JP2004035369A - Method of manufacturing optical fiber preform - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing an optical fiber preform for cleaning the surface of a quartz rod material by flame polishing so as to suppress the occurrence of cracks in the quartz rod material. <P>SOLUTION: A rod material 2 is obtained by heating and drawing a primary preform 1 in a furnace 5. A gas burner 22 is provided above the furnace 5, and stains or defects on the surface of the rod material 2 are eliminated by blowing flame 21 onto the rod material immediately after drawing. Strain caused by blowing of the flame 21 does not occur in the rod material 2 since blowing of the flame 21 is performed before the rod material 2 is cooled down. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to 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.
[0002]
[Prior art]
A method of manufacturing a preform of an optical fiber made of quartz glass includes a step of manufacturing a primary preform having a core portion at a central portion and a clad portion outside the core portion, and a cladding outside the primary preform. And providing a quartz glass. The latter process is provided for improving the productivity because it takes a very long time to make the clad portion the required thickness only with the primary base material, and the productivity is significantly reduced. There are generally three methods used in the process of manufacturing the primary base material: VAD, OVD, and MCVD. On the other hand, as a method of forming a clad outside the primary base material, an external method such as an OVD method and a rod-in-tube method are known.
[0003]
The rod-in-tube method is a method of forming another quartz glass that becomes a cladding outside the primary preform.The primary preform is inserted into another quartz glass tube, fused, integrated and stretched to form an optical fiber. It is a method of using as a base material.
[0004]
In the rod-in-tube method, in recent years, for the purpose of cost reduction, it has been practiced to increase the length of a primary base material by using a large-diameter primary material and then drawing it by heating to form a rod material.
[0005]
In addition, since it is also important to guarantee the quality, it is necessary to inspect the refractive index profile of the primary base material after heating and stretching, as it is, or by cutting the upper and lower ends of the rod material as it is after stretching the primary base material. I have. Thereafter, a working rod for handling is connected to one or both ends of the bar using a glass lathe, and then HF etching is performed or a flame is applied to the bar surface to remove dirt and scratches on the surface of the bar. To perform flame polishing. If the surface of the bar is dirty or scratched, air bubbles will enter the base material when inserted into the quartz glass tube and integrated, resulting in a defective product with poor optical characteristics when used as an optical fiber for the product. . The bar material whose surface has been cleaned in this way is inserted into a quartz tube and fused and integrated.
[0006]
[Problems to be solved by the invention]
However, when HF etching is performed, spots remain on the surface of the bar due to subsequent washing and drying, and the portion causes bubbles in the base material.
[0007]
When cleaning the surface of a bar by flame polishing, high temperature due to flame becomes a problem. That is, after the primary base material is heated and drawn into a bar, the bar is conveyed to a glass lathe and fixed, and then subjected to flame polishing. To make the temperature high. In this case, distortion remains in the base material. Furthermore, after the flame polishing, the rod is removed from the glass lathe, carried to the insertion process, inserted into a quartz tube, and heated and integrated by fusion. However, once the temperature is cooled, the temperature becomes high in the fusion-integration step, so that the strain causes cracks, and cracks are frequently generated in the bar.
[0008]
The present invention has been made in view of such circumstances, and an object of the present invention is to provide a method of manufacturing an optical fiber preform in which the surface is cleaned by flame polishing so that cracks do not occur in the quartz rod. Is to do.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the number of steps of cooling the bar and then raising the temperature again is at most one.
[0010]
Specifically, the invention according to claim 1 is directed to a method for manufacturing an optical fiber preform by a rod-in-tube method.
[0011]
Then, a primary base material stretching step of heating and stretching the primary base material to obtain a rod, a flame polishing step of spraying a flame onto the surface of the rod to remove dirt and scratches, and the dirt and scratch removed rod An insertion step of inserting the material into a quartz tube, and an integrating step of fusing and integrating the inserted bar with the quartz tube, wherein the flame polishing step is a step of stretching the primary base material. Immediately after that, the above-mentioned bar is performed in a state where the temperature is higher than a predetermined flame polishing temperature.
