JP2002249332A - Apparatus for producing optical fiber preform and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production apparatus of an optical fiber preform capable of maintaining good airtightness in a large-sized pipe. SOLUTION: The production apparatus for producing an optical preform is provided with a handling jig 100 fixed to the upper end of a large-sized pipe 111 used in a rod in tube method and a clamping part 200 for clamping the handling jig 100. The handling jig 100 has an interior cavity 105 into which gas or fluid is introduced. The handling jig 100 is forcibly cooled by introducing gas or fluid into the cavity 105.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical fiber preform manufacturing apparatus and an optical fiber preform manufacturing method. In particular, the present invention relates to an apparatus for manufacturing an optical fiber preform using a rod-in-tube method, and a method for manufacturing an optical fiber preform using the manufacturing apparatus.

[0002]

2. Description of the Related Art As a method for producing an optical fiber preform,
OVD (Outside Vapor-phase Deposition) method, VAD
(Vapor-phase Axial Deposition) method and MCVD
(Modified Chemical Vapor Deposition) method is mainly used. When an optical fiber preform is manufactured by using the VAD method or the MCVD method, a method of forming a clad occupying most of the optical fiber preform by another process is adopted from the viewpoint of improving productivity. 1 of this method
One is the rod-in-tube method (JP-B-56-458).
No. 67, Japanese Unexamined Patent Publication No. 1-230441, etc.).

An example of the rod-in-tube method will be described with reference to FIG. First, a core glass rod (including a part that becomes a part of a core and a clad) 12 manufactured by a VAD method or an MCVD method is inserted into a cladding pipe 11, and then the glass rod 12 and the cladding pipe 11 are inserted. Are heated by an electric furnace (heater) 13 to integrate them into an optical fiber preform 14. When the glass rod 12 and the clad pipe 11 are integrated using the pressure difference between the inside and the outside of the clad pipe 11, the pressure inside the clad pipe 11 is reduced.

Next, a conventional optical fiber preform manufacturing apparatus 1000 used to execute the rod-in-tube method will be described with reference to FIG. Manufacturing equipment 10
No. 00 is disclosed in JP-A-53-133304.

[0005] The manufacturing apparatus 1000 includes:
A first holding member 151 for holding the glass rod 12, a second holding member 152 for holding the glass rod 12, and a heater 13 are provided. First holding member 151 and second holding member 152
Can move the clad pipe 11 and the glass rod 12 downward at independent feed rates. Therefore, by adjusting the respective feed speeds of the clad pipe 11 and the glass rod 12, an optical fiber preform 14 having a specified core / clad ratio (C / C) can be obtained.

[0006] Above the clad pipe 11, a vent portion 16 connected to a vacuum pump (not shown) is formed as a branch pipe of the clad pipe 11.
A ring-shaped lid 17 is provided in the opening 121 at the upper end of the cover. The inside 15 of the clad pipe 11 whose upper surface is closed by the lid 17 can be depressurized by using a vacuum pump connected to the air vent 16. When the rod-in-tube method is performed in this state, the glass rod 12 heated by the heater 13 and the clad pipe 11 are integrated by the pressure difference between the inside and outside of the clad pipe 11, and the optical fiber preform 14 is obtained. Thereafter, the optical fiber preform 14 moves downward, and is processed into an optical fiber core through a drawing step or the like.

[0007]

However, the conventional manufacturing apparatus 1000 has the following problems. In the case of using a large-diameter clad pipe 11 in the conventional manufacturing apparatus 1000, such a clad pipe 11 is very thick. Extremely difficult.
For example, it is not realistic to form the vent portion 16 in the clad pipe 11 having an outer diameter of about 180 mm or more.

Further, a technique of providing a jig to close the opening at the upper end of the clad pipe 11 without forming the vent portion 16 in the clad pipe 11 is disclosed in Japanese Patent Application Laid-Open Nos. 2000-185928 and 3048338. It has been disclosed. However, even with these techniques, when the large-diameter clad pipe 11 is used, the following problem occurs. That is, in the case of manufacturing an optical fiber preform using the large-diameter clad pipe 11, since a large electric furnace 13 is used, the amount of heat generated from the electric furnace 13 becomes extremely large,
As a result, the jig provided on the clad pipe 11 is heated more than necessary. If the jig is heated more than necessary, the dimensions of the jig may be out of order, and the airtightness in the clad pipe 11 cannot be maintained. In addition, an axis shift between the jig and the clad pipe 11 also occurs. further,
If a sealing material is provided between the jig and the clad pipe 11, the sealing material may not exhibit a sealing function and may not be able to maintain the airtightness in the clad pipe 11.

