JP2002053333A - Method and device for manufacturing optical fiber preform - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a device for manufacturing a preform in which welding of a synthetic quartz tube with an upper dummy tube, sealing, collapsing and cooling are all automatically executed when the perform is manufactured by an over jacket method after putting the quartz tube on a core rod produced by MCVD method or VAD method. SOLUTION: In the method for manufacturing the perform in which the synthetic quartz tube 1 is put on the core rod 3 and then is collapsed, all processes from sealing of the synthetic quartz tube 1 to fusion with the core rod 3 and cooling are automatically controlled. The upper dummy tube 9 of thin thickness is supported so that a lower end part thereof is located in a low temperature region at an upper part of an electric furnace 5, the synthetic quartz tube 1 is supported so that an upper end part thereof is located in a high temperature region of the electric furnace 5 while flowing an inert gas in the synthetic quartz tube 1 of thick thickness from a lower dummy tube 2. After an upper end face of the synthetic quartz tube 1 is sufficiently melted, the upper dummy tube 9 is gradually dropped to be welded with the molten face. Thereafter, the electric furnace 5 is moved downward and then collapsing is executed. These operations are automatically controlled by using a controller 25 in which the operations are programmed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an MCVD method and a VA method.
Over jacketing method (Over Jacketing M), in which a synthetic quartz tube is covered over a core rod manufactured by the D method and collapsed
The present invention relates to a method and an apparatus for manufacturing a preform for an optical fiber (hereinafter, simply referred to as a preform) by an ethod.

[0002]

2. Description of the Related Art Conventionally, when a preform is manufactured by an over-jacket method by covering a quartz tube serving as a clad on a core rod manufactured by an MCVD method or a VAD method,
A method is generally adopted in which an upper dummy tube is welded and connected to the upper end of a synthetic quartz tube in which a core rod has been incorporated in advance and sealed. On the other hand, with the improvement of the optical fiber manufacturing technology for drawing a preform, the preform has been increased in size and used with a diameter of 60 to 100 mm. Therefore, with the increase in the diameter of the preform, a method in which the heating means is changed from a burner to an electric furnace and the quartz tube is overjacketed has been advantageous in terms of thermal efficiency. Cracks having a large diameter are apt to generate cracks due to thermal strain, but the use of an electric furnace has a merit that cracks due to thermal strain are less likely to occur because the temperature gradient becomes gentle.

[0003] However, in order to evacuate the inside of the synthetic quartz tube, the work of welding and connecting the upper dummy tube to the upper end of the synthetic quartz tube in the electric furnace must be performed by intuition because the inside of the electric furnace is not visible. First of all, it was a very difficult task that required careful attention. In particular, when using an electric furnace with a long heating zone to weld the upper dummy tube to the synthetic quartz tube in the furnace, the problem is that the thick synthetic quartz tube and the thin dummy tube are externally connected. When simultaneously heated in an electric furnace that cannot be observed from above, the upper dummy tube with a small heat capacity is softened first and easily melts off, so welding connection between tubes with different wall thicknesses requires extremely skill. .

[0004] As described above, it is difficult to weld a dummy tube and a synthetic quartz tube by hand in an electric furnace in which the joining state is not visible at the time of connection.
Further, in the evacuation and collapse start step, the upper dummy tube is connected, the inside of the synthetic quartz tube into which the core rod is incorporated is evacuated, and then the collapse is performed while moving the heating furnace. At this time, the method of evacuating the inside of the synthetic quartz tube includes a method of simultaneously evacuating the upper and lower dummy tubes or a method of evacuating the lower dummy tube. Is often incomplete, so that there is a problem in that contaminant gas in the furnace is sucked at the time of evacuation to generate an extremely large amount of bubbles at the joint interface between the core rod and the synthetic quartz tube. As a countermeasure, if the thickness of the upper dummy tube is increased in accordance with the thickness of the synthetic quartz tube, there is an economic problem that the material cost of the upper dummy tube which is not a product increases.

[0005] Even if the connection between the upper dummy pipe and the synthetic quartz pipe is perfect, even if only a small amount of contaminant gas flows backward in the pipe downstream of the purge gas and in the upper dummy pipe, a large amount of bubbles are generated at the bonding interface. There was a problem that occurred. In addition, the electric furnace is turned off at the same time as the end of the collapse due to the increase in diameter, and the collapsed preform rod is cooled, but the inside of the electric furnace is kept warm by the heat insulating material of the electric furnace. Because the caliber is large and the heat capacity is large, the cooling rate is slow and it takes more than 60 minutes for cooling,
Productivity was poor due to the long cooling time.

