JP2015074600A - Method of manufacturing optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing an optical fiber that reduces pressure change in a drawing furnace and change of a flow of gas caused as drawing of a glass perform advances, and suppresses external diameter variation of an optical fiber small.SOLUTION: There is provided a method of manufacturing an optical fiber in which a dummy bar 13 is connected to an upper end of a glass preform 11 for optical fiber which has a diameter reduced part 11c at an upper part, and the glass preform for optical fiber is heated and fused in a drawing furnace so as to draw an optical fiber. A member 25 having volume which is 50% or larger of the space between the diameter reduced part of the glass preform and a furnace tube is arranged at the position of the diameter reduced part, and the optical fiber is drawn.

Description

  The present invention relates to an optical fiber manufacturing method in which a dummy rod is connected to a reduced diameter portion at the upper end of an optical fiber glass preform, and the optical fiber glass preform is heated and melted in a drawing furnace to draw the optical fiber. .

  Optical fiber drawing using an optical fiber drawing furnace (hereinafter referred to as a drawing furnace) is performed by heating and melting an optical fiber glass base material (hereinafter referred to as a glass base material) mainly composed of quartz with a heater or the like. Is called. Since the temperature in the drawing furnace at this time is as high as about 2000 ° C., carbon having excellent heat resistance is used for the parts in the drawing furnace. This carbon has the property of being oxidized and consumed in a high-temperature oxygen-containing atmosphere. For this reason, it is necessary to keep the inside of a drawing furnace in the atmosphere of noble gases, such as argon gas and helium gas, and nitrogen gas (henceforth inert gas etc.).

Normally, the glass base material is vitrified by depositing glass particles on a small-diameter seed rod, so the boundary between the upper end of the straight barrel (also called the main body) and the seed rod is tapered. A dummy rod having the same diameter is connected to the seed rod, and is suspended and supported in the core tube of the drawing furnace.
As described above, since the diameter of the glass base material is greatly changed, it is very difficult to seal the tapered portion when the tapered portion whose diameter is greatly changed passes through the upper end of the drawing furnace. In addition, when the diameter changes greatly, the volume of the drawing furnace space changes as the drawing progresses, and the flow of gas in the drawing furnace changes, so the outer diameter fluctuation of the optical fiber may increase. . Therefore, for example, in Patent Document 1, a pipe having substantially the same diameter as the glass base material is disposed above the glass base material so that the sealed state is maintained even when the tapered portion passes, and the glass base material is also provided. It has been disclosed that the volume of the upper space of the glass base material is kept substantially constant and fluctuations in the outer diameter are suppressed even when the wire drawing is continued.
Further, in Patent Document 2, an inner cylinder pipe is provided at the upper part of the drawing furnace, a space in the inner cylinder pipe is partitioned by a plurality of sets of partition plates, and the volume of the upper space of the glass base material is kept constant. A technique for suppressing fluctuation is disclosed.

JP 2011-84409 A Japanese Patent Laid-Open No. 11-343137

However, in the method of Patent Document 2, when the reduced diameter portion of the glass base material approaches the heating portion, the temperature of the reduced diameter portion locally increases due to thermal radiation of the so-called “shoulder” portion of the glass base material. As the reduced diameter part approaches the heater, the gas flow (also called natural convection) changes in the space above the glass base material (such as the position of the reduced diameter part), and this gas flow causes pressure fluctuations in the drawing furnace. affect. This phenomenon is unlikely to occur when helium gas with high thermal conductivity is used as the furnace gas, but it is likely to occur with argon gas, nitrogen gas, etc. with low thermal conductivity. Outer diameter fluctuation also increases.
In the method of Patent Document 1, since the space at the position of the reduced diameter portion of the glass base material is enclosed, convection does not occur in this space, but when the reduced diameter portion of the glass base material approaches the heating portion, There is a problem that the pipe and the glass base material are welded. If they are welded, it will be necessary to separate them later, and it will be difficult to reuse the pipes. On the other hand, if the pipe is separated from the glass base material, the space volume cannot be kept constant, and it is difficult to suppress fluctuations in the outer diameter.

  The present invention has been made in view of the above situation, and reduces fluctuations in pressure and gas flow in the drawing furnace caused by drawing of the glass base material, and reduces fluctuations in the outer diameter of the optical fiber. It aims at providing the manufacturing method of the optical fiber to suppress.