The present invention has been made in view of the above points, and a main object of the present invention is to provide an apparatus for manufacturing an optical fiber preform capable of maintaining good airtightness in a large pipe, and an apparatus for manufacturing the same. An object of the present invention is to provide a method of manufacturing an optical fiber preform using the method.

[0010]

An apparatus for manufacturing an optical fiber preform according to the present invention comprises a handling jig attached to the upper end of a large pipe used in the rod-in-tube method, and a holding portion for holding the handling jig. With
A cavity into which gas or liquid is introduced is formed inside the handling jig, and the handling jig is forcibly cooled by introducing the gas or liquid into the cavity.

In one embodiment, the handling jig comprises a first jig, a second jig, and a third jig, and the first jig, the second jig, and the third jig are ,
Each comprises a cylinder having an upper opening and a lower opening through which a primary base material used in the rod-in-tube method penetrates, and the first jig is provided inside the cylinder constituting the first jig. The second jig has a second opening for performing main evacuation of differential evacuation, and the third jig has a first opening for performing rough evacuation of differential evacuation. An end face of the first jig where the lower opening is located is in contact with an upper end of the large pipe, and an end face of the second jig where the lower opening is located is The end face of the first jig where the upper opening is located is in contact with the end face of the second jig where the upper opening is located, and the end face of the third jig where the lower opening is located is in contact with the end face of the third jig where the lower opening is located. The gap between the large pipe and the primary base material is defined by the rough exhaust from the first opening and the second It is reduced by the differential pumping between the main exhaust from the mouth portion.

In one embodiment, the large-sized pipe is a large-sized pipe with a dummy pipe concentrically connected to a dummy pipe, and the end face of the first jig where the lower opening is located is formed by the dummy pipe. Touched to the top.

In one embodiment, a held portion having a taper portion having a taper angle of 30 ° to 60 ° with respect to a side surface of a center portion of the dummy pipe portion is provided on a side surface near an upper end of the dummy pipe portion. And the first jig includes:
A holding part for holding the held part is provided.

[0014] In one embodiment, the outer diameter of the large pipe is about 180 mm, and the gap between the large pipe and the primary base material is about 2 mm or less.

The method for producing an optical fiber preform according to the present invention comprises a large pipe with a dummy pipe in which a dummy pipe is connected to a large pipe used in the rod-in-tube method, and a primary preform used in the rod-in-tube method. A first step of preparing, a second step of vertically positioning a longitudinal direction of the large pipe with the dummy pipe, and a handling jig in which a cavity into which gas or liquid is introduced is formed, A third step of attaching a handling jig having an exhaust opening for evacuating a gap between the large pipe and the primary base material to an upper end of the large pipe with the dummy pipe, and a large pipe with the dummy pipe A fourth step of inserting the primary base material into the inside, and performing exhaust from the exhaust opening of the handling jig, thereby forming the large pie. A fifth step of depressurizing a gap between the handling jig and the primary base material; a sixth step of cooling the handling jig by introducing a gas or a liquid into the cavity of the handling jig; And performing a sixth step of moving the large pipe and the primary base material downward into a heating furnace while performing the sixth step, thereby integrating the large pipe and the primary member. Include.

In one embodiment, in the first step, a large pipe with the dummy pipe is provided on a side surface near an upper end of the dummy pipe, and a taper angle of 30 ° or more with respect to a side surface of a central portion of the dummy pipe. Prepare a large pipe with a dummy pipe including a dummy pipe provided with a held portion having a 60 ° taper portion, and, as the primary base material, a primary base material with a dummy rod connected with a dummy rod. The third step comprises preparing a first jig, a second jig, and a third jig comprising a cylinder having an upper opening and a lower opening through which the primary base material penetrates. The first portion having the hollow portion inside and having a holding portion for holding a held portion of the dummy pipe.
A jig, the second jig having a second opening for performing main evacuation of differential evacuation, and the third jig having a first opening for performing rough evacuation of differential evacuation are prepared. Step (a)
Contacting an end face of the first jig where the lower opening is located with an upper end of the dummy pipe;
(B) holding the large pipe with the dummy pipe by engaging the holding section of the jig with the held section of the dummy pipe, and holding the jig connected to the first support and vertically movable up and down. A step (c) of gripping the first jig by means, and contacting a lower end of the second jig with an upper end of the first jig, so that an upper end of the first jig is contacted with the second jig. Attaching (d), contacting the lower end of the third jig with the upper end of the second jig, and placing the third jig on the upper end of the second jig.
And a step (e) of attaching a jig, wherein the fourth step includes using a chuck for a rod that is connected to a second support and that can vertically move up and down. This is performed by grasping and then moving the chuck for a rod downward, and the exhaust from the exhaust opening in the fifth step is a rough exhaust from the first opening and a main exhaust from the second opening. Performed by differential exhaust with exhaust.

