JP3189968B2 - Optical fiber drawing method and optical fiber drawing furnace - Google Patents

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 capable of suppressing fluctuations in the diameter of a fiber and an optical fiber drawing furnace used for the method.

[0002]

2. Description of the Related Art Generally, an optical fiber is drawn by heating and softening a rod-shaped optical fiber base material in an optical fiber drawing furnace and stretching it. As one means of reducing the manufacturing cost of the optical fiber, the length of the optical fiber base material is reduced and the setup change is reduced, and the continuous drawing operation of the optical fiber over several hundred kilometers is realized. ing.

[0003] An optical fiber drawing furnace used for drawing such a long optical fiber preform includes:
As disclosed in Japanese Patent Application Laid-Open No. 2-6349, a chimney for accommodating an upper portion of an optical fiber preform above a furnace tube surrounded by a heater for heating a lower end portion of the optical fiber preform. An upper chamber is formed, and forms a semi-enclosed space communicating with the furnace tube. Then, an inert gas such as helium or nitrogen is supplied to the upper end of the upper chamber, the upper chamber and the furnace tube communicating with the upper chamber are kept in a non-oxidizing atmosphere, and the optical fiber preform in the heated and molten state is heated. An optical fiber is drawn from the lower end.

[0004]

SUMMARY OF THE INVENTION In an optical fiber drawing furnace having an upper chamber, the optical fiber base material is shortened and the optical fiber occupies the upper chamber as the operation of drawing the optical fiber progresses. The storage space for the base material gradually becomes vacant. For this reason, the inert gas located here becomes easy to flow, and the temperature difference with the inert gas located inside the furnace tube is increased. As a result, the space between the periphery of the furnace tube and the upper end of the upper chamber becomes larger. A convection phenomenon of the inert gas occurs.

When the convection of the inert gas occurs, the flow of the gas forming the atmosphere at the lower end of the optical fiber preform in the heating softened state becomes unstable, and the diameter variation of the drawn optical fiber. Tends to be considerably large, and it is difficult to obtain desired quality as a product.

In order to prevent such a convection phenomenon of the inert gas in the upper chamber, Japanese Unexamined Patent Publication No. 2-6349 discloses a method of supplying an inert gas having a flow rate capable of destroying the convection phenomenon to the upper chamber. It has been proposed to.

However, in this method, at least 0.4 per second is used.
For example, when the inner diameter of the core tube and the upper chamber is 100 mm, it is necessary to secure a flow velocity of about 0.5 m. In order to form a swirling flow with a velocity of
As much as 281 liters of inert gas per minute must be supplied with a 25 mm diameter support rod. Even if the volume of the inert gas expands several times due to the high temperature atmosphere in the furnace,
It is necessary to supply at least 60 to 80 liters of inert gas per minute under standard conditions, which increases running costs.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to prevent a convection phenomenon of an atmospheric gas in an upper chamber without supplying a large amount of inert gas into a furnace, and to stably draw an optical fiber having a uniform diameter. To provide an optical fiber drawing method and a drawing furnace for the same.

[0009]

Means for Solving the Problems A first aspect of the present invention is as follows.
The lower end of the optical fiber preform supported by the support rod is located in the furnace tube, and the remaining portion of the optical fiber preform is housed in an upper chamber communicating with the upper end of the furnace tube. By heating and melting the lower end of the optical fiber base material by a heater surrounding the optical fiber, the optical fiber is drawn,
The space formed between the upper end of the upper chamber and the upper end of the optical fiber preform increases by supplying the optical fiber preform to the furnace tube side along with the optical fiber drawing process. In the optical fiber drawing method,
The upper end of the upper chamber is heated and kept warm.

Here, the upper end of the upper chamber is set at 10
0 ° C to 700 ° C, preferably 200 ° C to 400 ° C
It is effective to heat and keep the temperature within the range.

