JP2004161563A - Method and apparatus for drawing optical fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for drawing an optical fiber, in which the volume change occupied by gas in the inside of a furnace body can be suppressed and by which a high quality optical fiber free from the diameter fluctuation can be drawn. <P>SOLUTION: A gas feeding unit 17 for blowing out a seal gas toward the inner peripheral side is provided at an upper inlet of a drawing furnace 11. A closing member 31 which is formed to have an outer diameter nearly equal to that of the optical fiber preform 21 and hung from an engaging member 32 arranged at the upper part than the optical fiber preform 21 is arranged at the diameter reduced part 21b of the optical fiber preform 21 sent into the inside of the drawing furnace 11 at least after the diameter reduced part 21b comprising a shoulder part at the upper end of the optical fiber preform 21 has arrived at the upper inlet of the drawing furnace 11. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical fiber drawing method and an optical fiber drawing apparatus that can stably draw an optical fiber by using a gas seal.
[0002]
[Prior art]
The optical fiber is manufactured by supplying a base material made of a material such as quartz from the upper part of the drawing furnace, heating and melting the front end portion in the drawing furnace, and pulling down from the front end of the base material to reduce the diameter. I have.
In the drawing furnace shown in FIG. 6, an insertion opening for inserting a base material 2 is formed in a gas diffuser 1 installed above a drawing furnace 3, and the gas diffuser 1 is inerted toward the base material 2 from the gas diffuser 1. gas F ₁ is ejected (refer to Patent Document 1).
[0003]
The gas sealing is usually performed by blowing an inert gas onto the base material at the upper end of the drawing furnace. The blown out inert gas divides into an upward flow that flows upstream and a downward flow that hits the base material. Of these, the upward flow prevents oxygen from entering through the gap between the base material and the furnace tube. In addition, the downward flow is released from a shutter provided at the lower part of the drawing furnace, thereby preventing oxygen from entering from below. Due to such a gas flow, the inside of the drawing furnace is always maintained at a positive pressure with respect to the atmospheric pressure.
[0004]
[Patent Document 1]
JP-A-62-176938 (page 3, FIG. 1)
[0005]
[Problems to be solved by the invention]
By the way, when the base material is to be drawn, if the space between the upper part of the furnace body and the base material is sealed with gas, a reduced diameter portion caused by a difference in diameter between the base material and the dummy rod suspending the base material is generated. When the gas enters the inside of the furnace, the volume occupied by the gas inside the furnace body changes, and as a result, the gas flow changes, which results in a fluctuation in the diameter of the drawn optical fiber.
[0006]
The present invention has been made in view of the above circumstances, and provides an optical fiber drawing method and a drawing apparatus capable of suppressing a change in volume occupied by gas inside a furnace body and drawing a high-quality optical fiber without a diameter change. It is intended to provide.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the method for drawing an optical fiber of the present invention comprises the steps of: feeding an optical fiber preform from above into a drawing furnace in which a sealing gas is jetted toward an inner peripheral side at an upper entrance; An optical fiber drawing method for drawing an optical fiber reduced in diameter to a predetermined outer diameter by heating and softening in a drawing furnace, wherein at least the reduced diameter portion at the upper end of the optical fiber preform is located above the drawing furnace. After reaching the entrance, above the reduced diameter portion of the optical fiber preform, it was formed to have substantially the same outer diameter as the optical fiber preform, and the end face on the optical fiber preform side was formed in a shape along the reduced diameter portion. A sealing member is provided, and the space between the upper entrance of the drawing furnace and the sealing member is gas-sealed with a sealing gas.
