JPS6016376B2 - Manufacturing method of optical fiber material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to an improved method of manufacturing optical fiber materials.

Conventionally, as a method for manufacturing low-loss optical fiber materials,
There is a method called internal soot deposition method (MCVD method) as shown in FIG. This method moves the local heating source 2 back and forth,
A desired glass is deposited on the inner wall of the cylindrical glass tube 1, and the deposited glass has uniformity in the film thickness and the amount of added elements in the longitudinal direction on the raw material inlet side, as shown in Fig. 2. There were problems such as the low effective utilization of raw materials (approximately 50%), and the vertical diameter of the starting material cylindrical glass tube during the manufacturing process. SUMMARY OF THE INVENTION An object of the present invention is to provide an improved method for manufacturing an optical fiber material that eliminates the above-mentioned problems.

According to the study results of the present inventors, if the area immediately before the heating source is cooled, the amount of deposited fine particles such as Si02 (referred to as 5 (soot) in Fig. 1) that reacts in the gas phase and is generated increases. was discovered.

The reason for this increase in the amount of soot deposited cannot be clearly stated, but there is a general phenomenon that when particulates are present in a gas with a temperature gradient, the particulate concentration increases at locations with lower temperatures.

Even when fine particles collide with a solid wall, if the solid wall is at a lower temperature, the probability of this collision (probability of adhesion) increases. This is a phenomenon called thermal brecipitrite, and although it has been known for a long time, the established theory regarding its principle is still unclear.

In the present invention, it is considered that the probability of adhesion of soot to the inner wall of the pipe increases as the difference between the gas (soot) temperature and the inner wall of the silica/Gyp pipe increases based on the same principle.

Furthermore, according to the study results of the present inventors, by forcibly cooling not only immediately before the heating source but also immediately after the heating source, the length of the non-uniform part regarding the thickness of the deposited glass layer and the amount of added elements can be shortened. It has been found that this method has the effect of reducing the deformation of glass tubes.

The present invention has been made by taking advantage of the above phenomenon.

Next, the present invention will be explained with reference to an embodiment shown in FIG.

1 is a cylindrical glass tube; 2 is a local heating source;
A desired glass medium is deposited on the inner wall of the glass tube 1 by reciprocating the glass tube 1 several times.

3 indicates raw material gas.

41 is a cooling source that forcibly cools the area immediately before the heating source; 42 is a cooling source that forcibly cools the area immediately before the heating source;
In both cases, ring-shaped pipes are installed at intervals on the outer wall of the glass tube 1, and non-oxidizing gas such as Ar or N3C02 is blown onto the glass tube wall, or cooling water is allowed to flow through the spiral pipe for cooling. .

As described above, by heating the glass tube wall immediately in front of the heating source 2 while cooling it, the amount of deposited fine particles (soot) generated by reacting in the gas phase within the glass tube wall increases on average, and the effective use of raw materials is achieved. Utilization (yield) increases.

In addition, cooling immediately after the heating source 2 not only increases the yield, but also increases the uniformity in the longitudinal direction of the glass material for optical fibers, so a material with a long effective length can be obtained, and the starting material of the glass tube can be Since deformation is reduced, an optical fiber material with good dimensional accuracy of the core diameter can be obtained, and is extremely effective in manufacturing optical fibers. Hereinafter, embodiments of the present invention will be explained while comparing them with the conventional MCVD method.

The present invention applies not only to glasses made of the following materials, but also to glass films that can be produced by similar methods, such as Si02-B03 glass, S
It can be widely applied to i02-P205 glass, etc.

Comparative Example 1 A Sj02-Jake02 glass film was produced using the apparatus shown in FIG.

A quartz tube with an outer diameter of 20 ribs and a wall thickness of 1.5 ribs was used as the glass tube 1 as a starting material.

SIC14 and QC1 at room temperature are used as raw materials for glass synthesis.
Bubble oxygen as a carrier into 4 (each 20
0cc/min, 160cc/min), and the surplus 02 to 5
00 cc/min and introduced into the quartz tube of 1. heating source 2
While heating the glass tube to approximately 14,000C, the heating source was moved 20 times at a speed of 8/min to apply S to the inner wall of the tube.
When the i02-Kai02 film was prepared, there were about 40 areas of non-uniformity in film thickness on the raw material inlet side, and about 5 areas of non-uniformity in Ge02 concentration. Furthermore, the effective utilization of SIC14 was approximately 50%. The outer diameter of the quartz tube is approximately 30 mm before and after heating.
About 4% of stripes appeared. Comparative Example 2 One nozzle was installed behind the moving heating source 2 (42 in Fig. 3) to blow out N2 gas at a rate of 20 som/min in one direction, and while moving in synchronization with the heating source, When Sj02-G02 waists were made under the same conditions as described in Comparative Example 1, the deformation of the quartz tube became large after 10 movements.