According to a second aspect of the present invention, there is provided an upper chamber having an upper end through which a support rod for supporting an optical fiber preform passes and accommodating the optical fiber preform, and communicating with the upper chamber. A furnace tube having an upper end, and a heater surrounding the furnace tube for heating and melting the lower end portion of the optical fiber preform, for drawing an optical fiber from the lower end portion of the optical fiber preform. An optical fiber drawing furnace in which a space formed between an upper end of the upper chamber and an upper end of the optical fiber preform increases by supplying the optical fiber preform to the furnace tube side with the optical fiber preform. An annular heater for surrounding the upper end of the upper chamber and heating the upper end of the space is further provided.

Here, it is preferable that the apparatus further comprises a temperature sensor for detecting an ambient temperature at an upper end of the space, and heater control means for controlling the operation of the heat retaining heater based on information detected from the temperature sensor. In this case, the heater control means controls the temperature of the heater so that the ambient temperature at the upper end of the space detected by the temperature sensor is in the range of 100 ° C to 700 ° C, preferably in the range of 200 ° C to 400 ° C. It is effective to control the operation of.

[0013]

The optical fiber preform is drawn from the lower end while the optical fiber preform is heated by a heater, the optical fiber preform occupying the upper chamber is moved downward, and the support rod is moved into the upper chamber. Send in. As the optical fiber drawing operation progresses, the space in the upper chamber gradually increases, and the ambient temperature tends to decrease.

According to the present invention, the upper end of the upper chamber is heated by the heat retaining heater, thereby preventing the lowering of the ambient temperature at the upper end of the upper chamber.

If the apparatus further comprises a temperature sensor for detecting the ambient temperature at the upper end of the upper chamber, and heater control means for controlling the operation of the heat retaining heater based on information detected from the temperature sensor, the heater control means comprises: The ambient temperature at the upper end of the upper chamber detected by the temperature sensor is 1
00 ° C to 700 ° C, preferably 200 ° C to 400 ° C
The operation of the heat retention heater is controlled so as to be in the range of ° C., thereby preventing the convection phenomenon of the atmospheric gas in the upper chamber.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an optical fiber drawing furnace according to the present invention capable of realizing the optical fiber drawing method of the present invention will be described.
This will be described in detail with reference to FIGS.

As shown in FIG. 1 showing a cross-sectional structure of an optical fiber drawing furnace according to the present embodiment, a cooling jacket 11 is formed around the furnace and a heat insulating material 12 is lined at a central portion of a stainless steel furnace body 13. An annular carbon heater for drawing and drawing an optical fiber 16 by heating and melting the lower end of an optical fiber base material 15 supplied inside the furnace tube 14 is provided around the cylindrical tube 14. 17 is provided concentrically with the furnace tube 14. Base material for optical fiber 15
The upper end of the support rod 18 is connected to the lower end of the support rod 18. The upper end of the support rod 18 is suspended by a chuck (not shown), and is sequentially fed to the core tube 14 as the optical fiber 16 is drawn. It has become.

The lower end of the furnace tube 14 is connected to an extension tube 21 projecting downward from the furnace body 12 and forming a lower chamber 20 through a cooling jacket 19 inside. A seal plate 23 having an opening 22 through which the optical fiber 16 passes is formed at the center. In the two cooling jackets 11, 19 described above,
A refrigerant circulating supply device (not shown) is connected, and by controlling the supply of the refrigerant from the refrigerant circulating supply device into the cooling jackets 11 and 19, the atmospheric temperature in the core tube 14 and the lower chamber 20 together with the carbon heater 17 is controlled. The temperature is maintained.

At the upper end of the furnace tube 14, the furnace 1
A base material storage tube 25 projecting upward from 2 and forming an upper chamber 24 inside is connected to the upper end of the core tube 14.
A gas introduction cylinder 27 formed of a heat-resistant alloy such as Inconel surrounded by a heat insulating material 26 is provided around the base material storage cylinder 25.
Is arranged. At the lower end of the gas introduction cylinder 27,
Gas supply pipe 28 connected to an inert gas supply source (not shown)
A plurality of gas introduction ports 29 communicating with the upper chamber 24 are formed at the upper end of the base material storage cylinder 25.

That is, the inert gas from the inert gas supply source is supplied from the gas supply pipe 28 through the gas inlet 29 through an annular gap formed between the gas inlet tube 27 and the base material storage tube 25. An inert gas such as helium or nitrogen is supplied to the upper end of the chamber 24 to maintain the inside of the furnace in an inert gas atmosphere.