[0006]

SUMMARY OF THE INVENTION The object of the present invention is to
When manufacturing a preform by the over-jacket method by covering a core rod manufactured by the VD method or the VAD method with a quartz tube, welding and sealing of the synthetic quartz tube and the upper dummy tube are performed.
An object of the present invention is to provide a method and an apparatus for manufacturing a preform in which everything from collapse to cooling is automatically performed.

[0007]

According to a method of manufacturing a preform of the present invention, there is provided a method of manufacturing a preform in which a synthetic quartz tube is covered on a core rod and the core tube is collapsed. It is characterized in that all processes up to are automatically controlled. Other inventions
In a method of manufacturing a preform in which a synthetic quartz tube is covered by a core rod and collapsed, a thin upper dummy tube is supported such that its lower end is located in a low-temperature region above an electric furnace, and a thick synthetic quartz tube is provided. While flowing an inert gas from the lower dummy tube, the synthetic quartz tube is supported so that its upper end is located in the high temperature region of the electric furnace, and after the upper end surface of the synthetic quartz tube has sufficiently melted, A method for manufacturing a preform, characterized in that a dummy tube is gradually lowered and welded, and then an electric furnace is moved downward to perform automatic control using a control device programmed to perform collapse.

In this control device, the upper dummy tube is welded to the upper end surface of the synthetic quartz tube, and then evacuated from the upper dummy tube. After the degree of vacuum reaches 4 × 10 ⁻⁴ Pa or more, the lower dummy tube is removed. Is started, and the electric furnace is moved downward while the vacuum is evacuated from the upper and lower dummy tubes to perform the collapse. At this time, after evacuation from the upper dummy pipe for a predetermined time, it is preferable to start evacuation from the lower dummy pipe. After the completion of the collapsing, the heating power is turned off, the electric furnace is raised to the upper end of the synthetic quartz tube, and air is blown to cool the synthetic quartz tube. The lower part of the synthetic quartz tube is connected to a lower dummy tube made of natural quartz.

An apparatus for manufacturing a preform according to the present invention is an apparatus for manufacturing an optical fiber preform in which a synthetic quartz tube is covered on a core rod and is collapsible, and a vertically movable upper chuck for gripping a thin upper dummy tube. When,
A lower chuck for gripping the lower dummy tube, a vertically movable electric furnace capable of providing a low-temperature region and a high-temperature region, an exhaust system capable of evacuating the upper dummy tube and the lower dummy tube,
Having an inert gas supply system from the lower dummy tube, moving the upper dummy tube to a predetermined position, raising the temperature of the electric furnace, welding the upper dummy tube and the synthetic quartz tube, evacuation, collapses, electric furnace It is characterized in that a control device is provided for automatically controlling each operation of the movement and cooling of the work based on a preset program. The control device is programmed to control each operation according to a time schedule.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to connect an upper dummy tube for sealing to a synthetic quartz tube with good reproducibility in an electric furnace, in addition to positional accuracy of the upper dummy tube, welding is performed by thermal transient. Accurate time control is necessary to connect using the phenomenon. Therefore, the method for manufacturing a preform of the present invention is to automatically control all steps from sealing of the synthetic quartz tube to fusion with the core rod and cooling in the collapsing process of covering the synthetic rod with the core rod. is there.

In the present invention, the upper dummy tube is supported in the low temperature region above the electric furnace controlled to a predetermined temperature by the elevating device, and the upper end of the synthetic quartz tube is located at the heat center (maximum temperature region) of the electric furnace. In such a manner, the temperature is raised to a temperature at which welding can be performed, and the temperature is maintained for a predetermined time, and the upper end surface of the synthetic quartz tube is sufficiently melted, and the upper dummy tube is gradually lowered to the fused surface to form a synthetic quartz tube. By melting and welding several tens of millimeters, the thick synthetic quartz tube and the thin dummy tube can be connected with good reproducibility inside the electric furnace.

