JP2003034546A - Method for producing glass preform for optical fiber and device used for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an optical fiber glass preform in which a glass pipe is completely collapsed without leaving an uncollapsed portion while the roundness of a core glass is being maintained. SOLUTION: A glass rod 1 for core is fitted into a glass pipe 2 for cladding, and the glass pipe 2 for cladding is collapsed and integrated with the glass rod 1 for core through heating and softening with a burner 3 while being depressurized. When the cross section of the integrated glass preform is designated S1 and the cross section of a jetting port of hydrogen gas for the burner is designated S2, S1/S2 is made in the range of 10-30.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for manufacturing an optical fiber glass preform in which a glass rod for core is inserted into a glass pipe for cladding and is heated and softened to be integrated.

[0002]

2. Description of the Related Art As one of the methods for manufacturing a large-diameter optical fiber glass preform, a glass rod for a core is prepared in advance, and this glass rod for a core (hereinafter referred to as a glass rod) is used as a cladding quartz. A method is known in which a glass rod is inserted into a glass pipe (hereinafter referred to as a glass pipe), and the glass pipe is integrated with the glass rod by a process called collapse, in which the glass pipe is heated and softened to be crushed. The glass rod is made by chemical vapor deposition (C).
VD method), external CVD method (Outer Vapor Deposition)
: OVD method), Vapor phase Axial Depos
ition: VAD method) or the like, and is formed by adding a dopant for increasing the refractive index.

Conventionally, as a method for producing an optical fiber glass preform by collapsing a glass pipe on a glass rod, for example, Japanese Patent Publication No. 2000-51093 is known. In this manufacturing method, a glass rod is inserted into a glass pipe using a vertical lathe, and then the glass pipe is preheated by a furnace and heated by a burner until the glass pipe reaches a softening point. Then, the air in the gap between the glass rod and the glass pipe is evacuated to reduce the pressure, and the glass pipe is collapsed and integrated on the glass rod.

However, when the vertical lathe is used, the glass rod may be deformed by its own weight during heating at the start of the collapse, and it is difficult to align the axes of the glass rod and the glass pipe, and the axes are not aligned. If collapsed in the state, the roundness of the glass rod to which the dopant is added deteriorates. Also, to preheat the glass pipe using a furnace,
The equipment becomes complicated, it takes time to raise the temperature to the preheating temperature, and it is expected that work efficiency will decrease. Then, the glass rod and the glass pipe with a large diameter, when manufacturing a large-sized optical fiber glass preform, the area ratio of the burner flame to the glass preform area becomes small, it is not possible to sufficiently heat the inside, Uncrushed glass pipe may be left behind.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and facilitates axial alignment using a horizontal lathe, maintains the roundness of the core glass, and crushes the glass pipe. An object of the present invention is to provide a method and an apparatus for manufacturing an optical fiber glass preform that is collapsed without leaving any residue.

[0006]

The method for producing a glass preform for optical fibers according to the present invention comprises inserting a glass rod for core into a glass pipe for cladding and heating and softening the glass pipe for cladding with a burner while reducing the pressure. A method of manufacturing a glass preform for an optical fiber, which is crushed and integrated with a glass rod for core, wherein a cross-sectional area of the integrated glass preform is S1.
When the cross-sectional area of the gas ejection port of the hydrogen gas ejection port of the burner is S2, S1 / S2 is 10 to 30.

Further, in the apparatus for producing a glass preform for optical fibers of the present invention, the glass rod for core is inserted into the glass pipe for clad, and the glass pipe for clad is heated and softened by a burner while being decompressed to be crushed. An optical fiber glass base material manufacturing device integrated with a glass rod, comprising a horizontal lathe device for concentrically supporting a core glass rod for a glass pipe for cladding, and a cross-sectional area of the integrated glass base material is S1. Then, the cross-sectional area S2 of the gas ejection port of the hydrogen gas ejection port of the burner is 1/10 to S1.
It is characterized by being set to 1/30.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described with reference to the drawings. 1 is a schematic view of the collapse process, FIG. 2 (A) is an a-a sectional view before the collapse of FIG. 1, and FIG. 2 (B) is a bb sectional view after the collapse of FIG. In the figure, 1 is a glass rod for core, 2 is a glass pipe for cladding, 3 is a burner, and 4 is a gap.