The base material storage cylinder 25 and the gas introduction cylinder 27
A top plate 31 having a large-diameter opening 30 through which the optical fiber base material 15 can pass is attached to the upper end of the top plate 31. The top plate 31 has a small-diameter opening 32 through which the support rod 18 penetrates. The shutter ring 33 is overlaid. Also,
At the upper end of the heat insulating material 26 for keeping the inside of the upper chamber 24 warm, an annular heat retaining heater 34 surrounding the upper end of the heat insulating material 26 and heating the upper end of the upper chamber 24 is attached. The heater 34 includes a control device 3 for controlling on / off of energization to the heat retaining heater 34.
5 is connected. The control device 35 includes a temperature sensor 36 for detecting the ambient temperature at the upper end of the upper chamber 24.
And the detection information from the temperature sensor 36 is output to the control device 35.

The upper end of the upper chamber 24 is appropriately heated by the heat retaining heater 34 so that thermal convection of the atmospheric gas does not occur between the upper end of the upper chamber 24 and the portion surrounded by the furnace tube 14. Because

FIG. 2 shows the distribution of the furnace temperature along the upper end to the lower end of the furnace just before the end of the drawing operation for the optical fiber base material 15. The solid line is the case of the present invention, and the broken line is the conventional case where the heat retaining heater 34 is not used. In other words, in the conventional optical fiber drawing furnace that does not use the heat retaining heater 34, the temperature of the upper end of the upper chamber 24 immediately before the end of the drawing operation for the optical fiber base material 15 has dropped to 100 ° C. or less. I understand.

FIG. 3 shows the temperature change in the center of the upper chamber as the drawing operation progresses. Similar to FIG. 2, the solid line is the case of the present invention, and the broken line is the conventional case where the heat retaining heater 34 is not used. This is the case where an optical fiber preform 15 having a length of 800 mm is used, and when the extra length becomes less than the first half, the conventional optical fiber drawing furnace rapidly sharpens the central part of the upper chamber 24 in the vertical direction. It can be seen that the temperature of the sample decreases.

FIG. 4 shows a change in the variation of the outer diameter of the drawn optical fiber 16. Similar to FIGS. 2 and 3, the solid line is the case of the present invention, and the broken line is the conventional case where the heat retaining heater 34 is not used. According to FIG. 4, it can be seen that when the extra length of the optical fiber base material 15 is less than the first half, the variation of the outer diameter of the optical fiber 16 gradually increases.

Incidentally, when the optical fiber 16 having a wire diameter of 125 μm is spun using the optical fiber drawing furnace shown in FIG.
As a result of examining the relationship between the ambient temperature at the upper end of the sample and the variation in the outer diameter of the drawn optical fiber 16, a correlation as shown in FIG. 5 could be obtained.

From the above results, when the ambient temperature of the upper end of the upper chamber 24 of the optical fiber drawing furnace is lower than 100 ° C., the variation of the outer diameter of the optical fiber 16 is ± 0.4.
It is necessary to maintain the ambient temperature at the upper end of the upper chamber 24 of the optical fiber drawing furnace at 100 ° C. or higher, since it is increased to μm or more. In particular, when it is necessary to make the fluctuation amount ± 0.2 μm or less, it is preferable to keep the ambient temperature at the upper end of the upper chamber 24 at 200 ° C. or more. The ambient temperature at the upper end of the upper chamber 24 is set to 4
When the temperature is maintained at 00 ° C. or higher, the variation in the outer diameter of the optical fiber 16 can be suppressed to less than ± 0.1 μm. Since the amount cannot be further improved, the ambient temperature at the upper end of the upper chamber
0 ° C to 700 ° C, preferably 200 ° C to 40 ° C
It is effective to keep the temperature in the range of 0 ° C.

From the above, the control device 3 described above is used.
5 controls on / off of energization of the heat retaining heater 34 based on the detection information from the temperature sensor 36 so that the ambient temperature at the upper end of the upper chamber 24 is about 300 ° C. The variation is set to ± 0.1 μm.

