JPH08133776A - Production of optical fiber preform and sintering furnace - Google Patents

Abstract

PURPOSE: To provide a process for producing an optical fiber preform constituted to continuously execute sintering and subsequent cooling within the same muffle in a process for producing the optical fiber preform. CONSTITUTION: The part 2b upper than the heating means installing section of the muffle 2 installed with the heating means 3 on its outer periphery is so formed as to be made properly dividable by a shutter mechanism 4. Sintering is executed by opening this shutter mechanism 4 and inserting the perforated optical fiber preform from above at the time of sintering. The optical fiber preform 13 is pulled up to the upper part 2b of the muffle 2 and the shutter mechanism 4 is closed at the time of cooling the optical fiber preform 13 vitrified to transparent glass after the sintering. A cooling gas is then supplied from the outside into the upper part 2b of the muffle 2 to cool the optical fiber preform 13 in the muffle 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an optical fiber preform for cooling an optical fiber preform after sintering, dehydration, and sintering in a manufacturing process of the optical fiber preform, and a sintering furnace therefor. Is.

[0002]

2. Description of the Related Art Conventionally, in the manufacture of an optical fiber preform, when a soot deposit having glass particles deposited, that is, a porous optical fiber preform is sintered, dehydrated, or sintered, the porous optical fiber is used. The base material is placed in a muffle of a sintering furnace, hung down and heated, and thereby transparent glass is formed. Then, the optical fiber preform after the transparent vitrification was taken out from the sintering furnace and naturally cooled in the air outside the furnace.

[0003]

However, since the heat treatment temperature in the above sintering furnace is about 1500 to 1600 ° C., the optical fiber preform taken out of the muffle immediately after the sintering is used. Has a high surface temperature of about 1000 ° C. Therefore, an air flow such as an ascending air current is generated around the surface of the optical fiber preform, and as a result, there is a problem that foreign matter, dust, dust in the air adheres to the preform surface. The adherence of such foreign matters significantly reduces the strength of the optical fiber strand obtained from the optical fiber preform, and is a major cause of proof test (PT) fracture. Further, in natural cooling in the air, it takes a long time to decrease to a predetermined temperature, so that there is a problem that cooling efficiency is poor and improvement in productivity cannot be expected.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above conventional circumstances. First, the invention according to claim 1 is transparent by sintering a porous optical fiber preform. This is a method for producing an optical fiber preform in which vitrification is followed by forced cooling.

Next, in the invention described in claim 2, the upper part can be appropriately divided by the shutter mechanism by the heating means installation portion of the muffle having the heating means installed on the outer periphery, and the shutter is provided at the time of sintering. While the mechanism is opened, the porous optical fiber preform is inserted from above to perform sintering, while the transparent vitrified optical fiber preform is cooled after the sintering. While pulling up to the upper part of the muffle, closing the shutter mechanism, and supplying a cooling gas from the outside into the upper part of the muffle, of the optical fiber preform for cooling the optical fiber preform in the muffle. There is a manufacturing method.

According to the third aspect of the invention, a shutter mechanism for freely dividing the muffle into two parts is provided on the upper side by the heating means installation part of the muffle having the heating means installed on the outer periphery. The upper part of the muffle is located in a sintering furnace for the optical fiber preform provided with a cooling gas supply port and an exhaust port.

[0007]

In the invention described in claim 1, the cooling after sintering is forcibly performed by supplying a cooling gas or the like.
Therefore, efficient cooling is possible.

According to the second aspect of the present invention, by the action of the shutter mechanism, the sintering and the subsequent cooling are continuously performed in the same muffle. Therefore, good workability and efficient cooling are possible.

According to the third aspect of the present invention, the inside of the muffle can be appropriately divided into two by the shutter mechanism, and the upper portion of the divided muffle is provided with the cooling gas supply port and the exhaust port. It is possible to supply a cooling gas and obtain a sintering furnace having a good cooling space closed from the outside.

[0010]

1 to 2 show an embodiment of a method for producing an optical fiber preform and a sintering furnace therefor according to the present invention. In the figure, 1 is a sintering furnace, 2 is a muffle that extends in the vertical direction of the sintering furnace 1, 3 is an outer periphery of the muffle 2, and a heater installed near the upper part of the lower half side (lower part) 2a thereof. A heating mechanism such as 4 is a shutter mechanism capable of appropriately dividing the muffle 2 into two parts from a portion slightly above the portion where the heating means 3 is installed (substantially the central portion), and 5 is an upper portion 2b of the muffle 2. A cooling gas supply port opened downward, 6 is also an upper part 2b of the muffle 2.
It is an exhaust port for the cooling gas that is opened toward the upper side of.

In the sintering furnace 1, the shutter mechanism 4 has, for example, a shutter plate 4a that crosses the substantially central portion of the muffle 2. Therefore, if this shutter plate 4a is slid to the outside of the muffle 2, the shutter mechanism 4 is opened (opened), and as shown in FIG. It has the same structure as the sintering furnace. On the other hand, the shutter plate 4a
The shutter mechanism 4 is closed by sliding it to the side of the muffle 2 and crossing it, and as shown in FIG. 2, the inside of the muffle 2 is divided into upper and lower parts, and the upper part 2b becomes a closed space. When the cooling gas is supplied to the closed upper portion 2b from the supply port 5 and is exhausted from the exhaust port 6 and circulated, the sintering furnace 1 having an ideal cooling space closed from the outside is obtained. To be

Therefore, in order to carry out the method for manufacturing an optical fiber preform according to the present invention, first, the shutter plate 4a of the shutter mechanism 4 is opened and supported by the dummy rod 11 as shown in FIG. A porous optical fiber preform 12 made of a soot deposit is put in the muffle 2.
The muffle 2 is gradually hung down to the heating means installation portion. Then, the porous optical fiber preform 12 is heated by the heating means 3 from its lower end side (heating temperature = about 15).
00 to 1600 ° C). As a result, the porous optical fiber preform 12 is gradually vitrified from the lower end to gradually become the transparent optical fiber preform 13. When dehydration is also performed at the time of this sintering, a mixed gas of He and a dehydrating agent is supplied from the lower end side of the muffle 2. In this way, if all of the porous optical fiber preform 12 is made into transparent glass, the dehydration / sintering process is completed.

