JP2004043200A - Method of supporting optical fiber preform - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the disorder of the flow of a gas caused by the rapid fluctuation of furnace pressure at a place where a supporting tube for a clad begins to enter into the furnace in drawing. <P>SOLUTION: In the manufacture of the optical fiber by heating and fusing the tip part of an optical fiber preform constituted of a core rod and a synthetic quartz pipe into which the core rod is inserted and drawing the core rod and the synthetic quartz tube while integrating, the method of supporting the optical fiber preform is performed by inserting the core rod into the synthetic quartz tube provided with a supporting tube having an inside diameter larger than the inside diameter of the synthetic quartz tube in one end. The outside diameter of the supporting tube is equal to or smaller than the outside diameter of the synthetic quartz tube. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a communication optical fiber.
[0002]
[Prior art]
The optical fiber is made of quartz glass as a base material. Quartz glass, unlike ordinary glass materials, is extremely difficult to melt while maintaining high purity. For this purpose, a base material having a predetermined refractive index distribution is synthesized in advance, melt-softened using a heating furnace, stretched thinly, and spun.
[0003]
As a method of synthesizing a base material, an MCVD method, a VAD method, an OVD method, and the like have been devised. There is also known a method in which a central part including a core (hereinafter referred to as a core rod) is manufactured by these manufacturing methods, and a cladding part is heated and integrated using a quartz tube as a base material, and the integration is performed simultaneously with drawing. Have been.
[0004]
An electric furnace is usually used for the heating furnace described above, and the temperature is 2000 ° C. or higher. The base material is inserted into an electric furnace, the tip is heated and melted, stretched and spun. When the spinning is in a steady state, the tip shape of the base material is stabilized by forming a meniscus determined by the outer diameter and viscosity of the base material, the temperature distribution by the heating furnace heater, the drawing speed, and the like. When the gap between the inserted core rod and the quartz tube is reduced by, for example, suctioning with a vacuum pump, the core rod and the quartz tube are integrated by heating in the meniscus portion, and can be drawn by thinly stretching.
[0005]
In order to insert the core rod into the hollow portion of the quartz tube, for example, a method as shown in FIG. 5 is used. Since the cladding 51 becomes a fiber, it is necessary to protect the outer surface. A support tube 52 is attached to facilitate handling such as gripping during work or attachment to equipment. It is more advantageous that the core rod 54 has the same effective length as that of the quartz tube 51, and a support rod 55 is attached to facilitate handling.
[0006]
For example, the support rod 55 attached to the core rod 54 is gripped by a chuck 56 on a vertically operable lathe, and the support tube 52 of the clad 51 is gripped by the chuck 53. Then, the core rod 54 is gradually lowered in the direction of the arrow in FIG. 5 and inserted into the hollow portion of the quartz tube 51.
[0007]
[Problems to be solved by the invention]
Conventionally, a vertical or horizontal lathe has been used to insert the core rod into the hollow portion of the quartz tube, or another jig has been used. However, if the quartz tube or the core rod is bent or inclined at the time of insertion, the core rod rubs the inner wall of the quartz tube. This danger increases as the gap between the quartz tube and the core rod becomes smaller and as the core rod and the like become longer.
[0008]
Scratching causes damage to the outer surface of the core rod or the inner surface of the quartz tube, which causes fluctuations in the outer diameter of the fiber and the generation of bubbles in the fiber during drawing. The insertion work is performed while stabilizing the positions of the core rod and the quartz tube so as not to rub, so that it takes time and effort.
[0009]
At the time of insertion, for example, the support rod provided on the core rod is gripped by a jig and inserted into the hollow portion of the clad. However, if the gripping jig may touch the pipe, it cannot be inserted any further. In order to prevent touch, it is necessary to elongate the support bar, for example. A longer length can cause rubbing as described above. Also, after insertion, the support rods protrude from the tube, hindering subsequent handling.
[0010]
In the case of a drawing furnace using carbon as a heat generating medium, it is necessary to prevent burning and consumption of carbon, and it is general to flow an inert gas to prevent air from entering the furnace during drawing. It is. By the way, when the outer diameter changes greatly at the place where the cladding support tube starts to enter the furnace, the pressure inside the furnace fluctuates rapidly and the gas flow is disturbed. As a result, the heat distribution in the furnace becomes unstable and the outer diameter of the fiber fluctuates.
