JP4655685B2 - Optical fiber drawing furnace and optical fiber drawing method - Google Patents

Description

  The present invention relates to an optical fiber drawing furnace and an optical fiber drawing method, and more particularly, to an optical fiber drawing furnace and an optical fiber drawing method using a large and long optical fiber preform.

  Generally, an optical fiber is manufactured using a manufacturing apparatus as shown in FIG. In this manufacturing apparatus, first, the optical fiber preform 101 is heated and melted in the drawing furnace 40 and then drawn vertically downward, whereby the optical fiber 102 is drawn from the furnace outlet 55. The drawing furnace 40 mainly includes a core tube 51 in which the optical fiber preform 101 is accommodated, a heater 54 for heating and melting the optical fiber preform 101, and an inner core in which the drawn optical fiber 102 is passed. And a tube 52. A core 53 is formed by the internal space of the core tube 51.

  The drawn optical fiber 102 is cooled by blowing the cooling gas in the cooling pipe 44 after the outer diameter is measured by the outer diameter measuring device 43. Then, after coating the resin around the optical fiber 102 in the coater 45 (for example, ultraviolet curable resin), the resin is cured by passing the optical fiber 102 through the resin curing furnace 46. As a result, the optical fiber 103 is obtained. The cooling, resin coating, and resin curing steps are repeated as appropriate. Thereafter, the traveling direction of the optical fiber 103 is changed by the turn pulley 47 and is wound around the winder 49 via the take-up capstan 48.

  Since the drawing furnace 40 needs to heat the quartz-based optical fiber preform 101 to about 2000 ° C., ceramics such as high-purity carbon and zirconia are generally used as the material of the core tube 51 and the inner core tube 52. Used.

  When an optical fiber is manufactured using a drawing furnace having a high purity carbon core tube 51 and an inner core tube 52, in order to prevent oxidation of the core tube 51 and the inner core tube 52 in the core 53, the core The inside of the core 53 is purged by the inert gas supplied into the core 53. At this time, depending on the flow direction of the inert gas, the drawing furnace has an upflow type in which the inert gas G flows upward as shown in FIG. 5 and an inert gas G in the downward direction as shown in FIG. Broadly divided into flowing downflow types.

  In the case of the upflow type, a reduced diameter portion (cylindrical member with a flange) 57 having a slightly larger diameter than the optical fiber preform 101 is provided on the upper portion of the core tube 51. The inert gas G is introduced from a gas inlet 58 provided below the drawing furnace, and flows upward in the core 53, and then the gap between the optical fiber preform 101 and the reduced diameter portion 57 (hereinafter referred to as an upper gap). ) To the outside of the core 53. An exhaust port 59 provided with a valve 59a for adjusting the pressure of the inert gas G in the core 53 is appropriately provided above the drawing furnace.

  On the other hand, in the case of the down flow type, an annular heat-resistant sealing member 67 having a hole having substantially the same diameter as that of the optical fiber preform 101 is provided on the upper portion of the core tube 51. The inert gas G is introduced from a gas inlet 68 provided above the drawing furnace, flows downward in the core 53, and then from a gap between the optical fiber 102 and the furnace outlet 55 (hereinafter referred to as a lower gap). It is exhausted out of the core 53. Below the drawing furnace, an exhaust port 69 provided with a valve 69a for adjusting the pressure of the inert gas G in the core 53 is appropriately provided.

  Further, there is a drawing furnace having a structure combining an upflow type and a downflow type (hereinafter referred to as a composite type) (see, for example, Patent Documents 1 and 2). The drawing furnace described in Patent Document 1 includes an upper inner core tube and a lower inner core tube inside a core tube (outer core tube). The inert gas supplied from below the drawing furnace is exhausted from above the drawing furnace via the lower inner core tube and the upper inner core tube. Further, the inert gas supplied from above the drawing furnace is exhausted from below the drawing furnace through the space between the outer core tube and the upper inner core tube and the space between the outer core tube and the lower inner core tube. The

JP-A-5-279070 JP 2003-206155 A

  None of the conventional upflow type, downflow type, and composite type draw furnaces have been considered for dust adhesion in the core tube and the exhaust path. In recent years, in order to reduce the cost of optical fibers, the optical fiber preform has been increased in size (increase in diameter) and lengthened. Along with this, the amount of dust generated during heating and melting of the optical fiber preform, and the amount of dust per optical fiber preform attached to the furnace core tube and the exhaust path tend to increase. As a result, dust adhering to the core tube and the exhaust passage cannot be ignored. The problem is that dust adhering to the core tube and exhaust path causes adverse effects such as reduced life of the core tube, uneven temperature distribution in the core, fluctuation and instability of internal pressure in the core, and dust backflow due to exhaust clogging. was there.

