JP2002356344A - Method for drawing optical fiber and wire drawing furnace for optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for drawing an optical fiber and a wire drawing furnace for the optical fiber capable of stably drawing an optical fiber preform having a dummy rod of different diameter over the full length of the preform. SOLUTION: This method for drawing an optical fiber comprises the steps of inserting an optical fiber preform 1 connected to the lower end of a dummy rod 13 into a furnace center pipe 11 from above, fusing the preform in the furnace center pipe 11 while descending it, and pulling out the drawn optical fiber from the lower part, wherein a cylindrical cap 20 having the same diameter as the outer diameter of the optical fiber preform 1 is made to put around the dummy rod 13 to form a pseudo-preform having the same diameter to be drawn.

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 method for forming an optical fiber by drawing and an optical fiber drawing furnace.

[0002]

2. Description of the Related Art Generally, an optical fiber is manufactured using an optical fiber drawing apparatus as shown in FIG.

As shown in FIG. 4, an optical fiber drawing apparatus comprises a drawing furnace 5 for melting an optical fiber preform 1 and drawing out the melted optical fiber preform from below to draw the same. A capstan 50 for pulling the optical fiber preform 1 from the drawing furnace 5, and coating sections 30 and 40 for coating the optical fiber wire drawn from the drawing furnace 5
And a winding bobbin 60 that winds up the coated optical fiber wire.

When drawing with this optical fiber drawing apparatus, the glass base material 1 is heated and melted in a drawing furnace 5,
After drawing as a fiber from the furnace lower port, the fiber is continuously coated with two layers of UV-curable resins having different hardnesses and wound.

[0005] 1 which is covered by the coating section 30
Generally, a resin having a relatively low elasticity is continuously coated as the resin of the layer, and a resin having a high elasticity is generally coated as the resin of the second layer to be covered by the coating section 40 in the subsequent stage.

Since the drawing furnace 5 needs to heat the quartz-based glass base material 1 to about 2000 ° C., ceramic or high-purity carbon such as zirconia is generally used as the material of the furnace tube.

Here, an example of a carbon core tube will be described.

When high-purity carbon is used as the core tube material, H is introduced into the core in order to prevent oxidation consumption of the core.
e, it is necessary to purge an inert gas such as Ar.

Since the fiber is continuously drawn out from the lower port of the furnace, an outlet having a diameter of several mm is formed, and a base material insertion port having a diameter slightly larger than the base material diameter is formed at the upper port.

[0010] Since the strength of the drawn fiber comes into contact with a solid before coating with the UV resin, the strength of the drawn fiber is deteriorated. On the other hand, the upper port is generally sealed with a heat-resistant material such as carbon felt, or a gas cylinder is provided and gas-sealed to maintain a positive core pressure.

In any of the sealing methods, when the outer diameter of the optical fiber preform 1 is relatively small, a quartz dummy rod or a dummy tube having the same diameter as the outer diameter of the preform 1 is fused to the preform 1 in advance. In advance, the base material 1 is inserted sequentially from the upper part of the drawing furnace 5 and drawn from the lower end of the base material 1 to form an optical fiber.

On the other hand, when the outer diameter of the optical fiber preform 1 is relatively large, it is difficult to connect a dummy rod or a dummy pipe having the same diameter as the outer diameter of the preform 1, so that the diameter is larger than the preform diameter. Connect a thin dummy stick.

However, when a dummy rod smaller than the outer diameter of the base material 1 is connected, and when sealing or gas sealing is performed with a heat-resistant material, when the connection portion enters the drawing furnace upper opening, the thin dummy rod is connected to the core. The gap with the inner surface of the tube becomes large, and it becomes impossible to maintain the inside of the core at a positive pressure, and it is virtually impossible to draw a wire. That is, the entire length of the base material cannot be drawn.

For this reason, an upper chamber system as shown in FIG. 5 is generally used for such a base material having a different diameter.

In this upper chamber system, a separate chamber 70 (base material feeding device) that covers the entire length of the base material is installed above the drawing furnace. A large passage hole 70h is formed, and the base material 1 is sequentially fed downward through the dummy rod 71 into the passage hole 70h.

[0016]

However, in the upper chamber method, the entire length of the base material can be drawn, but since the chamber 70 is formed at a height covering the entire base material, the extension of the dummy rod 71 is indispensable. In this case, the height of the drawing furnace is increased, and the equipment becomes large.

