KR20040089753A - Upper sealing structure and upper sealing method of optical fiber preform manufacturing apparatus - Google Patents

Abstract

PURPOSE: Provided is an upper part sealing structure for a device of manufacturing optical fiber preform, which prevents external air from infiltrating into a reaction chamber due to voids around a shaft when optical fiber preform is manufactured by vapor-phase axial deposition method. CONSTITUTION: The upper part sealing structure is for use in a device of manufacturing optical fiber preform comprising a reaction chamber for depositing glass microparticles formed by flame reaction of charge gas on a starting member attached at the front end of a shaft, and an upper chamber for drawing and housing a porous preform for optical fiber deposited on the upper part of the reaction chamber. The upper part sealing structure includes a dividable cover(5) disposed on the opening of the top of the upper chamber, wherein the cover(5) has a central hole through which the shaft pass, a divided space(8) and an inlet(10) for clean gas. The clean gas introduced into the cover is run out toward both sides of the inner part and the outer part of the reaction chamber from the space inside of the cover along the shaft.

Description

UPPER SEALING STRUCTURE AND UPPER SEALING METHOD OF OPTICAL FIBER PREFORM MANUFACTURING APPARATUS}

The present invention relates to an optical fiber base material manufacturing apparatus for manufacturing an optical fiber base material by the VAD method, and more particularly, to an upper sealing structure and an upper sealing method of an optical fiber base material production apparatus capable of stably producing a high quality optical fiber base material.

As a manufacturing method of an optical fiber base material, the VAD method is well known. In this method, the apparatus which consists of the following structures is used, for example. In this apparatus, a core deposition burner and a clad deposition burner are provided in the reaction chamber, and a starting member is attached to the tip of the shaft and suspended in the reaction chamber. The glass (Si0 ₂ ) fine particles produced by the flame hydrolysis reaction of the source gas such as SiCl ₄ and the like are deposited on the tip of the starting member, and the starting member is rotated and pulled up with the growth of the deposit to the core layer and the cladding layer. The porous optical fiber base material which consists of these is manufactured.

In the VAD method, for example, SiCl ₄ is used as the source gas, but it generates hydrochloric acid gas as a by-product together with SiO ₂ fine particles by hydrolysis reaction in an oxyhydrogen salt. Since it is difficult to seal the reaction chamber so that hydrochloric acid gas does not leak from the reaction chamber, it is necessary to reduce the pressure in the reaction chamber rather than the external atmosphere.

As a result, if there is a gap, outside air flows into the reaction chamber from there. If the outside air is clean, there is no particular problem. However, in the work chamber in which a plurality of manufacturing apparatuses are installed, fine powder of SiO ₂ adhered in the reaction chamber flows out of the reaction chamber and floats during cleaning of the apparatus performed between batches of manufacturing. Doing. If the fine powder penetrates from the gap into the reaction chamber of the apparatus in operation, it adheres to the porous substrate being deposited and causes bubbles or foreign substances to be generated in the glass substrate obtained by transparent vitrification.

Among the gaps, the most difficult to seal is the periphery of the shaft suspended from the outside into the reaction chamber. The shaft is attached so as to be movable upward or downward while rotating by a drive system provided outside the reaction chamber. During the production of the porous base material, the fine powder of Si0 ₂ is attached to the shaft, so that the sealing structure in contact with the shaft scrapes off the fine powder of Si0 ₂ into the reaction chamber, causing bubbles or foreign matter. Therefore, the space | gap of the grade which does not contact a shaft is needed around the shaft.

In addition, the upper part of the reaction chamber has an opening so that the porous base material can be taken out, and in order to make the void around the shaft as small as possible during manufacturing, this opening is closed by an upper cover in which an opening through which the shaft penetrates is opened. have.

An object of the present invention is to provide an upper sealing structure and an upper sealing method for an optical fiber base material production apparatus in which no outside air penetrates into the reaction chamber from the voids around the shaft when the optical fiber base material is produced by the VAD method.

1 is a schematic cross-sectional view showing an example of an optical fiber base material manufacturing apparatus used in the present invention.

2 is an enlarged schematic perspective view showing an example of the upper sealing structure of the present invention;

3 is a schematic cross-sectional view of the upper sealing structure shown in FIG.

