JPH092832A - Fiber drawing method of optical fiber and optical fiber drawing furnace - Google Patents

Abstract

PURPOSE: To provide a fiber drawing furnace equipping a furnace core tube for supplying a preform, a heater surrounding the furnace core tube and an upper chamber linked to the upper end of the furnace core tube, capable of suppressing the convection of an inert gas between the neighborhood of the furnace core tube and the upper end part of the upper chamber by keeping the temperature at the upper end part of the upper chamber constant by heating. CONSTITUTION: The method for fiber drawing of an optical fiber is constituted by delivering a preform for the optical fiber 15 connected to the lower end of a supporting rod 18 successively to the side of a furnace core tube 14 accompanying to the fiber drawing, supplying an inert gas to the upper chamber 24 of the furnace core tube 14 through a gas supplying pipe 28, a gas introducing cylinder 27 and a gas introducing port 29, installing a heater 34 for keeping the temperature of the upper chamber 24, and controlling it with a regulating device 35 and a temperature sensor 34. On the verge of the completion of the fiber drawing work of the preform for the optical fiber 15, the temperature at the upper end part of the upper chamber 24 is lowered to <=100 deg.C in the case of not using the heater 34 for keeping the temperature, but by keeping the temperature at 100-700 deg.C with installing the heater 34 for keeping the temperature, the increase in the difference of a temperature of the inert gas in the inside of the furnace core tube is prevented and a good quality product with less line diameter variations can by stably produced.

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 wire diameter and an optical fiber drawing furnace used therefor.

[0002]

2. Description of the Related Art Usually, an optical fiber is drawn by heating and softening a rod-shaped base material for an optical fiber in an optical fiber drawing furnace and stretching it. As one means of reducing the manufacturing cost of this optical fiber, it has been attempted to lengthen the optical fiber preform and reduce the number of setup changes, and it is possible to achieve continuous drawing work of optical fibers for hundreds of kilometers. ing.

An optical fiber drawing furnace used for drawing such a lengthened base material for an optical fiber is
As disclosed in Japanese Patent Application Laid-Open No. 2-6349, a chimney for storing the upper part of the optical fiber preform above the core tube surrounded by a heater for heating the lower end of the optical fiber preform. The upper chamber is formed into a semi-enclosed space that communicates with the inside of the core 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 inside of the furnace core tube communicating with the same are held in a non-oxidizing atmosphere, and the base material for an optical fiber in a heated and melted state The optical fiber is drawn from the lower end.

[0004]

In the optical fiber drawing furnace in which the upper chamber is formed, the optical fiber preform is shortened as the optical fiber drawing work progresses, and the optical fiber occupies the upper chamber. The storage space for the base material gradually becomes empty. Therefore, as a result of the inert gas located here easily flowing and the temperature difference between the inert gas located inside the core tube becoming large, as a result, between the periphery of the core tube and the upper end of the upper chamber. A convection phenomenon of the inert gas will occur.

When such an inert gas convection occurs, the gas flow forming the atmosphere at the lower end of the optical fiber preform in the heat-softened state also becomes unstable, and the fluctuation of the wire diameter of the drawn optical fiber. Has a tendency to become considerably large, and it becomes difficult to obtain a desired quality as a product.

In order to prevent such a convection phenomenon of an inert gas in the upper chamber, Japanese Patent Laid-Open No. 2-6349 discloses a method of supplying an inert gas to the upper chamber at a flow rate capable of destroying the convection phenomenon. It is suggested to do so.

However, at least 0.4 per second is possible with this method.
Since it is necessary to secure a flow velocity of ~ 0.5 m, for example, when the inner diameter of the core tube and the upper chamber is 100 mm, 0.5 m per second along the inner peripheral wall of the upper chamber for a length of 50 cm in the vertical direction. In order to form a swirling flow of
With a support rod diameter of 25 mm, 281 liters of inert gas must be supplied per minute. 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 as much as 60 to 80 liters of inert gas per minute in the standard state at a minimum, which increases running cost.

[0008]

It is an object of the present invention to prevent the convection phenomenon of atmospheric gas in the upper chamber without supplying a large amount of inert gas into the furnace and to stably draw an optical fiber having a uniform diameter. (EN) Provided is an optical fiber drawing method and a drawing furnace therefor.

[0009]

The first aspect of the present invention is as follows.
A core tube to which the optical fiber base material is supplied, a heater surrounding the core tube, and a support rod connected to the upper end of the core tube to accommodate the optical fiber base material and to support the optical fiber base material. Using an optical fiber drawing furnace having an upper chamber penetrating therethrough, in an optical fiber drawing method in which the lower end of the optical fiber preform is melted by heating to draw an optical fiber, the upper end of the upper chamber The method for drawing an optical fiber is characterized in that the above is heated and kept warm.