Further, since the entire base material 1 is accommodated in the drawing furnace, the setting of the base material 1 is complicated, and furthermore, when the base material 1 is inserted in a high temperature state of the drawing furnace, the base material 1 is melted in the chamber 70. Therefore, it is difficult to insert the base material 1 continuously, and it is necessary to lower the temperature of the drawing furnace every time one base material 1 is drawn. Therefore, there remains a problem in mass productivity of optical fibers.

An object of the present invention is to provide an optical fiber drawing method and an optical fiber in which a dummy rod can stably draw an optical fiber preform having a different diameter over the entire length without using a large facility such as an upper chamber. An object of the present invention is to provide a drawing furnace.

[0019]

According to a first aspect of the present invention, an optical fiber preform connected to a lower end of a dummy rod is inserted into a furnace tube from above and melted in the furnace tube. In the optical fiber drawing method in which the optical fiber preform is drawn down from below and drawn down, a dummy cap is covered with a cylindrical cap having the same diameter as the outer diameter of the optical fiber preform to form a pseudo-preform diameter preform. Then, draw a line.

According to a second aspect of the present invention, a column-shaped insertion opening for an optical fiber preform is formed in an upper portion, and an outlet from which the optical fiber preform is melted and drawn out is formed in a lower portion, and is arranged vertically. Furnace tube, a dummy rod formed with a diameter smaller than the optical fiber preform diameter and connected to an upper part of the optical fiber preform, holding the dummy rod, and lowering the optical fiber preform. An optical fiber drawing furnace having a mechanism and a heater provided to surround the furnace tube and melting the optical fiber preform,
A cylindrical portion whose outer diameter is equal to the outer diameter of the optical fiber preform and whose lower end is in contact with the upper end of the optical fiber preform, and has an inner diameter substantially equal to the outer diameter of the dummy rod provided at the upper end of the cylindrical portion A cylindrical cap having a ring-shaped upper lid is provided.

According to a third aspect of the present invention, a stopper claw is provided at an upper end portion of the cylindrical cap so as to be hooked on the insertion opening of the furnace tube when lowered together with the base material.

According to a fourth aspect of the present invention, the difference between the inner diameter of the ring-shaped upper lid and the outer diameter of the dummy rod is 0.5 mm or less.

According to a fifth aspect of the present invention, a gas flow path is connected to the furnace tube, and a gas flow control mechanism such as a variable valve is provided in the gas flow path.

According to the above construction, when the optical fiber preform descends and the portion to be fused with the dummy rod passes through the upper part of the furnace tube, the gas flow resistance is reduced since the preform diameter is equal to the cylindrical cap diameter. Approximately, the core pressure does not change, and the drawing is stably continued.

Further, when the optical fiber preform descends and the upper end of the cylindrical cap reaches the upper part of the furnace tube, the stopper claw is hooked, and thereafter only the preform is fed into the drawing furnace.

[0026]

Next, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

In this embodiment, a case will be described in which a cylindrical quartz-based optical fiber preform having an outer diameter of φ100 mm is used for drawing.

FIG. 1 is a schematic view of an optical fiber drawing furnace according to the present invention.

As shown in FIG. 1, the optical fiber drawing furnace according to the present invention has a cylindrical portion 11a in which an insertion opening 10i of the optical fiber preform 1 is formed at an upper upper portion and an optical fiber preform 1 A furnace core tube 11 formed at a lower furnace lower port with an outlet 10o through which the material is melted and drawn out is vertically arranged, and a heater 12 for melting the optical fiber preform 1 is provided so as to surround the furnace tube 11. Have been.

The core tube 11 is made of high-purity carbon, and it is necessary to heat the glass base material 1 to about 2000 ° C. Therefore, in order to prevent the core from being oxidized and consumed, such as He, Ar, etc. Inert gas must be purged, and a gas flow path 14 for introducing gas into the core tube 11 is connected to maintain a positive pressure in the core, and a variable valve 15 and the like are provided in the gas flow path 14. Is provided. Then, the upper opening is sealed with a heat-resistant material such as carbon felt, or the cylindrical portion 1 as in the present embodiment.
1a is installed and gas-sealed.

