JP2012082089A - Method for manufacturing optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an optical fiber capable of reducing drawing cost without damaging uniformity of the outer diameter of the optical fiber.SOLUTION: In this method for manufacturing an optical fiber for drawing an optical fiber preform P heated and melted in a core 13, while purging the core 13 inside by inert gases G1, G2 from an upper part and a lower part of the core 13 of a drawing furnace 10, the inert gas G1 for purging from the upper part of the core 13 is Ar, and the inert gas G2 for purging from the lower part of the core 13 is He.

Description

  The present invention relates to an optical fiber manufacturing method for drawing an optical fiber preform heated and melted in a core of a drawing furnace.

  Generally, an optical fiber is manufactured using a manufacturing apparatus as shown in FIG. In this manufacturing apparatus, first, in the drawing furnace 40, the optical fiber preform 101 is heated and melted, and then the optical fiber 102 is drawn from the furnace outlet 55 by drawing vertically downward. 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. The steps of cooling, resin coating, and resin curing are repeated as appropriate, whereby the optical fiber 103 is obtained. 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., the core tube 51 and the inner core tube 52 are generally made of ceramics such as high-purity carbon and zirconia. Is 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, the drawing furnace is roughly classified into an upflow type in which the inert gas flows upward and a downflow type in which the inert gas flows downward depending on the flow direction of the inert gas.

  By the way, when the optical fiber preform 101 is put in and out of the core 53 of the drawing furnace 40, outside air may be mixed in the core 53. When this outside air reacts with carbon that is a constituent material of the core tube 51 when the optical fiber preform 101 is heated, it is oxidized and burned to generate dust. Further, when the optical fiber preform 101 is melted, dust is generated due to evaporation of quartz.

  In the upflow type, the dust is exhausted together with the inert gas from the gap provided in the upper part of the core tube 51. For this reason, there is a possibility that dust adheres to the surface of the optical fiber preform 101. In the down flow type, the dust is exhausted together with the inert gas from the gap provided in the lower part of the core tube 51. For this reason, dust may adhere to the surface of the optical fiber 102 and the optical fiber 102 may be reduced in strength.

  There is a drawing furnace having a structure combining the upflow type and the downflow type (hereinafter referred to as a composite type) for the above problems (see, for example, Patent Document 1). In the combined type drawing furnace, the inside of the core is purged with inert gas from the upper and lower parts of the drawing core, and the vicinity of the junction where the inert gas purged from the upper part and the inert gas purged from the lower part join together Since both inert gases are discharged, it is possible to suppress dust from adhering to the optical fiber preform and the optical fiber.

  He is generally used as an inert gas for purging the core. By using He with a large kinematic viscosity coefficient, the inert gas supplied into the core is maintained in a laminar flow state, and fluctuations in the internal pressure in the drawing furnace are suppressed to stabilize the outer diameter of the optical fiber. This is to make it happen.

JP 2006-240930 A

  By the way, He is expensive among the inert gases, which causes an increase in the drawing cost of the optical fiber. For this reason, an alternative with an inexpensive inert gas is required.

  However, if an inert gas other than He is used as the inert gas for purging the inside of the core, the inert gas supplied into the core tends to be in a turbulent state, and the fluctuation of the internal pressure in the drawing furnace increases. In some cases, the outer diameter of the optical fiber becomes unstable.

  Accordingly, an object of the present invention is to solve the above-described problems and provide an optical fiber manufacturing method capable of reducing the drawing cost without impairing the uniformity of the outer diameter of the optical fiber.

  The present invention was devised to achieve the above object, and is an optical fiber that is heated and melted in the core while purging the inside of the core with an inert gas from the upper and lower portions of the core of the drawing furnace. In the method of manufacturing an optical fiber in which a base material is drawn, the optical fiber is purged from the upper part of the core and Ar, and the inert gas purged from the lower part of the core is He.

  The flow rate of Ar purged from the upper part of the core is preferably 10 L / min, and the flow rate of He purged from the lower part of the core is preferably 10 L / min.

  Ar is in contact with the optical fiber preform, and He is in contact with the drawn optical fiber, and both inert gases may be discharged from the vicinity of the junction of Ar and He.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the optical fiber which can reduce drawing cost can be provided, without impairing the uniformity of the outer diameter of an optical fiber.

It is a schematic block diagram of the drawing furnace used for the manufacturing method of the optical fiber which concerns on one embodiment of this invention. (A), (b) is a perspective view of the exhaust path formation member used with the drawing furnace of FIG. It is a whole schematic diagram of an optical fiber manufacturing apparatus.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  First, the drawing furnace used for the manufacturing method of the optical fiber which concerns on this Embodiment is demonstrated.