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

A second aspect of the present invention is to provide a core tube to which the optical fiber preform is supplied, a heater surrounding the furnace core tube, and the optical fiber preform connected to the upper end of the core tube. An optical fiber drawing furnace having an upper chamber through which a supporting rod for supporting the optical fiber preform penetrates and provided with an annular heat insulation heater surrounding the upper chamber and heating an upper end of the upper chamber. An optical fiber drawing furnace characterized by the above.

Here, a temperature sensor for detecting the ambient temperature of the upper end of the upper chamber, and a heater control means for controlling the operation of the warming heater based on the detection information from the temperature sensor may be further provided. Desirably, in this case, the heater control means sets the ambient temperature of the upper end of the upper chamber detected by the temperature sensor to 10
Range of 0 ° C to 700 ° C, preferably 200 ° C to 400 ° C
It is effective to control the operation of the heat retention heater so as to be in the range.

[0013]

The optical fiber preform is drawn from the lower end while heating the optical fiber preform by the heater, the optical fiber preform occupying the inside of the upper chamber is moved downward, and the supporting rod is placed in the upper chamber. Send in. The space inside the upper chamber gradually increases with the progress of the drawing operation of the optical fiber, and the ambient temperature here tends to decrease.

According to the present invention, by heating the upper end portion of the upper chamber with the heat retention heater, it is possible to prevent the ambient temperature at the upper end portion of the upper chamber from lowering.

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

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the optical fiber drawing furnace according to the present invention which can realize the optical fiber drawing method of the present invention,
This will be described in detail with reference to FIGS.

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

To the lower end of the core tube 14, an extension cylinder 21 is connected which projects downward from the furnace body 12 and forms a lower chamber 20 inside with a cooling jacket 19 connected to the lower end. A seal plate 23 having an opening 22 at the center through which the optical fiber 16 penetrates is attached. In the two cooling jackets 11 and 19 mentioned above,
By connecting a refrigerant circulation supply device (not shown) and controlling the supply of the refrigerant from the refrigerant circulation supply device into the cooling jackets 11 and 19, the ambient temperature in the furnace core tube 14 and the lower chamber 20 together with the carbon heater 17 is controlled to a predetermined value. It is designed to be held at temperature.

At the upper end of the core tube 14, the furnace body 1
A base material storage cylinder 25 that projects upward from 2 and forms an upper chamber 24 inside is connected to the upper end of the core tube 14.
Around the base material storage cylinder 25, a gas introduction cylinder 27 formed of a heat-resistant alloy such as Inconel surrounded by a heat insulating material 26.
Is arranged. At the lower end of the gas introducing 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 inside of 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 passes through the gas introduction port 29 from the annular gap formed between the gas supply pipe 28 and the gas introducing cylinder 27 and the base material accommodating cylinder 25. An inert gas such as helium or nitrogen is supplied to the upper end portion of the chamber 24 to keep 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 preform 15 can pass is attached to the upper end of the, and a small-diameter opening 32 through which the support rod 18 penetrates is formed in the top plate 31. The shutter ring 33 is superposed. Also,
At the upper end portion of the heat insulating material 26 for keeping the inside of the upper chamber 24 warm, an annular warming heater 34 that surrounds the upper end portion of the heat insulating material 26 and heats the upper end portion of the upper chamber 24 is attached. The heater 34 includes a control device 3 for controlling ON / OFF of energization of the heat retaining heater 34.
5 is connected. The control device 35 includes a temperature sensor 36 that detects the ambient temperature of the upper end of the upper chamber 24.
Are connected, and the detection information from the temperature sensor 36 is output to the control device 35.

The heat-retaining heater 34 appropriately heats the upper end of the upper chamber 24 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 core tube 14. It is.

By the way, FIG. 2 shows the distribution of the temperature inside the furnace from the upper end to the lower end of the furnace immediately before the end of the drawing work for the optical fiber preform 15. The solid line is the case of the present invention, and the broken line is the conventional case where the heat insulation heater 34 is not used. That is, in the conventional optical fiber drawing furnace that does not use the heat-retaining heater 34, the temperature of the upper end portion of the upper chamber 24 has dropped to 100 ° C. or lower just before the end of the drawing work for the optical fiber preform 15. I understand.

FIG. 3 shows the temperature change in the central portion of the upper chamber as the wire drawing work progresses. Similar to FIG. 2, the solid line represents the case of the present invention, and the broken line represents the conventional case in which the heat retaining heater 34 is not used. This is a case where the optical fiber preform 15 having a length of 800 mm is used, and when the surplus length is less than the first half, the conventional optical fiber drawing furnace abruptly increases the vertical central portion of the upper chamber 24. It can be seen that the temperature of is decreasing.

