Furnace for drawing optical fiber preform to make optical fiber and method for drawing optical fiber using the same

Abstract

A furnace for drawing an optical fiber includes a body having an upper and lower openings for supplying a preform and discharging a drawn optical fiber, a heating unit installed in the body for receiving and melting the preform, an atmosphere blocking tube installed to the lower opening for discharging the drawn optical fiber and blocking the optical fiber from the atmosphere, an upper introduction port formed at an upper portion of the body for introducing an inert gas toward the preform and partially discharged outside through a gap between the preform and the upper opening, a central and lower introduction ports formed at central and lower portions for introducing an inert gas into the body, a first flow guiding means for guiding the inert gas introduced through the central introduction port upward and then flowed down along a surface of the preform, and a second flow guiding means for guiding the inert gas introduced through the lower introduction port upward and then discharged outside through the atmosphere blocking tube along a surface of the drawn optical fiber.

What is claimed is:  
     
         1 . A furnace for drawing an optical fiber comprising: 
 a furnace body having an upper opening for supplying a preform and a lower opening for discharging an optical fiber drawn from the preform;    heating means installed in the furnace body, the heating means receiving and melting the preform therein in order to draw the preform;    an atmosphere blocking tube installed at the lower opening for ensuring the passage of the drawn optical fiber therein, the atmosphere blocking tube protecting the drawn optical fiber from the external atmosphere;    an upper introduction port formed at an upper portion of the furnace body for introducing an inert gas toward the preform, the inert gas being partially discharged outside through a gap between the preform and the upper opening;    a central introduction port formed at a central portion of the furnace body for introducing an inert gas into the furnace body;    a lower introduction port formed at a lower portion of the furnace body for introducing an inert gas into the furnace body;    a first flow guiding means for guiding the inert gas introduced through the central introduction port upward along the melting area of the heating means so that the inert gas collides with the inert gas introduced through the upper introduction port and then flows toward a lower portion of the furnace body along the surface of the preform; and    a second flow guiding means for guiding the inert gas introduced through the lower introduction port upward along the melting area of the heating means so that the inert gas collides with the inert gas introduced through the central introduction port and is then discharged outside through the atmosphere blocking tube along the surface of the drawn optical fiber.    
     
     
         2 . A furnace for drawing an optical fiber according to  claim 1 , wherein the heating means include: 
 a first graphite core tube installed spaced apart from the wall of the furnace body in order to form the melting area therein for receiving and melting the preform; and    a second graphite core tube installed, spaced apart from the wall of the furnace body, at a lower portion of the first graphite core tube.    
     
     
         3 . A furnace for drawing an optical fiber according to  claim 2 , wherein the first graphite core tube heats at a temperature of 2,100˜2,300° C. and the second graphite core tube heats at a temperature of 1,600˜1,800° C.  
     
     
         4 . A furnace for drawing an optical fiber according to  claim 2 , wherein the first graphite core tube heats at a temperature of 2,100˜2,300° C. and the second graphite core tube receives a heat from the first graphite core tube and then transfers the heat to the preform.  
     
     
         5 . A furnace for drawing an optical fiber according to  claim 2 , wherein the first flow guiding means include: 
 a passage between the first graphite core tube and the wall of the furnace near the central introduction port;    a support flange extended from the wall of the furnace body for supporting the second graphite core tube; and    a passage formed between the first and second graphite core tubes in which an upper end of the second graphite core tube having a diameter smaller than the first graphite core tube is partially inserted into the first graphite core tube.    
     
     
         6 . A furnace for drawing an optical fiber according to  claim 5 , wherein the passage between the first and second graphite core tubes is formed near a neck-down zone of the preform.  
     
     
         7 . A furnace for drawing an optical fiber according to  claim 2 , wherein the second flow guiding means includes: 
 a passage formed between the second graphite core tube and the wall of the furnace body near the lower introduction port; and    a passage formed between the atmosphere blocking tube and the second graphite core tube.    
     
     
         8 . A furnace for drawing an optical fiber according to  claim 1 , 
 wherein a flow rate of the inert gas at the central introduction port is 3˜4 times as large as a flow rate of the inert gas at the upper introduction port, and    wherein a flow rate of the inert gas at the lower introduction port is 2˜3 times as large as a flow rate of the inert gas at the upper introduction port.    
     
     
         9 . A furnace for drawing an optical fiber according to  claim 1 , further comprising a ring-shaped spraying sleeve having a plurality of nozzles for supplying the inert gas introduced through the upper introduction port evenly to the preform.  
     
     
         10 . A furnace for drawing an optical fiber according to  claim 1 , wherein the atmosphere blocking tube is as long as the drawn optical fiber has a temperature of about 1,200˜1,300° C. at the exit of the atmosphere blocking tube.  
     
     
         11 . A furnace for drawing an optical fiber according to  claim 10 , wherein the length of the atmosphere blocking tube is in the range of 2.0˜2.5 m.  
     
     
         12 . A furnace for drawing an optical fiber according to  claim 10 , wherein the upper end of the atmosphere blocking tube is positioned 200˜250 mm below a neck-down zone of the preform.  
     
