JP3836583B2 - Manufacturing method of optical fiber preform - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention particularly relates to a method of manufacturing a preform for an optical fiber by a rod-in-tube method in which a glass pipe is covered with a glass pipe to integrate the two.
[0002]
[Prior art]
Conventionally, as a method of manufacturing this type of optical fiber preform, as shown in FIG. 4, the above-mentioned glass is maintained while maintaining a relatively thin glass pipe (jacket tube) 1 serving as a cladding in a reduced pressure state. A rod-in-tube method is known in which a pipe 1 and a glass rod 2 inserted into the glass pipe 1 are welded and integrated. In this case, after inserting the glass rod 2 into the glass pipe 1 vertically supported by the chuck 6b, the outer peripheral surface 2 of the auxiliary pipe 5 welded to one end side (upper end side) in the vertical direction of the glass pipe 1 is used. The three portions are heated to form inwardly protruding protrusions 7 and 7, and the tip of each protrusion 7 is spotted on the outer peripheral surface of the glass rod 2, so that the upper end side of the glass rod is connected to the glass pipe. The glass rod 2 is supported by sealing the opening of the auxiliary pipe 5 welded to the other end side (lower end side) of the glass pipe 1 while being supported at the axial center position 1. Then, the glass pipe 1 and the glass rod 2 are forcedly sucked from the opening of the auxiliary pipe 5 on the upper end side to bring the annular gap 9 between the glass pipe 1 and the glass rod 2 into a reduced pressure state and maintain this. Are sequentially heated from the lower end side to the upper end side by an annular electric furnace (not shown), and both are sequentially welded to be integrated. 6a is a chuck for supporting the auxiliary rod 4 coaxially joined to the lower end of the glass pipe 2, and 6c is a chuck for supporting the auxiliary pipe 5 on the upper end side.
[0003]
[Problems to be solved by the invention]
By the way, in the conventional optical fiber preform manufacturing method, since the upper end side of the glass rod is supported by doting, it is difficult to accurately position the glass rod at the axial center position of the glass pipe. There is a problem that the amount of eccentricity with respect to the axial center position of the glass rod becomes large. Therefore, in order to reduce the influence of the eccentric amount, a method of reducing the gap (clearance) between the outer peripheral surface of the glass rod and the inner peripheral surface of the glass pipe is employed.
[0004]
However, since the dimensions of the glass pipe and the glass rod may not be completely uniform due to manufacturing errors, etc., reducing the clearance may cause the glass pipe and the glass rod to rub. Become. If such rubbing occurs, it may cause bubbles in the base material and also in the optical fiber. In addition, since the dimensional error of the glass pipe and the glass rod as described above becomes longer as the length becomes longer, it becomes more difficult to manufacture a long optical fiber preform.
[0005]
Further, residual distortion due to heating may remain in the protrusion, and the glass pipe or the like may be cracked due to the residual distortion. When such a crack occurs, there is a possibility that bubbles are generated in the base material and further in the optical fiber due to the fine fragments.
[0006]
In addition, in the production of an optical fiber preform, ΔN (specific refractive index difference), which is a characteristic of an optical fiber, and C / C (core / cladding ratio) that is proportional to the square root value of ΔN ) Is set, and a product matching the set value is manufactured. However, since there is a restriction that the clearance must be reduced, glass glass is first coated on a glass rod to increase its outer diameter, and then the glass whose outer diameter is increased It is necessary to take a method of repeating the coating several times, such as manufacturing the base material corresponding to the setting C / C by inserting the rod into the glass pipe and coating again with the clearance reduced. It becomes.
[0007]
The present invention has been made in view of such circumstances, and an object of the present invention is to inconvenience in manufacturing an optical fiber preform by accurately positioning the glass rod at the axial center position of the glass pipe. Is to facilitate the manufacture.