[0012]
According to the manufacturing method of the first aspect, flame polishing is performed in a state where the rod is higher than a predetermined flame polishing temperature before the rod is cooled from the primary base material stretching step. Even if heated to a high temperature, cracks hardly occur, and an optical fiber having good optical characteristics can be obtained. That is, after completion of the primary base material stretching step, flame polishing is performed in the next step before the bar is cooled, so that flame polishing is performed again under the condition that the temperature difference between the surface where the temperature tends to decrease and the central part where the temperature does not easily decrease is small. As a result, the surface temperature is increased, so that the distortion remaining inside the bar after the flame polishing step is suppressed to a small value, and no crack is generated. Here, the predetermined flame polishing temperature is the temperature of the bar at the start of flame polishing, in which the bar is subjected to flame polishing, and after the reheating after cooling, distortion such that cracks begin to occur. The temperature at the time of flame polishing varies depending on the diameter and length of the bar, the processing speed of flame polishing, the temperature of flame polishing, and the like. The surface temperature of the bar is preferably 200 ° C. It is more preferable because it becomes certain. At this time, the temperature at the center of the bar is estimated to be several hundred degrees higher than the surface temperature.
[0013]
Next, the invention according to claim 2 is directed to a method for manufacturing an optical fiber preform by a rod-in-tube method.
[0014]
Then, a primary base material stretching step of heating and stretching the primary base material to obtain a rod, a flame polishing step of spraying a flame onto the surface of the rod to remove dirt and scratches, and the dirt and scratch removed rod An inserting step of inserting the material into the quartz tube, and an integrating step of fusing and integrating the inserted bar with the quartz tube. The inserting step is performed immediately after the flame polishing step. In this case, the insertion is performed in a state in which the temperature of the bar is higher than a predetermined insertion temperature, and the insertion and the fusion-integration are continuously performed temporally.
[0015]
According to the manufacturing method of the second aspect, the rod is inserted into the quartz tube at a temperature higher than a predetermined insertion temperature and before the rod is cooled after the flame polishing step is completed and continuously. Since they are fused and integrated, it is possible to prevent cracks from occurring in the bar. That is, since the process of cooling the bar and then raising the temperature again is performed at most once, no crack is generated. Here, the predetermined insertion temperature means that while the bar material, which has been heated by the flame polishing, is being cooled, cracks are generated when the bar material is inserted into the quartz tube and heated again for fusion and integration. This is the temperature at the beginning of the insertion of the bar into the quartz tube. The temperature at the time of insertion varies depending on the diameter and length of the bar, the processing speed and temperature of flame polishing, the time from the start of insertion to the start of attachment and integration, and the like, and the surface temperature is preferably 200 ° C. In addition, the term “continuously performing the insertion and the fusion and integration” means that the rod is fused immediately after the insertion so as to prevent cracks due to cooling of the rod between the insertion and the fusion and integration. Initiating the integration, for example, performing the insertion step and the integration step at the same place so as not to move between the steps, and performing the two steps consecutively.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0017]
As an example, FIG. 1 shows a manufacturing process of an optical fiber preform (preform) in which a primary preform is formed by a VAD method and a clad portion is formed by a rod-in-tube method. The first sooting is a process of stacking soot in a rod shape. Next, through a sintering step of sintering the rod-shaped soot to form a primary base material of the soot, the primary base material is heated and drawn into a rod material in a primary base material stretching step. Then, the bar is subjected to flame polishing (removal of dirt and scratches by flame polishing) in a flame polishing step. Next is an insertion step of inserting a quartz rod into a quartz tube. Then, the gap between the rod inserted in the integration step and the quartz tube is heated to a low pressure state with a vacuum pump, and the two are fused and integrated, and simultaneously heated and stretched to obtain a preform having a desired diameter.
[0018]
In the above-mentioned steps, the fusion integration of the rod and the quartz tube and the stretching may be performed in separate steps, and the fusion integration and the stretching need not be performed simultaneously. Further, the primary base material may be manufactured by using the OVD method or the MCVD method.
[0019]
Although not shown in the drawing, the preform is heated and drawn in the subsequent step of drawing to form an optical fiber.
[0020]
The present invention is characterized by a step of extending the primary base material in FIG. 1, a step of flame polishing, and a step of insertion into a quartz tube.
[0021]
-Embodiment 1-
FIG. 2 is a side view of a portion where the primary base material has been stretched and flame polishing has been performed from a portion where the stretching has been completed to form a bar. That is, here, the primary base material stretching step and the flame polishing step are performed. Although the productivity increases when the primary base material 1 is increased in size, in order to insert it into the quartz glass tube, it is necessary to stretch and reduce the diameter. Here, a primary base material 1 having a diameter of 100 mm and an effective length of 750 mm is heated and stretched in a furnace 5 to form a bar 2 having a diameter of 50 mm and a length of 3000 mm.