After the upper dummy tube is connected to the upper end of the synthetic quartz tube, while the electric furnace is slowly moved downward at the collapse speed, the upper dummy tube is evacuated to a vacuum, and when the inside of the tube is completely evacuated. Then, evacuation is started from the lower dummy tube, and the collapse is performed while the evacuation is performed from both the upper and lower dummy tubes. The control of each of the above operations is based on the information of the temperature sensor and the position sensor (or the operation amount of the elevating device). Automatically controlled by

Hereinafter, the present invention will be described in more detail with reference to the drawings. FIG. 1 is a system diagram showing an outline of the present invention. FIGS. 2 to 6 are schematic explanatory views showing the manner of collapsing the synthetic quartz tube and the core rod according to the procedure. Figure 1
1, a core rod 3 supported by a core rod support tube 4 is set in a synthetic quartz tube 1. A lower dummy tube 2 is connected to a lower end of the synthetic quartz tube 1 and fixed by a lower chuck 7. A carbon dummy tube 6 is provided outside the lower dummy tube 2. The upper dummy tube 9 is gripped by the upper chuck 8 and supported at a predetermined position in the electric furnace 5 by the elevating device 16.

The electric furnace 5 is installed so as to be able to move up and down along a guide 18 by an elevating device 17, and a plurality of temperature sensors 19 are attached to the electric furnace 5, and based on this information, a temperature is controlled by a control device to a predetermined temperature. Controlled. A vacuum pump 2 is installed in the vacuum system and purge gas supply system lines.
0, a pressure gauge 21 is attached, and the opening and closing of a bypass valve 22, an exhaust valve 23, and a purge gas supply valve 24 are controlled by a control device 25, so that evacuation and supply of a purge gas are performed. Reference numeral 26 denotes a cooling unit for cooling the preform rod after the collapse, for example, a fan.

Further, the collapse will be described according to the procedure with reference to FIGS. FIG. 2 shows a case where the core rod 3 is placed in the synthetic quartz tube 1 and set as shown in the figure, and then supported so that the upper end of the synthetic quartz tube 1 is located in the high temperature region of the electric furnace, and the elevating device 16 (FIG. 1) to support the lower end of the upper dummy tube 9 so that the lower end is located in the low temperature region at the upper end of the electric furnace. Next, in order to prevent diffusion of the contaminant gas in the furnace into the synthetic quartz tube 1 and the core rod surface into the synthetic quartz tube 1, the temperature is increased while flowing a purge gas from the lower dummy tube 2, and the temperature is maintained for a predetermined time. The upper end surface of the quartz tube 1 is melted. The temperature in the high temperature region and the low temperature region of the electric furnace is controlled by the control device 25 based on the temperature information of the temperature sensor 19.

When the upper end surface of the synthetic quartz tube 1 becomes a sufficiently molten surface, the upper dummy tube 9 is gradually lowered,
When approaching the upper end surface of the synthetic quartz tube 1, the descent speed is further reduced (see FIG. 3) and lowered, and the lower end portion of the upper dummy tube 9 is melted and welded to the upper end surface of the synthetic quartz tube 1 (see FIG. 4). After the welding, the purge gas is reduced, the vacuum pump 20 is started, and the vacuum is exhausted from the upper dummy pipe to complete the welding. After a predetermined time has elapsed or the predetermined degree of vacuum has been reached, the supply of the purge gas is stopped. Vacuum evacuation is also started from the dummy tube 2 to start collapsing, and the electric furnace 5 is slowly moved downward (see FIG. 4 → FIG. 5).

After the collapse is completed, the heating power is turned off. After a predetermined time has elapsed, the electric furnace 5 is quickly raised to the upper end of the synthetic quartz tube 1 and the collapsed preform rod is cooled by the electric fan 26. Cooling after the end of the collapse is surrounded by heat insulating material in the electric furnace, and the cooling rate is slow and takes a long time. Therefore, the electric furnace is raised at the same time as the end of the collapse, and forced cooling is performed using a cooling means such as a fan. This can significantly reduce the cooling time. These operations are performed by the control device 25 by the lifting devices 16 and 17, the electric furnace 5, the lifting devices 16 and 17, the vacuum pump 20, the valves 22 and 23,
24.

Moving the upper dummy tube to the predetermined position;
All processes including heating of the electric furnace, welding of the upper dummy tube and the synthetic quartz tube, evacuation, collapses, moving and cooling of the electric furnace, are performed in advance in addition to information from the temperature sensor and the like. It is automatically controlled by a command from a control device, for example, a microcomputer based on a program (time schedule). As a result, the connection between the synthetic quartz tube and the upper dummy tube can be replaced by a manual operation with low reproducibility and a difficult manual operation, and can be replaced by automatic control without manual operation. In addition, it is possible to prevent the contamination of the upper dummy tube from flowing back into the tube, and to produce a preform rod without bubbles at the joint interface between the core rod and the synthetic quartz tube with good reproducibility and high production efficiency.