  An object of the present invention created in view of the above circumstances is an optical fiber preform, an optical fiber, a furnace core tube, and an optical fiber drawing furnace in which there is no possibility of dust adhering to an exhaust path, and an optical fiber drawing method. Is to provide.

To achieve the above object, an optical fiber drawing furnace according to the present invention is an optical fiber drawing furnace for drawing an optical fiber preform heated and melted in the core while purging the inside of the core with an inert gas.
A core tube forming the core;
A first inert gas supply means for supplying an inert gas in a downflow from above the drawing furnace into the furnace core tube;
A second inert gas supply means for supplying an upflow of inert gas into the furnace core tube from below the drawing furnace;
An inner core tube provided in the lower part of the core tube,
An exhaust path forming member that is provided so as to close a gap between the core tube and the inner core tube, and includes an insulating material;
The exhaust path forming member has an exhaust path for exhausting both the up-flow and down-flow inert gases purged in the core to the outside of the core tube, and the inlet of the exhaust path located inside the core tube is The up-flow inert gas and the down-flow inert gas that merge in the vicinity of the center of the core are positioned so as to be able to suck in the inert gas.

Here, the exhaust path forming member is constituted by a thick-walled pipe, and a plurality of exhaust paths that communicate the inside and outside of the core tube are connected to the thick-walled main body part at predetermined intervals in the circumferential direction of the thick-walled body part. You may make it provide. The exhaust path forming member is composed of an annular flange portion and a plurality of pipe portions, and has the same number of through holes as the number of pipe portions in the flange portion at a predetermined interval in the circumferential direction of the flange portion, and The through hole and the hole inside the pipe portion may be communicated with each other.
Furthermore, the heat insulating material constituting the exhaust path forming member is preferably a carbon heat insulating material.

On the other hand, the optical fiber drawing method according to the present invention is an optical fiber drawing method for drawing an optical fiber preform heated and melted in the core while purging the inside of the core with an inert gas.
Using a draw furnace in which an inner core tube is provided in the lower part of the core tube forming the core, and an exhaust path forming member made of a heat insulating material is provided so as to close a gap between the core tube and the inner core tube, When drawing the optical fiber preform by heating, melting,
A down flow inert gas is supplied into the core tube from above the drawing furnace, and an up flow inert gas is supplied to the inside of the core tube through the inner core tube from below the drawing furnace. contacting the inert gas of the down flow, in the optical fiber is contacted with the inert gas of the upflow is the core at the merging location of the inert gas of the inert gas and the down-flow of the upflow Both inert gases supplied to the inside of the core tube from near the center are exhausted outside the core tube through the exhaust path forming member.

  According to the present invention, an excellent effect is exhibited that there is no risk of dust adhering to the core tube and the exhaust path.

  A preferred embodiment of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 shows a schematic structural diagram of an optical fiber drawing furnace according to a preferred embodiment of the present invention.

  As shown in FIG. 1, the optical fiber drawing furnace 10 according to the present embodiment draws the optical fiber preform P heated and melted in the core 13 in the direction of arrow A2 (downward in FIG. 1). Thus, the optical fiber OF is manufactured. The optical fiber drawing furnace 10 mainly includes a core tube 11, a furnace shell 16, and an inner core tube 12.

  The core tube 11 is composed of a tube material having an opening end in the vertical direction, and a part in the longitudinal direction of the optical fiber preform P having the rod R is accommodated in the upper opening end. The inner space of the core tube 11 forms the core 13. The rod R is provided so as to be movable in the direction of arrow A1 (vertical direction in FIG. 1).

  A furnace shell 16 is provided so as to surround the core tube 11. A heater (heating means) 14 for heating and melting the optical fiber preform P is provided in the furnace shell 16. The heater 14 is disposed so as to surround the vicinity of the central portion in the length direction (vertical direction in FIG. 1) of the core tube 11. The furnace shell 16 has a water cooling structure, and cooling water circulation means (not shown) for circulatingly supplying the cooling water W is connected to the upper surface wall 16 a and the lower surface wall 16 b of the furnace shell 16. As a result, the furnace shell 16 is cooled with water, and overheating of the furnace shell 16 is prevented.