[0017] The outer diameter of the large pipe is about 180 mm, the c / c value (cladding / core value) of the primary base material is 3.6 or more, and the large pipe and the primary pipe in the fifth step are combined. The gap with the primary matrix is about 2 mm or less.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An apparatus for manufacturing an optical fiber preform according to an embodiment of the present invention will be described with reference to FIG. Note that the present invention is not limited to the following embodiments.

FIG. 3 schematically shows a cross-sectional configuration of the manufacturing apparatus of the present embodiment. The manufacturing apparatus shown in FIG. 3 includes a handling jig 100 attached to the upper end of a large pipe 111 used in the rod-in-tube method, and a gripper 200 that grips the handling jig 100. The holding unit 200 has a configuration that can be moved up and down while holding the jig 100, and is connected to the tower frame 300. Part of the handling jig 100 (101)
Inside the cavity 105 into which gas or liquid is introduced.
Are formed. By introducing gas or liquid (for example, water) into the cavity 105, the handling jig 100 can be forcibly cooled.

In the present embodiment, the large pipe 111
The dummy pipe 111a is concentrically connected to the upper part of the large pipe 111. That is, the dummy pipe 111
A large pipe 111 with a is used. The dummy pipe 111a has a role as an extension pipe for extending the length of the large pipe 111, and by providing the dummy pipe 111a, the material of the optical fiber preform in the rod-in-tube method up to near the end of the large pipe 111 Can be used as the large pipe 111. In the present embodiment, the upper end 111c of the dummy pipe 111a included in the large pipe 111 is brought into contact with the end face 100c of the jig 100.

The large pipe 111 is, for example, a glass pipe manufactured by an OVD method or the like, while the primary base material 112 is, for example, a glass rod for a core or a glass rod for a core and a clad. Primary base material 112
For example, a glass rod obtained by sintering a glass fine particle deposit obtained by depositing glass fine particles by a VAD method, or a solidification by forming a core glass on the inner surface of a clad pipe using an MCVD method. Glass rods can be used. The outer diameter D1 of the large pipe used in this embodiment is 180 mm,
The inner diameter D2 is 49 mm. On the other hand, the columnar primary base material 1
12 has an outer diameter D3 of 45 mm, and a gap (gap) between the primary base material 112 and the large pipe 111 is 2 mm. Note that the outer diameter D1 at the upper part of the dummy pipe 111a is
Is also 180 mm, like the outer diameter D1 of the large pipe.

Hereinafter, the structure of the handling jig 100 will be described in detail.

The handling jig 10 according to the present embodiment
0 has a structure in which three parts are stacked,
First jig 101, second jig 102, and third jig 103
It is composed of First jig 101, second jig 102
The third jig 103 is formed of a cylindrical body having an upper opening and a lower opening through which the primary base material 112 passes, and is formed of stainless steel (for example, SUS316). The inner diameter D4 of the cylindrical body is 55 mm, which is 10 mm larger than the outer diameter D3 (45 mm) of the primary base material 112. In this embodiment, the handling jig 100
Is composed of three parts, but the jig 100 may be composed of two parts by integrating the first jig 101 and the second jig 102.

The first jig 101 has a hollow portion 1 inside a cylindrical body.
05, and a part of the hollow portion 105 is connected to the hose joint portion 160. The first jig 101 can be forcibly cooled by supplying the gas or the liquid introduced into the hose joint 160 to the cavity 105. In this embodiment, water is used as a cooling medium, and the jig No. 101 is water-cooled. Outer diameter D
When using a super-large type large pipe 111 of 180 mm, the furnace used by the rod-in-tube method also becomes large, and the heat of the furnace may cause the first jig 101 to be excessively heated. In the present embodiment, the water-coolable first jig 101 is provided closest to the largest pipe 111, and the most heated portion of the handling jig 100 is water-cooled to prevent the handling jig 100 from being excessively heated.
To prevent the airtightness inside the large pipe 111 from deteriorating.

In this embodiment, the end face 100c of the first jig 101 where the lower opening 100b is located is in contact with the upper end 111c of the large pipe 111 (dummy pipe 111a). The first jig 110 is provided with a holding section 190 for holding the large pipe 111, and the holding section 190 holds the holding section 111 d of the dummy pipe 111 a.
, The handling jig 100 and the large pipe 111 are fixed to each other. The held portion 111d of the dummy pipe 111a is
In order to improve the fixation by the holding portion 190, the held portion 111d has a taper angle of 3 with respect to the side surface of the central portion of the dummy pipe 111.
A taper of 0 ° to 60 ° is formed. That is,
Due to this tapered portion, the holding portion 190 is held by the held portion 111d.
Can be easily engaged.

