JP2004339024A - Method of manufacturing optical fiber preform and preform suspension instrument used for suspending the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing an optical fiber preform by which connection of a suspension shaft suspended in a heating furnace to the optical fiber preform is easily and precisely carried out and a suspension instrument used for suspending the preform. <P>SOLUTION: In suspending the optical fiber preform in a heating furnace and heating, the optical fiber preform is suspended by preferably providing a plurality of projecting parts 23 or recessed parts on a a preform holding part 22 of the optical fiber preform 1, inserting the projecting parts 23 or recessed part into the preform suspension instrument 28 provided in the lower end of the suspension shaft 4 and putting a fixing member into the lower end of the projecting part 23 or the recessed part. A horizontal surface 26 making an angle of 90° with the center axis of the optical fiber preform is provided on the projecting parts 23 or the recessed part provided in the preform holding part 22 and is placed on the preform suspension instrument 28 with the fixing member 30 to enable the optical fiber preform to be suspended. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method of manufacturing a preform for optical fibers which is suitably used in a process of hanging a large-sized preform for optical fibers into a heating furnace and performing a heat treatment at a high temperature, and a preform suspender used for hanging.
[0002]
[Prior art]
The optical fiber preform is heated at a high temperature, such as a step of dehydrating and sintering the porous preform to form a transparent glass, or a step of stretching a preform ingot obtained by forming a transparent glass to a predetermined diameter. It is manufactured through the steps of:
The porous base material is manufactured by depositing a clad portion on the surface of the starting core member by an OVD (external attachment) method, and after dehydrating the material in a dehydration furnace, is attached to a shaft in the next sintering step. It is suspended in a sintering furnace, heated by a heater, and transparently vitrified at a temperature of 1350 ° C. to 1500 ° C. to obtain a base material ingot. The large-sized preform ingot is further subjected to a heat treatment and stretched into, for example, a preform having a diameter size convenient for drawing an optical fiber.
In this specification, the preform for an optical fiber is a generic term including a porous preform and a preform ingot which are intermediate products, and a preform used for drawing an optical fiber.
[0003]
FIG. 1 is a schematic cross-sectional view showing an example of an optical fiber preform stretching apparatus. The optical fiber preform 1 is coupled to a lower end of a hanging shaft 4 supported by an optical fiber preform supply mechanism 3 at a preform holding portion 2 provided on the upper part thereof, and is suspended therefrom. It is supplied to the heating furnace 5 by the supply mechanism 3 moving downward.
The optical fiber preform 1 is heated and softened at 1600 to 2100 ° C. by a heater 6 provided in a heating furnace 5 and stretched. Below the heating furnace 5, there is provided a take-off mechanism (not shown) for taking out the optical fiber base material (preform) 7 which has been drawn and reduced in diameter.
[0004]
An example of joining the hanging shaft 4 hung in the heating furnace 5 and the optical fiber preform 1 will be described with reference to FIGS. 2 to 5 (see Patent Document 1).
FIG. 2 is a cross-sectional view showing a coupling state between the hanging shaft 4 and the optical fiber preform 1, and FIG. 3 is a perspective view showing this.
A tubular coupling unit (hereinafter, referred to as a shaft tube) 8 is attached to the tip of the hanging shaft 4, and the shaft tube 8 has a concave portion 9 into which the base material gripping portion 2 of the optical fiber base material 1 is inserted. Further, the shaft tube 8 is provided with a through hole 10 at a position eccentric from the center line and perpendicular to the center line.
[0005]
The base material holding portion 2 of the base material 1 for an optical fiber is provided with a notch 11. The connection between the base material gripper 2 and the shaft tube 8 is performed by inserting the base material gripper 2 into the shaft tube 8 and inserting the notch 11 of the base material gripper 2 into the through hole 10 of the shaft tube 8. This is performed by inserting the coupling pin 12.