[0019]

[Example] Outer diameter 80mmφ, inner diameter 24mmφ, length 1,
In the lower part of the synthetic quartz tube 1 of 000 mm, the outer diameter is 40 mmφ,
A core rod support tube 4 is inserted into a tube to which a lower dummy tube 2 made of natural quartz having an inner diameter of 24φ and a length of 300 mm is welded in advance, a gas stopper is attached to the end of the tube, and an outer diameter manufactured by a VAD method. The core rod 3 having a diameter of 22 mm and a length of 1,050 mm was washed and set in the synthetic quartz tube 1. As shown in FIG. 2, the lower dummy tube 2 is mounted on the lower chuck 7 of a glass lathe (not shown) equipped with the electric furnace 5, the synthetic quartz tube 1 and the core rod 3 are set, and the outer diameter is set on the upper chuck 8. 47mmφ, inside diameter 24mmφ, length 1,250
The upper dummy tube 9 made of natural quartz having a diameter of 2 mm was mounted. Ar gas was flowed into the electric furnace 5 at a rate of 10 liters / minute from the top, 1 liter / minute from the center, and 10 liters / minute from the bottom.

Further, the synthetic stone into which the core rod 3 has been inserted.
Purging the inside of the synthetic quartz tube from the lower dummy tube 2 of the English tube 1
500cm He gas for^Three/ Min, Ar gas 2,000
cm ^Three/ The lower end surface 14 of the upper dummy tube is
Low temperature in the electric furnace 5 80 mm above the upper end surface of the quartz tube 1
And the upper end of the synthetic quartz tube 1 is heated by the electric furnace 5.
After being placed in the center (maximum temperature area), the temperature of the electric furnace 5 is raised.
To 2,050 ° C and reach this temperature before synthesis
Several hundred seconds (for example, until the upper end surface of the quartz tube 1 is sufficiently melted)
After holding for 300 seconds), as shown in FIG.
5 mm above the synthetic quartz tube at a speed of 60 mm / min.
And then slowly lower at 25mm / min.
Melts the lower end of the dummy tube 9 by several tens of mm (for example, 25 mm)
The synthetic quartz tube 1 was welded.

At this time, the temperature of the upper dummy tube 9 approaches the center of heat as it descends, so that it can be adjusted at this descending speed. The lower the temperature, the higher the temperature
If the speed is too fast, the drive will be too hard and the pipes will be damaged. However, by automatically performing this operation using a control device (for example, a microcomputer), it is possible to accurately eliminate the thermal transient without time delay. The upper dummy tube can be welded by utilizing.

Subsequently, after the upper dummy tube 9 is connected to the synthetic quartz tube 1, the electric furnace 5 is slowly lowered downward at a collapse speed (for example, at a speed of 10 mm / min) while only He is used as a purge gas for 50 cm. ³ / Diversion,
Start evacuation from the upper dummy tube 9 and make 3 × 10
After evacuation to ⁴ Pa or more (after 20 to 100 seconds from the start of evacuation of the upper dummy tube), subsequently, after 20 to 100 seconds from the start of evacuation of the upper dummy tube (for example, after 80 seconds)
Then, vacuum evacuation was started also from the lower dummy tube 2.

Subsequently, while continuing the vacuum evacuation from the upper and lower dummy tubes, the electric furnace 5 as the heating source was moved downward by 10 mm.
The tube was driven at a speed of / min, and collapsed sequentially from the top of the synthetic quartz tube 1. When the electric furnace reaches the lower end after the collapse, the heating power of the electric furnace is turned off, and after 5 minutes, the electric furnace is moved to the upper end of the collapsed preform rod at a speed of 130 mm / min. And then taken out after 30 minutes.

Moving the upper dummy tube to the predetermined position;
The operations of raising the temperature of the electric furnace, welding the upper dummy tube and the synthetic quartz tube, evacuating, collapsing, moving and cooling the electric furnace are performed in addition to information from the temperature sensor and the like, in addition to a preset program (time). The schedule was automatically controlled by a command from a control device, for example, a microcomputer. As a result, it was possible to produce a high quality preform without foam defects with good reproducibility and high production efficiency.