The first jig 101 is provided with a gripped portion 101d gripped by the gripping portion 200. The gripping portion 200 grips the gripped portion 101d of the first jig 101, so that the handling jig is provided. The tool 100 and the large pipe 101 are connected to the tower frame 3 via the grip 200.
00. Further, the first jig 101 also plays a role of improving the centering (centering) of the primary base material 112 on the large pipe 111.

Although not shown in FIG. 3, the primary base material 112 is also gripped by a gripper (not shown) that can be raised and lowered independently of the gripper 200. In the case of such a configuration, the large pipe 111 and the primary base material 112 can be moved at independent feed speeds. Therefore, the respective feed rates of the large pipe 111 and the primary preform 112 can be appropriately adjusted, and an optical fiber preform having a desired core / cladding ratio (C / C) can be easily obtained. The primary base material (VAD rod) 11
As 2, a primary base material in which a dummy rod (extension rod) is concentrically connected may be used, and the dummy rod portion may be gripped by a rod chuck.

The second jig 102 includes the first jig 101 and the third jig 102.
The end face provided between the jigs 103 and where the lower opening of the second jig 102 is located is in contact with the end face where the upper opening of the first jig 101 is located. Further, the second jig 1
The end face of the third jig 103 where the upper opening is located is in contact with the end face where the lower opening of the third jig 103 is located.

The third jig 103 is provided on the second jig 102, and a first opening 110 for performing rough exhaust is formed on a side surface of the third jig 103. In the present embodiment, two first openings 11 are provided on the side surface of the third jig 103.
0 is formed. On the other hand, a second opening 120 for performing main exhaust is formed on a side surface of the second jig 102. In the present embodiment, in addition to the second opening 120, a third opening 130 for introducing a nitrogen gas (or an argon gas or a helium gas) is also formed on the side surface of the second jig 102. In addition, the third opening 130 can be used not only for introducing nitrogen gas but also for main exhaust. Also, the first to third openings 110 and 12
Hose joints 150 for exhausting under reduced pressure and for introducing nitrogen gas are attached to 0 and 130.

The first jig 101 and the second jig 101 in this embodiment
The heights H1, H2, and H3 of the jig 102 and the third jig 103 are about 260 mm, about 115 mm, and about 100 mm, respectively. Further, in the present embodiment, in order to improve the sealing between the jig 100 and the large pipe 111 and the sealing inside the jig 100, the gap between the dummy pipe 111 a and the first jig 101 is reduced. 1 jig 101
Between the second jig 102 and the second jig 102
Sealing materials 181 and 1
82 and 183 are inserted, and they are in contact with each other via a sealing material. Of these sealing materials, at least a half of the sealing material 183 is used. In other words, the seal member 183 includes a pair of semi-annular seal members. Since the sealing material 183 has a half-split structure, even after the third jig 103 is once provided on the second jig 102, the contact between the second jig 102 and the third jig 103 may occur. When the state is released, the second jig 1
The seal member 183 can be easily inserted between the second jig 103 and the third jig 103. Further, in the present embodiment, the third
A seal member 184 having a half-split structure is also provided above the jig 103. The seal member 184 on the upper part of the third jig 103 and the seal member 183 between the second jig 102 and the third jig 103 are fixed by the shell clamp 180.

Below the large pipe 111 and the primary base material 112, a heating furnace (not shown) having a heater is provided. As such a heating furnace, for example, a carbon resistance heating furnace or a high-frequency induction heating furnace can be used.
When the inside of the large pipe 111 is decompressed and the large pipe 111 and the primary base material 112 are respectively moved to the heating furnace at a desired feed rate, the heating of the heater causes the integration of the large pipe 111 and the primary base material 112. Are sequentially performed to obtain an optical fiber preform. The obtained optical fiber preform is processed into an optical fiber core wire through a known stretching step, drawing step, and the like.

In the manufacturing apparatus of this embodiment, the handling jig 100 and the sealing material 181 can be protected from the heat of the heating furnace having a large amount of heat by the first jig 101 which can be cooled by water. Airtightness can be maintained. In addition, since differential exhaust by the rough exhaust from the first opening 110 and the main exhaust from the second opening 120 in the handling jig 100 can be performed, the large pipe 111 and the primary base material 112 Fine adjustment of the gap pressure is facilitated. As a result, the gap between the large pipe 111 and the primary base material 112 can be brought to an appropriate reduced pressure state. The reason why the gap between the large pipe 111 and the primary base material 112 needs to be appropriately reduced in pressure will be described below.