  The inner core tube 12 is made of a tube material having a diameter smaller than that of the core tube 11, and at least a part of the inner core tube 12 in the longitudinal direction is provided at the lower opening end of the core tube 11. A metal (for example, stainless steel) pipe 71 having the same diameter as the inner core 12 may be connected to the lower end of the inner core 12 as appropriate. Of course, instead of connecting the pipe material 71, the inner core tube 12 may be formed long.

  A first inert gas supply means 72 is provided at the top of the optical fiber drawing furnace 10. More specifically, a cylindrical member 73 is provided so as to surround the core tube 11 in contact with the upper surface wall 16 a of the furnace shell 16. The cylindrical member 73 includes a cylindrical portion 73a and a flange portion 73b formed at a non-top wall side end of the cylindrical portion 73a. A first gas supply line (not shown) provided with a gas tank is connected to a through hole 73c formed in the cylindrical portion 73a. An annular heat-resistant sealing member 78 having a hole having substantially the same diameter as the optical fiber preform P is provided on the upper portion of the flange portion 73b. In the heat-resistant sealing member 78, for example, the size of the hole is adjusted so that the diameter of the hole can be reduced or increased according to the outer diameter of the optical fiber preform P. Alternatively, a plurality of heat-resistant sealing members 78 having different hole sizes may be prepared in advance, and may be selectively used according to the outer diameter of the optical fiber preform P. The heat-resistant sealing member 78 seals the optical fiber preform P and the drawing furnace body.

  A second inert gas supply means 75 is provided at the lower part of the optical fiber drawing furnace 10. More specifically, the disk material 76 is connected to the lower end of the tube material 71. A hole 76 a having the same diameter as the inner diameter of the tube material 71 is provided at the center of the upper surface of the disk material 76. A through hole 76b having a smaller diameter is provided at the center bottom of the hole 76a, and the through hole 76b forms the furnace outlet 15. The diameter of the through hole 76b is set to be slightly larger than the outer diameter of the optical fiber OF. A through hole 76c that communicates with the hole 76a is formed in the peripheral surface of the disk member 76, and a second gas supply line (not shown) having a gas tank is connected to the through hole 76c.

  An exhaust path forming member 20 is mounted around an end of the inner core tube 12 on the side of the core tube (upper end in FIG. 1), thereby closing the gap between the core tube 11 and the inner core tube 12. The exhaust path forming member 20 is made of a heat insulating material. The heat insulating material is a material that hardly exchanges heat and hardly transfers heat. For example, the heat insulating material contains air inside. Here, the lower wall 16b of the furnace shell 16 and the lower end of the exhaust path forming member 20 are preferably formed flush with each other.

  As shown in FIG. 2, the exhaust path forming member 20 is composed of a thick tube, and the inner core tube 12 is fitted into the hole 21 at the center thereof. Further, the exhaust path forming member 20 includes an exhaust path 23 that connects the upper end surface and the lower end surface of the thick-walled body portion 22 in order to communicate the inside and the outside of the core tube 11. A plurality of exhaust paths 23 are provided along the longitudinal direction (vertical direction in FIG. 2) of the thick-walled main body 22 and at a predetermined interval in the circumferential direction (six are illustrated at regular intervals in FIG. 2). It is done.

  An exhaust furnace shell 17 is provided in contact with the lower wall 16 b of the furnace shell 16 so as to surround the inner core tube 12 and the exhaust path forming member 20. A space surrounded by the exhaust furnace shell 17 and the inner furnace core tube 12 forms an exhaust chamber 18. The exhaust chamber 18 communicates with the core 13 through the exhaust path 23 of the exhaust path forming member 20 and also communicates with the exhaust line 19 connected to the through hole 17 a of the exhaust furnace shell 17. The volume of the exhaust chamber 18 is formed to be larger than the volume of all the exhaust paths 23 in the exhaust path forming member 20. The exhaust line 19 may include a valve (not shown) for controlling the internal pressure.

  The heat insulating material constituting the exhaust path forming member 20 is not particularly limited as long as it is a material that can be used in the core 13, that is, a material having heat resistance that can withstand a high temperature of about 2000 ° C. And carbon heat insulating material (foamed carbon) having good properties and heat resistance.