The core glass rod 1 (hereinafter referred to as a glass rod) may be formed in various forms depending on the type of optical fiber. For example, a single mode fiber and a multimode fiber have different thicknesses to be used, and a step index (SI) fiber and a graded index (GI) fiber have different core refractive index distributions. These glass rods 1 are made of a dopant (for example, GeO ₂ ) for increasing the refractive index by various methods such as a CVD method, an OVD method, a VAD method and the like.
Is added to form a porous glass base material, and then the glass material is formed into a transparent glass.

In the depressed clad fiber in which the outer circumference of the core is lower than that of the cladding, a dopant (for example, fluorine) for lowering the refractive index is added to the outside of the glass rod 1 having the higher refractive index. It is possible to use an externally attached glass or a glass pipe formed by collapsing a glass pipe. Quartz glass of high purity is generally used for the glass pipe 2 for cladding (hereinafter referred to as glass pipe).

The burner 3 has a configuration in which an oxygen gas ejection port and a hydrogen gas ejection port, which will be described later, are arranged in a coaxial cylindrical shape. The burner 3 is arranged on the side of the glass pipe 2 and is configured to make either the glass pipe 2 or the burner 3 relatively movable. Further, means (not shown) for reducing the pressure in the gap 4 between the glass rod 1 and the glass pipe 2 is provided.

In the above structure, first, the glass rod 1 is inserted into the glass pipe 2 as shown in FIG.
Both ends of each are arranged coaxially by a chuck of a horizontal lathe (not shown) and are rotatably supported. Glass rod 1
A gap 4 (about 0.5 mm to 1 mm) between the glass pipe 2 and the glass pipe 2 is the crushed amount. One end side of the glass pipe 2 is heated and melted by the burner 3 and fused with the glass rod 1,
One end of the gap 4 between the glass rod 1 and the glass pipe 2 is sealed. Next, the inside of the glass pipe 2 is decompressed by the burner 3 by vacuuming, and the glass pipe 2 is sequentially heated and softened toward the end opposite to the sealed end. The heat-softened glass pipe 2 ′ is crushed by a negative pressure due to a reduced pressure as shown in FIG. 2 (B), and is collapsed and integrated on the glass rod 1. By using a horizontal lathe, the glass rod 1 can be fixed at both ends and then the glass pipe 2 can be collapsed, and workability and circularity can be easily ensured.

3 and 4 schematically show the burner 3, FIG. 3 is a sectional view in the axial direction of the burner, and FIG. 4 is a radial direction cc of FIG.
FIG. In the figure, 5 is an oxygen gas ejection port, 6 is a hydrogen gas ejection port, and 7 is a burner end. The burner 3 is formed in a cylindrical shape in which _two ports, an inner O ₂ jet port 5 and an outer H ₂ jet port 6, are concentrically arranged, and the tapered burner end 7 forms O ₂ gas and H ₂ gas. Are configured to be mixed. The burner 3 has a burner diameter (the outer diameter φ of the end 7 depending on the thickness of the glass pipe 2).
The cross sectional area S2 of the H ₂ jet port 6, the cross sectional area S _{3 of} the O ₂ jet port, etc. are changed. The port cross-sectional areas S2 and S3 are the effective cross-sectional area of the gas ejection port and do not include the wall thicknesses t1 and t2 of the port wall.

FIG. 5 is a diagram showing the results of examining the suitability of the outside diameter D of the glass preform after the collapse and the type of burner used. In the studied Examples 1 to 4, the burner 3 has a relatively small diameter of 10φ (outer diameter 10 mm) and a relatively large diameter of 13φ (outer diameter 13 mm) of two types A and B. Prepared. Note that more types of burners can be prepared depending on the thickness of the glass base material.

FIG. 6 is a diagram showing the temperature distribution at the fusion interface by the burner during collapse. With burner 3,
When the glass rod 1 and the glass pipe 2 are heated, the temperature distribution at the interface changes as shown in the figure due to the difference in burner diameter. When the burner diameter is small, the temperature change is large in a narrow heat zone, and when the burner diameter is large, the temperature change is relatively flat and nearly flat in a wide heat zone.

Example 1 shown in FIG. 5 has a length of 270 mm,
This is an example of performing a collapse using a 10φ burner when obtaining an optical fiber glass base material having a relatively small diameter with a glass base material outer diameter D after the collapse of 26 mm. The cross-sectional area S2 of the H ₂ jet port of the 10φ burner was 21.76 mm ² , O ₂
The ejection port cross-sectional area S3 was set to 4.15 mm ² and the cross-sectional area ratio S2 / S3 was set to 5.25. When the cross-sectional area of the glass preform after the collapse was calculated from the outer diameter D to be S1, the ratio S1 / S2 to the cross-sectional area S2 of the H ₂ ejection port 6 was 19.07. The H ₂ gas flow rate was 74 (SLM) and the O ₂ gas flow rate was 33 (SLM). The glass pipe surface temperature at the time of collapse is 1700 ° C, which is an almost appropriate heating temperature.
The condition of the interface between the glass rod 1 and the glass pipe 2 is good, there is no crushed residue, and the core non-circularity is 0.4% or less, which is almost satisfactory. The core non-circularity is a percentage obtained by dividing the difference between the maximum core diameter and the minimum core diameter by the average core diameter.

