Optical fiber drawing methods and drawing furnaces

Abstract

Drawing methods and drawing furnaces for drawing an optical fiber with small non-circularity by simple drawing system are provided. An optical fiber preform is received into a muffle tube and heated by a primary heater placed to surround the muffle tube. The optical fiber preform is heated such that a starting position of a meniscus portion is higher in its position than the top of the primary heater, wherein the meniscus portion is created at the bottom portion of the optical fiber preform.

1 . An optical fiber drawing furnace, comprising:
 a muffle tube to receive an optical fiber preform;   a primary heater to heat inside of the muffle tube, which is placed around the muffle tube concentrically with the muffle tube; and   a furnace body to accommodate the muffle tube and the primary heater;   wherein the optical fiber drawing furnace satisfies the relationship 2E≧L≧1.5E where E is the inner diameter of the muffle tube and L is a distance between the highest temperature point and a point, which is 400° C. lower than the highest temperature and located in the upper side of the muffle tube.   
     
     
         2 . The optical fiber drawing furnace in  claim 1 , further comprising a sub-heater, which is placed on top of the primary heater. 
     
     
         3 . The optical fiber drawing furnace in  claim 1 , further comprising a first insulator around the outside of the primary heater in the furnace body, and a second insulator, which has higher thermal conductivity than the first insulator and is placed on top of the primary heater in the furnace body to surround the muffle tube. 
     
     
         4 . The optical fiber drawing furnace in  claim 1 , wherein the muffle tube has a thick tube portion, which is thicker than the adjacent portion of the primary heater, placed on top of the primary heater.