Further, FIG. 4 shows the change in the variation of the outer diameter of the drawn optical fiber 16. Similar to FIGS. 2 and 3, the solid line represents the case of the present invention, and the broken line represents the conventional case in which the heat retention heater 34 is not used. According to FIG. 4, when the extra length of the optical fiber preform 15 is less than the first half, the variation of the outer diameter dimension of the optical fiber 16 gradually increases.

By the way, when the optical fiber 16 having a diameter of 125 μm is spun by the optical fiber drawing furnace shown in FIG.
As a result of investigating the relationship between the ambient temperature at the upper end of the and the variation in the outer diameter dimension of the drawn optical fiber 16, the correlation as shown in FIG. 5 could be obtained.

From the above results, when the ambient temperature at the upper end of the upper chamber 24 of the optical fiber drawing furnace becomes lower than 100 ° C., the variation of the outer diameter of the optical fiber 16 is ± 0.4.
Since it increases to μm or more, it is necessary to maintain the atmospheric temperature at the upper end of the upper chamber 24 of the optical fiber drawing furnace at 100 ° C. or more. In particular, when the fluctuation amount needs to be ± 0.2 μm or less, it is preferable to maintain the atmospheric temperature of the upper end portion of the upper chamber 24 at 200 ° C. or higher. Also, the ambient temperature at the upper end of the upper chamber 24 is set to 4
When the temperature is kept at 00 ° C or higher, the fluctuation amount of 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 24 is set to 10
In the range of 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.
Reference numeral 5 controls on / off of energization to 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 around 300 ° C. The amount of fluctuation is set to ± 0.1 μm.

[0029]

According to the optical fiber drawing method and apparatus of the present invention, since the annular heat-retaining heater which surrounds the upper chamber and heats the upper end of the upper chamber is provided, the optical fiber preform is shortened. When the storage space for the optical fiber preform, which was occupied in the upper chamber, gradually becomes open, the upper end of this upper chamber is heated and kept warm, resulting in a large temperature difference with the inert gas located inside the core tube. Therefore, it is possible to suppress the convection phenomenon of the inert gas between the periphery of the core tube and the upper end of the upper chamber. As a result, it is possible to stably manufacture an optical fiber of good quality with a small variation in the wire diameter over the entire length of the optical fiber preform.

[Brief description of 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 temperature distributions in the vertical direction of the optical fiber drawing furnace of the embodiment shown in FIG. 1 and the conventional optical fiber drawing furnace, respectively, in a state where the excess length of the optical fiber preform is shortened.

FIG. 3 is a graph showing temperature changes at the upper end of the upper chamber in the example shown in FIG. 1 and the conventional optical fiber drawing furnace.

4A and 4B are graphs showing a process of fluctuations in the diameter of the optical fiber in the embodiment shown in FIG. 1 and the 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 amount of variation in the diameter of the optical fiber.

[Explanation of symbols]

 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 Tube 22 Opening 23 Seal Plate 24 Upper Chamber 25 Base Material Storage Tube 26 Heat insulating 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

Claims (5)

[Claims] 1. A furnace core tube to which a base material for an optical fiber is supplied, a heater surrounding the furnace core tube, an upper end of the furnace core tube to accommodate the base material for the optical fiber, and the base material for the optical fiber. Using an optical fiber drawing furnace having an upper chamber through which a supporting rod that supports the optical fiber drawing method, wherein the lower end of the optical fiber preform is heated and melted to draw the optical fiber, An optical fiber drawing method, characterized in that the upper end of the upper chamber is heated and kept warm. 2. The upper end of the upper chamber is at 100 ° C.
The optical fiber drawing method according to claim 1, wherein the temperature is kept warm by heating in the range of 700 ° C, preferably in the range of 200 ° C to 400 ° C. 3. A core tube to which an optical fiber preform is supplied, a heater surrounding the core tube, an upper end of the furnace tube is connected to accommodate the optical fiber preform and the optical fiber preform. An optical fiber drawing furnace having an upper chamber through which a supporting rod for supporting the upper chamber penetrates, the optical fiber drawing furnace comprising an annular heat insulation heater surrounding the upper chamber and heating an upper end of the upper chamber. . 4. A temperature sensor for detecting an ambient temperature of an upper end portion of the upper chamber, and a 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 has an atmospheric temperature of the upper end of the upper chamber detected by the temperature sensor in a range of 100 ° C. to 700 ° C., preferably 200 ° C.
The optical fiber drawing furnace according to claim 4, wherein the operation of the heat retention heater is controlled so as to be in the range of 400 ° C to 400 ° C.