     
         13 . A furnace for drawing an optical fiber comprising: 
 a furnace body having an upper opening for supplying a preform and a lower opening for discharging an optical fiber drawn from the preform;    a first core tube installed spaced apart from the wall of the furnace body to form a first passage between the first core tube and the wall of the furnace body, the first core tube forming a melting area therein to heat and melt the preform;    a second core tube installed spaced apart from the wall of the furnace body to form a second passage between the second core tube and the wall of the furnace body, the second core tube having a diameter smaller than the first core tube so as to be partially inserted into a lower end of the first core tube to thereby form a third passage between the first and second core tubes;    an upper introduction port formed at an upper portion of the furnace body for introducing an inert gas toward the preform, the inert gas being partially discharged outside through a gap between the preform and the upper opening;    a central introduction port communicated with the first passage formed between the first core tube and the wall of the furnace body for introducing an inert gas into the first passage;    a lower introduction port communicated with the second passage formed between the second core tube and the wall of the furnace body for introducing an inert gas into the second passage;    a support flange interposed between the first and second passage to divide the first and second passages; and    an atmosphere blocking tube installed at the lower opening for forming a fourth passage in which the inert gas introduced through the second passage flows between the second core tube and the atmosphere blocking tube, the atmosphere blocking tube ensuring the passage of the drawn optical fiber therein to protect the drawn optical fiber from the external atmosphere.    
     
     
         14 . A furnace for drawing an optical fiber according to  claim 13 , wherein the third passage is formed near a neck-down zone of the preform.  
     
     
         15 . A furnace for drawing an optical fiber according to  claim 13 , 
 wherein a flow rate of the inert gas at the central introduction port is 3˜4 times as large as a flow rate of the inert gas at the upper introduction port, and    wherein a flow rate of the inert gas at the lower introduction port is 2˜3 times as large as a flow rate of the inert gas at the upper introduction port.    
     
     
         16 . A furnace for drawing an optical fiber according to  claim 13 , further comprising a ring-shaped spraying sleeve having a plurality of nozzles for supplying the inert gas, introduced through the upper introduction port, evenly to the preform.  
     
     
         17 . A furnace for drawing an optical fiber according to  claim 13 , wherein the atmosphere blocking tube is as long as the drawn optical fiber has a temperature of about 1,200˜1,300° C. at the exit of the atmosphere blocking tube.  
     
     
         18 . A furnace for drawing an optical fiber according to  claim 17 , wherein the length of the atmosphere blocking tube is in the range of 2.0˜2.5 m.  
     
     
         19 . A furnace for drawing an optical fiber according to  claim 17 , wherein the upper end of the atmosphere blocking tube is positioned 200˜250 mm below a neck-down zone of the preform.  
     
     
         20 . A method for drawing an optical fiber by melting a preform in a furnace which includes a furnace body having an upper opening for supplying a preform, a lower opening for discharging an optical fiber drawn from the preform, and upper, central and lower introduction ports for introducing an inert gas; heating means installed in the furnace body to receive and melt the preform in a melting area therein; and an atmosphere blocking tube installed at the lower opening to ensure the passage of the drawn optical fiber therein, wherein the method comprises the steps of: 
 (a) supplying a preform into the melting area through the upper opening;    (b) melting the preform by heating the preform with the heating means;    (c) drawing an optical fiber from a melted portion of the preform at its lower end;    (d) introducing an inert gas through the upper introduction port so that the inert gas is partially discharged outside through a gap between the preform and the upper opening;    (e) introducing an inert gas through the central introduction port so that the inert gas flows upward in the melting area and collides with the flow of inert gas introduced through the upper introduction port, and then flows downward along a surface of the preform; and    (f) introducing an inert gas through the lower introduction port so that the inert gas flows upward along the melting area and then collides with the inert gas introduced through the central introduction port, and is then discharged outside through the atmosphere blocking tube along the surface of the drawn optical fiber.    
     
     
         21 . A method of drawing an optical fiber according to  claim 18 , wherein the step (e) includes the steps of: 
 supplying an inert gas through a passage formed between a wall of the furnace body and a first cylindrical core tube installed in the furnace body; and    guiding the inert gas, having passed through the passage between the wall of the furnace body and the first core tube, to an upper portion of the melting area through a passage between an inner side of the first core tube and an outer side of an upper portion of a second core tube installed in the furnace body wherein an upper end of the second core tube is partially inserted into a lower end of the first core tube.    
     
     
         22 . A method of drawing an optical fiber according to  claim 20 , wherein the step (f) includes the steps of: 
 supplying an inert gas through a passage formed between a wall of the furnace body and the second core tube; and    guiding the inert gas, having passed through the passage between the wall of the furnace body and the second core tube, to an upper portion of the melting area through a passage formed between the atmosphere blocking tube and the second core tube.    
     
     
         23 . A method of drawing an optical fiber according to  claim 20 , wherein a flow rate of the inert gas at the central introduction port is 3˜4 times as large as a flow rate of the inert gas at the upper introduction port, and 
 wherein a flow rate of the inert gas at the lower introduction port is 2˜3 times as large as a flow rate of the inert gas at the upper introduction port  
 
     
     
         24 . A method of drawing an optical fiber according to  claim 20 , wherein the step (c) further includes the step of adjusting a temperature of the drawn optical fiber to be maintained to about 1,200˜1,300° C. while the drawn optical fiber moves out of the atmosphere blocking tube.