[0006]
[Patent Document 1]
JP-A-2001-287916 (pages 2, 3; FIGS. 1, 2)
[0007]
[Problems to be solved by the invention]
There is some gap between the preform gripping portion 2 of the preform for optical fiber inserted into the shaft tube and the inner wall 13 of the shaft tube 8. In consideration of the workability when connecting the base material gripping portion 2 and the shaft tube 8, the larger the gap, the better the workability. However, if the gap is large, the preform holding portion 2, that is, the preform 1 for optical fiber has an inclination with respect to the vertical axis. FIG. 4 is a schematic diagram schematically showing a state in which the base material gripping portion 2 is inclined from the vertical axis.
[0008]
In FIG. 4, since the gap between the inner wall 13 of the shaft tube 8 and the base material gripping portion 2 is large, the base material gripping portion 2 is inclined, and the optical fiber preform 1 has an inclination angle of 14 and the base material gripping portion. It can be seen that the two central axes 15 are inclined with respect to the vertical axis 16 of the shaft tube 8.
FIG. 5 shows a state where the optical fiber preform 1 is hung down on the optical fiber preform stretching apparatus in a state where the inclination angle 14 exists in the optical fiber preform 1. In this case, the central axis 18 of the optical fiber preform 1 is inclined with respect to the vertical axis 17 of the stretching device. When the optical fiber preform 1 is stretched in this state, the center 19 of the softened portion of the optical fiber preform 1 is eccentric from the center 20 of the heater.
[0009]
The amount of eccentricity 21 between the center 19 of the softened portion and the center 20 of the heater has a close relationship with the bending of the preform 7 after the base material is stretched, and the heat received by the preform 7 is not uniform on the peripheral surface. As the eccentricity 21 increases, the bending of the preform 7 increases. The amount of eccentricity 21 increases as the gap between the inner wall 13 of the shaft tube 8 and the base material gripping portion 2 increases. Therefore, in order to reduce the bending of the stretched preform 7, it is desirable that the gap between the inner wall 13 of the shaft tube 8 and the base material gripping portion 2 is small.
[0010]
However, making the gap small deteriorates the workability when inserting the base material gripping part 2 into the concave portion of the shaft tube 8, so that a gap that is too small is not preferable. Further, since the base material gripping portion 2 is made of quartz glass, the processing accuracy is very poor, and the variation in the outer diameter is large. For this reason, in order to ensure that all of the manufactured base material gripping parts 2 can be inserted into the concave portions 9 of the shaft tube 8, the base material gripping parts 2 are manufactured to be small.
[0011]
When the preform gripping portion 2 manufactured with a small outer diameter in the range of variation is used, the inclination angle 14 of the optical fiber preform 1 is larger than that having an average outer diameter. Although it is technically possible to process the base material gripping portion 2 with high accuracy, the manufacturing cost is extremely high, and thus is not very realistic when the number of manufacturing lots is large. As described above, the connecting portion between the preform gripping portion 2 of the preform 1 for an optical fiber and the hanging shaft 4 has to satisfy conflicting requirements of easiness of work and coupling accuracy.
In the above, the example in which the optical fiber base material (base material ingot) is suspended in the stretching device and the drawing process is performed has been described. However, the optical fiber base material (porous base material) is suspended in the sintering device and the transparent glass is drawn. In the case where the optical fiber is preformed, if the optical fiber base material is in an eccentric or inclined state, inconveniences such as bending and a difference in sintering degree depending on parts are caused.
[0012]
The present invention relates to a method for manufacturing a preform for optical fiber, which can easily and accurately attach a drooping shaft and a preform for optical fiber that are suspended in a heating furnace, and a preform suspender used for hanging. It is intended to provide.
[0013]
[Means for Solving the Problems]
Means for Solving the Problems The present inventors have solved the above-mentioned problems as a result of intensive studies, that is, the method for manufacturing an optical fiber preform of the present invention is a method in which In doing so, a convex portion or a concave portion is provided in the preform holding portion of the optical fiber preform, and the convex portion or the concave portion is inserted into a preform hanging member provided at the lower end of the hanging shaft, and the lower edge of the convex portion is provided. The stop member is inserted into the portion or the concave portion, and the optical fiber base material is suspended.
