JPS63182234A - Production of optical fiber parent material - Google Patents

Abstract

PURPOSE:To produce an optical fiber parent material stably and at high yield without causing foam generation nor stripping by controlling partly the surface temp. of deposit of fine glass particles formed at the external periphery of a cylindrical starting material. CONSTITUTION:An ejecting port 4 for cooling gas is provided to a foot of a burner 3 for synthesizing fine glass particles. Measurement of temp. of the part A where the fine glass particles begin to deposit to the rod 1 of the starting glass and the part B near the boundary between the rod 1 and the burner are executed with a temp. measuring sensor 51. Then, the flow rate of the cooling gas from an ejecting port 4 is increased in accordance with the result of this temp. measurement if it is higher than specified temp., or it is decreased if it is lower than the specified temp. Further, the part A is heated if necessary by providing another heat source to the foot of the ejecting port 4, whereby the temp. of the parts A, B, are controlled by cooling the part B. It is preferred that the temp. difference between the part A and the part B is within 200 deg.C and the temp. of the part A is >=600 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to the production of optical fiber preforms, and more particularly to a novel method capable of producing optical fiber preforms stably and with high yield.

[Conventional technology]

As a method for manufacturing optical fiber base material, Japanese Patent Application Laid-Open No. 48-73
The so-called 1-external attachment method, as described in Japanese Patent No. 522, involves hydrolyzing a glass raw material such as SIC T4 around a solid quartz rod as a starting material. After depositing the glass particles such as 5i02 produced by this process to form a composite consisting of the starting material and the glass particle deposit, the composite is heat-treated in a high-temperature furnace to deposit the glass particles. In this method, a transparent glass layer is further formed on the outer periphery of the starting material by sintering the body part to obtain an optical fiber preform.

[Problem that the invention seeks to solve]

When obtaining a transparent glass body as a base material for an optical fiber by the above conventional method, bubbles may be generated on the interface between the starting material and the outer glass layer during sintering and transparentization, or bubbles may be generated on the interface between the starting material and the outer glass layer. There were problems such as peeling from the layer.

The present invention solves these problems and allows stable and stable production of a glass base material by sintering and making transparent a composite consisting of a starting material gaff slot and a glass fine particle deposit without generating bubbles or peeling. The aim is to provide a new method that can be manufactured with high yield.

[Means for Solving the Problems] The present invention provides a material for synthesizing glass fine particles from near one end of a substantially cylindrical starting material that rotates about its own axis, onto the outer periphery of the starting material. The glass particles generated by supplying the glass raw material into the flame of the burner begin to be deposited, and by moving the burner relatively parallel to the axis of the starting material, the glass particle deposit body is deposited on the starting material. This method of manufacturing an optical fiber base material is characterized by partially controlling the surface temperature of the glass particle deposit in the method of forming it on the outer periphery. It is something that can be solved.

In a particularly preferred embodiment of the present invention, the temperature difference between the part where the glass particulate deposit starts to be deposited on the starting rod and the part of the glass particulate deposit near the interface with the starting rod is within 200°C, and The above-mentioned method includes controlling the temperature so that the former temperature is 600'C or higher.

Also particularly preferred is the above method in which a cooling gas is used as a means for controlling the surface temperature of the glass particle deposit. At this time, it is preferable to use an inert gas whose temperature is below room temperature as the cooling gas.

The various problems described above are caused by the fact that the bulk density of the glass fine particle deposit varies rapidly locally, especially near the starting glass rod surface, resulting in non-uniformity during sintering and transparency. This is thought to be because the contraction progresses. Figure 2 shows the bulk density distribution in the radial direction of the glass particle deposit, and the one indicated by the broken line is the result of the conventional method, in which the bulk density rapidly increases near the starting rod, and then the outer periphery. It can be seen that there is a sudden drop in direction.