[0011]
[Means for Solving the Problems]
In order to solve the above-described problem, a first aspect of the present invention is to heat and melt a distal end portion of an optical fiber preform composed of a core rod and a synthetic quartz tube in which the core rod is inserted into a hollow portion, When manufacturing an optical fiber by drawing while integrating the core rod and the quartz synthetic tube,
A method for supporting an optical fiber preform, wherein the core rod is inserted into the synthetic quartz tube having a support tube having an inner diameter larger than the inner diameter of the synthetic quartz tube at one end.
[0012]
According to a second aspect of the present invention, there is provided an optical fiber preform characterized in that the outer diameter of the support tube has a dimension equal to the outer diameter of the synthetic quartz tube, or has a smaller dimension. This is a drawing support method.
[0013]
According to a third aspect of the present invention, when the support tube is welded to the end of the synthetic quartz tube, the outside of the welded portion between the end of the synthetic quartz tube and the support tube is formed of the synthetic quartz tube. This is a method for supporting an optical fiber preform, characterized by shaping with an iron so as to be equal to the outer diameter.
[0014]
A fourth aspect of the present invention is a method for drawing and supporting an optical fiber preform, wherein the material of the support tube is natural quartz.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described with reference to embodiments. The present invention heats and melts the tip of an optical fiber preform composed of a core rod and a synthetic quartz tube into which the core rod is inserted into a hollow portion, and draws the core rod and the quartz synthetic tube while integrating them. When manufacturing an optical fiber, a supporting tube having an inner diameter larger than the inner diameter of the synthetic quartz tube is provided at one end of the synthetic quartz tube, and the core rod is inserted into the synthetic quartz tube. This is a method of supporting a fiber preform.
[0016]
According to the present invention, in manufacturing an optical fiber, a central portion including a core rod is manufactured, and a synthetic quartz tube is used in a portion corresponding to a clad, and these are heated and integrated, and the integration is drawn. At the same time, the efficiency of inserting the core rod material into the synthetic quartz tube can be improved. Further, when the base material is set in a drawing apparatus, and the tip is melted and stretched and spun into a fiber, the dimensional characteristics of the obtained fiber can be kept good.
[0017]
In addition, to facilitate handling, a support tube is attached to the synthetic quartz tube, and the inner diameter of the support tube is made larger than the inner diameter required for the synthetic quartz tube, so that the outer surface of the core rod and the inner wall of the synthetic quartz tube during insertion work are set. This has the effect of reducing the risk of scratching. Further, even if the support rod attached to the core rod is short, the core rod can be inserted into the synthetic quartz tube without the holding jig being in the way. As a result, the support bar of the rod does not jump out of the tube after insertion, and handling becomes easy.
[0018]
Generally, a carbon resistance furnace is used for drawing, but when oxygen is mixed at a high temperature, it reacts with the furnace material and burns. Therefore, an inert gas is flowed to prevent air from entering. In general, the end of the synthetic quartz tube on the drawing end side is connected to a supporting portion connected for gripping the synthetic quartz tube. However, when the outer diameter of the supporting portion starts to enter the furnace and fluctuates greatly, the pressure in the furnace fluctuates rapidly. Therefore, the gas flow is disturbed, the heat distribution becomes unstable, and the outer diameter of the fiber fluctuates.
[0019]
The present invention is characterized in that in order to prevent this, the outer diameters of the synthetic quartz tube and the support tube are matched. Even if the outer diameter is adjusted in advance, the flesh rises at the time of connection and the diameter of this portion may fluctuate.
[0020]
As an additional effect, the thickness of the support tube is reduced, and the weight is reduced. Therefore, the purchase cost is reduced and the handling becomes advantageous. If the material is natural quartz, the cost can be further reduced. In addition, since the size of the support rod of the core rod is shortened, there is a similar cost reduction effect.
[0021]
FIGS. 3 and 4 show schematic views when the core rod according to the present invention is inserted into a quartz tube. Arrows in FIG. 3 indicate the insertion direction. Incidentally, the ratio between the outer diameter and the inner diameter of the synthetic quartz tube is determined from the refractive index distribution characteristics of the core rod in order to obtain predetermined fiber characteristics. Usually, the outer diameter of the core rod 35 is smaller than the inner diameter of the synthetic quartz tube 31.
[0022]
When inserting the core rod 35 into the synthetic quartz tube 31, if the synthetic quartz tube 31 or the core rod 35 is bent or inclined, the core rod 35 may rub the inner wall of the synthetic quartz tube 31. The smaller the gap, and the longer the core rod 35 or the synthetic quartz tube 31, the greater the possibility of rubbing.
[0023]
Incidentally, the inner diameter of the support tube 32 does not directly affect the fiber characteristics. Therefore, by making the inner diameter of the support tube 32 larger than the inner diameter of the synthetic quartz tube 31, the risk of contact between the outer surface of the core rod and the inner wall of the synthetic quartz tube during the insertion operation can be reduced. Further, since the work is facilitated, the time can be reduced.