[0022]
Specifically, the work rod portion 8 having a small diameter at the lower end of the primary base material 1 is gripped and fixed by the lower chuck 6. A working rod 3 is connected 7 to the upper end of the primary base material 1, and the upper end of the working rod 3 is gripped by the upper chuck 4. By sending the lower chuck 6 upward, the primary base material 1 is heated and softened in the furnace 5, and is stretched by pulling the upper chuck 4 upward. The diameter of the bar 2 is determined by the feeding speed of the lower chuck 6 and the pulling speed of the upper chuck 4. At this time, since the bar 2 is longer than 3 m, it is preferable to extend it upward from the viewpoint of handling. However, the equipment may be arranged upside down and extended downward.
[0023]
Above the furnace 5, a gas burner 22 is installed, and a flame 21 is sprayed on the surface of the stretched rod 2 that has just come out of the furnace 5 to incinerate or vaporize dirt and scratches to clean them. ing. The central portion of the bar 2 to which the flame 21 is sprayed is several hundred degrees Celsius lower than the heating and stretching temperature in the furnace 5, but is 1000 ° C. or higher. When the flame 21 is sprayed, the surface of the bar 2 becomes 1500 ° C. or more. However, since the temperature difference from the center portion is several hundred ° C., even if the bar 2 is flame-polished at this temperature, the bar 2 There is almost no increase in distortion. That is, the temperature of the bar 2 is higher than the predetermined flame polishing temperature. A plurality of burners 22 may be provided around the bar 2 for flame polishing so that the surface of the bar 2 is evenly polished by flame. For the same reason, flame polishing may be performed while rotating the bar 2 around the central axis.
[0024]
During this process, the connection state between the work bar 3 and the bar 2 is kept as it is, and any part of the upper portion of the bar 2 and the work bar 3 is cut and reconnected, or another work bar is connected. It is preferable not to change the connection from the viewpoint of preventing bending and eccentricity of the bar.
[0025]
After the flame polishing is completed, the bar 2 is inserted into the quartz tube 11 as shown in FIG. The rod 2 is moved or held in a vertical state from the end of the previous step to the end of the insertion step. However, in the insertion stage, the upper chuck 4 is replaced with the insertion chuck 14. From the end of the inspection process to the end of the insertion process, the connection between the work bar 3 and the bar 2 is kept as it is, and any part of the upper portion of the bar 2 and the work bar 3 is cut and re-cut. It is preferable not to connect or reconnect to another working rod from the viewpoint of preventing bending and eccentricity of the rod 2.
[0026]
In order to support the quartz tube 11, an auxiliary tube 12 having a slightly larger inner diameter than the quartz tube 11 is coaxially connected to the upper portion of the quartz tube 11 (the side having the opening into which the bar 2 is inserted). The upper portion of the auxiliary pipe 12 is gripped by the gripping member 9 and is maintained in a vertical state. Specifically, the quartz tube 11 has an outer diameter of 182 mm, an inner diameter of 54 mm, and a length of 2,000 mm, and the auxiliary tube 12 has an outer diameter of 182 mm, an inner diameter of 62 mm, and a length of 800 mm.
[0027]
After the center axis of the bar 2 is aligned with the center axis of the quartz tube 11, the bar 2 is lowered and inserted into the auxiliary tube 12 and subsequently into the quartz tube 11. The chuck 14 is lowered with high precision so that the two central axes do not shift on the way, and the bar 2 is inserted.
[0028]
Here, if the bar 2 keeps the vertical state and the connection state between the work bar 3 and the bar 2 as it is after the stretching process of the primary base material, the central axis of the bar 2 Is not eccentric, so that the rod 2 does not contact the inner wall of the quartz tube 11.
[0029]
Next, as shown in FIG. 4, the whole of the bar 2 and the quartz tube 11 are fused and integrated and stretched simultaneously.
[0030]
In order to perform the fusion and integration, a pressure reducing cap 17 previously placed on the upper end of the auxiliary pipe 12 is connected to a vacuum pump, and the gap between the quartz pipe 11 and the rod 2 is set to a low pressure state. In this state, when heating is performed in the furnace 16 from the lower ends of the quartz tube 11 and the bar 2, the gap between the two disappears and the two are fused and integrated. At the same time, it is stretched downward to obtain a preform 15 having a desired diameter. Since the flame polishing is performed immediately after the primary base material stretching step, no crack is generated in the bar 2 in this step.