[0008]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, the invention according to claim 1 inserts a glass rod which becomes a part of a core or a core and a clad into a glass pipe which becomes a clad, and between the glass pipe and the glass rod. It is premised on a manufacturing method of an optical fiber preform in which the glass pipe and the glass rod are welded and integrated while reducing the gap. In this method, one end of the auxiliary rod formed by a hollow pipe having substantially the same outer diameter as the glass rod is abutted in series with one end of the glass rod so as to extend coaxially, and the joining end of the auxiliary rod Is positioned in the gap between the glass pipe held vertically by the chuck and the glass rod, and each of the other end side of the glass rod and the auxiliary rod on the one end side is supported by the chuck. Thus, the glass rod is supported at two points separated from each other in the axial direction, and the glass pipe and the glass rod are positioned so as to be coaxial, and then both ends of the glass pipe are sealed, and the auxiliary In this method, the space of the gap is decompressed by suction through a communication hole and an inner hole opened in the vicinity of the joining end of the flange.
[0009]
In the above configuration, the other end of the glass rod, the auxiliary rod in one end thereof, since the glass rod itself is supported by a chuck at two points of both sides of the glass pipe, the glass rod, the chuck Therefore, it is easy to accurately position the glass pipe held vertically so that the amount of eccentricity can be made as small as possible. Thereby, it becomes possible to manufacture the optical fiber preform by increasing the clearance between the glass rod and the glass pipe, and it is possible to reliably avoid rubbing the glass pipe and the glass rod. . Even if the glass pipe and the glass rod are long and the dimensional error is large, the clearance can be increased, so that the glass pipe and the glass rod are avoided from rubbing each other. Easy and reliable manufacturing of the base material is achieved. Furthermore, since both ends of the glass pipe are sealed, an annular gap between the glass pipe and the glass rod becomes a sealed space. As a result, the gap can be efficiently decompressed. In addition, unlike the case of scoring, the glass pipe can be prevented from being damaged. For this reason, it becomes possible to eliminate the inconvenience in the production of the optical fiber preform. In addition, since there is no restriction on the clearance, it is possible to manufacture an optical fiber preform corresponding to the set C / C by a single coating only by determining the cross-sectional area ratio between the glass rod and the glass pipe. The production of the optical fiber preform is facilitated.
[0010]
Further, as the auxiliary rod, one having a communication hole for communicating the inner hole with the annular gap may be used. Specifically, as in the second aspect of the present invention, an auxiliary rod in which a through hole penetrating in the radial direction from the inner hole is formed as a communication hole, or from the open end as in the third aspect of the present invention. An auxiliary rod in which a concave groove that is concave in the axial direction is formed as a communication hole may be used.
[0011]
In the case of the above configuration, it is possible to obtain a more specific configuration of the communication hole, and it is possible to reliably reduce the pressure of the gap by connecting the gap and the inner hole.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0013]
FIG. 1 shows an optical fiber preform manufacturing apparatus according to an embodiment of the present invention, in which 1 is a jacket tube as a glass pipe to be a cladding, and 2 is a core and a part of the cladding manufactured by the VAD method. The VAD rod 3 as a glass rod, 3 is an auxiliary rod attached to one end (upper end) of the VAD rod 2 so as to be coaxial with the VAD rod 2, and 4 is the other end (lower end) of the VAD rod 2 in the vertical direction. ) Is an auxiliary rod attached so as to be coaxial with the VAD rod 2.
[0014]
One end of each of the auxiliary pipes 5 and 5 is welded to both ends of the jacket tube 1, and the openings at the other ends of the auxiliary pipes 5 and 5 are sealed by heat treatment.
[0015]
The VAD rod 2 has substantially the same length as the jacket tube 1 and is inserted into the jacket tube 1 so that both ends of the VAD rod 2 are positioned corresponding to both ends of the jacket tube 1, respectively.
[0016]
The auxiliary rod 3 is a pipe having the same diameter as that of the VAD rod 2, and through holes 3a and 3a serving as communication holes penetrating in the radial direction from the inner wall are provided near the lower end of the auxiliary rod 3, as shown in FIG. Is formed.
