JPS59455B2 - Method for manufacturing doped silica glass - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing doped silica glass of high purity and a controlled refractive index used for optical glass fibers and the like.

Doped silica glass, which is mainly composed of silica and contains small amounts of other metal oxides, is seen as a promising material for optical transmission glass fibers due to its low optical loss and good controllability of refractive index. .

Conventionally, doped silica glass has been disclosed in Japanese Unexamined Patent Application Publication No. 49-19970.
As shown in No. 9, halides such as silicon tetrachloride and germanium tetrachloride are used as starting materials, and these are converted into oxides in an oxidizing high-temperature gas and sintered.
It is known to be manufactured by molding this and heating it again to melt and vitrify it.

In this case, the molded product must be heated again, which makes the process complicated and divided into two.
During this time, there is a drawback that light loss increases due to contamination. Another method for synthesizing doped silica is to directly vitrify it using a vapor component that can be converted into an oxide to obtain a glass lump. In this case, the process is simple and purity can be easily maintained. However, for vitrification, approximately 15
A high temperature of 00° C. or higher is required, which increases the vapor pressure of the oxide in the glass composition, making it difficult to perform appropriate doping. The present invention eliminates these drawbacks and uses a simple and easy process to maintain high purity of the glass and easily control the dopant concentration distribution of desired metal oxides. It is characterized by sintering and vitrifying oxide fine powder in a single process, and its purpose is to easily obtain doped silica glass with a controlled refractive index and low optical loss. .

In the present invention, a mixed oxide fine powder having a desired glass component composition is formed around the heated heating element, and in particular, mixed oxide fine powder having a desired glass component composition is reacted with an oxidizing high temperature gas. A mixed oxide fine powder with a glass component composition produced by the reaction between a gas mixture with a composition such as that produced by the reaction with an oxidizing high-temperature gas is attached, and vitrification is performed from the adjacent part by heating with a rod-shaped heating element. According to this method, the glass component can be sintered at a relatively low temperature, preventing vaporization, and at the same time, it can be vitrified by successive heating and melting from the inside, so there is no loss of components and the glass can be formed. This is something that can be further developed.

Usually, there are various types of doped silica glass depending on the type of dopant, but using silica glass doped with 15 weight percent germania as an example, the difficulties in manufacturing it are as follows. .

Figure 1 shows germania (GeO2) and boron oxide (B2).
This is the vapor pressure curve of O3) at high temperature (see Samsonov, ed., Oxide Handbook).

As can be seen from this figure, considerable vaporization of GeO2 occurs at temperatures above about 1150)C. That is, above this temperature GeO2
Maintaining this will result in substantial defects. Therefore, the formation of germanium oxide and its deposition on the starting material must occur at temperatures below about 1150°C. On the other hand, the above 85% S
It is known that vitrification of iO2-15%GeO2 occurs at temperatures above about 1400C.

In view of the fact that the properties of such compositional components create harsh conditions for vitrification, the method of the present invention for easily and easily obtaining doped silica glass with a controlled desired composition,
Examples will be specifically explained in detail below.

FIGS. 2 and 3 are partially sectional side views of steps for explaining the manufacturing method of the present invention.

As shown in the drawing, a carbon rod 1 with a thickness of 6 m11 and a length of 500 weights is rotated at 30 times per minute and energized to generate heat. In this state, a nozzle 5 is used on the carbon rod 1, and a raw material gas whose SiCl4/GeCl4 ratio is adjusted so that the weight ratio of SiO2 and GeO2 is 85%/15% is fed through a raw material transport pipe 6 through a pipe 7. The flame 4 is sprayed with a mixture of oxidizing high-temperature gases. In this way, a sintered layer 3 of SiO2-GeO2 is formed around the carbon rod 1. When the thickness of the sintered layer 3 reaches about 10 mm, the current applied to the central carbon rod 1 is increased to raise the temperature and maintain it at about 1600°C.
Then, the formation of the vitrified layer 2 is gradually progressed from the inside. At this time, naturally, a sintered layer continues to be deposited around it. FIGS. 2 and 3 are in this state. The surrounding sintered layer 3 is always adjusted to have a thickness of about 10 mm, and the vitrified layer 2 is produced. However, in the final stage, the bottom layer is vitrified. In this way, a germania-doped silica glass having a length of 350 mm and an outer diameter of 40 mT1L was obtained. After that, the central carbon rod was pulled out and melted to obtain a glass body uniformly doped with GeO2 in the shape of a solid tube.What we paid particular attention to in this process was that as the outer diameter of the sintered body increased, the heat capacity changed. As a result, the amount of heat required for vitrification increased, and the amount of electricity applied was gradually increased to achieve appropriate vitrification.

In addition, this method was able to prevent dopant loss because GeO2 alone shows a vapor pressure curve as shown in Figure 1, but by forming a mixed fine powder sintered body with SIO2, the vapor pressure increases. This seems to be due to the extreme decline.

In the above example, the glass is uniformly doped with GeO2, but the same method can also be used for glasses that have a dopant concentration distribution gradient in the radial direction by controlling the amount of raw material transported, and for dopants other than GeO2 such as B2O3. It is clear that it can be manufactured by

Further, silicon carbide or the like may be used instead of the central carbon rod, and as a temperature raising method, a high frequency induction heating method can be used in addition to the above-mentioned resistance heating.

As is clear from the above description, the present invention simplifies the process of producing doped silica glass by sequentially performing the steps of generating mixed oxide fine powder, sintering, and vitrifying, and prevents contamination during the process. High purity can be maintained, and defects due to dopant vaporization are prevented, making it easier to control the dopant distribution, that is, the refractive index distribution. Such a glass of high purity and controlled refractive index with low optical loss is extremely useful as a material for optical transmission glass fibers with low transmission loss and large signal transmission capacity.

[Brief explanation of the drawing]

FIG. 1 is a graph showing vapor pressure-temperature curves of GeO2 and B2O3. FIG. 2 is a side view showing a cross-section of a main part of a process product during a manufacturing process in an embodiment of the present invention. FIG. 3 is a cross-sectional view taken along the line - in FIG. 2. 1... Carbon rod, 2... Vitrified layer, 3... Sintered layer, 4... Frame, 5... Nozzle, 6... Raw material transport pipe, 7... Gas pipe.

Claims (1)

[Scope of Claims] 1. Steam having a component composition that reacts with a mixed oxide fine powder having a glass component composition or an oxidizing high temperature gas to produce a mixed oxide fine powder having a glass component composition around a rod-shaped heating element. 1. A method for producing doped silica glass, which comprises blowing a glass body together with an oxidizing high-temperature gas to adhere reaction product fine powder, sintering the glass, and simultaneously vitrifying it by heating with an internal heating element. 2. Production of doped silica glass according to claim 1, wherein the vapor having a composition that reacts with the oxidizing high-temperature gas to produce mixed oxide fine powder is a mixture gas of metal halides. Method. 3. Claims 1 and 2, wherein the vapor having a composition that reacts with the oxidizing high-temperature gas to produce mixed oxide fine powder is a mixed gas of silicon tetrachloride and germanium tetrachloride. A method for producing doped silica glass as described in .