JP2695556B2 - Method of manufacturing base material for optical fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical fiber preform, and more particularly to a method for manufacturing an optical fiber preform that provides an optical fiber with low transmission loss.

[0002]

2. Description of the Related Art A base material for an optical fiber is usually obtained by subjecting a silicon compound such as silicon tetrachloride to flame hydrolysis in an oxyhydrogen flame, and producing fine silica powder on a carrier such as rotating quartz glass. It is made by depositing on a porous glass base material and then making it into a transparent glass.This porous glass base material needs to be dehydrated and sintered before it becomes a transparent glass. The dehydration sintering is usually performed in the presence of chlorine gas (Cl ₂ gas) as a dehydrating agent.

Since this chlorine gas is extremely corrosive, it is enclosed in a liquefied state in a container such as a steel cylinder, but this cylinder is particularly large due to the high pressure gas control method. The thickness of the rotting margin is specified, which is 3 mm when the internal volume is 1,000 liters or less and 5 mm when the internal volume exceeds 1,000 liters.

[0004]

However, in the liquid chlorine filled in the steel container, chlorides of various heavy metals eluted in the chlorine are usually contained in concentrations of several ppb to several ppb.
Due to the ppm order of contamination, the use of such chlorine gas as a dehydrating agent for the porous glass matrix contaminates the porous glass matrix with chlorides of this heavy metal and is therefore made from it. However, the optical fiber made of the base material has a disadvantage that the transmission loss is large.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a method for producing a base material for an optical fiber which solves such disadvantages, and it contains chlorine filled in a metal container to supply chlorine contained therein. In a method for producing a base material for an optical fiber by subjecting a porous glass base material to dehydration sintering in an atmosphere and then making it into a transparent glass, the residual chlorine content in the metal container is measured.
3 kg for containers with an internal volume of 1,000 liters or less
5kg for items with an internal volume of 1,000 liters or more
It is characterized in that the weight is managed as described above .

That is, the present inventors have conducted various studies as a result of various studies on a method for solving the disadvantage due to the incorporation of heavy metal chloride in dehydration sintering using chlorine of the porous glass base material,
The vapor pressure of heavy metal chloride is 1 / 1,000 compared to the vapor pressure of chlorine.
From the following, chlorine in the container is virtually free of heavy metal chlorides immediately after the start of use, and this heavy metal chloride is mixed with chlorine gas by using liquefied chlorine in the container due to the use of chlorine gas. found that but is reduced heavy metal chlorides contained in the accordingly Yuku been gradually concentrated, heavy metal chlorides is <br/> cormorants I is mixed into chlorine when exceeding a certain limit Therefore, in order to prevent the mixing of heavy metal chloride into this chlorine, the chlorine remaining amount in the container should be 1,000 L or less.
About 3kg or more, with an internal volume of 1,000 liters or more
As a result, the present invention was completed after confirming that the weight should be controlled to 5 kg or more . This will be described in more detail below.

[0007]

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing an optical fiber over preform capable of producing low optical Fiber transmission loss, which chlorine was made of such as an external method porous glass preform When dehydrating and sintering in the presence of, the residual chlorine content of the chlorine filled in the metal container is calculated as follows :
For 000 liters or less, 3 kg or more, internal volume 1,
For 000 liters or more, the weight is controlled to 5 kg or more .

The production of low optical fiber preforms according to the present invention involves flame hydrolysis of a silicon compound such as silicon tetrachloride in an oxyhydrogen flame, and the fine silica powder generated therein is used for spinning quartz glass or the like. A porous glass base material is made by depositing it on a carrier, and this porous glass base material is dehydrated and sintered in a chlorine-containing atmosphere in which a chlorine gas filled in a metal container is supplied, and then this is made into a transparent glass. It is done by doing.

However, in this dehydration-sintering process, the chlorine gas used here is filled in a metal container such as a steel cylinder, and this chlorine gas is highly corrosive. As a result, the metal container is eroded, and as a result, this chlorine gas contains chlorides of heavy metals from several ppb to several ppm.
When the heavy metal chloride is mixed in the chlorine gas used for dehydration sintering, the porous glass preform is contaminated with the heavy metal chloride, and this is mixed in the optical fiber preform. If this is done, there is a risk that the transmission loss of the optical fiber to be manufactured will be large.