[0014]
It is preferable that the number of convex portions or concave portions provided in the base material holding portion of the optical fiber base material is plural. By providing a horizontal surface perpendicular to the central axis of the optical fiber preform on the convex or concave portion provided in the preform holding portion, and loading the preform hanging member via a stopper member at the horizontal surface, the optical fiber The base material can be hung. Alternatively, the convex or concave portion is provided with a conical portion centered on the central axis of the optical fiber preform, and the conical portion is loaded on the preform suspender via a stopper member, thereby providing an optical fiber preform. Wood can also be hung.
[0015]
Further, the base material suspending device of the present invention is a base material provided at the lower end of a hanging shaft for hanging the optical fiber base material when the optical fiber base material is hung in a heating furnace and subjected to heat treatment. A hanging tool, wherein a base material holding portion of an optical fiber base material is inserted from below into a lower portion of the base material hanging device, and is engaged with a convex portion or a concave portion provided on the base material holding portion via a stopper member. It is characterized in that a corresponding through-hole portion is provided.
[0016]
The base material hanging tool can be composed of two members that are vertically divided. In addition, these two members may be configured by a supporting member that supports the connecting member and the stopping member connected to the hanging shaft, and the connecting member and the supporting member may be connected via the connecting member. The stop member has a ring shape and is composed of a plurality of members.
It is preferable to use a heat-resistant inorganic material appropriately selected from fine ceramics, carbon, carbon fiber reinforced carbon, quartz glass, silicon nitride coated with silicon carbide, and the like for these base material suspenders and stopper members. .
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an optical fiber preform, in particular, an example of manufacturing an optical fiber preform by stretching a preform ingot will be described in detail with reference to FIGS. 6 to 10 based on the following examples. The present invention is not limited to these embodiments, and can be applied to various heat treatments such as a dehydration / sintering treatment of a porous base material.
[0018]
【Example】
(Example 1)
FIG. 6 shows an example of the shape of the base material gripping portion according to the present invention. The base material holding portion 22 is provided with a convex portion 23 and a convex portion 24, and a lower surface of at least one of the convex portions has a plane (flange surface) perpendicular to the central axis 25 of the base material holding portion 22. Is provided. This flange surface functions as a horizontal plane for loading an optical fiber preform when the preform holding portion 22 is connected to the preform suspender attached to the hanging shaft. In this embodiment, the convex portions 23 and 24 are provided with flange surfaces 26 and 27, respectively.
[0019]
In this embodiment, the convex portions 23 and 24 are provided at two places of the preform holding portion 22. However, when the purpose is only to make the optical fiber preform drip into the heat treatment apparatus, the convex portion is 1. It is enough. However, considering the convenience of transporting the optical fiber preform in the factory, providing two or more convex portions is more convenient for the delivery and storage of the optical fiber preform, and the transport is very convenient. It will be easier.
[0020]
FIG. 7 shows a hanging state of the optical fiber preform provided with the preform holding portion.
The optical fiber preform is suspended at a convex portion 23 of the preform hammer 22 by a preform suspender 28 attached to the lower end of the hanging shaft 4. The base material hanger 28 includes an upper hanger 28A and a lower hanger 28B.
[0021]
In order to hang the optical fiber base material on the base material hanging device 28, the convex portion 23 of the base material hawker portion 22 is inserted into the base material hanging device 28 from the through hole portion 29, and then the edge of the through hole portion 29 is formed. The stop members 30A and 30B are fitted to the steps provided in the portions, and are placed on the stop members 30A and 30B with the flange surface 26 of the convex portion 23, whereby the optical fiber base material is hung down. The insertion of the stop members 30A and 30B into the base material hanging tool 28 is performed through windows 31 provided on the side (two right and left locations) of the lower hanging tool 28B. This is shown in a perspective view in FIG.