In the rod-in-tube method, as described above, the gap between the large pipe 111 and the primary base material 112 must be decompressed.
Due to the effect of the residual gas adsorbed on the inner peripheral surface of the large pipe 111, bubbles are generated inside the manufactured optical fiber preform. Since the generation of air bubbles causes poor loss or poor connection, the part where the air bubbles are generated must be discarded. On the other hand, if the degree of pressure reduction is increased, the generation of air bubbles can be prevented, but since the large pipe 111 tries to reduce the diameter rapidly, the curvature of the reduced diameter portion becomes large, and the uneven thickness increases. As a result, when the large-sized pipe 111 and the primary base material 112 are integrated, there is a disadvantage that the core is eccentric. Such eccentricity of the core tends to be particularly large in the case of the large glass pipe (large pipe 111) used in the present embodiment. An appropriate value may be determined as appropriate according to manufacturing conditions such as dimensions of the large pipe 111 and the primary base material 112 to be used. Table 1 below shows the pipe pressure reduction degree (kPa) obtained by the experiment of the present inventor and the bubbles (pieces / base material 10) inside the base material.
0 mm) and the mode field eccentricity (μm) of the optical fiber are shown together with the manufacturing conditions.

[0034]

[Table 1]

In Table 1, D0 and d0 of the samples a to k are the outer diameter and inner diameter (mm) of the large pipe 111 before stretching, and d is the primary base material (glass rod) before stretching. 112 (mm). Here, the “degree of pressure reduction” means the degree of the pressure reduced based on the atmospheric pressure. Samples a to g are examples in which a relatively large large pipe 111 is used, and samples h to k are examples in which a relatively large large pipe 111 is used.

As can be seen from samples a and h, when the degree of pressure reduction is high (100.0 kPa), the generation of bubbles can be suppressed, but the amount of eccentricity increases. On the other hand, as can be seen from samples g and k, when the degree of pressure reduction is low (3.3 kPa), the amount of eccentricity can be suppressed, but the generation of bubbles increases. Therefore, when manufacturing an optical fiber preform, it is necessary to determine an appropriate degree of pressure reduction and maintain such a reduced pressure state.

Since the manufacturing apparatus of this embodiment has the handling jig 100 which can be cooled, the outer diameter D1 is 1
Super large large pipe 1 such as 80mm or more
Even when 11 is used, the influence of the heat from the heating furnace can be reduced, and as a result, the airtightness in the large pipe 111 can be maintained well. Further, since the manufacturing apparatus of this embodiment has a structure capable of differential evacuation, the pressure in the gap between the large pipe 111 and the primary base material 112 can be easily finely adjusted. That is, by appropriately adjusting the rough exhaust and the main exhaust, it is easy to reduce the degree of decompression to neither unnecessarily high nor low.

In this embodiment, a pump having an exhaust capacity of 500 liters / minute or more, preferably about 1000 liters / minute, is used as a vacuum pump for rough exhaust and main exhaust. Note that nitrogen gas can be introduced from the third opening 130. However, this is to suppress generation of bubbles as much as possible.
The air in the gap between the large pipe 111 and the primary base material 112 before being integrated is replaced with nitrogen. After the replacement with nitrogen, integration of the large pipe 111 and the primary base material 112 is performed.
The main exhaust is performed from the opening 130.
In the manufacturing apparatus of the present embodiment, a vacuum pump (not shown)
The first to third openings 11 via the hose joint 150
0, 120, and 130.

In this embodiment, the feed rate of each of the large pipe 111 and the primary base material 112 is adjusted so that the core / clad ratio (C / C) is 3.6 or more (typically about 4). An optical fiber preform is manufactured. This is because when the rod-in-tube method is used, if the core / clad ratio (C / C) is less than 3.6, the large pipe 1
This is because it is empirically known that the loss of the fiber becomes significantly large due to the absorption loss due to the impurities (for example, OH ⁻ ) remaining at the interface between the first preform 112 and the primary preform 112.

Further, the inventor of the present application has found that when a large pipe 111 having an outer diameter of 180 mm is used, if the gap (clearance) between the large pipe 111 and the primary base material 112 is about 2 mm, the fiber eccentricity (μm) can be reduced. Found by experiment. FIG. 4 shows the results.

FIG. 4 shows the relationship between the clearance (mm) and the fiber eccentricity (mode field eccentricity of the optical fiber; μm).
15 shows an example in which the clearance is 2 mm. As can be seen from FIG. 4, the smaller the clearance, the smaller the fiber eccentricity tends to be. When the clearance is 2 mm, the fiber eccentricity is about 0.1 μm. It is desirable to adjust the length of the dummy pipe 111a or adjust the first jig 101 and the grip 200 so that the primary base material 112 is well-centered. Further, the clearance may be set to 2 mm or less.

Next, a method of manufacturing an optical fiber preform by the above-described manufacturing apparatus will be described with reference to FIGS. FIG. 5 is a flowchart for explaining the method for manufacturing an optical fiber preform of the present embodiment.

