JPH05270851A - Production of optical fiber preform - Google Patents

Abstract

PURPOSE:To produce the optical fiber preform having characteristics stable in an axial direction by generating always stable air flow within a deposition box regardless of the growing degree of soot. CONSTITUTION:The dummy soot 3 having the shape meeting the shape of the deposited and grown soot is mounted into a target 2 and glass particulates thereafter are deposited on the target within the deposition box to grow the soot 1, by which always the stable air flow is formed within the deposition box regardless of the degrees of the growth of the soot.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an optical fiber preform by a CVD method such as a VAD method or an external attachment method, and more particularly to improvement of a soot (glass fine particle) deposition step in the process.

[0002]

2. Description of the Related Art When an optical fiber preform is manufactured by a CVD method such as a VAD method or an external attachment method, an oxyhydrogen flame is generated from a burner and a raw material gas of glass such as silicon tetrachloride and a dopant material are contained therein. A gas is sent in to generate fine glass particles (fine particles of silicon dioxide) by a hydrolysis reaction, and these are deposited on a target to form a columnar porous soot. Then, by heating this porous soot, OH groups are removed (dehydration) and transparent vitrification (sintering) is performed. In this way, a transparent glass preform is produced, and this is melted and drawn and spun to form a thin optical fiber.

Conventionally, this deposition process is as shown in FIG.
In order to avoid exposure of the OH group or impurities to the outside air, the deposition box 5 is shielded from the outside air. That is, the glass raw material gas is introduced into the oxyhydrogen flame of the burner 4 to generate glass fine particles,
This adheres to the lower end of the target 2, and the soot 1 accumulates and grows. At this time, when the target 2 is rotated and pulled up, the soot 1 is attached to the lower end of the target 2.
Will be deposited and grown in a columnar shape. The deposition box 5 is arranged so as to cover the periphery of the soot 1 and the burner 4. The deposition box 5 includes an inlet-side opening 6 and an outlet-side opening 7, and a scrubber (not shown) is arranged in the outlet-side opening 7 to suck the air in the deposition box 5. A rectifier (not shown) or the like is arranged in the inlet-side opening 6 so that the flow of air from the inlet-side opening 6 to the outlet-side opening 7 is regulated as much as possible. Above the deposition box 5, there is an opening 8 for raising the target 2 and the soot 1.
Is provided.

In this way, the deposition is performed in the deposition box 5, and as shown in FIGS.
Are sequentially grown to obtain a soot 1 having a required size.

[0005]

However, in the conventional deposition process, the air flow in the deposition box 5 changes as the deposition of soot progresses, and therefore the physical flow in the axial direction of the optical fiber preform is physically increased. However, there is a problem in that there are various fluctuations and optical fluctuations. That is, suit 1
6, the air in the center and above passes through the periphery of the thin target 2, so that the air flows from the inlet side opening 6 toward the outlet side opening 7 with almost no obstruction. When suit 1 grows a little, it becomes like FIG. In FIG. 7, the grown soot 1 blocks the flow of air near the center, but the upper air flows unhindered because there is only the target 2 in that part. When the soot 1 has grown considerably, it looks like FIG. 8, and most of the air flow is blocked by this grown soot 1. Thus, since the air flow changes at each time point, the deposition state changes with time, and as a result, the optical characteristics of the soot 1 and the transparent glass preform made therefrom change axially. Will end up.

In view of the above, the present invention makes it possible to produce an optical fiber preform having stable characteristics in the axial direction by always generating a stable air flow in the deposition box regardless of the growth degree of soot. It is an object of the present invention to provide a method of manufacturing an optical fiber preform that can be performed.