[0017]
The jacket tube 1 is held vertically by a chuck 6b, while the auxiliary rod 4 and auxiliary rod 3 are held by chucks 6a and 6c, respectively, and the jacket tube 1 is held by the chucks 6a, 6b and 6c. 1 and VAD rod 2 are positioned so as to be coaxial with each other.
[0018]
Below, the manufacturing method of the preform | base_material for optical fibers using the said embodiment is demonstrated.
[0019]
First, the jacket tube 1 is held vertically by the chuck 6b, and the auxiliary pipes 5 and 5 are connected to the respective open ends of the jacket tube 1.
[0020]
Next, the VAD rod 2 connected with the auxiliary rod 4 is inserted into the jacket tube 1 and the auxiliary rod 3 is connected to the upper end thereof. The VAD rod 2 is held by the auxiliary rod 4 and the auxiliary rod 3 by means of 6a and 6c, respectively. Then, the position is adjusted so that the jacket tube 1 and the VAD rod 2 are coaxial. Then, the openings of the auxiliary pipes 5, 5 are heated, and the inner peripheral surfaces of the auxiliary pipes 5, 5 are welded to the outer peripheral surface of the auxiliary rod 3 or the auxiliary rod 4, respectively. The openings of 5 and 5 are sealed. At this time, the through holes 3a and 3a of the auxiliary rod 3 are located in the sealed space 8 formed by the jacket tube 1 and the auxiliary pipes 5 and 5, and the sealed space 8 and the inner hole 3b are connected to the above-described auxiliary holes 3 and 5a. It will be in the state connected via the through-holes 3a and 3a.
[0021]
If the suction is forced from the opening on the upper end side of the auxiliary rod 3 in this state, the pressure in the sealed space 8 can be maintained below the atmospheric pressure through the through holes 3a and 3a of the auxiliary rod 3. Then, the jacket tube 1 and the VAD rod 2 are inserted into an annular electric furnace (not shown), and the upper end from the lower end of the jacket tube 1 and the VAD rod 2 is maintained while maintaining the sealed space 8 below atmospheric pressure as described above. Then, the inner peripheral surface of the jacket tube 1 and the outer peripheral surface of the VAD rod 2 are welded together and can be integrated to manufacture an optical fiber preform.
[0022]
Since the VAD rod 2 is supported at both ends by gripping the auxiliary rod 3 and the auxiliary rod 4, it is easy to adjust the position so that it is coaxial with the jacket tube 1, and the accuracy is high. You will be able to position well. Therefore, even if the clearance between the inner peripheral surface of the jacket tube 1 and the outer peripheral surface of the VAD rod 2 is increased, the amount of eccentricity can be reduced as much as possible. It is possible to reliably avoid rubbing the two. In addition, since the clearance can be increased, a long base material can be manufactured without being affected by dimensional errors even when long ones are used as the jacket tube 1 and the VAD rod 2. Will be able to. Furthermore, there is no risk of the projections being damaged as in the conventional case of holding the glass rod 2 by scoring (see FIG. 4), and the cause of bubbles in the base material and optical fiber is reliably removed. Will be able to.
[0023]
In addition, since there is no restriction of reducing the clearance, it is only necessary to determine the cross-sectional area ratio between the jacket tube 1 and the VAD rod 2 and perform coating once in order to match the set value of C / C. . Thereby, the manufacture of the optical fiber preform can be facilitated.
[0024]
<Other embodiments>
In addition, this invention is not limited to the said embodiment, Various other embodiments are included. That is, in the above embodiment, the auxiliary pipes 5 and 5 are welded to both ends of the jacket tube 1, but the present invention is not limited to this, and both end openings of the jacket tube 1 itself may be sealed.
[0025]
In the above embodiment, the auxiliary rod 4 is welded to the lower end of the VAD rod 2, but the present invention is not limited to this. For example, the VAD rod 2 that extends further to the lower end side is used. May be held by the chuck 6a.