First, a large pipe 111 with a dummy pipe 111a and a primary base material 112 are prepared (step S).
1). The large pipe 111 used in the present embodiment is a super large glass pipe having an outer diameter of 180 mm. The large pipe 111 with the dummy pipe 111a can be purchased. The portion of the dummy pipe 111a is reusable and can be reused about five times.
In addition, the primary base material 112 can be manufactured by a known technique. As the primary base material 112, a primary base material with a dummy rod in which dummy rods are concentrically connected may be prepared.

Next, the longitudinal direction of the large pipe 111 is positioned vertically (step S2). For example, the large pipe 111 may be raised from the horizontal to the vertical by the large pipe conveying device. A basket 350 of a large-sized pipe conveying device is shown around the large-sized pipe 111 in FIG.

Next, the dummy pipe 1 of the large pipe 111
The jig 100 is mounted on 11a (step S3). The attachment of the jig 100 may be performed as follows.

First, the first jig 101 is attached.
First, the lower end surface 100c of the first jig 101 is arranged so as to contact the upper end 111c of the dummy pipe 111a,
Next, the holding portion 111d of the dummy pipe 111a is engaged with the holding portion 190 of the first jig 101. 1st jig 1
01 is a dummy pipe 111
The first jig 101 is securely fixed to the large pipe 111 with the dummy pipe 111a because the first jig 101 is configured to be properly hooked on the tapered part of the held part 111d. The lower end face 10 of the first jig 101
It is preferable to dispose a sealing material 181 between the first pipe 0c and the upper end 111c of the dummy pipe 111a.

Next, the large pipe 111 is moved to the upper part of the electric furnace (not shown) together with the basket 350, and the first jig is attached to the holding portion (tower frame receiving stand) 200 connected to the tower frame 300 of the electric furnace. The gripped portion 101d of 101 is set, and the cage 350 is removed. Thereby, the gripper 200
The first jig 101 and the large pipe 111 are fixed to the tower frame 300 by gripping the gripped portion 101d. After that, the second jig 102 is provided on the first jig 101, and then the third jig 103 is provided on the second jig 102.
At this point, the second jig 102 and the third jig 103
The sealing material 183 is not provided between the above and the sealing material 183 is inserted in a later step.

Next, the jig 100 and the large pipe 11
The primary base material (glass rod) 112 is inserted into 1 (step S4). The insertion of the primary base material 112 may be performed as follows.

First, the primary base material 112 prepared in step S1
Is gripped by a rod chuck (not shown) located above the jig 100. In the present embodiment, in step S1, a primary base material 112 with a dummy rod is prepared, and the dummy rod portion of the primary base material 112 is gripped and fixed to a rod chuck. The rod chuck is connected to a tower frame (not shown) different from the tower frame 300 to which the grip 200 is connected, and is configured to be able to move up and down independently of the grip 200.

Next, the rod chuck (not shown) is pulled down and inserted sequentially into the third jig 103, the second jig 102, the first jig 101, the dummy pipe 111a, and the large pipe 111. Go. At the stage after insertion, since the dummy rod portion of the primary base material 112 is located between the third jig 103 and the second jig 102, the third jig 103 and the second jig 102 , And a half-sealed sealing material 183 is inserted between them, and then the shell jig 180 is used to tighten the third jig 103 and the second jig 10.
2 is fixed. Although the inside of the sealing material 183 does not contact the surface of the dummy rod portion of the primary base material 112, the sealing material 183 has a shape approaching the surface of the dummy rod portion. The sealing material 183 having such a shape can function as a pressure partition during differential pumping.

The reason why the sealing material 183 is not inserted between the third jig 103 and the second jig 102 before the primary base material 112 is inserted will be described below. That is, the primary base material 1
If the sealing material 183 is present before the insertion of the base material 12, the opening in the jig 100 becomes narrower, and the primary base material 112 and the sealing material 183 rub when the primary base material 112 is inserted. This is because the primary preform 112 may be damaged and bubbles may be generated in the optical fiber preform. As in the present embodiment, after the primary base material 112 is inserted, the sealing material 18 is inserted.
If 3 is inserted, even if the sealing material 183 contacts the dummy rod portion, the portion of the primary base material 112 will not be damaged. In the present embodiment, the third jig 103
The sealing material 1 having the same shape as the sealing material 183
84 are provided, and the sealing material 184
At the time of differential evacuation, air, dust, or moisture can be prevented from entering through the upper opening 100a of the jig 100 as much as possible.