The uneven length of the film thickness on the raw material inlet side of this material is approximately 2
On the 5th side, the non-uniform part of the 02 concentration was about 3 sides, which was improved compared to Comparative Example 1, but the effective utilization of SIC14 was about 50
%, which was the same as Comparative Example 1. Comparative Example 3 A nozzle was installed behind the heating source to blow out N2 gas in a ring shape around the quartz tube 1 at an amount of 20 pm/min.
When a Si02-W02 film was prepared under the same conditions as described in 1., it was found that the quartz tube was hardly deformed even after the heating source was moved 20 times, and it was found to be effective in preventing deformation.

However, the effective utilization of SIC14 was not improved.
Embodiment 1 of the present invention A nozzle is installed in front of the heating source (FIG. 3, 41) for blowing out N2 gas in a ring shape around the quartz tube 1 at an amount of 20 som/min.
Sj02 under the same conditions as described in Comparative Example 2.
- When a Ge02 film was created, the outer diameter of the quartz tube was reduced by only about 10% after the heating source was moved 20 times, and the uneven length of the film thickness on the raw material inlet side of this material was about 35 ribs. Although the non-uniform part of Q02 concentration was improved to about 45 kites, it was further confirmed that the effective utilization of SIC14 was about 65%, which is significantly more effective than Comparative Example 1.

Example 2 of the present invention Nozzles that blow out in a ring shape around the quartz tube 1 were installed before and after the heating source, and while blowing N2 gas to the quartz tube at an amount of 20 evening/minute, the same process as described in Comparative Example 2 was carried out. When a Si02-W02 film was prepared under the same conditions as above, there was almost no deformation of the quartz tube after the second heating source was moved, and the non-uniform part of the film thickness on the raw material inlet side was approximately 25 ribs. The non-uniform part of the snake 02 concentration is about 30, and the effective utilization of SIC14 is about 65%, which is effective for the effective utilization of raw materials as well as the uniformity of the concentration and the deformation of the outer diameter compared to Comparative Example 1. It was confirmed that

In the present invention, as explained above, by cooling immediately before the heating source, the effective utilization of the raw material of the optical fiber material is improved.

In addition to the above, thermal deformation of the quartz tube was reduced by cooling both immediately before and immediately after the heating source.
It was confirmed that the dimensional accuracy of the core and cladding was improved and that the film thickness was evenly deposited.

When using a resistance heating element as the heating element, it is desirable to use a non-oxidizing gas such as Ar or N2 in order to make the heating element less susceptible to deterioration due to oxidation.

If deterioration of the heating element due to oxidation is not a problem, air can be used as the cooling gas.

[Brief explanation of drawings]

Figure 1 is a schematic diagram showing the conventional internal sooting method, Figure 2 is a diagram showing non-uniformities in the thickness and additive concentration of the glass deposited layer in the longitudinal direction of the glass material, and Figure 3 is the method according to the present invention. It is a schematic diagram showing an internal soot application method. 1 is a glass tube, 2 is a heating source, 3 is a raw material gas, 41, 42
indicates a cooling source. O diagram O 2 diagram O wo diagram

Claims (1)

[Claims] 1. A raw material gas for glass formation is supplied into a cylindrical glass tube, and a local heating source is moved along the cylindrical glass tube to locally heat the inner wall of the cylindrical glass tube. An optical fiber material for depositing a desired glass layer, characterized in that a cooling source synchronized with the local heating source is provided immediately before the local heating source to forcibly cool the glass tube portion immediately before the local heating. manufacturing method. 2. A method for manufacturing an optical fiber material according to claim 1, characterized in that a nozzle that blows gas in a ring shape onto the outer wall of a glass tube is used as a cooling source. 3. In the method according to claim 1 or 2, a resistance heating element is used as a heating source and an Ar, a cooling source is used as a cooling source.
A method for manufacturing an optical fiber material, characterized by using a non-oxidizing gas such as N_2 and CO_2.