JP2003206155A - Spinning furnace and method for manufacturing optical fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spinning furnace and a method for manufacturing an optical fiber by which fluctuation of an outside diameter of drawn optical fiber can be suppressed to a very small extent even when spinning linear velocity is high. <P>SOLUTION: An outside core tube 3 penetrates a spinning furnace body 1 provided with a heater 2. An inside upper core tube 4 and an inside lower core tube 5 are concentrically provided inside the outside core tube 3 via some space near a top end molten part 11 of an optical fiber preform 10. Inert gas supply ports 6 are respectively provided inside the inside upper core tube 4 and inside the inside lower core tube 5. The optical fiber 12 is manufactured by thermally melting and drawing a top end part of the optical fiber preform 10 while making clean inert gas flow through a space between the inside upper core tube 4 and the optical fiber preform 10 and a space between the inside lower core tube 5 and the optical fiber 12. Further, in this case, preferably the inert gas is made to flow through a space between the outside core tube 3 and the inside upper core tube 4 or a space between the outside core tube 3 and the inside lower core tube 5. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spinning furnace and an optical fiber manufacturing method capable of suppressing fluctuations in the outer diameter of an optical fiber drawn from an optical fiber preform.

[0002]

2. Description of the Related Art Generally, a silica-based optical fiber widely used in the field of optical communication is prepared by heating and melting an optical fiber base material containing silica glass as a main component in a spinning furnace. It is manufactured by drawing from the fusion zone.

FIG. 5 is a sectional view showing an example of a spinning furnace conventionally used for manufacturing an optical fiber. In FIG. 5, reference numeral 1 is a spinning furnace main body. The spinning furnace body 1 has a heater 2
And the core tube 3 is attached. Then, in drawing, the optical fiber preform 10 is inserted into the core tube 3 heated by the heater 2 at a constant speed to heat and melt the tip of the optical fiber preform 10 (not shown). An optical fiber 12 having a predetermined outer diameter is manufactured by drawing the melted portion 11 at a predetermined speed using a take-out machine.

When the optical fiber preform 10 is heated until it melts, dust such as Si and SiO ₂ is generated. Further, the furnace tube 3 is usually made of carbon having excellent heat resistance, and when heated to a high temperature, a part of the carbon reacts with dust such as Si and SiO ₂ generated from the optical fiber preform 10. As a result, SiC dust is generated. If such dust adheres to the optical fiber preform or the drawn optical fiber, the outer diameter of the optical fiber 12 may fluctuate or the strength may decrease. Therefore, in order to prevent these dusts from adhering, an inert gas supply port 6 is provided in the spinning furnace, and an inert gas such as He, Ar, or N ₂ is supplied through an inert gas supply pipe 7 to the core. It is made to flow inside the tube 3.

[0005]

Recently, the optical fiber 12 has been used.
In order to reduce the manufacturing cost of the optical fiber preform, an attempt has been made to increase the size of the optical fiber preform 10 and increase the spinning linear velocity. When the optical fiber 12 is spun using a conventional spinning furnace,
When the spinning linear velocity is about 300 to 600 m / min, it can be produced without any problem, but when the spinning linear velocity is increased to about 1000 m / min or more, there is a problem that the outer diameter variation of the drawn optical fiber 12 becomes large. . If the fluctuation of the outer diameter of the optical fiber 12 is large, it becomes difficult to attach the optical fiber 12 to the connector, or the splicing loss at the time of fusion splicing becomes large, which is a problem.

The present invention has been made in view of the above circumstances, and manufacturing of a spinning furnace and an optical fiber capable of suppressing the outer diameter variation of the drawn optical fiber 12 to be extremely small even if the spinning linear velocity is increased. Provide a way.

[0007]

Means for Solving the Problems The above-mentioned problems are as follows: a spinning furnace main body having a heater, an outer core tube penetrating the spinning furnace main body, and a concentric inside of the outer core tube above the heater. An inner upper core tube and an inner lower core tube concentrically inside the outer core tube, the inner lower core tube being provided below the heater, and the inner upper core tube and the inner lower core tube. The solution is provided by a spinning furnace characterized in that an inert gas supply port is provided inside each. In this spinning furnace, further, in the gap between the inner upper core tube or the inner lower core tube and the outer core tube,
An inert gas supply port for supplying an inert gas can be provided.