[0007]

In order to achieve the above object, in the method of manufacturing an optical fiber preform according to the present invention, a dummy soot having a shape corresponding to the shape of the deposited / grown soot is attached to a target. The feature is that glass particles are deposited on the target in the deposition box to grow soot. Since the dummy soot corresponding to the shape of the soot is attached to the target, the air flow in the deposition box is affected by the dummy soot even when the soot is not grown yet and is small. Since this dummy soot has the same shape as the grown soot, even when the soot is small, it can influence the air flow as when the soot grows large. Therefore, the influence on the air flow is the same regardless of whether the soot is small or large, and regardless of the growth degree of the soot, the same air flow can always be obtained in the deposition box. As a result, it is possible to prevent the optical characteristics of the soot (optical fiber preform) from changing in the axial direction due to the temporal change of the deposition state, and the optical fiber preform having stable characteristics in the axial direction. Can be easily manufactured.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows an embodiment of the present invention. As shown in this figure, a dummy soot 3 having an outer diameter similar to that of the deposited soot 1 is attached to a target 2. Such a dummy suit 3
On the target 2, and then glass particles are deposited on the lower end of the target 2 by the VAD method to form the soot 1.
Grow.

That is, the soot 1 is initially small as shown in FIG. 2, and then gradually grows to become as shown in FIGS. When suit 1 is small, it looks like Fig. 2, but
At this time, since the dummy soot 3 provided close to the soot 1 is located inside the deposition box 5, the air flow above the soot 1 hits the dummy soot 3 and is affected by this. Further, when the soot 1 has grown to some extent, it becomes as shown in FIG. 3, and the dummy soot 3 close to the soot 1 also becomes an obstacle to the air flow at this time. Suit 1
4 grows significantly, the dummy soot 3 is in a state of protruding from the upper opening 8 to the outside as shown in FIG. At this time, the flowing air becomes blocked by the grown soot 1.

Therefore, regarding the influence of the soot 1 and the dummy soot 3 on the air flow in the deposition box 5, the influence of the dummy soot 3 is larger when the soot 1 is small, but the influence of the soot 1 is larger when the soot 1 is larger. Becomes larger, the influence of the dummy suit 3 becomes smaller,
Can be said. In other words, whether suit 1 is small or large,
The effect on the air flow combined with the dummy soot 3 does not change much. Therefore, regardless of the growth degree of the soot 1, the same air flow can be always generated in the deposition box 5. As a result, the deposition state does not change much when the soot 1 is small or large, the optical characteristics of the soot 1 can be stabilized in the axial direction, and the optical fiber preform having the stable characteristics in the axial direction is obtained. Can be easily manufactured.

It should be noted that the dummy soot 3 may have a solid cylindrical shape or a hollow and umbrella-like shape, and its outer shape may generally correspond to the final outer shape of the deposited soot 1. However, it is desirable to obtain the optimum shape by experiments.

[0012]

As described above, according to the method of manufacturing an optical fiber preform of the present invention, even if the soot grows sequentially, the same air flow is always generated in the deposition box regardless of the growth degree. Can be As a result, it is possible to prevent the deposition state from changing so much when the soot is small or large, to stabilize the optical characteristics of the soot in the axial direction, and to provide a light having stable characteristics in the axial direction. The fiber preform can be easily manufactured.

[Brief description of drawings]

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

FIG. 2 is a cross-sectional view showing one process of deposition in the example.

FIG. 3 is a cross-sectional view showing the next process of deposition in the example.

FIG. 4 is a cross-sectional view showing a further step of the deposition in the example.

FIG. 5 is a schematic diagram of a conventional example.

FIG. 6 is a cross-sectional view showing one process of deposition in the conventional example.

FIG. 7 is a cross-sectional view showing the next process of deposition in the example.

FIG. 8 is a cross-sectional view showing a further step of the deposition in the example.

[Explanation of symbols]

 1 Soot 2 Target 3 Dummy soot 4 Burner 5 Deposition box 6 Inlet side opening 7 Outlet side opening 8 Upper opening

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koichi Takahashi 1440 Rokuzaki, Sakura City, Chiba Prefecture Fujikura Electric Wire Co., Ltd. Sakura Factory

Claims (1)

[Claims] 1. A dummy soot having a shape corresponding to the shape of the soot expected after growth is attached to the target, and then glass fine particles are deposited on the target in the deposition box to grow the soot. Optical fiber preform manufacturing method.