Next, when the insertion of the primary base material 112 is completed, the pressure in the large pipe 111 is reduced (step S).
5). In the present embodiment, the degree of pressure reduction in the gap between the large pipe 111 and the primary base material 112 is controlled to an appropriate value by performing differential evacuation in this pressure reduction step. Before the decompression step is performed, the third jig 102
Nitrogen gas is introduced as a purge gas from the opening 130, whereby the large pipe 111 and the primary base material 112 are introduced.
Is preferably replaced with nitrogen gas. That is, when a very large large pipe 111 having an outer diameter of 180 mm is used, even if the clearance between the large pipe 111 and the primary base material 112 is about 2 mm, the capacity of the gap is large, and in order to prevent the generation of bubbles, It is preferable to replace the air present in the gap between the large pipe 111 and the primary base material 112 with nitrogen gas. Note that, instead of the nitrogen gas, another gas such as an argon gas may be used.

After the replacement of the nitrogen gas, the introduction of the nitrogen gas from the third opening 130 is stopped, and then the rough exhaust from the first opening 110 of the third jig 103 and the second exhaust of the second jig 102 are performed. The differential exhaust is performed by the main exhaust from the second opening 120 and the third opening 130. If one-step exhaust only for the main exhaust is performed, the upper opening 100a of the jig 100
Air, dust or moisture may enter from the air. By performing rough exhaust together with main exhaust, large pipes 111
It is possible to prevent air, dust, or moisture from entering the inside of the device, and fine adjustment of the pressure can be easily performed as in the state where the upper portion is sealed. In this embodiment,
Since the seal members 183 and 184 are provided in the jig 100, the decompression step can be performed more suitably.
Since the appropriate degree of pressure reduction depends on the manufacturing conditions, it may be set appropriately according to the conditions. The reason for stopping the introduction of nitrogen gas during this differential evacuation is that while introducing nitrogen gas,
This is because, when the large pipe 111 and the primary base material 112 are integrated, bubbles are easily generated. therefore,
In step S5, the introduction of nitrogen gas is stopped, and the third
The opening 130 functions as an opening for main exhaust.

Next, the first jig 101 is cooled by introducing water into the cavity 105 of the first jig 101 (step S6). Then, while cooling the first jig 101,
The large pipe 111 and the primary base material 112 are integrated with each other in a state where the degree of reduced pressure is appropriately set in the step S5 (step S7). The integration of the large pipe 111 and the primary base material 112 is performed by moving the large pipe 111 and the primary base material 112 downward and placing them in an electric furnace. In the present embodiment, since the integration is performed while performing step S6, the influence of the heat of the heating furnace having a large amount of heat can be reduced, and the handling jig 100 and the sealant 181 can be protected. As a result, the integration can be performed with good airtightness, so that a good optical fiber preform can be obtained. Also, the jig 100 and the large pipe 111
Therefore, an optical fiber preform with less eccentricity can be obtained. Instead of using the optical fiber preform as a final product, a known drawing step or the like may be performed on the obtained optical fiber preform after the step S7 to process the optical fiber core.

[0055]

According to the present invention, the handling jig can be forcibly cooled, so that the influence of the heat of the heating furnace can be reduced. Therefore, the airtightness in the large pipe can be kept good. As a result, an optical fiber preform with few bubbles and small core eccentricity can be favorably manufactured. In particular, it can be suitably applied to the rod-in-tube method using a large pipe having an outer diameter of 180 mm or more. Further, when performing differential exhaust by rough exhaust from the first opening and main exhaust from the second opening in the handling jig, the pressure in the gap between the large pipe and the primary base material is finely adjusted. It becomes easier.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a rod-in-tube method.

FIG. 2 is a cross-sectional view showing a conventional optical fiber preform manufacturing apparatus.

FIG. 3 is a cross-sectional view schematically showing an optical fiber preform manufacturing apparatus according to an embodiment of the present invention.

FIG. 4 is a graph showing the relationship between clearance and fiber eccentricity.

FIG. 5 is a flowchart illustrating a method for manufacturing an optical fiber preform according to the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Clad pipe 12 Glass rod 13 Heater 14 Optical fiber preform (preform) 15 Inside of clad pipe 16 Vent part 17 Lid 100 Jig 101 First jig 102 Second jig 103 Third jig 105 Cavity 110 1st opening 120 2nd opening 130 3rd opening 111 Large pipe 111a Dummy pipe 112 Primary base material 150, 160 Hose joint 180 Shell clamp 181, 182, 183, 184 Sealing material 190 Holding unit 200 Holding unit 300 Tower holder

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor, Nagasada Shinsada 4-3 Ikejiri, Itami-shi, Hyogo Mitsubishi Electric Cable Industry Co., Ltd. Itami Works F-term (reference) 4G021 BA01

Claims (8)