In manufacturing an optical fiber, an outer core tube is penetrated into a spinning furnace main body having a heater, and an inner upper core tube is concentrically provided inside the outer core tube and above the heater. , Concentrically inside the outer core tube, an inner lower core tube is provided below the heater, an optical fiber preform is suspended inside the inner upper core tube, and a tip portion of the optical fiber preform is Projecting from the lower end of the inner upper core tube, while flowing an inert gas into the inner upper core tube and the inner lower core tube, the tip of the optical fiber preform is heated and melted by the heater. The drawn optical fiber is drawn out from the optical fiber base material through the inside of the inner lower core tube to the outside of the spinning furnace. It can be made extremely small suppress the outside diameter fluctuation. In order to further suppress the fluctuation of the outer diameter of the optical fiber, when performing the drawing of the optical fiber, in addition to the inner side of the inner upper core tube and the inner side of the inner lower core tube,
Further, it is preferable to flow an inert gas also in a gap between the inner upper core tube or the inner lower core tube and the outer core tube.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail based on the embodiments. FIG. 1 is a sectional view showing an example of the spinning furnace of the present invention. In FIG. 1, reference numeral 1 is a spinning furnace main body. A heater 2 and an outer core tube 3 are attached to the spinning furnace body 1. Above the outer core tube 3,
The inner upper core tube 4 is concentrically provided with respect to the outer core tube 3 with a predetermined gap. Below the outer core tube 3, an inner lower core tube 5 is provided concentrically with the outer core tube 3 with a predetermined gap. The inner upper core tube 4 and the inner lower core tube 5 are the optical fiber preform 1
They are opposed to each other with a space corresponding to the vicinity of the fused portion 11 at the tip of 0.

An inert gas supply port 6 for supplying an inert gas through an inert gas supply pipe 7 is provided inside the inner upper core tube 4 and the inner lower core tube 5. As a result, a clean inert gas can be made to flow in the gap between the inner upper core tube 4 and the optical fiber preform 10 and the gap between the inner lower core tube 5 and the drawn optical fiber 12. It has become.

The drawing of an optical fiber using such a spinning furnace can be carried out, for example, as follows. First, the optical fiber preform 10 is suspended in the inner upper core tube 4, and the tip of the optical fiber preform 10 is projected from the lower end of the inner upper core tube 4. Then, a clean inert gas is flown through the gap between the inner upper core tube 4 and the optical fiber preform 10 and the gap between the inner lower core tube 5 and the drawn optical fiber 12. Then, the front end portion of the optical fiber preform 10 is heated by the heater 2 to be melted and drawn by a take-up machine (not shown). Then, the obtained optical fiber 12 is taken out of the spinning furnace through the inside of the inner lower core tube 5.

By drawing the optical fiber in this way, the radiant heat from the heater 2 is blocked by the inner upper core tube 4, so that only the tip of the optical fiber preform 10 is heated, and the upper part is higher. Hardly heated. Therefore, the tip of the optical fiber preform 10 is efficiently and uniformly heated, and the neck-down shape of the fusion zone 11 becomes uniform. Further, since the radiant heat from the heater 2 is blocked by the inner lower core tube 5, the optical fiber 12 is hardly heated and is uniformly cooled. Therefore, fluctuations in the outer diameter of the optical fiber 12 due to uneven heating or cooling are suppressed.

By flowing a clean inert gas into the inner upper core tube 4 and the inner lower core tube 5, the optical fiber preform 10 and the optical fiber 12 are cooled by the inert gas. Further, since the dust is discharged and the adhesion of the dust is prevented, the fluctuation of the outer diameter of the optical fiber 12 and the reduction of the strength are suppressed. In order to further suppress the fluctuation of the outer diameter of the optical fiber 12, an inert gas for supplying an inert gas to the gap between the inner upper core tube 4 or the inner lower core tube 5 and the outer core tube 3 is further used. A gas supply port (not shown) is provided, and the inner upper core tube 4 or the inner lower core tube 5 and the outer core tube 3 are provided.
It is preferable to flow an inert gas also in the gap between and. Thereby, the inner upper core tube 4 or the inner lower core tube 5 is
The inconvenience that dust adheres to and accumulates in the gap between the outer core tube 3 and the outer core tube 3 is suppressed.

Inner upper core tube 4 and inner lower core tube 5
As a material constituting the above, any material that has high heat resistance and is used for the conventional core tube 3 can be used.
Examples of such materials include carbon and ceramics. Particularly, carbon is preferable because it has a high endothermic property and is inexpensive.

The inner diameter of the inner upper core tube 4 is 60 to 15 when the outer diameter of the optical fiber preform 10 is φ50 to 125 mm.
The inner diameter of the inner lower core tube 5 is preferably 20 to 50 mm regardless of the outer diameter of the optical fiber preform 10. If these inner diameters are less than the lower limit values, the distance between the inner upper core tube 4 and the optical fiber preform 10 and the distance between the inner lower core tube 5 and the optical fiber 12 become too narrow, so that dust is difficult to be discharged. In addition, dust is likely to adhere to the optical fiber preform 10 and the optical fiber 12, which is not preferable. When the inner diameters of the inner upper core tube 4 and the inner lower core tube 5 exceed the upper limit,
The size of the spinning furnace becomes unnecessarily large, and the optical fiber preform 1
This is not preferable because the efficiency of heating 0 decreases.