  Examples of the constituent material of the core tube 11 and the inner core tube 12 include ceramics such as high-purity carbon and zirconia.

The both inert gases G1 and G2 are preferably He gas having a large diffusion coefficient, but are not particularly limited thereto, and may be Ar gas or N ₂ gas. Further, both the inert gases G1, G2 may be the same type or different types.

  In the present embodiment, the case where the exhaust path forming member 20 is an integral type has been described as an example, but the present invention is not particularly limited thereto. For example, as shown in FIG. 3, the exhaust path forming member 30 may be a separate type composed of an annular flange portion 32 and at least one pipe portion 35. The flange portion 32 is provided with a plurality of through holes 34 as many as the number of the tube portions 35 at a predetermined interval in the circumferential direction (six holes are shown at regular intervals in FIG. 3). The flange part 32 and each pipe part 35 are connected so that each through hole 34 and the hole 36 of each pipe part 35 communicate with each other. Alternatively, the connection between the flange part 32 and each pipe part 34 may be made to fit each pipe part 35 into each through hole 34 of the flange part 32. The through hole 34 and the hole 36 form the exhaust path 23. The flange portion 32 and the pipe portion 35 of the exhaust path forming member 30 are all made of a heat insulating material, but are not limited to this, and at least the surface of the through hole 34 of the flange portion 32 and the hole 36 of each pipe portion 35. The exhaust path forming member 30 having a heat insulating layer may be used.

  Next, the operation of the present embodiment will be described.

  The core 13 of the optical fiber drawing furnace 10 is heated by the heater 14. An inert gas G <b> 1 is supplied from above the optical fiber drawing furnace 10 via the first inert gas supply means 72. Further, the inert gas G <b> 2 is supplied from below the optical fiber drawing furnace 10 via the second inert gas supply means 75.

  The optical fiber preform P is melted by the heating of the heater 14, and the optical fiber OF is drawn. Here, above the drawing furnace, the gap between the optical fiber drawing furnace 10 and the optical fiber preform P is almost completely sealed by the heat-resistant sealing member 78. Moreover, although the space | interval between the lower exit 15 and the optical fiber OF is open below the optical fiber drawing furnace 10, the gap is very small. Therefore, almost the entire amount of the inert gas G1 is guided into the core 13 through the gap between the core tube 11 and the optical fiber preform P. Further, most of the inert gas G2 is introduced into the core 13 through the gap between the inner core tube 12 and the optical fiber OF.

  Similarly to the upflow type drawing furnace shown in FIG. 5, the inert gas G <b> 2 supplied from below the inner core tube 12 flows upward in the inner core tube 12, and It is ejected into the core 13 from the upper end. Thereby, the purge in the inner core tube 12 is performed. Similarly to the downflow type drawing furnace shown in FIG. 6, the inert gas G <b> 1 supplied into the core 13 from the upper end side of the core tube 11 passes through the gap between the core tube 11 and the optical fiber preform P. The gas flows downward, thereby purging the core 13.

  Since both the inert gases G1 and G2 after the purge are kept almost airtight in the core 13, they reach the vicinity of the center of the core 13 and then flow toward a lower pressure. Here, an exhaust small chamber 18 is formed on the downstream side of the exhaust path forming member 20 disposed facing the core 13, and the exhaust small chamber 18 has a larger volume than the exhaust path 23, and It is kept at a lower pressure than in the core 13. Therefore, both the inert gases G1 and G2 flow to the exhaust chamber 18 and the exhaust line 19 through the exhaust path forming member 20, and are quickly exhausted without staying in the core 13. As a result, both the inert gases G1 and G2 do not flow backward, the high temperature optical fiber OF is always in contact with the clean upflow inert gas G2, and the optical fiber preform P is always clean. It contacts with the downflow inert gas G1.