Example 2 has the same length of 270 mm, and has an outer diameter D of the glass preform after collapse for improving the productivity of the optical fiber.
This is an example of performing a collapse using the same 10φ burner as in Example 1 when obtaining an optical fiber glass preform having a relatively large diameter of 33.5 mm. The cross-sectional area ratio S2 / S3 of the H ₂ ejection port and the O ₂ ejection port is 5.25, which is the same as in Example 1,
Cross-sectional area S1 of glass base material after collapse and H ₂ ejection port 6
The ratio S1 / S2 to the cross-sectional area S2 of was 40.45.
The H ₂ gas flow rate was 74 (SLM) and the O ₂ gas flow rate was 33 (SLM). As a result, the glass pipe surface temperature during the collapse was 1650 ° C., which is not a particularly low temperature, but some uncrushed residue was generated at the interface between the glass rod 1 and the glass pipe 2, and the core non-circularity was 0.84%, which was a little. The result is unsatisfactory. It is considered that the reason for this is that the range of the heat zone by the burner shown in FIG. 6 is narrow for the 10φ fiber with respect to the outer diameter D of the glass base material, and thus the uncrushed residue is caused due to insufficient heat.

Based on the results of Example 2, in Example 3, the glass mother was used.
When the material outer diameter D is increased, the heat zone is increased.
We thought that it was necessary, and made the burner outer diameter thicker 13φA
Collapse was performed using a burner. Outside the burner
Since the diameter was 1.3 times, the cross-sectional area of the gas ejection port (H₂
Jet port cross-sectional area S2 + O₂Ejection port cross-sectional area S3) also
It was set to about 1.3 times. H at this time₂Jet port cross-sectional area
21.89 mm for S2 ², O₂The jet port cross-sectional area S3
12.56 mm²And the cross-sectional area ratio S2 / S3 is 1.75.
And In addition, after the collapse, the glass base material cross-sectional areas S1 and H
₂The ratio S1 / S2 of the jet port 6 to the cross-sectional area S2 is 41.
It was 45. In addition, H₂Gas flow rate is 150 (SL
M), O₂The gas flow rate was 50 (SLM).

As a result, the glass pipe surface temperature during the collapse was 1360 ° C. Since the temperature did not rise sufficiently, the negative pressure was increased to cause the collapse. Although the crushing residue did not occur due to the expansion of the heat zone and the increase of the negative pressure, the core non-circularity greatly deteriorated to 2.36%. As a result of investigating the reason why the surface temperature does not rise, the proportion of the O ₂ ejection port cross-sectional area S3 was increased, whereas the H ₂ ejection port cross-sectional area S2 was not increased and the heat quantity was insufficient. It is thought to be due to.

In Example 4, the outer diameter of the glass base material after collapsing was 2
When increasing from 6 mm to 34 mm, the increase in cross-sectional area is 2
The outer diameter is the same for the 13φB burner because it doubles.
Then, the gas ejection port cross-sectional area (H₂Jet port cross-sectional area S
2 + O₂The ejection port cross-sectional area S3) was almost doubled. This
H when₂Jet port cross-sectional area S2 is 43.96m
m ², O₂Jet port cross-sectional area S3 is 7.07 mm²When
Then, the cross-sectional area ratio S2 / S3 was set to 6.22. After the collapse
Glass base material cross-sectional areas S1 and H₂Cross-sectional area S of ejection port 6
The ratio S1 / S2 of 2 was 20.64. In addition, H₂
Gas flow rate is 150 (SLM), O₂Gas flow rate is 50 (S
LM).

As a result, the glass pipe surface temperature during collapse was 1860 ° C., a sufficient temperature was obtained in a wide heat zone, and the negative pressure was the same as in Example 1, but no crushing residue was generated. Further, the core non-circularity was 0.23%, which was a good result.