[0022]
The weight of the optical fiber preform is such that the convex portion 23 formed on the preform gripping portion 22 is fitted into the step formed on the peripheral edge of the through-hole portion 29 and is supported by the flange surface 26 of the convex portion 23. . The joining surface of the stepped portion that is in contact with the flange surface 26 is machined so as to be in close contact with the flange surface 26. Therefore, since the optical fiber preform is loaded by the circumferential surface surrounding the central axis 32 of the optical fiber preform, that is, the flange surface 26, the connection point with the preform hanger 28 is a fulcrum. It does not cause typical vibration (swing). Therefore, it is possible to continue the heat treatment of the optical fiber preform under stable conditions.
[0023]
The present invention has various diameters only by changing the inner diameter of the stop member 30 by using the stop member 30 at the time of joining the base material hanging member 28 and the base material holding portion 22 of the optical fiber base material. The optical fiber preforms of various sizes can be hung down on the preform hanger 28 attached to the lower end of the hanging shaft 4.
[0024]
Furthermore, since the shape of the stopper member is simple, precision processing is easy, and even when the optical fiber preform hangs, the center axis 32 of the optical fiber preform coincides with the vertical axis of the heat treatment apparatus. For example, when the optical fiber base material is drawn into a preform having a small diameter, it is possible to obtain a preform having a very small bend.
[0025]
(Example 2)
FIG. 9 shows another embodiment of the present invention.
The base material hanging member 33 includes a connecting member 34, a supporting member 35, and a connecting member 36 for connecting the connecting member 34 and the supporting member 35, and the connecting member 34 is connected to the hanging shaft 4. The connection between the base material hanging tool 33 and the base material hammer 22 of the optical fiber base material can be performed in the same manner as in the first embodiment.
[0026]
In this embodiment, the number of components of the base material hanging tool 33 is larger than that of the embodiment 1 shown in FIGS. However, since the shape of each part is extremely simple, it is very easy to manufacture each member as compared with the base material hanger 28 of the first embodiment. When the optical fiber preform was stretched into a preform having a small diameter, the bending was very small, and the same as that of Example 1 was obtained.
In this embodiment, the connecting member 36 is constituted by four columnar members. However, the form of the base material hanging device of the present invention is not limited to this, and any number of members are possible. Desirably, the number is 3 to 5.
[0027]
FIGS. 10A and 10B show a comparison between the bend of the preform manufactured in Example 1 and the bend of the preform manufactured by the above-described conventional technique. FIG. 10A shows the relative frequency distribution of the bend of the preform, and FIG. 14 shows a cumulative relative frequency distribution. The length of the manufactured preform is 1100 mm / piece. In the figure, in the prior art, the preform having a bend of 0.2 mm or less was only 10% of the whole, but in Example 1, it was improved to 70%.
[0028]
In each of the first and second embodiments, a convex portion is provided in the base material holding portion of the optical fiber preform, and a horizontal plane perpendicular to the center axis of the optical fiber preform is provided on the lower edge of the convex portion. Has been described, the lower edge portion of the convex portion, provided with a conical portion with the center axis of the optical fiber preform as the center line, a stop member having a shape corresponding to the shape of the conical portion Alternatively, the optical fiber preform may be suspended on the preform hanging tool by hanging the preform.
[0029]
Further, a concave portion is formed in the base material holding portion in place of the convex portion, and a horizontal plane perpendicular to the central axis of the optical fiber preform is provided at least on the upper edge side of the concave portion, or the center of the optical fiber preform is provided. By providing a conical portion with the axis as the center line, and loading the preform hanging member via the stopper member, the optical fiber preform may hang down, and the same effect as in the case of the convex portion can be obtained. Can be
[0030]
【The invention's effect】
At the convex portion or the concave portion provided on the base material holding portion of the optical fiber preform, the preform is loaded on the preform hanging tool via the stopper member, and the optical fiber preform is drooped into the heat treatment apparatus, thereby extremely A preform with a small bend can be obtained.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view schematically showing an optical fiber preform stretching apparatus.
FIG. 2 is a cross-sectional view showing an example of a state in which a conventional hanging shaft and an optical fiber preform are joined together.