[0008]
According to the optical fiber drawing method of the present invention, even if the drawing of the optical fiber proceeds and the reduced diameter portion which is the shoulder of the optical fiber preform enters the drawing furnace, the diameter of the optical fiber preform is reduced. Since a sealing member having an outer diameter substantially equal to that of the optical fiber preform and having an end face on the optical fiber preform side formed along the reduced diameter portion is disposed above the portion, the gas inside the furnace is The change in volume occupied by the gas is suppressed, thereby preventing the change in the flow of the seal gas such as the inert gas supplied into the furnace, the fluctuation in the diameter of the optical fiber caused by the change in the gas flow is suppressed, and the stable The optical fiber can be drawn with the adjusted diameter, and a high-quality optical fiber can be drawn.
[0009]
In addition, the sealing member may be configured by a plurality of members, and the plurality of members may be movable in accordance with the deformed reduced diameter portion.
Further, the closing member may be suspended from the engaging member disposed on the upper part.
[0010]
Further, the sealing member may be placed on the reduced diameter portion of the optical fiber preform so that the end faces thereof are in contact with each other, and more preferably, the sealing member is slightly spaced from the reduced diameter portion of the optical fiber preform. It may be arranged open.
The gas may flow out from the end face of the sealing member to the reduced diameter portion of the optical fiber preform.
[0011]
Further, the optical fiber drawing apparatus of the present invention has a drawing furnace provided with a gas supply device for ejecting a sealing gas toward an inner peripheral side at an upper entrance, and is fed into the drawing furnace from above and heated. An optical fiber drawing apparatus for drawing an optical fiber reduced in diameter to a predetermined outer diameter by drawing a softened optical fiber preform from a lower end, wherein the diameter of the optical fiber preform is reduced by a shoulder at an upper end of the preform. Above the part, a sealing member formed to have substantially the same outer diameter as the outer diameter of the optical fiber preform, and an end face on the optical fiber preform side formed in a shape along the reduced diameter portion, is formed from the optical fiber preform. Are also suspended from the engaging member disposed above.
[0012]
According to the optical fiber drawing apparatus of the present invention, even if the drawing of the optical fiber proceeds and the reduced diameter portion, which is the shoulder of the optical fiber preform, enters the drawing furnace, the diameter of the optical fiber preform is reduced. Since a sealing member having an outer diameter substantially equal to that of the optical fiber preform and an end face on the optical fiber preform side formed along the reduced diameter portion is disposed in the portion, the gas occupied in the furnace is occupied. A change in volume is suppressed, thereby preventing a change in the flow of a seal gas such as an inert gas supplied into the furnace, and suppressing a change in the diameter of the optical fiber caused by a change in the gas flow, thereby achieving a stable diameter. Thus, an optical fiber can be drawn, and a drawing apparatus capable of drawing a high-quality optical fiber can be provided.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of an optical fiber drawing method and a drawing apparatus according to the present invention will be described in detail with reference to the drawings.
1 and 2 show a drawing furnace constituting an optical fiber drawing apparatus according to an embodiment of the present invention. Although the drawing apparatus is shown in a half-split state in FIG. 1, the drawing apparatus has a shape in which the axis of the optical fiber preform is a symmetric axis.
As shown in the figure, the drawing furnace 11 has a cylindrical furnace tube 13 made of carbon and provided with a heating part 12 on the outer periphery.
The outer periphery of the furnace tube 13 is covered with a heat insulating material 14, and the outer periphery is further covered with a furnace body 15.
[0014]
An upper lid 16 is provided on the upper part of the furnace tube 13. The upper lid 16 is formed with a cylindrical portion 16a having substantially the same inner diameter as the furnace tube 13. The gas outlets 17 are provided at three or more locations on the outer peripheral side at substantially equal intervals in the circumferential direction. From 16b, a sealing gas made of an inert gas such as argon, nitrogen, helium or the like is blown substantially evenly around the inner periphery (see arrow) to perform gas sealing. Substantially the same means a difference of 1 to 5 mm with respect to the diameter. The flow rate of the gas blown for gas sealing is preferably about 10 to 30 l / min.
A cylindrical furnace extension 19 made of a heat insulating material is provided below the furnace tube 13.