  In the method of manufacturing an optical fiber according to the present invention, a dummy rod is connected to the upper end of an optical fiber glass preform having a reduced diameter portion at the upper portion, and the optical fiber glass preform is heated and melted in a drawing furnace. An optical fiber manufacturing method for drawing an optical fiber having a volume of 50% or more of a space between the reduced diameter portion and a core tube at a position of the reduced diameter portion of the optical fiber glass preform. Arrange the members and draw the optical fiber.

  According to the present invention, even when the reduced diameter portion approaches the heating position due to the drawing of the glass preform, it is possible to reduce the pressure fluctuation in the drawing furnace, and to suppress the outer diameter fluctuation of the optical fiber. it can.

It is a figure explaining the outline of the manufacturing method of the optical fiber by one form of the present invention. It is a figure which shows the example of the member by this invention. It is a figure which shows the example of the other member by this invention. It is a figure which shows the relationship between the pressure fluctuation in a drawing furnace, and the outer diameter fluctuation | variation of an optical fiber. It is a figure which shows the relationship between the base material length in the drawing end end vicinity, and the pressure fluctuation in a drawing furnace. It is a figure which shows the other example of the drawing furnace used for this invention.

[Description of Embodiment of Present Invention]
First, the contents of the embodiments of the present invention will be listed and described.
The optical fiber manufacturing method of the present invention is as follows. (1) A dummy rod is connected to the upper end of the optical fiber glass preform having a reduced diameter portion at the upper portion, and the optical fiber glass preform is heated in a drawing furnace. An optical fiber manufacturing method in which an optical fiber is melted and drawn, wherein at least 50% of the space between the reduced diameter portion and the core tube is located at the reduced diameter portion of the glass preform for optical fiber. An optical fiber is drawn by arranging a member having a volume. As described above, since the space generated by the reduced diameter portion is filled with the member, convection of gas in the space portion can be suppressed. In addition, although the vicinity of the reduced diameter portion of the glass base material is locally high in temperature, the heat of this reduced diameter portion is dispersed by the member, so a sudden temperature change is relaxed and is not easily transmitted directly to the upper space, Natural convection due to heat in the upper space is also reduced. As a result, even if the reduced diameter portion approaches the heating position due to the drawing of the glass base material, it is possible to reduce the pressure fluctuation in the drawing furnace, and to suppress the fluctuation in the outer diameter of the optical fiber.

(2) The member is made of carbon or ceramics. Since the member is made of carbon or ceramics, it is not welded to the glass base material.
(3) The member has a cylindrical shape with a hole in the center, and the inner diameter of the lower end of the member is larger than the inner diameter of the upper end of the member. If it is a member of such a shape, it will be easy to fill the space between the reduced diameter part of the glass preform for optical fibers, and a core tube, and the above-mentioned effect can be acquired suitably.
(4) The gas inlet for allowing the in-furnace gas to flow into the drawing furnace is set so as not to exist above the upper end of the member from the start to the end of drawing of the optical fiber glass preform. Since the gas inlet is set to be lower than the upper end of the member, the flow of the gas in the furnace in the upper space is suppressed, which contributes to the reduction of pressure fluctuations in the drawing furnace.

(5) Engage the member above the reduced diameter portion of the optical fiber glass preform so that the load of the member is not directly applied to the reduced diameter portion of the optical fiber glass preform. A locking member for stopping is provided. Since the member is locked by the locking member and floats from the reduced diameter portion, no force is applied to the member, and the member does not break.
(6) The lower end of the member contacts the optical fiber glass preform. If the lower edge of the member is brought into contact with the optical fiber glass preform, the space inside the member is closed and does not lead to the space outside the member, so that gas convection in the space in the drawing furnace can be further suppressed. .
(7) A sleeve member having substantially the same diameter as the glass preform for optical fiber is disposed on the upper part of the member. Since the sleeve member (pipe material) is disposed on the member, the space volume in the drawing furnace can be kept small.

[Details of the embodiment of the present invention]
An outline of a manufacturing method of an optical fiber to which the present invention is applied will be described with reference to FIG. In the following, a resistance furnace that heats the core tube with a heater will be described as an example. However, the present invention can also be applied to an induction furnace in which a high-frequency power source is applied to the coil to induction-heat the core tube.
In the figure, 10 is a drawing furnace, 11 is an optical fiber glass base material, 12 is an optical fiber, 13 is a dummy rod, 14 is a connecting portion, 15 is a core tube, 16 is a heater, 17 is a heat insulating material, and 18 is a furnace. A housing, 19 is a lower chamber, 20 is an upper chamber, 21 is a lid, 21a is an upper end opening, 22 is a gas introduction path, 23 is a gas supply section, 24 is a measurement section, 25 is a member, and 26 is a locking tool. Show.

