JP2003054974A - Method for manufacturing optical fiber preform - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an optical fiber preform in which the surface of a quartz rod is cleaned and the quartz rod is put in a quartz pipe while keeping the cleaned state. SOLUTION: A quartz rod 2 obtained by drawing a soot sintered compact is inserted in an auxiliary pipe 12 and a quartz pipe 11 while cleaning the surface of the quartz rod 2 by polishing with a flame 21. Flame polishing is gradually carried out from the tip of the quartz rod 2 to be inserted first toward the upper part and the flame-polished part is quickly put in the auxiliary pipe 12 and the quartz pipe 11 as it is. The quartz rod 2 is therefore inserted in the quartz pipe 11 while keeping the cleaned state of the surface and the objective high quality optical fiber preform is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an optical fiber preform by a rod-in-tube method in which a quartz rod is inserted into a quartz tube.

[0002]

2. Description of the Related Art As a method for manufacturing an optical fiber preform,
The OVD method, the VAD method, and the MCVD method are mainly used. When the optical fiber preform is manufactured by using the VAD method or the MCVD method, a method of forming a clad that occupies most of the optical fiber by a separate process is used from the viewpoint of improving productivity. One of the techniques is a rod-in-tube method (see, for example, Japanese Patent Laid-Open No. 7-196332).

In recent years, for the purpose of cost reduction, the base material has been increased in size, and rods and tubes used in the rod-in-tube method have been increased in diameter and length (for example, Japanese Patent Laid-Open No. 7-1091).
No. 41). Along with that, the process of coaxially setting the rod and the tube has changed significantly. That is, conventionally, the rod was set on the tube with a glass lathe, and it was moved vertically above the electric furnace for fusion and integration.
Recently, it has become difficult to carry out the above process in a horizontal state due to the weight and size of the rod and tube used. Especially in the rod-in-tube method using a large tube, first hold the large tube vertically in an electric furnace that melts and integrates it, move the rod stretched above its central axis, and then clean the rod surface if necessary. To do so, flame polishing is performed in the vertical state, and finally the rod is lowered and set inside the tube.

[0004]

However, in the prior art, when the flame-polished rod is cooled, a phenomenon in which the surrounding dust is attracted to the rod causes dust to adhere to the rod. In addition, if the dirt removal of the rod and the insertion into the quartz tube are performed in separate steps, dust and dirt will adhere to the rod surface when the rod is moved, and when using an optical fiber, air bubbles will form on the dust and dirt adhesion part. Etc. have occurred and quality problems have occurred. In order to solve this problem, the manufacturing process is kept clean, but the problem has not been completely solved.

Further, when the flame is polished, the quartz on the surface of the rod sublimes into a gas, which solidifies in the non-flame portion, and a phenomenon called fume, which adheres to the quartz powder, also occurs. The fume adhering to the polished portion may deteriorate the quality of the optical fiber.

The present invention has been made in view of the above circumstances, and an object of the present invention is to insert a quartz rod into a quartz tube while keeping its state clean.
An object of the present invention is to provide a manufacturing method for manufacturing an optical fiber preform.

[0007]

In order to achieve the above object, the surface of the quartz rod is flame-polished and the cleaned portion is immediately inserted into the quartz tube.

Specifically, the invention of claim 1 is a method for producing an optical fiber preform by a rod-in-tube method in which a quartz rod is inserted into a quartz tube, in which flame is blown onto the surface of the quartz rod. In the process of inserting the quartz rod into the quartz tube while removing the dirt, the above flame is blown from the insertion end of the quartz rod to the other end, and the portion of the quartz rod that has been blown is blown. The optical fiber preform manufacturing method is characterized in that the optical fiber preform is inserted into the quartz tube immediately after the end.

According to the manufacturing method of the present invention, while the flame is blown from the insertion tip of the quartz rod to the other end, at the same time, the portion of the quartz rod that has been fired is immediately after the flame is blown. Since the quartz rod is inserted into the quartz tube, the quartz rod is inserted into the quartz tube while being kept clean.

[0010] Here, when the portion of the quartz rod that has been subjected to flame blowing is inserted into the quartz tube immediately after the flame has been blown, the portion of the quartz rod that has been cleaned by the flame blowing is cooled. Before the dust is sucked up, the quartz tube or the auxiliary tube connected to the quartz rod insertion port of the quartz tube is inserted. Specifically, the flame is blown immediately before the insertion port of the quartz tube or the auxiliary tube, and the temperature of the flame-blown portion of the quartz rod is 200 ° C. or higher. It is to insert a bar.

Next, in the invention of claim 2, in claim 1, in the above step of flame-blowing the quartz rod and inserting it into the quartz tube, from the opening of the quartz tube opposite to the quartz rod insertion port. A method of manufacturing an optical fiber preform characterized in that a gas is caused to flow into a quartz tube.

According to the manufacturing method of the present invention, it is possible to reliably prevent fume generated by flame polishing from adhering to the polished portion of the quartz rod.