Therefore, the present inventors controlled the bulk density of the glass fine particle deposit near the interface between the glass rod and the glass fine particle deposit in the production of a composite of a glass rod and glass fine particle deposit, which is a base material for an optical fiber. We came up with the idea of preventing the problems of bubbles generated during sintering and transparency of the glass particle deposit and peeling of the starting rod from the outer glass layer by making the glass particle uniform.

That is, an experimental equation such as the following equation (1) has been found between the bulk density and the deposition temperature, and it is understood that the bulk density generally increases as the temperature increases.

Here, P: Bulk density 9/-3 R: Gas constant cul/-mol T: Absolute temperature Therefore, in the production of a composite of a glass rod/glass fine particle deposit, the present invention aims to connect the starting gaff slot of the glass fine particle body with the glass By cooling the part B near the interface of the fine particle deposit using gas, the bulk density, which had risen rapidly in the conventional method as shown at the mouth in Figure 2, can be reduced, and the bulk density in this part can be reduced. This reduces the sudden difference in bulk density and makes the bulk density uniform. Furthermore, if the starting rod is cooled too much by the cooling gas, the starting rod may be heated in advance using a separately provided heat source. Such adjustment is possible by monitoring the temperature, and the bulk density can be made uniform precisely.

Hereinafter, the present invention will be specifically described with reference to the drawings. FIG. 1 is a schematic diagram of the present invention, in which a cooling gas outlet 4 is provided at the bottom of a burner 5 for synthesizing glass fine particles.

In addition, the temperature measurement sensor 51 measures the temperature of a portion A where glass fine particles begin to accumulate on the starting glass rod 1 and a portion B near the interface between the glass fine particles and the starting rod 1. Based on the result of this temperature measurement, the flow rate of the cooling gas from the cooling gas outlet 4 is increased if the temperature is higher than a predetermined temperature. When the temperature is lower than a predetermined temperature, the amount is reduced. Further, as mentioned above, another heat source is provided below the cooling gas outlet 4 to heat the part A in FIG. 1 if necessary and cool the part B to control the temperature of both parts. Bye.

In the present invention, the temperature difference between a portion A where the glass fine particles begin to accumulate on the starting rod and a portion B near the interface of the glass fine particles with the starting rod is within 200°C;
The temperature is preferably 600°C or higher. This is A
If the temperature of A and B does not reach 600°C, the growth of the glass fine particle deposit becomes unstable and it becomes very easy to break.If the temperature difference between A and B exceeds 200°C, it will become sintered and transparent. This is because the proportion of remaining bubbles becomes extremely large.

Examples of the cooling gas used in the present invention include N2,
An inert gas such as Hew Ar is preferred, and the temperature thereof is preferably room temperature or lower.

Note that the ratio of the cooling gas flow rate to the raw material flow rate and its absolute amount vary depending on the burner position and other conditions, so
- Although it cannot be generally limited, the effect on the raw material flow rate is within a negligible range, and the effects of the present invention can be fully guaranteed.

By doing as described above, the bulk density of the glass fine particles near the interface with the rod can be locally changed by the effect of the cooling gas, and the bulk density can be made uniform in the radial direction. As a result, shrinkage progresses more uniformly during sintering and transparency, so problems such as remaining bubbles and misalignment between the starting rod and the outer glass body can be successfully solved.

The solid line A in FIG. 2 is a curve showing the bulk density distribution in the radial direction of the glass fine particle deposit body produced according to the present invention,
Compared to the mouth curve created by the conventional method, the curve of the mouth is very uniform, which clearly shows the effect of the present invention. The shaded area in the figure represents the starting rod.

〔Example〕

Example 1 In the configuration shown in FIG. 1, an optical fiber preform was manufactured according to the present invention. A quartz rod with an outer diameter of 15 m was used as the starting rod. The burner for glass particle synthesis uses a concentric burner, and the burner is charged with 5 liters of raw material, fuel, and auxiliary gas.
iC4600cc/min, H240t/min, 0,251/
The glass rod
A composite of glass particulate deposits was manufactured.