[0026]
In the embodiment described above, the through hole 3a, 3a constitutes a communication hole for communicating the sealed space 8 and the inner hole 3b. However, the present invention is not limited to this, for example, as shown in FIG. You may comprise the communicating hole which connects the said sealed space 8 and the said inner hole 3b by the ditch | groove 3c dented in the axial direction from the end.
[0027]
In the above embodiment, the jacket tube 1 and the VAD rod 2 are welded by the annular electric furnace 10 as a heating source. However, the present invention is not limited to this, and the jacket tube 1 is used by using, for example, a burner as the heating source. The VAD rod 2 may be welded. In this case, it is preferable that both the jacket tube 1 and the VAD rod 2 are sequentially heated in the axial direction by the burner while rotating around the axis.
[0028]
Further, in the above embodiment, the auxiliary rod 3 is connected to the upper end of the VAD rod 2 so that the jacket tube 1 and the VAD rod 2 are welded from the lower end of the jacket tube 1 and the VAD rod 2 toward the upper end. However, the auxiliary rod 3 is connected to the lower end of the VAD rod 2 and the jacket tube 1 and the VAD rod 2 are welded from the upper end to the lower end of the jacket tube 1 and the VAD rod 2. May be performed.
[0029]
【The invention's effect】
As described above, according to the optical fiber preform manufacturing method in the first aspect of the invention, since the glass rod is supported at two points, the glass rod is held vertically by the chuck. It is easy to accurately place the glass pipe at the axial center position, the amount of eccentricity can be made as small as possible, and the inconvenience in the production of the optical fiber preform is eliminated, facilitating the production. Can be planned. Moreover, since the annular gap between the glass pipe and the glass rod becomes a sealed space, the gap can be efficiently decompressed.
[0030]
According to the invention of claim 2 or claim 3, in addition to the effect of the invention of claim 1, a more specific configuration of the communication hole can be obtained, and the gap and the inner hole are communicated. In this state, the gap can be surely decompressed.
[Brief description of the drawings]
FIG. 1 is an explanatory cross-sectional view showing an embodiment of the present invention.
FIG. 2 is a cross-sectional view showing an auxiliary rod.
FIG. 3 is a perspective view showing an auxiliary rod in another embodiment.
FIG. 4 is a view corresponding to FIG.
[Explanation of symbols]
1 Jacket tube (glass pipe)
2 VAD rod (glass rod)
3 Auxiliary rod 3a Through hole (communication hole)
3c Groove (communication hole)

Claims (3)

Insert the glass rod that becomes a part of the core or the core and the clad into the glass pipe that becomes the clad, and weld the glass pipe and the glass rod while reducing the gap between the glass pipe and the glass rod. In the manufacturing method of the optical fiber preform to be integrated,
One end of the glass rod is joined in series so as to extend coaxially by abutting one end of an auxiliary rod formed by a hollow pipe having substantially the same outer diameter as the glass rod,
The joining end of the auxiliary rod is positioned in the gap between the glass pipe and the glass rod held vertically by the chuck ,
By supporting each of the other end side of the glass rod and the auxiliary rod on the one end side with a chuck, the glass rod is supported at two points separated from each other in the axial direction, and the glass pipe and the glass rod are Adjust the position so that it is coaxial, then seal both ends of the glass pipe,
A method for producing a preform for an optical fiber, wherein the space in the gap is decompressed by suction through a communication hole opened in the vicinity of the joining end of the auxiliary rod and an inner hole of the auxiliary rod. In claim 1,
A method of manufacturing an optical fiber preform, wherein an auxiliary rod having a through-hole penetrating in a radial direction from an inner hole is formed as a communication hole. In claim 1,
A method of manufacturing an optical fiber preform, wherein an auxiliary rod having a concave groove that is recessed in an axial direction from an opening end is formed as a communication hole.

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