Therefore, when using this chlorine gas, it is necessary to prevent this heavy metal chloride from mixing into the chlorine gas. However, the vapor pressure of the heavy metal chloride is not the vapor pressure of chlorine.
Since it is 1 / 1,000 or less, mixing of this heavy metal chloride into chlorine reduces the liquefied chlorine in the container by using chlorine gas, and the heavy metal chloride contained in this is gradually concentrated, which is since it has been found to occur when exceeding the limit, the amount of chlorine remaining in the container,
3 kg for containers with an internal volume of 1,000 liters or less
5kg for items with an internal volume of 1,000 liters or more
If the weight is controlled as described above, this heavy metal chloride can be prevented from being mixed with chlorine.

Therefore, in the present invention, the amount of chlorine remaining in the container is set to be in the above range or more in order to prevent the incorporation of the heavy metal chloride into chlorine. Control of the amount of chlorine remaining in the container is required. bur has yo be performed by measuring a method or weight measuring pressure, in the case of pressure measurements of this that this pressure is affected by the temperature of the surrounding, also being affected by the evaporation rate of the chlorine gas From
Even if the use of chlorine is stopped at a predetermined pressure, the amount of liquefied chlorine actually remaining in the container varies widely.

Therefore, it is necessary to control the amount of chlorine remaining in this container by weight.
3 kg for containers with an internal volume of 1,000 liters or less
As mentioned above, it is preferable to set the weight to 5 kg or more for the one having an inner volume of 1,000 liters or more. In this way, the chlorine gas heavy metal chlorides from the container will not be mixed, so the light produced in this way fiber - drawing-out the resulting optical fiber from the preform - the loss resistance of 0.35 dB / miles
The following is given, with the advantage that it is not particularly large.

[0013]

Next, examples of the present invention and comparative examples will be described. Examples, Comparative Examples VAD method 100 mφ diameter, 1,000 mm length, density 0.25 g /
We made a porous glass base material for the core of cm ³ and made it from steel.
Chlorine gas filled in a 50 kg cylinder was placed at 3 g / min, and helium gas was fed at 2 g / min into a reaction furnace at 1,200 ° C.
After dehydration and sintering at 1, transparent glass was formed at 1,500 ° C to produce a quartz glass rod for core.

Then, the quartz glass rod for the core is covered with a synthetic quartz tube for the clad, and a preform for an optical fiber is prepared by the lot-incubation method, and then drawn at 1,900 ° C.
A 125 μm optical fiber was produced and the wavelength of this product was 1.3 μm.
The transfer loss at was measured. However, in this case, the amount of residual chlorine in the steel cylinder is controlled by weight, and the amount is set to 7 kg, 4 kg, 3 kg (Examples 1, 2, 3) or 0.5 kg, 0.3 kg (Comparative Examples 1, 2). Then, the transmission loss of the obtained optical fiber is as shown in Table 1,
In the case of the example, it was stable at 0.35 to 0.36 dB / km,
In the case of the comparative example, since the heavy metal chloride was mixed, the transmission loss was as high as 0.41 to 0.57 dB / km.

[0015]

[Table 1]

[0016]

As described above, according to the present invention, the porous glass base material is dehydrated and sintered in the chlorine-containing atmosphere in which chlorine is filled from the metal container, and then the glass material is transparentized into an optical fiber. -In the method of manufacturing a base metal for a container, the amount of residual chlorine in the metal container is determined by the internal volume of the container being 1,000 liters.
3kg or more and 1,000 liters in internal volume
For items over 5kg, we will control the weight to over 5kg ,
This without heavy metal chlorides that are present in the container is a porous glass preform no longer be incorporated into the chlorine gas is contaminated with heavy metals chlorides According, therefore now fiber-optic preform made transmission loss of the optical full <br/> Aiba chromatography obtained by drawing the stable to be able to suppress low,
Advantage is provided that can be stably obtained a good optical fiber over quality.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hideo Hirasawa, 2-13-1, Isobe, Annaka-shi, Gunma Shin-Etsu Chemical Co., Ltd., Isobe factory (72) Inventor, Kazuo Kamiya 2--13, Isobe, Annaka-shi, Gunma No. 1 Shin-Etsu Chemical Co., Ltd. Isobe factory (56) Reference JP-A-2-192426 (JP, A) JP-A-62-113717 (JP, A)

Claims (1)

(57) [Claims] 1. A method for producing an optical fiber preform by dehydrating and sintering a porous glass preform in a chlorine-containing atmosphere in which chlorine is filled from a metal container and then making the glass into transparent glass. , The residual chlorine amount in the metal container
3 kg for containers with an internal volume of 1,000 liters or less
5kg for items with an internal volume of 1,000 liters or more
A method for manufacturing a base material for an optical fiber, characterized in that the weight is controlled as described above.