The outlet 10o is formed to have a diameter of several mm, and the insertion opening 10i is formed to be slightly larger than the diameter of the base material.

The upper end of the optical fiber preform 1 is smaller than the outer diameter of the optical fiber preform 1 and has an outer diameter of 50 m.
A dummy rod 13 formed of m quartz is connected.

The dummy rod 13 is connected to a mechanism for rotating and lowering the optical fiber preform 1 at a predetermined speed, and is held by this mechanism.

Further, a cylindrical cap 20 is welded around the dummy rod 13 so that the lower end thereof is in contact with the upper end of the optical fiber preform 1.

This cylindrical cap will be described in detail with reference to FIG.

As shown in FIG. 3, the cylindrical cap has an outer diameter equal to the outer diameter of the optical fiber preform, that is, an outer diameter of φ1.
Quartz cylindrical part 21 of 00 mm and height of about 200 mm
A ring-shaped upper lid 22 made of SUS provided on the upper end surface of the cylindrical portion 21 and having an insertion hole 22h substantially equal to the outer diameter of the dummy rod; and a light provided on the outer peripheral portion of the upper end of the cylindrical portion 21. And a stopper claw 23 which is caught by the insertion opening of the core tube when lowered together with the fiber preform.

If the gap between the insertion hole 22h and the dummy rod is large, the gas flow is disturbed in the cylindrical cap near the end of the drawing and the outer diameter of the fiber fluctuates. The difference between the diameter of the dummy rod and the outer diameter of the dummy rod is 0.5
In this embodiment, the dummy rods are selected to be smaller than the outer diameter of the dummy rod by about 0.3 mm and are closed. That is, the insertion hole 22h of the ring-shaped upper lid 22 is formed slightly larger at φ53 mm in consideration of the variation in the outer diameter of the dummy bar.

Next, the optical fiber drawing method will be described with reference to FIGS.

When drawing with the optical fiber drawing furnace according to the present invention, as shown in FIG.
3 is inserted into the furnace core tube 11 from the insertion port 10i. Then, gas is introduced into the furnace tube 11 from the gas flow path 14,
The lower end of the optical fiber preform 1 is melted by the heater 12 while rotating and lowering the dummy rod 13 at a predetermined speed, and the optical fiber is drawn out from the lower outlet 10o as an optical fiber.

As described above, since the base material portion is located in the cylindrical portion 11a above the core tube 11 until the first half of the drawing, the cylindrical cap 20 does not contribute to the function at all.

Then, the optical fiber preform 1 descends, and the fused portion with the dummy rod 13 becomes a cylindrical portion 11a on the upper part of the furnace tube 11.
When passing through, since the outer diameter of the optical fiber preform 1 and the outer diameter of the cylindrical cap 20 are equal, the gas flow resistance in the cylindrical portion 11a becomes substantially equal, and the core pressure does not change, and Is continued.

When the diameter of the base material and the diameter of the cylindrical cap 20 are slightly different from each other, the internal pressure is controlled by the variable valve 15 in order to keep the core internal pressure constant. Is possible.

Then, as shown in FIG. 2, in the latter half of the drawing,
When the optical fiber preform 1 descends and the upper end of the cylindrical cap 20 reaches the cylindrical portion 11a above the furnace tube 11, the stopper claw 23 is caught, and thereafter, only the preform 1 is fed into the drawing furnace.

In this way, the gap between the inner surface of the core tube 11 and the outer surfaces of the base material 1 and the cylindrical cap 20 is constant until the entire base material is consumed and the drawing is completed.
You can draw stably until the end.

Further, since the cylindrical cap 20 is not heated to a temperature higher than the softening point at the time of drawing, it is not deformed and can be used repeatedly.

As described above, according to the present invention, the dummy rod 13 can stably draw the optical fiber preform 1 having a different diameter over the entire length without using a large facility such as an upper chamber.

Next, the grounds for setting the difference between the dummy rod insertion hole diameter on the upper surface of the cylindrical cap and the dummy rod outer diameter to 0.5 mm or less will be described.

The reason why the difference between the diameter of the dummy rod insertion hole on the upper surface of the cylindrical cap and the outer diameter of the dummy rod is 0.5 mm or less is to suppress the fluctuation of the outer diameter of the drawn glass fiber.