[0029]

According to the method and apparatus for drawing an optical fiber of the present invention, an annular heater for heating the upper end of the upper chamber surrounding the upper end of the upper chamber is provided. When the material becomes shorter and the storage space for the optical fiber preform occupied in the upper chamber gradually becomes empty, the upper end of the upper chamber is heated and kept warm to be inert with the inert gas located inside the furnace tube. Since the temperature difference can be prevented from increasing, the convection phenomenon of the inert gas between the periphery of the furnace tube and the upper end of the upper chamber can be suppressed. As a result, it is possible to stably produce an optical fiber of good quality with a small amount of wire diameter variation over the entire length of the optical fiber preform.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a schematic structure of an embodiment of an optical fiber drawing furnace according to the present invention capable of realizing the method of the present invention.

2 is a graph showing the temperature distribution along the vertical direction of the embodiment shown in FIG. 1 and the conventional optical fiber drawing furnace, respectively, in a state where the extra length of the optical fiber base material is shortened.

FIG. 3 is a graph showing a temperature change of an upper end portion of an upper chamber in the embodiment shown in FIG. 1 and a conventional optical fiber drawing furnace.

4 is a graph showing a process of changing the diameter of an optical fiber in the embodiment shown in FIG. 1 and a conventional optical fiber drawing furnace, respectively.

FIG. 5 is a graph showing the relationship between the ambient temperature at the upper end of the upper chamber and the variation in the diameter of the optical fiber.

[Explanation of symbols]

 REFERENCE SIGNS LIST 11 cooling jacket 12 heat insulating material 13 furnace body 14 core tube 15 optical fiber base material 16 optical fiber 17 carbon heater 18 support rod 19 cooling jacket 20 lower chamber 21 extension cylinder 22 opening 23 seal plate 24 upper chamber 25 base material storage cylinder 26 Insulation material 27 Gas introduction cylinder 28 Gas supply pipe 29 Gas introduction port 30 Opening 31 Top plate 32 Opening 33 Shuttering 34 Heat retention heater 35 Control device 36 Temperature sensor

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C03B 37/025-37/029

Claims (5)

(57) [Claims] 1. A lower end portion of an optical fiber preform supported by a support rod is located in a furnace tube, and the remaining portion of the optical fiber preform is accommodated in an upper chamber communicating with an upper end of the furnace tube. Then, the lower end portion of the optical fiber preform is heated and melted by a heater surrounding the furnace tube to draw an optical fiber, and the optical fiber preform is drawn toward the furnace tube along with the drawing process of the optical fiber. In the optical fiber drawing method in which the space formed between the upper end of the upper chamber and the upper end of the optical fiber preform increases by supplying, the upper end of the upper chamber is heated and kept warm. Characteristic optical fiber drawing method. 2. An upper end of the upper chamber is set at 100 ° C.
The optical fiber drawing method according to claim 1, wherein the temperature is kept at a temperature in a range of 700C, preferably in a range of 200C to 400C. 3. An upper chamber having an upper end through which a support rod for supporting an optical fiber preform penetrates and containing the optical fiber preform; a furnace tube having an upper end communicating with the upper chamber; A heater for heating and melting the lower end of the optical fiber preform surrounding the pipe, and the optical fiber preform is drawn along with the drawing process of the optical fiber from the lower end of the optical fiber preform. In an optical fiber drawing furnace in which a space formed between an upper end of the upper chamber and an upper end of the optical fiber preform increases by being supplied to the furnace tube side, the upper end of the upper chamber is surrounded by An optical fiber drawing furnace further comprising an annular heat heater for heating the upper end of the space. 4. A temperature sensor for detecting an ambient temperature at an upper end of the space, and heater control means for controlling an operation of the heat retaining heater based on detection information from the temperature sensor. The optical fiber drawing furnace according to claim 3. 5. The heater control means according to claim 1, wherein the temperature of the atmosphere at the upper end of said space detected by said temperature sensor is one.
00 ° C to 700 ° C, preferably 200 ° C to 400 ° C
The optical fiber drawing furnace according to claim 4, wherein the operation of the heat retention heater is controlled to be in a range of ° C.