<Explanation of symbols for the main parts of the drawings>

1: reaction chamber

2: upper chamber

3: shaft

4: porous base material

5: cover

6: hole

7a, 7b: bottom part

8: space

9a, 9b: partition

10: inlet

11: pressure gauge

The upper sealing structure of the optical fiber base material manufacturing apparatus of the present invention includes a reaction chamber for depositing glass fine particles generated by a flame reaction of a raw material gas on a starting member attached to a tip end of a shaft, and a porous base material for optical fibers deposited on an upper portion of the reaction chamber. An optical fiber base material manufacturing apparatus having an upper chamber for lifting up and storing a lid, wherein a cover that can be divided is provided on an opening of an upper end of the upper chamber, and the lid has a hole through which a shaft passes through the center and an inlet for clean gas. And a structure in which the clean gas flows out from the inner space of the lid along the shaft to both the inside and the outside of the reaction chamber.

What is necessary is just to provide a pressure gauge which measures the pressure of the space in a lid in an upper sealing structure, and to set the pressure of the space in a lid higher than an external pressure. Moreover, what is necessary is just to provide a partition so that a shaft may be enclosed in the space in a cover, and the clean gas introduced may not directly contact a shaft. As already mentioned, in order to prevent the outflow of hydrochloric acid gas, the pressure in an upper chamber is set lower than the external pressure.

It is preferable to use inert gas, such as air or nitrogen, for clean gas.

The upper sealing method of the optical fiber base material manufacturing apparatus of the present invention includes a reaction chamber for depositing glass fine particles generated by a flame reaction of a raw material gas to a starting member attached to a tip end of a shaft, and a porous base material for optical fibers deposited on an upper portion of the reaction chamber. An optical fiber base material manufacturing apparatus having an upper chamber for lifting up and storing a light source, the optical fiber base material manufacturing apparatus comprising: a dividing cover having a hole through which a shaft passes in a center, a partitioned space, and an inlet for clean gas, on an opening of an upper end of the upper chamber; The pressure in the space inside the lid is higher than the pressure inside and outside the reaction chamber, and the clean gas introduced into the lid is allowed to flow out from the space inside the lid to the inside and outside of the reaction chamber along the shaft.

Although the upper sealing structure of the optical fiber base material manufacturing apparatus of this invention is demonstrated in detail based on drawing, this invention is not limited to these aspects, A various aspect is possible.

1 is a schematic cross-sectional view showing an example of an optical fiber base material manufacturing apparatus used in the present invention, wherein an upper chamber 2 is installed at an upper portion of the reaction chamber 1, and a porous substrate 4 is disposed at a lower end of the shaft 3. It is suspended. The shaft 3 is movable upwards or downwards while rotating by a drive system (not shown) provided outside. On the opening of the upper end of an upper chamber, the cover 5 which can be divided | segmented is provided.

FIG. 2 is an enlarged schematic perspective view showing an example of the upper sealing structure of the present invention, and FIG. 3 is a schematic sectional view of FIG.

The cover 5 shown is an example which consists of two parts, and the shaft 3 is inserted into the hole 6 opened in the center. A space 8 partitioned by the bottom portions 7a and 7b is provided in the lid, and partitions 9a and 9b are installed on the bottom portions 7a and 7b of the lid 5 so that the shaft 3 is provided. A columnar tube is formed so as to surround.

The clean gas introduced from the inlet 10 into the space 8 flows like an arrow along the partitions 9a and 9b, and then from the space 8 along the shaft 3 to the inside of the reaction chamber 1. It spills on both sides of the outside. Reference numeral 11 is a pressure gauge for measuring the pressure of the space in the lid.

The pressure in the space in the lid is set to a positive pressure relative to atmospheric pressure so that clean gas can flow out to the outside. At this time, the interior of the upper chamber 2 and the reaction chamber 1 are set to a negative pressure with respect to the outside, so if the pressure of the space in the lid is set to a positive pressure with respect to atmospheric pressure, the space from the chamber in the lid to the interior of the reaction chamber 1 The gas also reliably flows out. Thereby, the invasion of the microparticles | fine-particles which cause bubbles or foreign matter from the periphery of the shaft 3 from the exterior to the upper chamber and reaction chamber inside can be suppressed.