Table 1 shows the difference between the diameter of the insertion hole and the outer diameter of the dummy rod.
The relationship with the fluctuation width of the glass fiber diameter drawn under the conditions is shown.

[0050]

[Table 1]

As shown in Table 1, when the diameter difference between the insertion hole and the dummy rod is 0.1 mm, the fluctuation range of the glass fiber outer diameter is ±
When the diameter difference is 0.2 μm and the diameter difference is 0.3 mm, the fluctuation width is ± 0.2
μm, when the diameter difference is 0.5 mm, the fluctuation width is ± 0.2 μm,
When the diameter difference was 0.7 mm, the fluctuation width was ± 0.4 μm, and when the diameter difference was 0.9 mm, the fluctuation width was ± 0.7 μm.

From the above, it can be seen that in order to suppress the fluctuation range of the glass fiber outer diameter to within 0.2 μm, it is necessary to make the difference between the insertion hole diameter and the dummy rod outer diameter 0.5 mm or less.

In this embodiment, the cylindrical cap 2
0 is made of quartz, but the material of the cylindrical cap 20 is not limited to quartz,
Other ceramic materials can be used as long as they have a heat resistance of about 00 ° C.

Needless to say, a rod-shaped or tubular dummy tube may be used as the dummy rod 13 connected to the optical fiber preform 1.

[0055]

In summary, according to the present invention, a dummy rod can stably draw an optical fiber preform having a different diameter over the entire length without using a large facility such as an upper chamber.

[Brief description of the drawings]

FIG. 1 is a schematic view of an optical fiber drawing furnace showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram for explaining a drawing method using the optical fiber drawing furnace of FIG. 1;

FIG. 3 is a perspective view of a cylindrical cap provided in the optical fiber drawing furnace of FIG. 1;

FIG. 4 is a schematic view of an optical fiber drawing apparatus.

FIG. 5 is a schematic view of an optical fiber drawing furnace provided with an upper chamber.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical fiber preform 11 Furnace tube 12 Heater 13 Dummy rod 14 Gas flow path 15 Variable valve (gas flow control mechanism) 20 Cylindrical cap 21 Cylindrical part 22 Ring-shaped upper lid 22h Insertion hole 23 Stopper claw

Continuation of the front page (72) Inventor Go Okubo 5-1-1, Hidaka-cho, Hitachi-shi, Ibaraki F-term in the Hidaka factory of Hitachi Cable, Ltd. (reference) 4G021 HA02

Claims (5)

[Claims] An optical fiber drawing method in which an optical fiber preform connected to a lower end of a dummy rod is inserted into a furnace tube from above, melted and lowered in the furnace tube, drawn out from below and drawn. An optical fiber drawing method, wherein a dummy cap is covered with a cylindrical cap having the same diameter as the outer diameter of the optical fiber preform to form a pseudo-preform diameter preform, and the drawing is performed. 2. A furnace tube having an upper portion formed with an insertion opening for a cylindrical optical fiber preform, and a lower portion formed with an outlet through which the optical fiber preform is melted and drawn out; A dummy rod formed to have a diameter smaller than the optical fiber preform diameter and connected to an upper portion of the optical fiber preform; a mechanism for holding the dummy rod and lowering the optical fiber preform; An optical fiber drawing furnace provided so as to surround a tube and having a heater for melting the optical fiber preform, wherein the outer diameter is equal to the outer diameter of the optical fiber preform and the lower end is in contact with the upper end of the optical fiber preform. An optical fiber drawing furnace, comprising: a cylindrical cap having a cylindrical portion to be formed and a ring-shaped upper lid provided at an upper end of the cylindrical portion and having an inner diameter substantially equal to the outer diameter of the dummy rod. 3. The optical fiber drawing furnace according to claim 2, wherein a stopper claw is provided at an upper end portion of the cylindrical cap so as to be caught by an insertion opening of the furnace tube when the cylindrical cap is lowered together with the base material. 4. The optical fiber drawing furnace according to claim 2, wherein a difference between an inner diameter of the ring-shaped upper lid and an outer diameter of the dummy rod is 0.5 mm or less. 5. The optical fiber according to claim 2, wherein a gas flow path is connected to the core tube, and a gas flow control mechanism such as a variable valve is provided in the gas flow path. Drawing furnace.