  When both the inert gases G1 and G2 flow into the exhaust chamber 18, when the exhaust path forming member is not provided (when the gap between the core tube 11 and the inner core tube 12 is directly passed), Since the upper wall 16a and the lower wall 16b have a water jacket structure, both the inert gases G1, G2 are rapidly cooled in the vicinity of the lower wall 16b. As a result, a large amount of dust adheres to the lower inner peripheral surface of the core tube 11 and the upper outer peripheral surface of the inner core tube 12. Therefore, in the optical fiber drawing furnace 10 according to the present embodiment, the exhaust path forming member 20 is provided in the gap between the core tube 11 and the inner core tube 12. Since the exhaust path forming member 20 is made of a carbon heat insulating material having excellent heat insulation and heat resistance, heat exchange between the inert gases G1 and G2 and the exhaust path 23 hardly occurs. Therefore, when both the inert gases G1 and G2 containing gaseous dust pass through the exhaust path 23 of the exhaust path forming member 20, the both inert gases G1 and G2 are not rapidly cooled.

  As a result, both the inert gases G1 and G2 pass through the exhaust path 23 while maintaining a high temperature state, so there is no possibility that dust will adhere to the exhaust path 23. Both the inert gases G1 and G2 that have passed through the exhaust path 23 are cooled in the exhaust chamber 18 that is cooler than the interior of the core 13. By this cooling, the gaseous dust contained in both the inert gases G1 and G2 is solidified and adhered (fixed) to the exhaust chamber 18.

  As described above, according to the optical fiber drawing furnace 10 according to the present embodiment, dust hardly adheres to the optical fiber preform P and the optical fiber OF. Therefore, the optical fiber OF obtained by drawing has very high strength because dust hardly adheres, and there is almost no possibility of disconnection in the middle of drawing. As a result, a long optical fiber OF can be obtained.

  Further, according to the optical fiber drawing furnace 10 according to the present embodiment, dust adheres not only to the optical fiber preform P and the optical fiber OF but also to the core tube 11 and the exhaust path 23 of the exhaust path forming member 20. There is hardly anything. The same applies to the case where the optical fiber OF is drawn using a large and long optical fiber preform P. Therefore, the life of the core tube 11 can be improved, the temperature distribution in the core 13 can be made uniform, and the internal pressure fluctuation in the core 13 can be suppressed. Further, since there is no possibility that the exhaust passage 23 is clogged with dust, there is no possibility that dust will flow back into the core 13.

  Moreover, dust can be fixed to an arbitrary position (desired position) in the exhaust path by appropriately coating the inner surface of the exhaust chamber 18 or both the inner surfaces of the exhaust chamber 18 and the exhaust line 19 with a heat insulating layer. If any position in the exhaust path is set to a position that can be easily accessed during maintenance, only the exhaust path at any position where dust adheres to the operation over time can be easily replaced or repaired. Can do. Therefore, even if it draws over a long time, it can prevent that various troubles accompanying dust adhesion occur in optical fiber drawing furnace 10.

  Further, by using the exhaust path forming member 30 having the structure shown in FIG. 3 instead of the exhaust path forming member 20 having the structure shown in FIG. 2, the manufacturing process of the exhaust path forming member is slightly complicated, but expensive. The amount of carbon heat insulating material used can be reduced, and the raw material cost can be reduced. Further, the contact area between the exhaust path forming member and the core tube 11 and the inner core tube 12 is smaller in the exhaust path forming member 30 than in the exhaust path forming member 20. For this reason, the exhaust path forming member 30 is more heat-insulating than the exhaust path forming member 20, that is, the heat retaining effect of both the inert gases G 1 and G 2 passing through the exhaust path 23.

  As described above, the present invention is not limited to the above-described embodiment, and it goes without saying that various other things are assumed.

  Next, although this invention is demonstrated based on an Example, this invention is not limited to these Examples.

  Three types of exhaust path forming members having the structure shown in FIG. 2 were produced. Each exhaust path forming member has a different constituent material, and is made of three types: a carbon heat insulating material (sample 1), a carbon material (sample 2), and a quartz glass (sample 3). The exhaust path forming members of Samples 1 to 3 were applied to the drawing furnace shown in FIG. 1 to draw the optical fiber.

  As a result, when the exhaust path forming member of Sample 1 was used, no dust adhered to the exhaust path. On the other hand, when the exhaust path forming member of Samples 2 and 3 was used, dust adhered to the exhaust path.

  From the above, in the drawing furnace according to the present invention using the exhaust path forming member composed of a heat insulating material, it can be confirmed that there is no dust adhering to the exhaust path as well as the core pipe and the inner core pipe. It was.