Inner upper core tube 4 and inner lower core tube 5
The thickness is preferably 1 mm or more. If the wall thickness of the inner upper core tube 4 and the inner lower core tube 5 is less than 1 mm, the effect of blocking the radiant heat from the heater becomes low, and further, the strength decreases and the handleability deteriorates, which is not preferable. The upper limit of the wall thickness of the inner upper core tube 4 and the inner lower core tube 5 is not particularly limited, but it is wasteful and uneconomical if the wall thickness is made thicker than necessary, so it is preferably 5 mm or less.

Helium (He), argon (Ar), nitrogen (N ₂ ) or the like can be used as the inert gas flowing inside the outer core tube 3, the inner upper core tube 4, and the inner lower core tube 5. . The flow rate of the inert gas depends on the outer diameter of the optical fiber preform 10 and the drawing speed, but in general,
It is preferably 1.0 to 20.0 liters per minute at room temperature. If the flow rate of the inert gas is less than 1.0 liter per minute, the effect of flowing the inert gas is small and the outer diameter fluctuation of the optical fiber 12 may increase, which is not preferable. Further, if the flow rate of the inert gas exceeds 20 liters per minute, the flow of the inert gas may become unstable, and expensive inert gas is economically disadvantageous, which is not preferable.

The type of the inert gas may be one type or two or more types. In order to stabilize the outer diameter of the optical fiber 12, He having a large diffusion coefficient is advantageous, so that He on the surface of the optical fiber preform 10 that affects the outer diameter of the optical fiber 12 or on the surface of the fusion zone 11 Is preferably flushed. However, since He is more expensive than Ar, it is preferable to use Ar at a position far from the optical fiber preform 10. For example, it is preferable to flow He inside the inner upper core tube 4 and the inner lower core tube 5, and a gap between the outer core tube 3 and the inner upper core tube 4,
And / or, Ar is preferably flowed in the gap between the outer core tube 3 and the inner lower core tube 5.

The installation position of the discharge port for discharging the inert gas to the outside of the spinning furnace 20 is not particularly limited, but, for example, the outer core tube 3 and the inner upper core tube 4 or the inner lower core tube 5 can be used.
It can be provided in the gap between and. In the case of upper exhaust, it can be provided in the gap between the outer core tube 3 and the inner upper core tube 4, and in the case of lower exhaust, it can be provided in the gap between the outer core tube 3 and the inner lower core tube 5.

Next, a comparison between the spinning furnace of the present invention and a conventional spinning furnace will be shown. The optical fiber 12 was manufactured using the spinning furnace of the example or the conventional example, and as shown in FIG. 2, the optical fiber 12 was coated to form the optical fiber strand 13. Figure 2
According to the apparatus shown in FIG. 1, the optical fiber strand 13 is manufactured as follows.

The optical fiber preform 10 is heated and melted in the spinning furnace 20 and drawn to form the optical fiber 12. The outer diameter of the optical fiber 12 is measured by an outer diameter measuring device 21, cooled by a cooling cylinder 22, coated with a primary coating resin by a primary coater 23, and then the primary ultraviolet lamp 24 is used to apply the primary coating resin. The coating resin is cured to provide the primary coating. In addition, the secondary coater 2
After the secondary coating resin is applied by 5, the secondary coating resin is cured by the second ultraviolet lamp 26 to provide the secondary coating, and the optical fiber strand 13 is formed. Then, the optical fiber strand 13 is taken up by a take-up machine 28 via a turn pulley 27, screened by a dancer 29, and then taken up by a take-up machine 30.

In the spinning furnace of the embodiment, the optical fiber preform 10 has an outer diameter of 90 mm and a length of 1000 mm, and the outer core tube 3 is a carbon tube having an inner diameter of 120 mm, a wall thickness of 3 mm and a height of 1000 mm. Is. The inner upper core tube 4 has an inner diameter of 110 mm, a wall thickness of 2 mm, and a height of 250 mm.
This is a carbon tube. The inner lower core tube 5 has an inner diameter 4
It is a carbon tube having a thickness of 0 mm, a wall thickness of 2 mm, and a height of 300 mm. The distance between the lower end of the inner upper core tube 4 and the upper end of the inner lower core tube 5 is 450 mm. He of 5 liters per minute is flowed inside the inner upper core tube 4 and the inner lower core tube 5, and the gap between the outer core tube 3 and the inner upper core tube 4 and the outer core tube 3 and the inner lower tube 3 liters of Ar per minute was flowed in the gap with the furnace tube 5.

