Pat. No. 5,106,400, U.S. Pat. No. 4,729,777, U.S. Pat. No. 4,385,916, and U.S. Pat. No. 4,118,212, which are hereby incorporated herein by reference as though fully set forth in their entirety.
A draw furnace will supply the heat to transform the solid glass into a molten state. The draw furnace has a heating element. Two common types of furnace heating elements are an induction element and a resistance element. Known resistance elements have two ends and a respective thick section adjacent each end. The two thick sections are separated by a thin section. The thin section has the highest current density and is the area where the heat is primarily generated. Graphite is a common choice of material of construction for a resistance heating element.
SUMMARY OF THE INVENTION
One aspect of the present invention is a rotationally symmetrical resistance heating element for a draw furnace. The heating element has at least two ends. Each one of the ends is cooled by a cooling element. The heating element also includes at least first and second high current density sections. The high current density sections are axially separated by at least one low current density section. Each high current density section has a smaller diameter than the low current density section. The current density of the low current density section is less than the current density of each high current density section.
In another aspect, the present invention includes a method of making an optical fiber. The method includes feeding raw materials for making an optical fiber into a multiple crucible apparatus forming a body of raw materials. The method further includes heating the body of raw materials with a furnace having a rotationally symmetrical resistance furnace heating element. The heating element has at least two ends and a cooling element at each end. The heating element further includes at least first and second high current density sections axially separated by at least one low current density section. The high current density sections have a smaller diameter than the low current density section. The current density of the low current density section is less than a current density of each high current density sections. An optical fiber is drawn from the multiple crucible apparatus.
The invention has the advantage that the body of raw materials is maintained at a temperature suitable for melting and a root of the drawn fiber is maintained at a temperature suitable for drawing. Another advantage of the invention is a hot zone of the furnace is extended to the ends of the heating element. The invention also has the advantage of maintaining the raw materials in the hot zone of the furnace and that the hot zone sharply drops off in an area where a root is formed. Additionally, the invention has the advantage of the creation of a specific thermal field in the furnace. The specific thermal field relates to an extended hot zone in a draw furnace that is suitable for use in the drawing of fiber by multiple crucible methods.
An additional advantage is that the furnace heating element allows the maximum use of the length of the furnace for glass fining. Furthermore, the invention has the advantage that it may be adapted for use with existing optical fiber draw equipment. It also may be adapted for use in a continuous furnace as part of a continuous process. The invention includes the further advantage that the residency time of the raw materials in the multiple crucible apparatus is sufficient to fine the raw materials.
Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments of the invention, and together with the description serve to explain the principles and operation of the invention.
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K. Fujii, “Continuous Fabrication Process of Glass Rod Fibres for Gradient Index Rod Lenses Using Double Pot Crucible”, Glass Technology, vol. 39, No. 5, Oct. 1998, pp. 173-178.
John E. Midwinter, “Fiber Pulling by Double-Crucible Apparatus”, Optical Fibers for Transmission, ISBN 0-471-60240-X, pp. 166-178 1979 (no month available).
Corning Incorporated
Krogh Timothy R.
Vincent Sean
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