  FIG. 1 is a schematic configuration diagram of a drawing furnace used in the optical fiber manufacturing method according to the present embodiment.

  As shown in FIG. 1, the drawing furnace 10 draws the optical fiber preform P heated and melted in the core 13 in the direction of arrow A (downward in FIG. 1) to produce an optical fiber OF. Is. The drawing furnace 10 mainly includes a core tube (outer core tube) 11, a furnace shell 16, and an inner core tube (inner core tube) 12.

  The core tube 11 is composed of a pipe material having an opening end at the top and bottom, and a part in the longitudinal direction of the optical fiber preform P is accommodated from the upper opening end. The inner space of the core tube 11 forms the core 13.

  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 circulating and supplying cooling water 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 pipe material having a diameter smaller than that of the core tube 11, and is provided at the lower opening end of the core tube 11 by inserting at least a part of the inner core tube 12 in the longitudinal direction. A tube 71 made of metal (for example, made of stainless steel) having the same diameter as the inner core tube 12 may be connected to the lower end of the inner core tube 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 in the upper part of the 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 on the upper portion of the cylindrical portion 73a (the side opposite to the core tube 11). 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 expanded in accordance with 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 drawing furnace 10. More specifically, the disk material 76 is connected to the lower end of the tube material 71. A hole 76a having the same diameter as the outer diameter of the tube 71 is provided in the center of the upper surface of the disk member 76, and the lower end of the tube 71 is inserted into the hole 76a. 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 the upper end of the inner core tube 12 (the end opposite to the pipe material 71), 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. 2A, the exhaust path forming member 20 is constituted by 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 passages 23 are arranged along the longitudinal direction of the thick body portion 22 (vertical direction in FIG. 2A) and at a predetermined interval in the circumferential direction (equal intervals in FIG. 2A). 6 are shown).

  An exhaust furnace shell 17 is integrally provided so as to contact the lower wall 16 b of the furnace shell 16 and 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 (tube material 71) 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.

  In the present embodiment, the case where the exhaust path forming member 20 shown in FIG. 2A is used has been described. However, the present invention is not limited to this. For example, the exhaust path as shown in FIG. The forming member 30 may be used. The exhaust path forming member 30 includes 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 portion 32 and each tube portion 35 may be made to fit each tube portion 35 into each through hole 34 of the flange portion 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. It may have a heat insulating layer.

  Next, a method for manufacturing an optical fiber according to the present embodiment will be described.

  First, the core 13 of the drawing furnace 10 is heated by the heater 14. An inert gas G1 is supplied from above the drawing furnace 10 via the first inert gas supply means 72, and inert from below the drawing furnace 10 via the second inert gas supply means 75. Gas G2 is supplied.

  Above the drawing furnace 10, the gap between the drawing furnace 10 and the optical fiber preform P is almost completely sealed with a heat-resistant sealing member 78. Further, below the drawing furnace 10, the space between the furnace outlet 15 and the optical fiber OF is open, but 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.

  The inert gas G <b> 2 supplied from below the inner core tube 12 flows upward in the inner core tube 12 and is jetted into the core 13 from the upper end of the inner core tube 12. As a result, the inner core tube 12 and the core 13 are purged. Further, the inert gas G1 supplied into the core 13 from the upper end side of the core tube 11 flows downward through the gap between the core tube 11 and the optical fiber preform P, thereby purging the core 13. Done.

  In this way, the heat of the heater 14 is transferred to the inert gas G1, G2 in the core 13 while purging the inside of the core 13 with the inert gas G1, G2 from the upper part and the lower part of the core 13 of the drawing furnace 10. The optical fiber preform P is melted to draw the optical fiber OF.

  In the optical fiber manufacturing method according to the present embodiment, Ar is used as the inert gas G1 purged from the upper part of the core 13 and He is used as the inert gas G2 purged from the lower part of the core 13.

  The reason why Ar is used for the inert gas G1 is that the price is lower than that of He, and the heat transfer coefficient and the kinematic viscosity coefficient are better than that of nitrogen of the same inert gas. Further, the inert gas G1 is Ar and the inert gas G2 is He. The reason why the inert gas G1 and G2 are less likely to be turbulent is that the He gas having an excellent kinematic viscosity coefficient is blown up. This is because the internal pressure of 11 is stabilized. The internal pressure of the core tube 11 may be about 30 Pa. Here, the case where the internal pressure of the core tube 11 is set to 30 Pa will be described.

