JPH05116977A - Production of optical fiber base material - Google Patents

Abstract

PURPOSE:To lower the cooling rate of soot and to lessen the generation of its cracks in a VAD method, etc., by stopping the combustion of a combustion gas after the end of the synthesis of the soot and decreasing the flow rate of the gases to be introduced into a reactor. CONSTITUTION:The outdoor air is introduced into the reactor 1 and while the gases are discharged from, for example, a discharge pipe 3, glass raw materials, etc., are flame hydrolyzed or oxidized to form fine glass particles. These fine particles are stuck and deposited on a supporting rod 5, by which the optical fiber base material (soot) A is produced. For example, an automatic valve 6 is provided on the above-mentioned discharge pipe 3 in the above- mentioned VAD method. The discharge rate of the gases is controlled by closing the above-mentioned valve 6 after the end of the synthesis of the soot A. As a result, the amt. of the gases in contact with the soot A is decreased and the cooling rate is lowered, by which the cracking of the soot A is substantially prevented.

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 a preform for optical fibers, which is suitable for producing a porous glass preform for optical fibers by a soot forming method.

[0002]

2. Description of the Related Art The VAD method is one of the methods for producing a porous glass preform for optical fibers. In the VAD method, as shown in FIG. 3, a gas such as outside air is flown into the reaction container 1 through an inflow port 2 and is discharged to the outside of the reaction container 1 through an exhaust pipe 3 while the inside of the reaction container 1 is discharged. Burning bar
A combustion gas and a glass raw material are ejected from Na-4, and the combustion gas is burned to cause a flame hydrolysis reaction or an oxidation reaction of the glass raw material to generate glass fine particles, which are supported by a supporting rod 5 made of quartz glass or the like. The porous glass base material (soot) A is synthesized by adhering to and depositing on the.

[0003]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In method D, when the synthesis of soot A is completed, combustion of combustion gas is stopped, but since exhaust is continued, the gas such as the outside air flowing into the reaction vessel 1 at that time is discharged. To A
The surface temperature of the soot A drops sharply as shown in FIG. However, since the soot A has a partially different density, when it is rapidly cooled like the gas, the soot A has a partially different shrinkage rate, which causes cracks in the soot A. There was a lot of things.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a glass preform for optical fibers, which prevents the soot from being cooled rapidly after the completion of soot synthesis and reduces the occurrence of cracks. Especially.

[0005]

[Means for Solving the Problems] The inventors of the present invention have made extensive studies to solve the above problems. As an example of this solution, it was considered to provide a valve on the inlet side and close the valve after the synthesis of the glass base material to reduce the inflow rate itself. However, in such a case, a negative pressure is generated in the reaction vessel, and there is a possibility that foreign matter may adhere to the synthesized glass base material. Therefore, the present invention was developed with a focus on reducing the amount of gas discharged from the reaction vessel 1 after completion of soot synthesis.

That is, according to the method for producing a glass preform for optical fibers of the present invention, as shown in FIG. 1, while the gas is introduced into the reaction vessel 1 from the outside and is discharged, the combustion gas is generated in the reaction vessel 1. In a method for producing a glass fiber by subjecting a glass raw material to a flame hydrolysis reaction or an oxidation reaction to produce glass fine particles, which are attached to and deposited on the supporting rod 5 to produce the optical fiber preform A. After stopping, the flow rate of the gas discharged from the reaction container 1 is reduced.

[0007]

In the method for producing a glass base material for an optical fiber of the present invention, when the combustion of combustion gas is stopped after the synthesis of soot A is completed, for example, an automatic valve provided in the exhaust pipe 3 as shown in FIG. Since 6 is closed to reduce the flow rate of the discharged gas, the flow rate of the gas flowing from the inflow port 2 is decreased, and as a result,
The amount of gas that directly hits the soot A decreases, the cooling rate of the soot A becomes slower, and the soot A is less likely to be cracked.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1 showing an example of a manufacturing apparatus for carrying out the method for manufacturing a glass base material for an optical fiber of the present invention, 1 is a reaction container for manufacturing the optical fiber base material, and 2 is a gas from the outside. Inlet 3 for inflow, exhaust pipe 3 for discharging gas in the reaction container 1, 4 combustion burner with combustion port 4a arranged in the reaction container 1, 5 generated in the reaction container 1 It is a support rod for adhering and depositing the glass particles. As these, existing ones and those improved for the present invention are used.

Reference numeral 6 in FIG. 1 denotes an automatic valve provided in the middle of the exhaust pipe 3. This automatic valve 6 automatically reduces the flow rate of the gas discharged from the reaction vessel 1, and it is automatically performed when the ejection of the combustion gas from the combustion burner-4 is stopped. I am doing it.

A is a soot such as a porous glass base material formed by depositing the glass particles on the support rod 5.

Using the apparatus for manufacturing a glass preform for optical fibers shown in FIG. 1, the discharge of gas was stopped and the inflow of gas from the outside was caused to occur to synthesize soot A. The surface temperature of the soot after the combustion was stopped is shown in FIG. As is clear from the figure, the soot cooling rate is slower in the present invention than in FIG. 4 showing the surface temperature change of the soot obtained by the conventional manufacturing method. Although only the VAD method is described in the above-mentioned embodiment, the present invention can be applied to other methods, for example, an external attachment method (OVD method).

[0012]

According to the method for producing a glass base material for an optical fiber of the present invention, the soot A is not rapidly cooled even if the combustion gas is stopped after the synthesis of the soot A is completed. , The occurrence of cracks is greatly reduced.

[Brief description of drawings]

FIG. 1 is an explanatory view of a method for manufacturing a glass base material for an optical fiber according to the present invention.

FIG. 2 is an explanatory diagram of a soot surface temperature in the method for producing a glass base material for an optical fiber according to the present invention.

FIG. 3 is an explanatory view of a conventional method for manufacturing a glass preform for optical fibers.

FIG. 4 is an explanatory diagram of a soot surface temperature in a conventional method for manufacturing a glass base material for an optical fiber.

[Explanation of symbols]

 1 Reaction Vessel 5 Support Rod A Glass Fiber Preform (Soot)

Claims (1)

[Claims] 1. A glass is produced by injecting a gas into the reaction vessel 1 from the outside and discharging the gas while burning a combustion gas in the reaction vessel 1 to cause a flame hydrolysis reaction or an oxidation reaction of a glass raw material. Generates fine particles and supports them 5
In the method for producing the optical fiber preform A by adhering and depositing it on the optical fiber, the flow rate of the gas discharged from the reaction vessel 1 is reduced after the combustion of the combustion gas is stopped. Manufacturing method of base material.