From the results of Examples 1 to 4 above, comprehensively,
Cross-sectional area S1 of glass base material after collapse and H of burner used
_It is preferable that the ratio S1 / S2 of the cross-sectional area S2 of the _two ejection ports is around 20 and within the range of 10-30. In other words, the cross-sectional area S2 of the H ₂ jet port is set to 1/10 to 1/30 of the glass base material cross-sectional area S1. If the amount of heat applied to the glass pipe 2 is small, crushing will be insufficient. However, if the heating amount is too large or an excessive crushing force is applied to the glass pipe, the non-circularity of the internal glass rod deteriorates. This is because if the glass rod in the glass pipe is doped with a dopant such as GeO ₂ , it is easily softened by heating, and when the glass pipe 2 is crushed, the roundness of the glass rod 1 is impaired, resulting in an ellipse. Because it is easy to deform. By setting the cross-sectional area ratio S1 / S2 within the above range, a sufficient temperature and heat zone corresponding to the thickness of the optical fiber glass preform can be obtained, and a glass pipe with a good non-circularity can be obtained. It can be crushed, and the crushed residue can be eliminated.

The burner H₂Jet port cross-sectional area S
2 and O₂The ratio S2 / S3 to the jet port cross-sectional area S3 is 5 to
It is preferably in the range of 7. H by burner₂gas
And O ₂When flame is generated by gas, H₂Gush poe
Constant port cross section instead of increasing cross section
As H₂To increase the heating amount by increasing the gas amount
You can, but H₂The gas flow velocity increases, and the glass base material
The surface of will be scraped off. Therefore, H₂Of gas
The flow velocity is constant, H₂Change the cross-sectional area of the ejection port
Is preferred. H₂Ejection port and O₂Disconnection of ejection port
By setting the area ratio S2 / S3 within the above range
The surface of the glass pipe can be heated to a specified temperature.
Wear.

[0024]

As is apparent from the above description, according to the present invention, it is possible to obtain a sufficient heating temperature and a heat zone necessary for the collapse in accordance with the thickness of the optical fiber glass preform to be manufactured. Therefore, the silica glass pipe for clad can be crushed while maintaining good roundness of the glass rod for core, and the crushed residue can be eliminated.

[Brief description of drawings]

FIG. 1 is a schematic diagram illustrating an embodiment of the present invention.

FIG. 2 is a diagram showing a cross section taken along the line aa and the line bb of FIG.

FIG. 3 is a vertical cross-sectional view illustrating the shape of a burner.

FIG. 4 is a diagram showing a cc cross section of FIG. 3;

FIG. 5 is a diagram showing a study result according to a specific example of the present invention.

FIG. 6 is a diagram showing a relationship between a burner and a heat zone.

[Explanation of symbols]

1 ... Glass rod for core, 2 ... Glass pipe for cladding, 3 ... Burner, 4 ... Gap, 5 ... Oxygen gas ejection port, 6 ... Hydrogen gas ejection port, 7 ... Burner end.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shinji Hasegawa             Sumitomoden 1 Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa             Ki Industry Co., Ltd. Yokohama Works (72) Inventor Shinobu Sekiguchi             Sumitomoden 1 Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa             Ki Industry Co., Ltd. Yokohama Works (72) Inventor Keiji Ogawa             Sumitomoden 1 Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa             Ki Industry Co., Ltd. Yokohama Works F-term (reference) 4G021 BA04

Claims (4)

[Claims] 1. A glass base material for an optical fiber in which a glass rod for a core is inserted into a glass pipe for a clad, and the glass pipe for a clad is heated and softened by a burner while being decompressed and crushed to be integrated with the glass rod for a core. And a cross-sectional area of the integrated glass base material is S1.
And S1 / S2 is 10 to 30 when the cross-sectional area of the gas outlet of the hydrogen gas outlet of the burner is S2. 2. When the cross-sectional area of the gas ejection port of the oxygen gas ejection port of the burner is S3, S2 / S3 is 5 to 5.
7. The method for producing a glass base material for an optical fiber according to claim 1, wherein the glass base material is 7. 3. The method for producing a glass preform for an optical fiber according to claim 1, wherein the glass rod for core is concentrically supported on the glass pipe for cladding by a horizontal lathe. 4. A glass base material for an optical fiber, wherein a glass rod for core is inserted into a glass pipe for clad, and the glass pipe for clad is heated and softened by a burner while being decompressed to be crushed to be integrated with the glass rod for core. Of the burner, wherein a horizontal lathe device for concentrically supporting the glass rod for core with the glass pipe for clad is provided, and the sectional area of the integrated glass base material is S1, the hydrogen gas ejection port of the burner is provided. Area S2 of the gas outlet of
Is set to 1/10 to 1/30 of the above S1.