  In the present embodiment, the flow rate of Ar purged from the top of the core 13 is 10 L / min, and the flow rate of He purged from the bottom of the core 13 is 10 L / min. The reason why the flow rates of Ar and He are 10 L / min each is that the internal pressure of the core tube 11 is most stable, and the fluctuation of the internal pressure of the core tube 11 is suppressed to about ± 0.2 Pa (29.8 to 30.2 Pa). It is because it can do. Thereby, the outer diameter of the optical fiber OF drawn is very stable.

  The two inert gases G1 and G2 after the purge merge near the center of the core 13 and are discharged from the vicinity of the merged portion. 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 the inside of the core 13. Is kept at a lower pressure. 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, and the high-temperature optical fiber OF is always in contact with the clean upflow inert gas G2 (here, He), and the optical fiber preform P Is always contacted with a clean downflow inert gas G1 (here Ar).

  In the drawing furnace 10, since the exhaust path forming member 20 made of a heat insulating material is provided, both the inert gases G1 and G2 are not cooled by the lower surface wall 16b of the water cooling structure and are kept at a high temperature to the exhaust chamber 18. Then, it is cooled in the exhaust chamber 18. At this time, the gaseous dust contained in both the inert gases G1 and G2 is solidified and adhered (fixed) to the exhaust chamber 18. Thus, since dust is discharged to the outside of the core 13, dust hardly adheres to the optical fiber preform P and the optical fiber OF, and an optical fiber OF having high strength can be obtained. As a result, it is possible to suppress disconnection during drawing and to obtain a long optical fiber OF.

  As described above, in the optical fiber manufacturing method according to the present embodiment, Ar is used as the inert gas G1 purged from the upper part of the core 13, and He is used as the inert gas G2 purged from the lower part of the core 13. Furthermore, the flow rates of Ar and He are each 10 L / min.

  This makes it possible to stabilize the inner pressure of the drawing furnace 10, that is, the inner pressure of the core tube 11, and draw an optical fiber OF having a stable outer diameter, even when using Ar, which is less expensive than He. Become. In other words, according to the present invention, the drawing cost can be reduced without impairing the uniformity of the outer diameter of the optical fiber OF.

  The present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the spirit of the present invention.

  As an embodiment of the present invention, when the drawing furnace 10 of FIG. 1 is used, Ar is used as the inert gas G1, He is used as the inert gas G2, and the flow rates of both the inert gases G1 and G2 are both 10 L / min. The internal pressure of the drawing furnace 10 (internal pressure of the core tube 11) was measured.

  As a conventional example, the internal pressure of the drawing furnace 10 when both the inert gases G1 and G2 are He, the flow rate of the inert gas G1 is 25 L / min, and the flow rate of the inert gas G2 is 10 L / min ( The internal pressure of the core tube 11) was measured. The measurement results are shown in Table 1.

  As shown in Table 1, in both the example and the conventional example, the internal pressure of the drawing furnace 10 was 29.8 to 30.2 Pa, and fluctuations in the internal pressure of the drawing furnace 10 were sufficiently suppressed. From this result, it was proved that the internal pressure of the core tube 11 was stabilized to the same level as before even when the inert gas G1 was changed to Ar and the flow rates of the two inert gases G1, G2 were 10 L / min.

  Moreover, in the above-mentioned Example, the outer diameter of the optical fiber OF for every drawing length was measured. The measurement results are shown in Table 2.

  As shown in Table 2, the outer diameter fluctuation of the optical fiber OF in the example was found to be ± 0.14 μm. This was equivalent to the conventional example. That is, according to the present invention, it is possible to achieve the same outer diameter uniformity of the optical fiber OF as that of the prior art while using inexpensive Ar and reducing the drawing cost.

10 Drawing furnace 11 Core tube 12 Inner core tube 13 Core P Optical fiber preform G1, G2 Inert gas

Claims (3)

In an optical fiber manufacturing method for drawing an optical fiber preform heated and melted in the core while purging the inside of the core with an inert gas from an upper part and a lower part of the core of the drawing furnace,
An optical fiber manufacturing method, wherein the inert gas purged from the upper part of the core is Ar, and the inert gas purged from the lower part of the core is He.   The method of manufacturing an optical fiber according to claim 1, wherein the flow rate of Ar purged from the upper part of the core is 10 L / min, and the flow rate of He purged from the lower part of the core is 10 L / min.   3. The light according to claim 1, wherein Ar is in contact with the optical fiber preform and He is in contact with the drawn optical fiber, and both inert gases are discharged from the vicinity of the junction of Ar and He. Fiber manufacturing method.

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