At this time, while measuring the temperature, He was flown through the cooling gas outlet for approximately 517 minutes. At this time, near the interface B
The temperature of is 8501:, the temperature near the rod surface A is 730
It was ℃.

The composite of the present invention obtained above was heated at a temperature of 1650°C.
Sintered and made transparent in e atmosphere. A total of 5 composites were obtained and made transparent in the same manner, and there were no residual bubbles or peeling between the gaff slot and the outer glass layer, and the transparentization was very successful.

Comparative Example 1 An optical fiber base material was manufactured under the same conditions as in Example 1 except that the cooling gas was not flowed.
The temperature near the interface B was about 900°C, and the temperature near the rod surface was about 680'C, a difference of more than 200°C. When the obtained composite was sintered in the same manner as in Example 1, no cracks occurred, but air bubbles remained at the starting rod interface over the entire length.

Comparative Example 2 Under the same conditions as in Example 1 above, except that the flow rate of 5iCt4 was changed to 1 t/min and the cooling gas was not flowed,
The production of the optical fiber base material was carried out twice. In one of these cases, the deposition surface began to deform during the deposition of glass particles, and about 1
Cracks appeared after some time. In addition, in the other case, cracks occurred during sintering. Under these manufacturing conditions, the temperature near the interface B is approximately 750°C, and the temperature near the rod surface A is 570°C.
Although the temperature difference between the two was within 200°C, the temperature near the rod surface did not reach 600°C.

From the results of the above Examples and Comparative Examples, it is possible to partially control the surface temperature of the glass particle deposit deposited on the starting rod, and in particular, for this control, a cooling gas is used to adjust the temperature near the starting rod surface and the temperature of the rod. The temperature difference near the interface of
℃ or less, and the temperature near the rod surface is 600℃ or higher, it is possible to form a deposited body without cracking, and also to avoid peeling of the outer glass layer or remaining bubbles during subsequent sintering. It can be seen that a glass base material with no carbon fiber can be obtained.

〔Effect of the invention〕

As explained above, the present invention makes it possible to manufacture a composite consisting of a starting glass rod and a glass fine particle deposit with a uniform bulk density distribution in the radial direction. It is also possible to prevent the outer glass layer from peeling off during the sintering process of the glass body and bubbles remaining in the glass body. Therefore, the present invention improves the manufacturing yield of optical fiber preforms, thereby making it possible to manufacture high-quality preforms at low cost.
This is a manufacturing method with great economic and quality effects.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view illustrating the implementation order of the present invention, @
FIG. 2 is a diagram showing the bulk density distribution in the radial direction of the glass fine particle deposit body manufactured by the present invention or the conventional method.

Claims (5)

[Claims] (1) From near one end of a substantially cylindrical starting material that is rotating about its own axis, onto the outer periphery of the starting material,
Glass particles generated by supplying a glass raw material into the flame of a burner for glass particle synthesis are started to be deposited, and the burner is moved relatively parallel to the axis of the starting material, thereby starting a glass particle deposit body. A method for manufacturing an optical fiber base material, characterized in that the surface temperature of the glass fine particle deposit is partially controlled in the method of forming the glass fine particle deposit on the outer periphery of the material. (2) The temperature difference between the part where the glass particulate deposit starts to accumulate on the starting rod and the part of the glass particulate deposit near the interface with the starting rod is within 200°C, and the temperature of the former is 600°C or more. A method for manufacturing an optical fiber preform according to claim 1, wherein the temperature is controlled so that the following is achieved. (3) A method for manufacturing an optical fiber preform according to claim 1 or 2, in which a cooling gas is used as a means for controlling the surface temperature of the glass particle deposit. (4) The method for manufacturing an optical fiber preform according to claim 3, wherein the cooling gas is an inert gas. (5) The method for manufacturing an optical fiber preform according to claim 3, wherein the temperature of the cooling gas is room temperature or lower.