[0015]
Then, the optical fiber preform 21 connected to the dummy rod 18 is fed into the drawing furnace 11 from the upper part thereof, and the front end thereof is heated and melted by the heat generating part 12, pulled out downward and reduced in diameter. The optical fiber 21a is used.
[0016]
In the present embodiment, when the optical fiber 21 a is drawn from the optical fiber preform 21 by the drawing furnace 11, the sealing member 31 is placed on the optical fiber preform 21.
The sealing member 31 has a cylindrical outer cylindrical body 31a having an outer diameter substantially the same as that of the optical fiber preform 21 (preferably in the range of about ± 1 mm), and is nested inside the outer cylindrical body 31a. The dummy rod 18 is inserted through the inner peripheral cylinder 31b.
[0017]
The outer cylindrical body 31a and the inner cylindrical body 31b that constitute the sealing member 31 each have a lower end face having a reduced diameter portion 21b formed by a shoulder of the optical fiber preform 21 generated by a difference in diameter from the dummy rod 18. Are formed in a shape substantially along the line. For example, if the reduced diameter portion 21b is tapered and the inclination of the taper is α, the lower end surface of the sealing member is tapered and has an inclination of α. When the sealing member is composed of a plurality of members, each member may be a cylindrical body nested as described above. Each cylinder may further be composed of a plurality of members. When used, each member does not leave a gap.
A disc-shaped engaging member 32 fixed to the dummy bar 18 is provided on the upper portion of the sealing member 31. The outer peripheral cylinder 31a and the inner peripheral cylinder 31b of the sealing member 31 Are suspended by suspension wires 33. The suspension wire 33 is slightly slackened in a state where the closing member 31 is placed on the reduced diameter portion 21b of the optical fiber preform 21.
[0018]
Then, by placing the sealing member 31 having an outer diameter substantially equal to the outer diameter of the optical fiber preform 21 on the upper part of the optical fiber preform 21, the drawing of the optical fiber 21a proceeds, Even if the reduced diameter portion 21b, which is the shoulder portion of the optical fiber preform 21, enters the drawing furnace 11, the change in volume occupied by the gas inside the furnace is suppressed, whereby the gas is supplied from the gas supply device 17 into the furnace. A change in the flow of the sealing gas is prevented, a change in the diameter of the optical fiber 21a caused by a change in the flow of the gas is suppressed, and the optical fiber 21a can be drawn with a stable diameter. 21a can be drawn.
[0019]
Further, as the drawing progresses and the heated and melted portion approaches the reduced diameter portion 21b, the reduced diameter portion 21b, which is the shoulder of the optical fiber preform 21, extends in the axial direction, and the inclination angle of the reduced diameter portion 21b with respect to the radial direction increases. growing.
When the reduced diameter portion 21b is deformed in this way, as shown in FIG. 3, the sealing member 31 moves the outer peripheral cylindrical body 31a and the inner peripheral cylindrical body 31b downward following the deformation of the reduced diameter portion 21b. I do.
Thereby, even if the reduced diameter portion 21b is deformed, the change in the volume occupied by the gas inside the furnace can be reliably suppressed, and the optical fiber 21a can be manufactured with a stable diameter.
[0020]
The engaging member 32 for suspending the closing member 31 may be fixed to the dummy rod 18 as described above, but is not fixed to the dummy rod 18 and is synchronized with the movement of the dummy rod 18 by a separate moving means. It may be made to fall down. In this case, when the reduced diameter portion 21b of the optical fiber preform 21 approaches the drawing furnace 11, the engaging member 32 may be lowered by the moving means, and thereafter, may be lowered in synchronization with the dummy rod 18. .
[0021]
As described above, the sealing member 31 may be placed on the reduced diameter portion 21b such that the end surface thereof is in contact with the reduced diameter portion 21b of the optical fiber preform 21, but the sealing member 31 is disposed with a slight gap. May be.