  The drawing furnace 10 shown in FIG. 1 includes a furnace casing 18, a lower chamber 19, and an upper chamber 20. The core tube 15 is formed in a cylindrical shape at the center of the furnace casing 18 and communicates with the lower chamber 19 and the upper chamber 20. The core tube 15 is made of carbon, and an optical fiber glass base material 11 (hereinafter referred to as a glass base material) is inserted into the core tube 15 through the upper chamber 20.

The upper chamber 20 has, for example, an inner diameter similar to that of the core tube 15 and is sealed (sealed) with a lid 21 disposed on the upper end thereof. An upper end opening 21 a is formed in the lid 21, and a dummy rod 13 made of the same kind of glass rod as the glass base material 11 is inserted therethrough.
A heater 16 is arranged in the furnace casing 18 so as to surround the furnace core tube 15, and a heat insulating material 17 is accommodated so as to cover the outside of the heater 16. The heater 16 heats and melts the glass base material 11 inserted into the core tube 15, and causes the optical fiber 12 that has been melted and reduced in diameter to hang down from the lower chamber 19.

The glass base material 11 is welded at a connecting portion 14 connected to the dummy bar 13 or connected and integrated through a connecting member. The glass base material 11 can be moved in the drawing direction (vertical direction) by a moving mechanism (not shown).
The drawing furnace 10 is provided with an in-furnace gas supply mechanism such as an inert gas. Specifically, a gas introduction path 22 is provided in the upper chamber 20. For example, an inert gas or the like in which argon gas and helium gas are mixed is sent into the reactor core tube 15, whereby the reactor core tube 15 and the heater are heated. 16 to prevent oxidation and deterioration around 16. The position where the in-furnace gas is supplied by the gas introduction path 22 is set to be lower than the upper end portion of the member 25. The supply amount of the inert gas or the like flows at a constant amount, or P control (Proportional Control), I control (Integral Control), D in the gas supply unit (also referred to as mass flow controller (MFC)) 23, D Control (Derivative Control: differential control) or various controls in which these are appropriately combined can be applied. However, the control method is not limited to these.

The inert gas or the like passes through the gap between the glass base material 11 and the core tube 15 and is released to the outside from the drawn optical fiber 12 and the shutter portion below the lower chamber 19.
The upper chamber 20 is provided with a measuring unit 24 for measuring the pressure in the drawing furnace 10. It is good also as providing the control part which receives this measurement result and hold | maintains the pressure fluctuation in the drawing furnace 10 to a predetermined value.

  2, the glass base material 11 has a reduced diameter portion 11c having a tapered portion 11b at the upper end portion of the straight body portion 11a, and the upper end portion of the reduced diameter portion 11c and the dummy bar 13 are connected to each other. 14 are connected. A heat-resistant member 25 is provided at the position of the reduced diameter portion 11c, and the temperature of the reduced diameter portion 11c is dispersed to alleviate a rapid temperature change.

  The member 25 is disposed so as to fill the space generated by the reduced diameter portion 11c, and the volume thereof is 50% or more of the space between the reduced diameter portion 11c and the core tube 15. The member 25 is made of carbon or ceramics, and the shape thereof may be a cylindrical shape with a hole in the center as shown in FIG. 1, the cross-sectional shape may be a rectangle, or the shape of the reduced diameter portion may be matched. The inner diameter at the lower end may be larger than the inner diameter at the upper end. As an example of the latter, a cup shape in which the outer peripheral edge of the disk as shown in FIG. 3 (A) extends downward, and a triangular cross section as shown in FIG. 3 (B) are shown. Regardless of the shape, an insertion hole 25a through which the dummy bar 13 is inserted is provided at the center portion thereof. The member 25 is fixed to the upper part of the reduced diameter part 11c or the dummy bar 13 using, for example, a ring 26a that engages with the upper part of the reduced diameter part 11c or the dummy bar 13. If the member 25 has a structure that can be divided, such as a split structure, after the glass base material 11 is set in the drawing furnace 10, the member 25 can be disposed in the reduced diameter portion 11 c of the glass base material 11. Therefore, workability is good and preferable.

  The position of the member 25 with respect to the reduced diameter portion 11c may be adjusted by placing, for example, a plurality of stacked spacers 26b on the ring 26a. Instead of this ring, the position may be fixed by using a pin that protrudes from the dummy bar 13 and engages with the member 25, for example.

