JP2003171139A - Optical fiber drawing furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical fiber drawing furnace in which the degradation of a furnace core pipe by oxidation and the deterioration of strength of an optical fiber are prevented by preventing the flow-in of atmospheric air in a furnace core. <P>SOLUTION: In the optical fiber drawing furnace 21 for drawing an optical fiber preform 23 to which a dummy rod 22 is connected in advance, a sheet like heat resistant sealing material 28 for preventing the flow-in of the atmospheric air to the inside of the furnace core 26 by sealing a gap between the optical fiber preform and an optical fiber preform inserting port 27 on the upper part of the furnace core pipe 25 of the drawing furnace 21 is provided in the optical fiber preform inserting port 27, a small chamber 29 covering the sheet like heat resistant sealing material 28 is formed above the optical fiber preform inserting port 27 and a sheet like sealing material 43 for sealing a gap formed between the dummy rod 22 and the optical fiber preform inserting port 35 in the upper part of the small chamber 29 is provided in the dummy rod 22 side of the outside of the small chamber 29. <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 an optical fiber drawing apparatus for drawing an optical fiber preform to which dummy rods are connected in advance, in an optical fiber drawing apparatus.

[0002]

2. Description of the Related Art FIG. 2 is a schematic view showing an optical fiber drawing apparatus, and FIG. 3 is a sectional view showing a conventional optical fiber drawing furnace.

As shown in FIG. 2, an optical fiber drawing device 1
After heating and melting the optical fiber preform 2 in the furnace core tube 11 of the drawing furnace 3 and pulling out the optical fiber 5 from the furnace lower port 4 of the drawing furnace 3, the hardness of the two layers is continuously different. It is a resin which is coated with a UV curable resin and wound up. The first layer is a coating die 6
In general, the resin having a relatively low elasticity is coated via the UV lamp 7, and the second layer is coated with the resin having a high elasticity via the coating die 8 on the downstream side and the UV lamp 9.

The drawing furnace 3 is a quartz-based optical fiber preform 2.
Since it is necessary to heat the furnace to about 2000 ° C,
As the material of No. 1, ceramic such as zirconia or high-purity carbon is generally used.

Here, the core tube 11 made of carbon will be described with reference to FIG. When high-purity carbon is used as the material of the core tube 11, it is necessary to purge the core 12 with an inert gas such as helium or argon in order to prevent the core 12 from being consumed by oxidation.

At the lower part of the core tube 11 of the drawing furnace 3, an optical fiber 5 is continuously drawn out, so that a furnace lower opening 4 having a diameter of several mm is formed, and at the upper part of the core tube 11 of the drawing furnace 3. An optical fiber preform insertion port 14 having a diameter slightly larger than the diameter of the optical fiber preform 2 is formed. At the optical fiber preform insertion port 14, a sheet-shaped heat-resistant sealing material 15 made of carbon felt or the like is provided in order to maintain a positive pressure inside the core 12.

A cylindrical small chamber 17 for covering the sheet-shaped heat-resistant sealing material 15 is formed above the optical fiber preform insertion port 14. An optical fiber preform insertion opening 18 having a diameter slightly larger than the diameter of the optical fiber preform 2 to be inserted is formed on the upper surface of the small chamber 17.

When the diameter of the optical fiber preform 2 is relatively small, a quartz dummy rod or a dummy tube having the same diameter as the preform diameter is previously fused to the optical fiber preform 2 and the drawing furnace 3 is used. It is sequentially inserted from the top and drawn from the end of the base material to form an optical fiber.

On the other hand, when the optical fiber preform 2 has a large diameter, it is difficult to connect a dummy rod or a dummy tube, so a dummy rod 16 thinner than the preform diameter is connected (FIG. 3).
reference). For such a different diameter base material, a pseudo-same diameter base material is formed by covering the connecting portion between the optical fiber base material 2 and the dummy rod 16 with a cylindrical cap 19 having the same diameter as the base material diameter.

[0010]

However, in the optical fiber drawing furnace 3, in the optical fiber preform 2 during drawing, the heat of the molten portion at the tip of the preform propagates through the preform regardless of the diameter. Then, heat is dissipated at the connecting portion 20 with the dummy rod 16 and locally becomes high temperature.