[0024]
Further, since the inner diameter of the support tube 32 can be increased, the holding jig 37 of the support rod 36 of the core rod 35 can also be inserted inside the support tube 32, and the core rod 35 including the support rod 36 even inside the synthetic quartz tube 31. Can be inserted, the support rod 36 of the core rod does not come out of the tube after the insertion, and the subsequent operation becomes easy.
[0025]
The outer diameter of the support tube 32 is the same as or slightly smaller than the outer diameter of the synthetic quartz tube 31. Therefore, the place where the support tube 32 starts to enter the furnace on the end side of the fiber drawing does not disturb the gas flow in the furnace. As a result, a change in the outer diameter of the fiber can be prevented.
[0026]
Even if the outer diameter of the synthetic quartz tube 31 and the outer diameter of the support tube 32 are the same in advance, the wall may rise when connected, and the diameter of this portion may fluctuate. Therefore, it is desirable to shape by fire processing.
[0027]
In addition, by increasing the inner diameter of the support tube 32, the thickness of the support tube 32 can be reduced. As a result, the weight of the support tube 32 is reduced, so that the cost is reduced and the handling becomes advantageous.
[0028]
Further, the present invention is characterized in that the material of the support tube is natural quartz. If the material is natural quartz, the cost can be further reduced. Furthermore, according to the present invention, the length of the rod support rod can be reduced, so that the weight is reduced and the cost is reduced.
[0029]
This will be further described with reference to FIGS. The inside of the quartz tube used for the synthetic quartz tube 31 is kept smooth without any foreign matter adhering to its surface. The quartz tube is set on a glass processing lathe, and a quartz support tube 32 is welded to one end.
[0030]
Further, according to the present invention, the ends of the synthetic quartz tube and the support tube are heated and melted by an oxygen / hydrogen flame, and the melted ends are pressed and welded to each other. It is shaped using a trowel so as to be approximately equal to the outer diameter of the quartz tube.
[0031]
In other words, the ends of the synthetic quartz tube and the support tube are heated with an oxygen / hydrogen flame, and both ends are pressed together for welding connection. Further, the outer diameter of the welded portion is shaped using a trowel so that the outer diameter is approximately equal to the tube. Is desirable.
[0032]
【Example】
Hereinafter, the present invention will be described with reference to examples. In the present embodiment, an example will be described in which a core material partially including a clad is manufactured by the VAD method, and a cladding portion is provided using a quartz tube to manufacture a single mode optical fiber. In practicing the present invention, a core material may be manufactured by another method, even if the profile is other than that of the present embodiment.
[0033]
As shown in FIG. 1, in the VAD method, silicon tetrachloride (SiCl ₄ ), germanium tetrachloride (GeCl ₄ ), oxygen (O ₂ ), and hydrogen (H ₂ ) are vaporized through a core burner 5 having a multi-tube structure. ), And the mixture was ignited and burned. A hydrolysis reaction was performed in a flame to obtain synthetic glass fine particles, which were sprayed on a seed rod 3 to form a porous preform 1. The seed rod 3 and the porous preform 1 are rotating counterclockwise as indicated by the arrows, and the upward arrow in the drawing is the direction in which the arrow is pulled up.
[0034]
A similar clad burner 7 is disposed above the core burner 5 in order to stabilize the characteristics of the porous base material 1 and is composed of silicon tetrachloride (SiCl ₄ ), oxygen (O ₂ ), and hydrogen (H ₂ ). The gas 11 was fed to cause a reaction, and a clad portion was provided on the outer periphery of the core soot. The porous base material 1 was heated to about 1500 to 1600 ° C. to obtain a transparent glass. In the single mode fiber, the dimensional ratio between the core and the clad is about 1:13, but that produced by the VAD method is 1: 4.5. Next, the core base material was stretched to produce a VAD core rod having an outer diameter of 30 mm.
[0035]
Separately, a quartz tube having an outer diameter of 90 mm and an inner diameter of 33 mm was prepared for a synthetic quartz tube. When the VAD core rod is inserted into the synthetic quartz tube, a predetermined ratio can be obtained. For example, FIG. 2 shows an example of the arrangement of a VAD core rod 23 having a VAD core rod core portion 21 at the center and a synthetic quartz tube 25.