Thereafter, as shown in FIG. 2, the transparent vitrified optical fiber preform 13 is pulled up to the upper portion 2b in the muffle 2, and when the pulling up is completed, the shutter plate of the shutter mechanism 4 is pulled up. 4a is closed, the inside of the muffle 2 is divided into two, and the upper portion 2a is made a closed space. At the same time, the upper part 2a of this muffle 2
From the supply port 5 for the cooling gas, for example, N ₂ , Ar, H
While supplying cooling gas such as e and air, its exhaust port 6
Remove from circulation.

As a result, the upper part 2b of the muffle 2 becomes a good cooling space which is closed from the outside. Therefore, immediately after sintering, the high temperature optical fiber preform 13 whose surface temperature is still close to 1000.degree. Are effectively cooled. In this case, since the outside air does not enter the upper part 2b of the muffle 2, foreign matter, dust, dust, etc. in the air are never brought in. Also, since the cooling gas is forcibly supplied, compared to conventional natural cooling in air,
Efficient cooling is performed.

Although the shutter mechanism 4 has the shutter plate 4a in which the opening / closing portion slides, the present invention is not limited to this, and a plurality of thin plates combined like a diaphragm mechanism of a camera lens can be used. However, a shutter mechanism that opens and closes by rotating these thin plates may be used.

[0016]

As described above, according to the present invention, the following excellent effects can be obtained. (1) First, according to the method for producing an optical fiber preform according to the present invention as set forth in claim 1, the transparent optical fiber preform in a high temperature state after sintering is forcibly cooled by supplying a cooling gas or the like. Therefore, as compared with the conventional natural cooling in air, excellent cooling efficiency can be obtained, and it is expected that the cooling time is shortened and the productivity is improved thereby. Of course, if this forced cooling is performed in a closed space such as a muffle, the problem that foreign matter, dust, dust, etc. in the air adhere to the surface of the base material is fundamentally solved.

(2) Next, according to the method of manufacturing an optical fiber preform according to the present invention as defined in claim 2, the muffle in the sintering furnace is appropriately divided into two, and the sintering and subsequent sintering are performed in the same muffle. Can be continuously cooled. Therefore, the amount of movement of the optical fiber preform is minimal, and this movement can also be automated, resulting in extremely good workability. Moreover, since this cooling is performed in a closed space, there is no inflow of external air. As a result, as in the case above,
The problem that foreign matter, dust, and the like in the air adhere to the surface of the base material is fundamentally solved. Furthermore, by the forced cooling by supplying the cooling gas, superior cooling efficiency can be obtained as compared with conventional natural cooling in air, and it can be expected that the cooling time is shortened and the productivity is improved.

(3) Further, according to the sintering furnace of the optical fiber preform according to the present invention as defined in claim 3, the inside of the muffle can be easily and quickly divided into two parts by the shutter mechanism. A closed ideal space for cooling can be formed in the upper part of the muffle.
In addition, since the upper part of the muffle is provided with a cooling gas supply port and an exhaust port, cooling gas can be introduced into the upper part of the closed muffle during cooling, and efficient cooling can be performed. You can

[Brief description of drawings]

FIG. 1 is a schematic explanatory view showing a sintering step and a function of a sintering furnace in a method for manufacturing an optical fiber preform according to the present invention.

FIG. 2 is a schematic explanatory view showing a cooling step and a function of a sintering furnace in the method for producing an optical fiber preform according to the present invention.

[Explanation of symbols]

 1 Sintering Furnace 2 Muffle 2a Lower part of muffle 2b Upper part of muffle 3 Heating means 4 Shutter mechanism 4a Shutter plate 5 Supply port 6 Exhaust port 11 Dummy rod 12 Porous optical fiber base material 13 Optical fiber base material

Claims (3)

[Claims] 1. A method for producing an optical fiber preform, which comprises sintering a porous optical fiber preform to obtain transparent glass and then forcibly cooling it. 2. A muffle in which a heating means is installed on the outer periphery is arranged such that an upper portion of the heating means installation portion can be appropriately divided by a shutter mechanism, and the shutter mechanism is opened during sintering to open the porous structure. While performing the sintering by inserting the optical fiber preform from above, at the time of cooling the transparent vitrified optical fiber preform after the sintering, while pulling the optical fiber preform to the upper part of the muffle, A method of manufacturing an optical fiber preform, characterized in that the shutter mechanism is closed, and a cooling gas is externally supplied into the upper part of the muffle to cool the optical fiber preform in the muffle. 3. A shutter mechanism capable of freely dividing the muffle into two parts is provided in the upper part by the heating part installation part of the muffle in which the heating part is installed on the outer periphery, and the upper part of the muffle is provided with: A sintering furnace for an optical fiber preform, which is provided with a cooling gas supply port and an exhaust port.