Therefore, as the drawing progresses, the optical fiber preform 2 is sequentially fed, and as shown in FIG. 3B, the connecting portion 20 between the optical fiber preform 2 and the dummy rod 16 is heat-resistant into a sheet form. When it reaches the vicinity of the sealing material 15, the heat dissipated from the connecting portion 20 may burn the carbon felt. As a result, the inside of the core cannot be maintained at a positive pressure, and the atmosphere flows into the core 12 through the optical fiber preform insertion port 18 formed on the upper surface of the small chamber 17, so that the core tube 11 is deteriorated due to oxidation and light. There is a problem that the strength of the fiber 5 is deteriorated and the drawing operation itself cannot be continued.

Therefore, the present invention has been devised to solve the above problems, and its purpose is to prevent the inflow of the atmosphere into the core to prevent the oxidation deterioration of the core tube and the strength deterioration of the optical fiber. An object of the present invention is to provide an optical fiber drawing furnace which can be prevented.

[0013]

[Means for Solving the Problems] To solve the above problems,
The present invention, in an optical fiber drawing furnace for drawing an optical fiber preform to which dummy rods are previously connected, seals a gap between the optical fiber preform and the optical fiber preform insertion port in the upper part of the core tube of the drawing furnace. A sheet-shaped heat-resistant sealing material is provided to prevent the inflow of air into the reactor core, and a small chamber for covering the sheet-shaped heat-resistant sealing material is formed above the optical fiber preform insertion port. On the dummy rod side, a sheet-like sealing material for sealing a gap between the optical fiber preform insertion port formed in the upper part of the small chamber is provided.

The dummy rod has a smaller diameter than the optical fiber preform, and the dummy rod is covered with a cylindrical cap having the same diameter as the optical fiber preform to form a pseudo same-diameter preform. It is preferable that a sheet-shaped sealing material that seals a gap with the optical fiber preform insertion port formed in the upper part of the small chamber is provided on the outer periphery of the same diameter preform.

Further, the distance between the sheet-shaped heat-resistant sealing material provided in the optical fiber preform insertion port in the upper part of the core tube of the drawing furnace and the optical fiber preform insertion port formed in the upper part of the small chamber is
It is preferable that the distance is larger than the distance between the connection portion of the dummy rod with the optical fiber preform and the sheet-shaped heat-resistant sealing material provided on the dummy rod side.

Further, it is preferable that the sheet-shaped heat-resistant sealing material is made of carbon felt.

Further, it is preferable that the sheet-shaped heat-resistant sealing material provided on the dummy rod side is located at a distance of 50 mm or more from the connection portion of the dummy rod with the optical fiber preform.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a sectional view showing a preferred embodiment of an optical fiber drawing furnace according to the present invention.

First, the structure of such an optical fiber drawing furnace will be described.

As shown in the figure, the optical fiber drawing furnace 21 according to this embodiment draws an optical fiber preform 23 in which dummy rods 22 are fused and connected in advance. The optical fiber drawing furnace 21 has a core tube 25 having a heating unit 24.

At the lower part of the furnace core tube 25, a furnace lower opening 34 for continuously drawing out the optical fiber 33 is formed. The furnace lower opening 34 is formed to have a diameter of several mm so as to avoid contact with the optical fiber 33 and keep the inside of the core 26 at a positive pressure.

The optical fiber preform 2 is provided on the core tube 25.
An optical fiber preform insertion port 27 for inserting 3 into the core 26 is formed. This optical fiber preform insertion port 27
Has a diameter slightly larger than the diameter of the optical fiber preform 23 to be inserted.

The optical fiber base material insertion port 27 is provided with a sheet-shaped heat-resistant sealing material 28 for sealing the gap with the optical fiber base material 23 to prevent the inflow of the atmosphere into the core 26. There is. The sheet-shaped heat-resistant sealing material 28 is made of carbon felt and is formed in a ring shape so as to surround the optical fiber preform 23 to be inserted.

A small chamber 29 for covering the above-mentioned sheet-shaped heat-resistant sealing material 28 is formed above the optical fiber preform insertion port 27. The small chamber 29 is defined by a cylindrical casing 32 having a lid 31 and is formed in a cylindrical shape. An optical fiber preform insertion port 35 for inserting the optical fiber preform 23 is formed in the lid 31 above the small chamber 29. Like the optical fiber base material insertion port 27, this optical fiber base material insertion port 35 has a diameter slightly larger than the diameter of the optical fiber base material 23 to be inserted.