  The optical fiber was drawn using the drawing furnace having the structure shown in FIG. As the optical fiber base material, an optical fiber having an outer diameter of 110 to 120 mm, a length of 1200 mm, and an optical fiber having a length of 1000 km per one was used. The inner diameter of the core tube was 130 mm, and the inner diameter of the inner core tube was 40 mm. Further, as the exhaust path forming member, the one having the structure shown in FIG. 2 was used, made of carbon heat insulating material, and the height was 150 mm. He gas was used as the inert gas.

  After drawing the optical fiber by 1000 km, the next optical fiber preform was immediately set in a drawing furnace, and the optical fiber was drawn continuously. This drawing process was repeated to draw a total of 5000 km.

  After the drawing, the inside of the drawing furnace was observed. As a result, no dust was observed in the exhaust path of the core tube, the inner core tube, the optical fiber preform, and the exhaust path forming member.

  In addition, a proof test was performed on an optical fiber having a length of 5000 km to examine the strength of the optical fiber. As a result, there were nine disconnections in the optical fiber, and a long optical fiber having an average passage length of 500 km could be obtained.

  As described above, by drawing the optical fiber using the drawing furnace according to the present invention, no dust adheres to the entire flow path through which the inert gas flows in the drawing furnace, and the light obtained by the drawing is obtained. It was confirmed that there was almost no dust adhesion on the fiber.

1 is a schematic structural diagram of an optical fiber drawing furnace according to a preferred embodiment of the present invention. FIG. 2 is an enlarged perspective view of an exhaust path forming member in FIG. 1. It is a modification of the exhaust path formation member of FIG. It is a whole schematic diagram of an optical fiber manufacturing apparatus. It is the structure schematic which shows an example of the conventional optical fiber drawing furnace. It is the structure schematic which shows the other example of the conventional optical fiber drawing furnace.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Optical fiber drawing furnace 11 Core tube 12 Inner core tube 13 Core 20 Exhaust path formation member 23 Exhaust path P Optical fiber preform G1, G2 Inert gas

Claims (5)

In an optical fiber drawing furnace for drawing an optical fiber preform heated and melted in the core while purging the inside of the core with an inert gas,
A core tube forming the core;
A first inert gas supply means for supplying an inert gas in a downflow from above the drawing furnace into the furnace core tube;
A second inert gas supply means for supplying an upflow of inert gas into the furnace core tube from below the drawing furnace;
An inner core tube provided in the lower part of the core tube,
An exhaust path forming member that is provided so as to close a gap between the core tube and the inner core tube, and includes an insulating material;
The exhaust path forming member has an exhaust path for exhausting both the up-flow and down-flow inert gases purged in the core to the outside of the core tube, and the inlet of the exhaust path located inside the core tube is An optical fiber drawing furnace characterized by being formed at a position where the up-flow inert gas and the down-flow inert gas that merge near the center of the core can be sucked.   The exhaust path forming member is composed of a thick tube, and a plurality of exhaust paths are provided in the thick body portion at a predetermined interval in the circumferential direction of the thick body portion to communicate the inside and outside of the core tube. The optical fiber drawing furnace according to claim 1.   The exhaust path forming member is composed of an annular flange portion and a plurality of pipe portions, and the flange portion is provided with the same number of through holes as the number of pipe portions at a predetermined interval in the circumferential direction of the flange portion, and The optical fiber drawing furnace according to claim 1, wherein the through hole and the hole inside the pipe portion are communicated with each other.   The optical fiber drawing furnace according to any one of claims 1 to 3, wherein the heat insulating material is a carbon heat insulating material. In the optical fiber drawing method of drawing the optical fiber preform heated and melted in the core while purging the inside of the core with an inert gas,
Using a draw furnace in which an inner core tube is provided in the lower part of the core tube forming the core, and an exhaust path forming member made of a heat insulating material is provided so as to close a gap between the core tube and the inner core tube, When drawing the optical fiber preform by heating, melting,
A down flow inert gas is supplied into the core tube from above the drawing furnace, and an up flow inert gas is supplied to the inside of the core tube through the inner core tube from below the drawing furnace. contacting the inert gas of the down flow, in the optical fiber is contacted with the inert gas of the upflow is the core at the merging location of the inert gas of the inert gas and the down-flow of the upflow A method of drawing an optical fiber, characterized in that both inert gases supplied from the vicinity of the center to the inside of the core tube are exhausted outside the core tube through the exhaust path forming member.

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