[0013]

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

FIG. 1 shows a manufacturing process of an optical fiber preform (preform) by the VAD method. The first sooting is a step of depositing soot, which is a silica glass particle, in a columnar shape downward in the axial direction of the starting material. Next, the cylindrical soot is sintered into a transparent sintered body, and the sintered body is heated and stretched into a rod. The rod is inserted into a quartz tube while flame-burning, the gap between the rod and the quartz tube is heated to a low pressure with a vacuum pump, and both are fused and integrated, and simultaneously drawn and stretched as desired. The outer diameter of the preform is

The stretching may be carried out after the rod material and the quartz tube are fused and integrated in the above step. Further, the manufacturing method of the bar material is not limited to the VAD method, and the bar material may be manufactured using the OVD method or the MCVD method.

The preform is not shown in the figure,
In the next drawing step, the fiber is heated and drawn to form an optical fiber.

The present invention is characterized by the steps of inserting it into a quartz tube and flame-polishing in FIG.

-Embodiment 1- FIG. 2 is a side view of a stretched sintered body. If the size of the sintered body is increased, the productivity will be increased. However, in order to insert the sintered body into the quartz tube, it is necessary to stretch it to reduce its diameter. Here, a sintered body 1 having a diameter of 100 mm and an effective length of 600 mm is heated and stretched in a furnace 5 and has a diameter of 50 mm and a length of 240 mm.
The rod 2 is 0 mm.

Specifically, the lower end of the sintered body 1 is chucked by the chuck 6
The work rod 3 is connected 7 to the upper end of the work rod 3, and the chuck 4 holds the upper end of the work rod 3. The sintered body 1 is heated in the furnace 5 to soften it, and while the chuck 6 feeds the sintered body 1 upward, the chuck 4 is pulled upward at a speed higher than the upward feeding speed of the chuck 6 to stretch it. Go. The diameter of the rod 2 is determined by the feed rate of the sintered body 1 and the pulling rate of the chuck 4. At this time, since the bar 2 has a length of more than 2 m, it is preferable to stretch it upwards from the viewpoint of handling, but it is also possible to arrange the equipment upside down and stretch downward.

Next, the quartz tube 1 is flame-polished on the rod 2.
1 (Fig. 3). Here, in the upper part of the quartz tube 11 (on the side where the opening into which the rod 2 is inserted), the auxiliary tube 12 serving as a holding portion of the quartz tube 11 has an inner diameter slightly larger than the quartz tube 11 and an outer diameter slightly smaller. Are concentrically connected to the quartz tube 11. Specifically, the quartz tube 11 has an outer diameter of 182 mm,
Internal diameter 54 mm, length 2000 mm, auxiliary tube 12
Has an outer diameter of 182 mm, an inner diameter of 85 mm, and a length of 1000 mm
Is.

In the flame-polishing and inserting step, first, the vertical rod 2 is placed above the quartz tube 11 so that the rod 2 and the central axis of the quartz tube 11 coincide with each other. A few cm from the auxiliary pipe 12
Install the burner 22 at a position several tens of cm above. The flame outlet of the burner 22 is directed obliquely upward so that the flame 21 is sprayed obliquely upward. The burner 22 is placed at a position where it does not interfere with the inserted rod 2 and the flame 21 can effectively clean the surface of the rod 2. When the rod 2 is lowered, it is flame-polished in order from the insertion tip, which is the lower end, upwards, and the cleaned portion of the rod 2 is sequentially inserted into the auxiliary pipe 12 and subsequently into the quartz pipe 11. To go. The chuck 4 is lowered with high accuracy so that the center axes of the rod 2 and the quartz tube 11 do not shift during the insertion, and the rod 2 is inserted.

Thus, since the rod 2 is inserted into the quartz tube 11 immediately after the flame polishing from the end of the flame polishing, the surface of the rod 2 is kept clean and a high quality preform can be obtained. At this time, the temperature of the rod 2 immediately after the end of the flame polishing is about 1500 ° C., and the rod 2 is inserted into the auxiliary pipe 12 before the temperature falls below 200 ° C., so that dust is prevented from being sucked up. More preferably, the bar 2 is 300 ° C
It is to insert into the auxiliary pipe 12 before it becomes less than. Also, the position of the burner 22 should be 10 to 30 from the auxiliary pipe 12.
It is more preferable that the height is above the cm in order to prevent cooling of the rod 2 before inserting the auxiliary pipe 12. To measure the temperature of the surface of the rod 2, an infrared temperature analyzer (Thermoviewer JTG-7000 series manufactured by JEOL Ltd.) may be used.

In order to burn the surface of the rod 2 evenly, a plurality of burners 22 may be installed around the rod 2 for flame polishing. Further, for the same reason, the rod 2 may be lowered while being rotated around the central axis.

Since the flame outlet of the burner 22 is directed obliquely upward, the fume generated by the flame polishing is blown upward and adheres to the upper side of the flame 21 of the rod 2 and the flame-polished rod 2 Hardly adheres to the part. There is no problem because the fumes attached above the flame 21 are blown again by the flame 21 and sublimate. In addition,
In order to more reliably prevent the fume from adhering to the surface of the rod 2 inserted in the quartz tube 11, forced exhaust is performed at the opening of the auxiliary tube 12 to remove fumes flying below the flame 21. Good.