Although not shown, an inert gas flow path for purging an inert gas such as nitrogen is connected to the core 26 and the small chamber 29 in order to prevent oxidative deterioration of the core tube 25. There is.

When the optical fiber preform 23 has a relatively large thickness, for example, a diameter of 100 mm, a diameter of 50 mm is formed on the upper portion thereof.
The mm dummy rod 22 is fused. A cylindrical cap 38 having a diameter φ100 mm equivalent to that of the optical fiber base material 23 and a height h1 = 200 mm is placed on the connecting portion 37 between the optical fiber base material 23 and the dummy rod 22. It covers the lower part of 22. This cylindrical cap 3
At 8, the pseudo same-diameter base material 39 is formed.

At the upper end of the cylindrical cap 38, the lid 3
Locking claw 41 for locking the cylindrical cap 38 to
Are formed. A sheet-like heat-resistant seal for sealing the gap between the optical fiber preform insertion port 35 and the cylindrical cap 38 when the cylindrical cap 38 is locked to the lid 31 is provided under the locking claw 41. A stopper 43 is provided. The sheet-shaped heat-resistant sealing material 43 is also made of carbon felt and formed in a ring shape, like the sheet-shaped heat-resistant sealing material 28 described above.

Optical fiber preform insertion port 2 above the core tube 25
The distance between the sheet-shaped heat-resistant sealing material 28 provided in 7 and the optical fiber preform insertion port 35 formed in the upper part of the small chamber 29 (equivalent to the height h2 of the small chamber 29) is the optical fiber mother material of the dummy rod 22. The connection portion 37 with the material 23 and the dummy rod 22 side (the lid portion 3
The distance from the sheet-shaped heat-resistant sealing material 43 provided on the cylindrical cap 38) locked to 1 (equal to the height h1 of the cylindrical cap 38).

The sheet-shaped heat-resistant sealing material 43 provided on the outer periphery of the cylindrical cap 38 on the dummy rod 22 side is
The dummy rod 22 is located at a distance of 50 mm or more from the connecting portion 38 with the optical fiber preform 23.

Specifically, the height h of the cylindrical cap 38
When 1 is 200 mm, the height h2 of the small chamber 29 is 300
mm, and the diameter is 200 mm. As a result, the distance between the sheet-shaped heat-resistant sealing material 28 provided in the optical fiber preform insertion port 27 above the core tube 25 and the optical fiber preform insertion port 35 formed above the small chamber 29 is also 300 mm.
Therefore, the above condition is satisfied.

Next, the operation will be described together with the optical fiber drawing process by the optical fiber drawing furnace 21 having the above structure.

First, at the start of drawing, as shown in FIG. 1A, the optical fiber preform 23 is long and the cylindrical cap 3
The sheet-shaped heat-resistant sealing material 43 of No. 8 is located above the lid 31 of the small chamber 29, but the optical fiber preform 23 comes into contact with the sheet-shaped heat-resistant sealing material 28 above the furnace core tube 25. The core 26 is sealed.

At this time, the connecting portion 37 between the optical fiber preform 23 and the dummy rod 22 is located in the small chamber 29, and the heat dissipated from the small chamber 29 does not burn the sheet-shaped heat-resistant sealing material 28. Absent.

Further, since the sheet-shaped heat-resistant sealing material 43 of the cylindrical cap 38 is separated from the connecting portion 37 between the optical fiber preform 23 and the dummy rod 22 by 50 mm or more, the connecting portion 3
It is not affected by the heat dissipated from 7.

Then, as the drawing progresses, the optical fiber preform 23
Is gradually shortened, as shown in Fig. 1 (b),
The cylindrical cap 38 is locked to the lid 31 above the small chamber 29, and the sheet-shaped heat-resistant sealing material 43 seals the small chamber 19 and the outside. Then, when the drawing is further advanced, the cylindrical cap 38 remains in that position because it is locked, and the optical fiber preform 23 and the dummy rod 22 are further lowered.