In the conventional spinning furnace, the core tube 3 is a carbon tube having an inner diameter of 110 mm, a wall thickness of 3 mm and a height of 1000 mm. Inside the core tube 3, 5 liters of He was flowed per minute.

A single-mode optical fiber is manufactured from an optical fiber preform 10 having an outer diameter of 90 mm and a length of 1000 mm, and urethane acrylate resin is used to make a two-layer coating with a primary coating diameter of 190 μm and a secondary coating diameter of 245 μm. Was set up. The setting value of this single mode optical fiber is
The outer diameter is 125 μm, the mold field diameter is 9.2 μm, and the cutoff wavelength is 1.25 μm.

At this time, the optical fiber 12 is drawn by changing the drawing speed in six ways, and the outer diameter measuring device 21 (model PK-2200) manufactured by Photokinetic Co. is used to draw the optical fiber 12 after drawing. The outer diameter was measured. FIG. 3 is a graph showing the outer diameter of the optical fiber 12 manufactured by using the spinning furnace of the example, and FIG. 4 shows the outer diameter of the optical fiber 12 manufactured by using the spinning furnace of the conventional example. It is a graph. In FIG. 3 and FIG. 4, “●” indicates the average value,
The “−” marks above and below the “●” mark indicate the maximum value and the minimum value, respectively.

As is clear from these results, according to the spinning furnace 20 of the embodiment, even if the drawing speed is increased to 1000 m / min or more, the fluctuation of the outer diameter of the optical fiber 12 is suppressed to a very small value. It was possible to manufacture an excellent optical fiber 12. According to the spinning furnace 20 of the conventional example, the obtained optical fiber 12 increases as the drawing speed increases.
The outer diameter variation of the sample became significantly large.

[0027]

As described above, the spinning furnace 2 of the present invention
By manufacturing the optical fiber 12 using 0, 10
Even when the speed is increased to 00 m / min or more, it is possible to manufacture the optical fiber 12 in which the outer diameter variation is extremely small. As a result, the manufacturing cost and productivity of the optical fiber 12 can be significantly improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of a spinning furnace of the present invention.

FIG. 2 is a diagram illustrating a method for manufacturing an optical fiber strand.

FIG. 3 is a graph showing an example of measured values of the outer diameter of an optical fiber manufactured using the spinning furnace of the example.

FIG. 4 is a graph showing an example of measured values of the outer diameter of an optical fiber manufactured by using a conventional spinning furnace.

FIG. 5 is a sectional view showing an example of a conventional spinning furnace.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Spinner main body, 2 ... Heater, 3 ... Outer core tube, 4 ... Inner upper core tube, 5 ... Inner lower core tube, 6 ... Inert gas supply port, 10 ... Optical fiber preform, 11 ... Melting part, 12 ... Optical fiber, 20 ... Spinning furnace.

Continued front page    (72) Inventor Munehisa Fujimaki             Fuji Co., Ltd. 1440 Rokuzaki, Sakura City, Chiba Prefecture             Kura Sakura Office

Claims (4)

[Claims] 1. A spinning furnace main body having a heater, an outer core tube penetrating the spinning furnace main body, and an inner upper core tube concentrically provided inside the outer core tube and above the heater. And an inner lower core tube provided concentrically inside the outer core tube below the heater, and an inert gas is provided inside the inner upper core tube and inside the inner lower core tube, respectively. A spinning furnace provided with an inert gas supply port for supplying the gas. 2. The spinning furnace according to claim 1, further comprising an inert gas supply port for supplying an inert gas to a gap between the inner upper core tube or the inner lower core tube and the outer core tube. A spinning furnace characterized by being provided with. 3. A spinning furnace main body having a heater is penetrated with an outer core tube, and an inner upper core tube is provided concentrically inside the outer core tube and above the heater, and inside the outer core tube. An inner lower core tube is concentrically provided below the heater, an optical fiber preform is suspended inside the inner upper core tube, and a tip portion of the optical fiber preform projects from a lower end of the inner upper core tube. And the inside of the inner upper core tube,
While flowing an inert gas to the inside of the inner lower core tube, the tip portion of the optical fiber preform is heated by the heater to be melted and drawn, and the optical fiber drawn from the optical fiber preform is drawn to the lower inside part. A method for producing an optical fiber, characterized in that the fiber is taken out of the spinning furnace through the inside of the core tube. 4. The method of manufacturing an optical fiber according to claim 3, wherein when the optical fiber is drawn, in addition to the inner side of the inner upper core tube and the inner side of the inner lower core tube, the method further comprises: A method for producing an optical fiber, characterized in that an inert gas is flown also in a gap between the inner upper core tube or the inner lower core tube and the outer core tube.