[0025]

According to the method of manufacturing a preform of the present invention, all of the above-mentioned operations are performed by automatic control using a control device, so that a high-quality preform can be efficiently produced without requiring any labor. Further, the thin upper dummy tube having a small heat capacity can be reliably welded to the synthetic quartz tube with good reproducibility by utilizing the thermal transient phenomenon. In addition, since the upper dummy tube is consumed in a small amount, the upper dummy tube can be cut and reused after the completion of the collapsing.
Can be reused more than once. Further, the gas in the furnace and the contamination of the upper dummy tube can be prevented from flowing back into the synthetic quartz tube, and a preform rod having no bubbles at the joint interface between the core rod and the synthetic quartz tube can be manufactured.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an outline of the present invention.

FIG. 2 is a schematic explanatory view showing a state where an upper dummy tube and a synthetic quartz tube are supported at predetermined positions in an electric furnace.

FIG. 3 is a schematic explanatory view showing a state in which an upper dummy pipe is lowered.

FIG. 4 is a schematic explanatory view showing welding of an upper dummy tube and a synthetic quartz tube.

FIG. 5 is a schematic explanatory view showing a state where a collapse is completed.

FIG. 6 is a schematic explanatory view showing a state of cooling after completion of the collapse.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Synthetic quartz pipe 2 Lower dummy pipe 3 Core rod 4 Core rod support pipe 5 Electric furnace 6 Carbon dummy pipe 7 Lower chuck 8 Upper chuck 9 Upper dummy pipe 10 Upper shield cylinder 11 Upper shield 12 Lower shield 13 Upper exhaust pipe 14 Upper dummy pipe Lower end surface 15 Welding part 16 Elevating device 17 Elevating device 18 Guide 19 Temperature sensor 20 Vacuum pump 21 Pressure gauge 22 Bypass valve 23 Exhaust valve 24 Purge gas supply valve 25 Control device 26 Fan

Claims (8)

[Claims] In a method of manufacturing an optical fiber preform in which a synthetic quartz tube is covered on a core rod and collapsed, all processes from sealing of the synthetic quartz tube to fusion with the core rod and cooling are automatically controlled. A method for producing a preform for an optical fiber. 2. A method for manufacturing an optical fiber preform in which a synthetic quartz tube is covered on a core rod and is collapsed, wherein a thin upper dummy tube is supported such that its lower end is located in a low temperature region above an electric furnace. While flowing an inert gas from the lower dummy tube into the thick synthetic quartz tube, the synthetic quartz tube is supported so that its upper end is located in the high temperature region of the electric furnace, and the upper end surface of the synthetic quartz tube is sufficiently melted. After that, after the upper dummy pipe is gradually lowered to the molten surface and welded,
A method of manufacturing a preform for an optical fiber, wherein the electric furnace is moved downward to perform automatic control using a control device programmed to perform a collapse. 3. An upper dummy tube is welded to the upper end surface of the synthetic quartz tube, and then evacuated from the upper dummy tube to a vacuum of 4 ×.
The controller is programmed to start evacuation from the lower dummy tube after the pressure becomes 10 ^-4 Pa or more, and to move the electric furnace downward while performing evacuation from the upper and lower dummy tubes to perform collapse. A method for producing an optical fiber preform according to claim 1. 4. The method of manufacturing an optical fiber preform according to claim 3, wherein after evacuating the upper dummy tube for a predetermined time, evacuating the lower dummy tube is started. 5. The optical fiber pump according to claim 1, wherein the heating power is turned off after the collapse, the electric furnace is raised to the upper end of the synthetic quartz tube, and air is blown to cool the synthetic quartz tube. How to make a renovation. 6. The method for manufacturing an optical fiber preform according to claim 1, wherein a lower dummy tube made of natural quartz is connected to a lower portion of the synthetic quartz tube. 7. An apparatus for manufacturing an optical fiber preform for covering a core rod with a synthetic quartz tube covered by a synthetic quartz tube, wherein the upper chuck is capable of ascending and descending to hold a thin upper dummy tube and a lower dummy tube. It has a lower chuck, a vertically movable electric furnace capable of providing a low-temperature region and a high-temperature region, an exhaust system capable of evacuating the upper dummy tube and the lower dummy tube, and an inert gas supply system from the lower dummy tube. Then, the operations of moving the upper dummy tube to a predetermined position, raising the temperature of the electric furnace, welding the upper dummy tube and the synthetic quartz tube, evacuating, collapsing, moving the electric furnace, and cooling are set in advance. An apparatus for producing an optical fiber preform, comprising: a control device for automatically controlling a preform based on a program. 8. The apparatus for manufacturing an optical fiber preform according to claim 7, wherein said control device is programmed according to a time schedule.