[0036]
The numbers shown in the arrows in FIG. 2 indicate the respective dimensional ratios, and when the outer dimension of the core portion 21 of the VAD core rod is 1, the size of the VAD core rod 23 is 4.5. In the synthetic quartz tube 25, when the outer size of the core portion 21 of the VAD core rod is 1, the outer size of the synthetic quartz tube 25 is 13.
[0037]
FIG. 3 shows a schematic diagram when the VAD core rod according to the present invention is inserted into a quartz tube. The inside of the quartz tube used for the synthetic quartz tube 31 is kept smooth without any foreign matter adhering to its surface. The quartz tube was set on a glass working lathe, and a quartz support tube 32 having an outer diameter of 90 mm and an inner diameter of 70 mm was welded to one end. After cooling, it was removed from the lathe.
[0038]
The ends of the synthetic quartz tube and the supporting tube are heated by an oxygen / hydrogen flame, and both ends are pressed and welded together. Further, the outer diameter of the welded portion is shaped using a trowel so that the outer diameter of the welded portion is substantially equal to the tube. did.
[0039]
Next, the VAD core rod 35 processed to a predetermined size was set on a lathe, heated by an oxygen / hydrogen flame to weld a support rod 36 made of quartz, and removed after cooling. The support rod 36 is made of natural quartz, and has dimensions of about 25 mm in outer diameter and about 300 mm in length.
[0040]
Next, the synthetic quartz tube 31 and the VAD core rod 35 were set on an insertion lathe that is driven vertically, and an insertion operation into the synthetic quartz tube 31 was performed. The support rod 36 of the VAD core rod 35 was fixed to a lathe with a chuck 37. The support tube 32 of the synthetic quartz tube 31 was fixed with a chuck 33. Then, the VAD core rod 35 was gradually lowered in the direction of the arrow in FIG. 3 and inserted into the hollow portion of the synthetic quartz tube 31.
[0041]
FIG. 4 shows a state where the VAD core rod is inserted into a synthetic quartz tube.
[0042]
Next, a vacuum device was attached to the upper tube portion of the support tube into which the VAD core rod prepared as described above was inserted, so that the inside could be sucked to a reduced pressure, and set in a drawing device. When the inside was gradually inserted into the furnace while the pressure was being reduced, the tip was heated and welding occurred, and this portion was further extended to start drawing.
[0043]
After that, as in the case of ordinary drawing, the glass body was pushed into the furnace while the fiber was being pulled, and the integration and fiberization proceeded simultaneously. The fiber was stretched with a take-off capstan, drawn so that the outer diameter of the glass became about 125 μm, applied with an ultraviolet curable resin so as to have a diameter of about 250 μm, and cured by irradiating ultraviolet rays.
【The invention's effect】
According to the present invention, since the insertion is performed without contaminating the inside of the tube or the surface of the core rod rod, when the finished base material is converted into a fiber in the drawing step, the fiber wire diameter defect is reduced.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a VAD method.
FIG. 2 is a dimensional ratio according to a VAD method.
FIG. 3 is a schematic diagram when a core rod is inserted into a synthetic quartz tube.
FIG. 4 is a schematic diagram in which a core rod is inserted into a synthetic quartz tube.
FIG. 5 is a diagram showing a conventional situation in which a core rod is inserted into a clad.
[Explanation of symbols]
Reference Signs List 1 porous base material 3 VAD seed rod 5 core rod burner 7 clad burner 9 gas 11 gas 21 VAD core rod core part 23 VAD core rod 25 synthetic quartz tube 31 synthetic quartz tube 32 support tube 33 chuck 35 core rod 36 support rod 37 chuck 51 Cladding 52 Support tube 53 Chuck 54 Core rod 55 Support tube 56 Chuck

Claims (4)

A core rod and a synthetic silica tube for inserting the core rod into the hollow portion are heated and melted at the distal end of the optical fiber preform, and the optical fiber is drawn by integrating the core rod and the quartz synthetic tube while drawing. When manufacturing,
A method for supporting an optical fiber preform, wherein the core rod is inserted into the synthetic quartz tube having a support tube having an inner diameter larger than the inner diameter of the synthetic quartz tube at one end. The method for supporting an optical fiber preform according to claim 1, wherein an outer diameter of the support tube has a size equal to or smaller than an outer diameter of the synthetic quartz tube. When welding the support tube to the end of the synthetic quartz tube, a trowel is used so that the outside of the welded portion between the end of the synthetic quartz tube and the support tube is equal to the outer diameter of the synthetic quartz tube. The method for supporting an optical fiber preform according to claim 1 or 2, wherein the optical fiber preform is shaped by using. The method for drawing and supporting an optical fiber preform according to any one of claims 1 to 3, wherein the support tube is made of natural quartz.

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