By the way, if the drawn optical fiber 21a is broken, the optical fiber preform 21 is pulled upward so that the optical fiber preform 21 is not melted during the recovery, and the heating of the drawing furnace 11 is performed. Drawn from the area.
At this time, if the sealing member 31 is arranged with its end face slightly spaced from the reduced diameter portion 21b of the optical fiber preform 21, even if the sealing member 31 is pulled out of the heating area and a temperature change occurs, the There is no possibility that the optical fiber preform 21 will be damaged due to a difference in linear expansion coefficient between the preform 21 and the sealing member 31. Even when the sealing member is placed on the reduced diameter portion of the optical fiber preform, if the sealing member is suspended from the engagement means, the engagement member is raised above the optical fiber preform at the time of disconnection. By pulling up, the sealing member and the optical fiber preform can be separated.
Therefore, it is preferable that the end surface of the sealing member 31 is disposed with a slight gap from the reduced diameter portion 21 b of the optical fiber preform 21.
[0022]
FIG. 4 shows a configuration in which a reflection type optical system sensor 41 is provided in the vicinity of the distal end portions of the outer peripheral cylindrical body 31a and the inner peripheral cylindrical body 31b constituting the closing member 31. The distance between the tip and the optical fiber preform 21 is measured by the sensor 41 in the sealing member 31 including the outer cylindrical body 31a and the inner cylindrical body 31b having the sensor 41, and based on the measurement result, The optical fiber preform 21 is arranged with a slight gap therebetween. When the reduced diameter portion 21b is deformed, the outer cylindrical body 31a and the inner cylindrical body 31b follow a state in which a slight gap is left with the deformation. In addition, a filter 42 that blocks visible light and hardly transmits heat is provided on the end surfaces of the outer cylindrical body 31a and the inner cylindrical body 31b, so that the measurement fluctuation of the sensor 41 by visible light and the influence of heat are suppressed. .
[0023]
An engaging member 32 for suspending the outer cylindrical body 31a and the inner cylindrical body 31b separately is provided, and these engaging members 32 are individually raised and lowered to separate the outer cylindrical body 31a and the inner cylindrical body 31b from each other. The material 21 may follow the reduced diameter portion 21b.
[0024]
Further, the sealing member 31 is hollow, and a gas is passed through the inside of the sealing member 31 or a pipe through which the gas is passed is provided to blow the gas onto the glass base material 21 from the lower surface of the sealing member 31 so that the end face of the sealing member 31 In this case, the effect of the gas seal by blowing out the gas from the cylindrical portion 16a to the inner peripheral side by the gas supply device 17 can be further enhanced.
[0025]
The sealing member 31 can reliably prevent breakage and damage due to heat by providing a cooling structure in which a cooling medium such as a liquid or gas flows to cool the inside. In addition, quartz, ceramics, metal, or the like can be used as the sealing member 31. In particular, in the case of metal, it is desirable to cool it by the above-described cooling structure or the like to prevent its melting.
[0026]
Fluctuation in diameter of an optical fiber when an optical fiber is drawn by a drawing device having a sealing member 31 made of a single member and a conventional drawing device not having the sealing member 31 as in the present embodiment. Were compared.
As shown in FIG. 5, in the case of the drawing apparatus not provided with the sealing member 31, the fluctuation of the diameter increases as the fiber distance of the optical fiber to be drawn increases, whereas the closing member 31 is provided. In the case of the drawing apparatus of this embodiment, it has been found that even if the fiber distance becomes long, the fluctuation of the diameter is suppressed, and a stable optical fiber can always be drawn.