The partitions 9a and 9b provided to surround the shaft 3 prevent the rapid clean gas introduced into the lid from directly contacting the shaft 1. When a gas having a high flow rate comes into contact with the shaft 3, vibration may occur in the shaft 3, or SiO ₂ adhering to the shaft surface may be suspended and returned to the reaction chamber to cause bubbles or foreign matters. There is a case.

In this embodiment, the general VAD apparatus shown in FIG. 1 is used. The apparatus has a cylindrical upper chamber above the reaction chamber, and an upper end of the upper chamber is an opening. The shaft moving upwards or downwards while rotating from this opening part is inserted.

(First embodiment)

An upper lid having a space therein was attached to the upper chamber above the reaction chamber. The upper cover is provided with an inlet for introducing clean air, and a pressure gauge for measuring the pressure of the space in the cover is attached. A partition is provided around the shaft in the upper cover so that clean air having a high velocity introduced from the air inlet does not directly contact the shaft.

The upper cover is configured to be divided into two parts because the shaft is inserted into the reaction chamber and then attached, and the shaft is sandwiched between the shafts and fixed to each other by a band. The combined surface of the upper cover is interposed with a sealing material made of a heat-resistant elastic material or the like to prevent the introduced air from flowing out of the gap.

The top cover was attached to a VAD apparatus provided in a work chamber in which a large number of fine particles were suspended, thereby producing a porous base material. During manufacture, the amount of clean air introduced was adjusted so that the pressure in the space inside the lid was higher than the pressure outside. As a result of transparent vitrification of the prepared porous base material, no bubbles or foreign substances were found in the optical fiber base material.

(First Comparative Example)

A porous base material was prepared under the same conditions as those of the first embodiment except that the top cover, which does not have a space partitioned inside the normal interior of the reaction chamber, was attached.

As a result of transparent vitrification of the prepared porous base material, a large number of bubbles or foreign substances were found in the optical fiber base material.

The present invention can stably produce a high quality optical fiber base material by having a configuration in which outside air does not penetrate into the reaction chamber to a device for manufacturing the optical fiber base material by the VAD method.

Claims (8)

An optical fiber base material having a reaction chamber for depositing glass fine particles generated by the flame reaction of the source gas on a starting member attached to the tip of the shaft, and an upper chamber for lifting up and storing the porous base material for the optical fiber deposited on the upper part of the reaction chamber. In the manufacturing apparatus, a cover which can be divided is provided on the opening of the upper end of the upper chamber, and the cover has a hole through which the shaft passes, a partitioned space and an inlet for clean gas, and the clean gas introduced into the cover. The top sealing structure of the optical fiber base material manufacturing apparatus characterized by the structure which flows out to the inside and the exterior of a reaction chamber from the space inside a cover along the shaft. The top sealing structure according to claim 1, further comprising a manometer for measuring the pressure of the space in the lid. The top sealing structure of Claim 1 or 2 in which the pressure of the space in a lid | cover is set higher than the external pressure. The top sealing structure according to any one of claims 1 to 3, wherein a partition is provided in the space inside the cover so as to surround the shaft. The upper sealing structure according to any one of claims 1 to 4, wherein the pressure in the upper chamber is set lower than an external pressure. The top sealing structure according to any one of claims 1 to 5, wherein the clean gas is an inert gas such as air or nitrogen. An optical fiber base material having a reaction chamber for depositing glass fine particles generated by the flame reaction of the source gas on a starting member attached to the tip of the shaft, and an upper chamber for lifting up and storing the porous base material for the optical fiber deposited on the upper part of the reaction chamber. In the manufacturing apparatus, on the opening of the upper end of the upper chamber, a dividable lid having a hole through which a shaft passes through, a partitioned space, and an inlet for clean gas is provided, and the pressure in the lid is spaced inside and outside the reaction chamber. The cleaning method of the optical fiber base material manufacturing apparatus of the optical fiber base material manufacturing apparatus characterized by the above-mentioned pressure being made to flow out to the inside and outside of the reaction chamber from the space inside a cover along the shaft. The top sealing method according to claim 7, wherein a partition is provided in the space inside the cover so as to surround the shaft.