At this time, the connecting portion 37 between the optical fiber preform 23 and the dummy rod 22 is located at the portion of the sheet-shaped heat-resistant sealing material 28, and the heat dissipated from the connecting portion 37 causes the sheet-shaped heat-resistant sealing. Material 28 may be burned down, but small room 29
However, since it is sealed from the outside by the sheet-shaped heat-resistant sealing material 43 above it, it is possible to prevent the atmospheric air from flowing into the core 26.

As the drawing further proceeds, as shown in FIG. 1C, the connecting portion 3 between the optical fiber preform 23 and the dummy rod 22 is formed.
7 descends into the core 26, and the core 26 and the small chamber 29 communicate with each other, but since the small chamber 29 is sealed from the outside, the atmosphere does not flow into the core 26.

As described above, according to the above construction, the core 26 or the small chamber 29 can be sealed from the outside in each drawing step, so that the core 26 can be kept at a positive pressure. It is possible to prevent the air from flowing into the core 26.

As a result, oxidation deterioration of the core tube 25 and strength deterioration of the optical fiber 33 can be prevented, and smooth and stable drawing can be performed.

In the above embodiment, the sheet-shaped heat-resistant sealing material 28, 43 is made of carbon felt or the like, but the material is not limited to this. Optical fiber base material 2
As long as the surface of 3 is not damaged, a heat-resistant material such as glass / ceramic may be used.

[0042]

In summary, according to the present invention, it is possible to prevent the inflow of the atmosphere into the core and prevent the oxidation deterioration of the core tube and the strength deterioration of the optical fiber.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a preferred embodiment of an optical fiber drawing furnace according to the present invention, where (a) is a cross-sectional view showing the first step of drawing, and (b) is drawing. 2C is a sectional view showing a second step, and FIG. 7C is a sectional view showing a third step of drawing.

FIG. 2 is a schematic diagram showing an overall configuration of an optical fiber drawing device.

3A and 3B are cross-sectional views showing a conventional optical fiber drawing furnace, wherein FIG. 3A is a cross-sectional view showing a first drawing process, and FIG. 3B is a cross-sectional view showing a second drawing process. It is a figure.

[Explanation of symbols]

21 Optical fiber drawing furnace 22 dummy stick 23 Optical fiber base material 25 core tube 26 core 27 Optical fiber base material insertion port 28 Sheet heat resistant sealant 29 small rooms 35 Optical fiber base material insertion port 37 Connection part (between optical fiber preform and dummy rod) 38 Cylindrical cap 39 Pseudo same diameter base metal 43 Sheet heat resistant sealant

Claims (5)

[Claims] 1. An optical fiber drawing furnace for drawing an optical fiber preform to which dummy rods are preliminarily connected, and a gap between the optical fiber preform and an optical fiber preform insertion port at the upper part of the core tube of the drawing furnace is sealed. A sheet-shaped heat-resistant sealing material for preventing the inflow of air into the core, and a small chamber for covering the sheet-shaped heat-resistant sealing material is formed above the optical fiber preform insertion port. An optical fiber drawing furnace, characterized in that a sheet-shaped sealing material for sealing a gap between the dummy rod outside and an optical fiber preform insertion port formed in the upper part of the small chamber is provided. 2. The dummy rod has a smaller diameter than the optical fiber preform, and the dummy rod is covered with a cylindrical cap having the same diameter as the optical fiber preform to form a pseudo same-diameter preform. The optical fiber drawing furnace according to claim 1, wherein a sheet-shaped sealing material is provided on the outer periphery of the same diameter base material to seal a gap between the optical fiber base material insertion port formed in the upper part of the small chamber. 3. The distance between the sheet-shaped heat-resistant sealing material provided in the optical fiber preform insertion port in the upper part of the core tube of the drawing furnace and the optical fiber preform insertion port formed in the upper part of the small chamber is the above. 3. The optical fiber drawing furnace according to claim 1, which is larger than a distance between a connection portion of the dummy rod with the optical fiber preform and a sheet-shaped heat-resistant sealing material provided on the dummy rod side. 4. The optical fiber drawing furnace according to claim 1, wherein the sheet-shaped heat-resistant sealing material is made of carbon felt. 5. The sheet-shaped heat-resistant sealing material provided on the dummy rod side is located at a distance of 50 mm or more from a connection portion of the dummy rod with the optical fiber preform. Fiber optic drawing furnace.