[0027]
【The invention's effect】
As described above, according to the method and apparatus for drawing an optical fiber of the present invention, even if the drawing of the optical fiber proceeds and the reduced diameter portion, which is the shoulder of the optical fiber preform, enters the drawing furnace. Since the reduced diameter portion of the optical fiber preform is provided with a sealing member formed to have substantially the same outer diameter as the optical fiber preform and the end face on the optical fiber preform side formed along the reduced diameter portion. Therefore, a change in the volume occupied by the gas inside the furnace is suppressed, whereby a change in the flow of a sealing gas such as an inert gas supplied into the furnace is prevented, and the diameter of the optical fiber caused by the change in the gas flow is reduced. The fluctuation can be suppressed, the optical fiber can be drawn with a stable diameter, and a high-quality optical fiber can be drawn.
[Brief description of the drawings]
FIG. 1 is a perspective view of a drawing furnace for explaining an optical fiber drawing method and a drawing apparatus of the present invention.
FIG. 2 is a sectional view of the drawing furnace showing a structure of a drawing furnace constituting the drawing apparatus.
FIG. 3 is a cross-sectional view of the drawing furnace showing a deformed state of the optical fiber preform in the drawing furnace.
FIG. 4 is a cross-sectional view of the sealing member showing a sealing member having a sensor.
FIG. 5 is a graph showing a comparison result between an optical fiber drawing method of the present invention and a conventional optical fiber drawing method.
FIG. 6 is a schematic structural view of a conventional drawing furnace.
[Explanation of symbols]
11 Drawing furnace 17 Gas supply device 21 Optical fiber preform 21a Optical fiber 21b Reduced diameter portion 31 Sealing member 31a Outer cylindrical body (cylindrical body)
31b Inner circumference cylindrical body (cylindrical body)
32 engagement member

Claims (7)

The optical fiber preform is fed from above into the drawing furnace which gushes the sealing gas toward the inner peripheral side at the upper entrance, is drawn from the front side in the feeding direction, is heated and softened in the drawing furnace, and is reduced in diameter to a predetermined outer diameter. An optical fiber drawing method for drawing an optical fiber,
At least after the reduced diameter portion at the upper end of the optical fiber preform reaches the upper entrance of the drawing furnace, the outer diameter of the optical fiber preform is formed to be substantially the same as the optical fiber preform above the reduced diameter portion of the preform. A sealing member whose end face on the optical fiber preform side is formed along the reduced diameter portion is provided, and a gas is sealed between the upper inlet of the drawing furnace and the sealing member with a sealing gas. A method for drawing an optical fiber, comprising: The method for drawing an optical fiber according to claim 1,
The method for drawing an optical fiber, wherein the closing member is composed of a plurality of members, and the plurality of members are movable following the reduced diameter portion to be deformed. A method for drawing an optical fiber according to claim 1 or claim 2,
The method for drawing an optical fiber, wherein the closing member is suspended from an engaging member disposed on an upper portion thereof. A method for drawing an optical fiber according to any one of claims 1 to 3,
An optical fiber drawing method, wherein the sealing member is placed on the reduced diameter portion of the optical fiber preform and the end faces thereof are kept in contact. A method for drawing an optical fiber according to any one of claims 1 to 3,
A method for drawing an optical fiber, comprising: disposing the sealing member with a slight gap from the reduced diameter portion of the optical fiber preform. A method for drawing an optical fiber according to claim 5,
A method for drawing an optical fiber, comprising: flowing gas from the end face of the sealing member to the reduced diameter portion of the optical fiber preform. It has a drawing furnace provided with a gas supply device for injecting a sealing gas toward the inner peripheral side at the upper entrance, and draws the heated and softened optical fiber preform from the lower end into the drawing furnace from above. An optical fiber drawing apparatus for drawing an optical fiber reduced in diameter to a predetermined outer diameter,
Above the reduced diameter portion formed by the shoulder at the upper end of the optical fiber preform, the outer diameter of the optical fiber preform is formed to be substantially the same as the outer diameter of the optical fiber preform, and the end face on the optical fiber preform side has the reduced diameter. An optical fiber drawing device, wherein a sealing member formed in a shape along the portion is suspended from an engaging member disposed above the optical fiber preform.

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