  Since the member 25 fills the space formed by the reduced diameter portion 11c by 50% or more, gas convection does not occur in this portion. In addition, a rapid temperature change between the reduced diameter portion 11c and the upper space that becomes high temperature can be reduced, and natural convection due to heat in the upper space can also be reduced.

FIG. 4 is a diagram showing the relationship between the pressure fluctuation in the drawing furnace and the outer diameter fluctuation of the optical fiber. As shown in FIG. 4, there is a correlation between the pressure fluctuation in the drawing furnace and the outer diameter fluctuation of the optical fiber, and the outer diameter fluctuation of the optical fiber increases as the pressure fluctuation increases.
Since argon gas has a thermal conductivity nearly 10 times lower than that of helium gas, argon gas or a gas obtained by mixing argon gas with helium gas is used as compared with the case where 100% helium gas is used as the drawing furnace gas. In this case, pressure fluctuation due to temperature unevenness is likely to occur, and the outer diameter fluctuation of the optical fiber becomes large. Even if nitrogen gas is used instead of argon gas, a similar result is obtained.

  Since there is a correlation between the pressure fluctuation in the drawing furnace and the outer diameter fluctuation of the optical fiber, the pressure fluctuation in the drawing furnace may be suppressed in order to suppress the outer diameter fluctuation of the optical fiber. For example, if the pressure fluctuation in the drawing furnace is ± 2.0 Pa or less, the outer diameter fluctuation of the optical fiber is reduced to ± 1.0 μm, and if the pressure fluctuation is reduced to ± 1.0 Pa, the outer diameter of the optical fiber is reduced. If the fluctuation is reduced to ± 0.4 μm and the pressure fluctuation is reduced to ± 0.5 Pa, the outer diameter fluctuation of the optical fiber can be suppressed to ± 0.15 μm.

  FIG. 5 is a diagram showing the relationship between the base metal length in the vicinity of the drawing end and the pressure fluctuation in the drawing furnace. The base material length 0 to 120 mm shown on the horizontal axis indicates the length of the glass base material drawn after that, when the diameter reduction start end of the upper part of the glass base material passes through the upper end of the core tube, 0 mm. In the vicinity of the drawing end, the straight body portion of the glass base material is lowered, and the reduced diameter portion is close to the heater.

As shown in FIG. 5, in the comparative example (drawing furnace in which the member 25 described in FIGS. 1 and 2 is not disposed), when the base material length reaches 110 mm, the pressure fluctuation in the drawing furnace becomes ± 5.0 Pa. From FIG. 4, it can be seen that the variation in the outer diameter of the optical fiber greatly exceeds ± 4.0 μm.
On the other hand, in the example (drawing furnace in which the member 25 described with reference to FIGS. 1 and 2 is disposed), even if the base metal length reaches 110 mm, the pressure fluctuation in the drawing furnace continues to be ± 0.5 Pa or less. It can be seen from FIG. 4 that the fluctuation of the outer diameter of the optical fiber can be maintained at ± 0.15 μm or less.

It should be noted that the gas inlet for supplying the in-furnace gas into the drawing furnace (the supply port of the gas supply unit 23 into the drawing furnace) is the upper end of the member 25 from the start to the end of the drawing of the optical fiber glass preform. It is preferable that it is set so as not to exist in the upper part. This is because if the gas inlet is at the upper part of the member 25, a gas flow occurs in the upper space, and a pressure fluctuation in the drawing furnace occurs.
In the embodiment of FIG. 5, the gas inlet is set so as not to exist above the upper end of the member 25 from the start to the end of drawing of the optical fiber glass preform.

  Moreover, in the member 25, if the lower end is lightly in contact with the glass base material, the space surrounded by the member 25 is closed and is not connected to the drawing furnace space. If 25 is a member made of carbon or ceramics, there is no fear of melting or welding to the glass base material even if the reduced diameter part of the glass base material approaches the heating part.

  In addition, since the diameter is changed in the reduced diameter portion, it is possible to engage (load) the member having the shape of FIG. 1 on this reduced diameter portion, but when a load of the member is directly applied to the reduced diameter portion, Since the member expands due to the heat of the reduced diameter portion that becomes high temperature and slides down and may crack after the cooling diameter reduction, it is preferable to provide a locking member to lock the member.