FIG. 3 is a perspective view of FIG. 2;
FIG. 4 is a schematic diagram schematically showing a state in which a base material gripping portion is inclined from a vertical axis in the coupled state shown in FIG. 2;
FIG. 5 is a schematic view showing a state in which the optical fiber preform is suspended in a stretching device in the coupled state of FIG. 4;
FIG. 6 is a schematic diagram showing a shape of a base material gripping portion used in Example 1.
FIG. 7 is a schematic view showing a hanging state of an optical fiber preform provided with the preform holding portion of FIG. 6;
FIG. 8 is a schematic diagram illustrating the connection between the base material hanging tool and the base material gripping portion.
FIG. 9 is a schematic diagram illustrating the connection between the base material hanging tool and the base material gripping portion used in the second embodiment.
10A and 10B are diagrams showing a comparison between the bending of a preform manufactured according to the present invention and the bending of a preform manufactured according to the related art, wherein FIG. 10A shows the relative frequency distribution of the bending of the preform, and FIG. The frequency distribution is shown.
[Explanation of symbols]
1. Optical fiber preform,
2,22 ... Base material gripper,
3. Supply mechanism,
4 ... hanging shaft,
5 ... heating furnace,
6 ... heater
7 ... Preform,
8 ... shaft tube,
9 ... recess,
10 ... through-hole,
11 ... notch,
12 ... connecting pin,
13 ... inner wall,
14 ... inclination angle,
15, 18, 25, 32 ... central axis,
16, 17… vertical axis,
19: Center of softened part,
20: heater center,
21 ... eccentricity,
23, 24 ... convex part,
26, 27 ... flange surface,
28, 33 ... base material hanging tool,
28A: Upper hanging tool,
28B: Lower hanging tool,
29 ... through-hole part,
30A, 30B ... stop member,
31 ... window,
34 connecting members,
35 ... support member,
36 ... Connecting member.

Claims (9)

At the time of performing the heat treatment by hanging the optical fiber base material in the heating furnace, a convex portion or a concave portion is provided in the base material gripping portion of the optical fiber base material, and the convex portion or the concave portion is provided at the lower end of the hanging shaft. A method of manufacturing a preform for an optical fiber, comprising inserting the stopper into a lower edge or a concave portion of the convex portion and hanging the preform for an optical fiber. The method of manufacturing an optical fiber preform according to claim 1, wherein the optical fiber preform has a plurality of convex portions or concave portions provided in the preform holding portion. A convex surface or a concave portion provided on the base material holding portion of the optical fiber preform is provided with a horizontal plane perpendicular to the center axis of the optical fiber preform, and the horizontal plane is loaded on the preform hanging tool via a stopper member. The method for producing a preform for an optical fiber according to claim 1, wherein the preform for an optical fiber is hung down. A convex or concave portion provided on the base material gripping portion of the optical fiber base material is provided with a conical portion having a center axis about the center axis of the optical fiber preform, and the conical portion is connected to the base material via a stopper member. The method for manufacturing an optical fiber preform according to claim 1 or 2, wherein the optical fiber preform is hung down by being loaded on a hanging tool. A base material hanging device provided at a lower end of a hanging shaft for hanging the optical fiber base material when the optical fiber base material is hung in a heating furnace and subjected to heat treatment, wherein the base material hanger is provided. A lower portion of the base member is provided with a through-hole portion for inserting a preform grasping portion of the preform for optical fiber from below and engaging with a convex portion or a concave portion provided in the preform grasping portion via a stopper member. A base material hanging tool characterized by the following. The base material hanger according to claim 5, wherein the base material hanger is constituted by two members vertically divided. The two members vertically divided are support members for supporting a connecting member and a stop member connected to the hanging shaft, and the connecting member and the supporting member are connected via a connecting member. The base material hanging tool as described. The base material hanging device according to claim 5, wherein the stopper member has a ring shape and is configured by a plurality of members. 9. The base material hanging member and / or the stopper member is made of a heat-resistant inorganic material appropriately selected from fine ceramics, carbon, carbon fiber reinforced carbon, quartz glass, silicon nitride coated with silicon carbide, and the like. A hanging material for a base material according to any one of the above.

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