Here, the rod 2 is used all the time after the step of stretching the sintered body.
Is kept in the vertical state, and the connecting state between the work rod 3 and the rod 2 is kept as it is, and any portion between the upper portion of the rod 2 and the work rod 3 is cut and reconnected, or If it is not connected to another work rod, the central axis of the rod 2 is held without being eccentric. Therefore, the bar 2
It is preferable that the rod 2 does not come into contact with or get stuck on the inner wall of the quartz tube 11 when it is inserted into the quartz tube 11.

Next, the fusion and integration of the entire rod 2 and the quartz tube 11 and the stretching are simultaneously performed (FIG. 4).

In order to perform fusion and integration, the upper end of the auxiliary tube 12 is covered with a decompression cap 17 and connected to a vacuum pump to bring the gap between the quartz tube 11 and the bar 2 to a low pressure state. In that state, when the quartz tube 11 and the rod 2 are heated from the lower end to the upper side in the furnace 16, the gap between the two disappears and they are fused and integrated. At the same time, the preform 15 having a desired diameter is drawn downward.

In the above process, if the bar is cooled after the flame polishing is finished, cracks due to strain are likely to occur at the last flame sprayed portion. Therefore, it is necessary to fuse and integrate the rod and the quartz tube as soon as possible after the end of flame polishing. According to the present invention, since the rod is inserted into the quartz tube while flame-polishing, the time from the end of flame-polishing to the fusion and integration of the rod and the quartz tube can be shortened as compared with the conventional method. That is, the method of the present invention is also advantageous for crack generation.

The method described above is only an example, and the present invention is not limited to this method. Another process may be inserted in the middle of the process, and the processing method of each process may be performed by another method.

Embodiment 2 FIG. 5 shows the steps of flame-polishing the rod 2 and inserting it into the quartz tube 11 of Embodiment 2. This step is different from the first embodiment, and the other steps are the same.

In the flame polishing of the rod 2 and the insertion process into the quartz tube 11 of the present embodiment, gas is introduced into the quartz pipe 11 from the opening (gas inlet) on the side opposite to the rod 2 insertion port of the quartz pipe 11. Inflow. For that purpose, a gas introduction cap 23 is connected to the gas inlet of the quartz tube 11. The gas to be introduced is preferably clean air substantially free of dust, nitrogen gas and the like. When this gas flows out from the rod 2 insertion port of the quartz tube 11, the fumes flying below the flame 21 are prevented from entering the quartz tube 11. In this way, it is possible to more reliably prevent fume adhesion to the surface of the rod 2 that has been flame-polished, and to obtain a high-quality optical fiber preform.

In the present embodiment, as in the first embodiment, a plurality of burners 22 may be provided, the bar 2 may be rotated, and forced exhaust may be performed.

[0033]

The present invention is carried out in the form as described above, and has the following effects.

While the quartz rod is flame-polished, the portion after the flame-polishing is immediately inserted into the quartz tube. Therefore, it is possible to insert the quartz rod into the quartz tube while keeping the surface of the quartz rod clean, and it is possible to obtain high quality without bubbles. Can manufacture optical fiber preforms.

In the process of flame-polishing the quartz rod and inserting it into the quartz tube, gas is introduced from the opening on the opposite side of the rod-insertion port of the quartz tube. It is possible to prevent and manufacture high quality optical fiber preform.

[Brief description of drawings]

FIG. 1 is a diagram showing a manufacturing process of an optical fiber preform.

FIG. 2 is a side view of the sintered body being stretched in the first embodiment.

FIG. 3 is a side view showing that the rod is flame-polished and inserted into the quartz tube in the first embodiment.

FIG. 4 is a side view of the rod and the quartz tube that are fused together and extended in the first embodiment.

FIG. 5 is a side view showing that a rod is flame-polished and inserted into a quartz tube in the second embodiment.

[Explanation of symbols]

1 Sintered body 2 bars 3 work rod 4 chuck 5 furnaces 6 chuck 7 connection 11 Quartz tube 12 Auxiliary pipe 15 Preform 16 furnaces 17 Decompression cap 21 flame 22 burners 23 Gas introduction cap

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Nobue Nagae             4-3 Ikejiri, Itami City, Hyogo Prefecture Mitsubishi Electric Cable             Industrial Co., Ltd. Itami Works F-term (reference) 4G021 BA03 BA04

Claims (2)

[Claims] 1. A method for manufacturing an optical fiber preform by a rod-in-tube method in which a quartz rod is inserted into a quartz tube, wherein the surface of the quartz rod is blown by a flame to remove dirt, and the quartz rod is made of quartz. In the process of inserting into the tube, the above flame is blown from the insertion end of the quartz rod to the other end, and the portion of the quartz rod after the flame is blown is inserted into the quartz pipe immediately after the flame is blown. A method for producing a characteristic optical fiber preform. 2. The method according to claim 1, wherein in the step of flame-blowing the quartz rod and inserting it into the quartz tube, a gas is introduced into the quartz tube through an opening on the side opposite to the quartz rod insertion port of the quartz tube. A method for manufacturing an optical fiber preform characterized by the above.