[Claims] 1. A handling jig attached to an upper end of a large pipe used in a rod-in-tube method, and a grip portion for gripping the handling jig, wherein a gas or a liquid is contained inside the handling jig. An apparatus for manufacturing an optical fiber preform, wherein a cavity to be introduced is formed, and the handling jig is forcibly cooled by introducing the gas or the liquid into the cavity. 2. The handling jig comprises a first jig, a second jig, and a third jig, wherein the first jig, the second jig, and the third jig are respectively
The first jig comprises a cylindrical body having an upper opening and a lower opening through which a primary base material used in the rod-in-tube method penetrates, and the first jig has a hollow portion inside a cylindrical body constituting the first jig. The second jig has a second opening for performing main exhaust of differential exhaust, and the third jig has a first opening for performing rough exhaust of differential exhaust. The end face of the first jig where the lower opening is located is in contact with the upper end of the large pipe, and the end face of the second jig where the lower opening is located is the first jig. The end face of the jig where the upper opening is located is in contact, and the end face of the second jig where the upper opening is located is in contact with the end face of the third jig where the lower opening is located. The gap between the large pipe and the primary base material may be roughly exhausted from the first opening and the second opening. It is reduced by the differential pumping between the main exhaust apparatus for manufacturing an optical fiber preform according to claim 1. 3. The large-sized pipe is a large-sized pipe with a dummy pipe concentrically connected to a dummy pipe, and the end face at which the lower opening of the first jig is located,
The apparatus for manufacturing an optical fiber preform according to claim 2, wherein the apparatus is in contact with an upper end of the dummy pipe. 4. A held portion having a tapered portion having a taper angle of 30 ° to 60 ° with respect to a side surface of a central portion of the dummy pipe portion is provided on a side surface near an upper end of the dummy pipe, The optical fiber preform manufacturing apparatus according to claim 3, wherein the first jig is provided with a holding portion for holding the held portion. 5. The outer diameter of the large pipe is about 180 mm, and the gap between the large pipe and the primary base material is:
The apparatus for manufacturing an optical fiber preform according to any one of claims 1 to 4, wherein the apparatus is about 2 mm or less. 6. A first step of preparing a large pipe with a dummy pipe in which a dummy pipe is connected to a large pipe used in a rod-in-tube method, and a primary base material used in a rod-in-tube method; A second step of vertically positioning a longitudinal direction of a large pipe with a pipe, and a handling jig in which a cavity into which gas or liquid is introduced is formed, wherein a gap between the large pipe and the primary base material is provided. A third step of attaching a handling jig having an exhaust opening for vacuuming the upper end of the large pipe with the dummy pipe, and a step of inserting the primary base material into the large pipe with the dummy pipe. Fourth step, a step of depressurizing a gap between the large pipe and the primary base material by exhausting air from the exhaust opening of the handling jig. A step of cooling the handling jig by introducing a gas or a liquid into the cavity of the handling jig; and performing the fifth step and the sixth step while performing the fifth step and the sixth step. A seventh step of moving each of said primary preforms downward and into a heating furnace, thereby integrating said large pipe and said primary member. 7. In the first step, as a large pipe with the dummy pipe, a taper angle of 30 ° to 60 ° with respect to a side face of a central portion of the dummy pipe is provided on a side face near an upper end of the dummy pipe. Prepare a large pipe with a dummy pipe including a dummy pipe provided with a held portion having a tapered portion, and, as the primary base material, prepare a primary base material with a dummy rod connected with a dummy rod, The third step is a first jig, a second jig, and a third jig made of a cylinder having an upper opening and a lower opening through which the primary base material penetrates. Having the cavity, and
A first jig having a holding portion for holding a held portion of the dummy pipe; a second jig having a second opening for performing main exhaust of differential exhaust; (A) preparing the third jig having a first opening for performing rough exhaust; and bringing an end face of the first jig where the lower opening is located into contact with an upper end of the dummy pipe. (B) engaging the holding portion of the first jig with the held portion of the dummy pipe to hold the large pipe with the dummy pipe; (C) gripping the first jig by means of a vertically movable gripping means; and contacting the lower end of the second jig with the upper end of the first jig, (D) attaching a second jig; and attaching the third jig to an upper end of the second jig. (E) attaching the third jig to the upper end of the second jig by bringing the lower end into contact, and the fourth step is a rod connected to the second support and capable of moving up and down in the vertical direction. This is performed by gripping a portion of the dummy rod of the primary base material using a chuck for the primary base material, and then moving the chuck for the rod downward. The method for manufacturing an optical fiber preform according to claim 6, wherein the method is performed by a differential evacuation between a rough evacuation from the first opening and a main evacuation from the second opening. 8. An outer diameter of the large pipe is about 180 mm, a c / c value (cladding / core value) of the primary base material is 3.6 or more, and the large pipe in the fifth step is used. The method of manufacturing an optical fiber preform according to claim 6 or 7, wherein a gap between the optical fiber and the primary preform is about 2 mm or less.