[0031]
In the present embodiment, since the bar 2 is subjected to flame polishing immediately after the primary base material stretching step and in a state where the temperature of the rod 2 is higher than a predetermined flame polishing temperature by the heat of the primary base material stretching step, distortion due to flame polishing is caused. Does not occur, and cracks do not occur in the bar 2 during the integration process, so that a high quality preform 15 can be obtained. Further, since the rod 2 is processed while being kept vertical after the primary base material stretching step, the rod 2 does not contact the inner wall of the quartz tube 11 and the inside of the quartz tube 11 is damaged. There is no.
[0032]
-Embodiment 2
In the second embodiment, as shown in FIG. 5, flame polishing is not performed on the bar 2 immediately after the primary base material 1 is stretched. Further, as shown in FIG. 6, the bar 2 is subjected to flame polishing immediately before insertion into the quartz tube 11. Although these two points are different from the first embodiment, the other steps are the same as those of the first embodiment, and the description of the same points will be omitted.
[0033]
The primary base material stretching step is the same as that of the first embodiment except that the flame polishing is not performed as shown in FIG.
[0034]
In the insertion step, as shown in FIG. 6, in addition to the state of the first embodiment, a burner 22 is installed so that flame polishing is performed immediately before the rod 2 is inserted into the auxiliary pipe 12. The conditions for flame polishing are almost the same as in the first embodiment. When the insertion of the rod 2 into the quartz tube 11 is completed, the fusion integration shown in FIG. 4 and the subsequent stretching are immediately performed. The temperature of the bar 2 at the time when the bar 2 is inserted into the quartz tube 11 is higher than a predetermined temperature at the time of insertion, and is melted before the bar 2 cools and distortion causing a crack occurs. Since the integration is performed, the preform 15 can be manufactured without cracks occurring in the bar 2.
[0035]
The operation and effect of the second embodiment are the same as those of the first embodiment.
[0036]
-Other embodiments-
The manufacturing method in the embodiment described so far is an example, and the present invention is not limited to this method. Another step such as an inspection step may be inserted in the middle, and the processing method of each step may be performed by another method. Further, the sizes of the primary base material 1, the bar material 2, and the quartz tube 11 are not particularly limited.
[0037]
【The invention's effect】
The present invention is implemented in the form described above, and has the following effects.
[0038]
Since the flame polishing of the bar is performed immediately after the primary preform is stretched or immediately before the quartz tube is inserted, cracks are prevented from being generated in the bar, and a high-quality optical fiber preform can be manufactured. it can.
[Brief description of the drawings]
FIG. 1 is a diagram showing a flow of a manufacturing process of an optical fiber preform.
FIG. 2 is a schematic sectional view of primary base material stretching and flame polishing according to the first embodiment.
FIG. 3 is a schematic side view showing a state where a bar of the first embodiment is being inserted.
FIG. 4 is a schematic side view of the first embodiment in which fusion integration and stretching are performed.
FIG. 5 is a schematic side view showing a state where a primary base material of Embodiment 2 is being stretched.
FIG. 6 is a schematic side view of the bar of Embodiment 2 subjected to flame polishing and insertion.
[Explanation of symbols]
1 Primary preform 2 Bar 11 Quartz tube 15 Preform (optical fiber preform)
21 Flame

Claims (2)

A method for manufacturing an optical fiber preform by a rod-in-tube method,
A primary base material stretching step in which the primary base material is heated and drawn into a bar,
A flame polishing step of spraying a flame on the surface of the bar to remove dirt and scratches,
An insertion step of inserting the bar having the dirt and scratches removed into a quartz tube,
An integration step of fusing and integrating the inserted bar material with the quartz tube,
The method for producing an optical fiber preform, wherein the flame polishing step is performed immediately after the primary preform stretching step and in a state where the rod is higher than a predetermined flame polishing temperature. A method for manufacturing an optical fiber preform by a rod-in-tube method,
A primary base material stretching step in which the primary base material is heated and drawn into a bar,
A flame polishing step of spraying a flame on the surface of the bar to remove dirt and scratches,
An insertion step of inserting the bar having the dirt and scratches removed into a quartz tube,
An integration step of fusing and integrating the inserted bar material with the quartz tube,
The insertion step is performed immediately after the flame polishing step and in a state in which the rod is higher than a predetermined insertion temperature, and the insertion and the fusion integration are temporally continuously performed. A method of manufacturing an optical fiber preform.

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