FIG. 6 is a diagram showing another example of a drawing furnace used in the present invention. In the above embodiment, an example of a drawing furnace sealed with a lid at the upper end of the upper chamber has been described. However, the drawing furnace shown in FIG. 6 has an insertion port for the glass base material 11 at the upper end of the furnace casing 18. And a first seal portion 32 for sealing a gap between the straight body portion 11a and the insertion portion.
A cylindrical upper chamber 34 having a height lower than that of the upper chamber 20 shown in FIG. 1 is provided on the first seal portion 32. A second seal portion 33 having a sealing function similar to that of the first seal portion 32 is disposed at the upper end of the upper chamber 34. The first seal portion 32 and the second seal portion 33 can be provided with gas supply ports 32a and 33a for supplying an inert gas or the like into the core tube.

  Reference numeral 30 denotes a sleeve member disposed around the outer periphery of the dummy bar 13. The sleeve member 30 is fixed to the lid member 31 and is disposed above the member 25. The sleeve member 30 is made of heat-resistant quartz glass, metal, carbon, SiC-coated carbon, or the like, and has an outer diameter. The outer diameter of the straight body portion 11a is preferably equal to or larger than 2/3 of the outer diameter of the straight body portion 11a. Moreover, it is preferable that the outer peripheral surface of the sleeve member 30 is processed such as grinding so as to have an accuracy equal to or higher than the outer diameter variation of the glass base material 11. In this case, the outer diameter of the member 25 is preferably the same as the outer diameter of the straight body portion 11a or 2/3 or more of the outer diameter of the straight body portion 11a.

The first seal portion 32 and the second seal portion 33 seal the outer peripheral surface of the glass base material 11, the member 25 and the sleeve member 30 in an annular shape so that outside air does not enter from the gap with the core tube, It is possible to prevent the inert gas in the furnace core tube from leaking outside.
Thus, since the member 25 made of carbon or ceramics is disposed between the sleeve member 30 and the glass base material 11, the sleeve member melts even when the sleeve member is disposed at a position closer to the reduced diameter portion. There is nothing, and the space volume in the drawing furnace can be kept small.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the meanings described above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 10 ... Drawing furnace, 11 ... Glass base material for optical fibers, 11a ... Straight body part, 11b ... Tapered part, 11c ... Reduced diameter part, 12 ... Optical fiber, 13 ... Dummy rod, 14 ... Connection part, 15 ... Core Pipes, 16 ... heaters, 17 ... heat insulation, 18 ... furnace casing, 19 ... lower chamber, 20, 34 ... upper chamber, 21 ... lid, 21a ... upper end opening, 22 ... gas introduction path, 23 ... gas supply section , 24 ... measurement part, 25 ... member, 25a ... insertion hole, 26 ... locking tool, 26a ... ring, 26b ... spacer, 30 ... sleeve member, 31 ... lid member, 32 ... first seal part, 32a, 33a ... gas supply port, 33 ... second seal part.

Claims (7)

An optical fiber manufacturing method in which a dummy rod is connected to an upper end of an optical fiber glass preform having a reduced diameter portion at an upper portion, and the optical fiber glass preform is heated and melted in a drawing furnace to draw the optical fiber. Because
An optical fiber for drawing an optical fiber by arranging a member having a volume of 50% or more of the space between the reduced diameter portion and the core tube at the position of the reduced diameter portion of the glass preform for optical fiber. Production method.   The optical fiber manufacturing method according to claim 1, wherein the member is made of carbon or ceramics.   The method of manufacturing an optical fiber according to claim 1, wherein the member has a cylindrical shape with a hole in the center, and an inner diameter of the lower end of the member is larger than an inner diameter of the upper end of the member.   2. The gas inflow port through which the in-furnace gas flows into the drawing furnace is set so as not to exist above the upper end of the member from the start to the end of drawing of the optical fiber glass preform. 4. The method for producing an optical fiber according to any one of items 1 to 3.   Engaging the member on the upper portion of the reduced diameter portion of the optical fiber glass preform so that the load of the member is not directly applied to the reduced diameter portion of the optical fiber glass preform. The manufacturing method of the optical fiber of any one of Claim 1 to 4 which provides a stop member.   The manufacturing method of the optical fiber of any one of Claim 1 to 5 with which the lower end of the said member contacts the said glass preform | base_material for optical fibers.   The optical fiber manufacturing method according to any one of claims 1 to 6, wherein a sleeve member having substantially the same diameter as that of the optical fiber glass preform is disposed on an upper portion of the member.

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