JPS5855087B2 - Method for manufacturing base material for optical fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a glass fiber preform containing little moisture.

Conventionally, this type of technology is known to be made by burning a combustible gas that does not contain hydrogen, such as cyanogen, carbon monoxide, or carbon dioxide, in oxygen, and then blowing silicon tetrachloride, etc. into the flame. .

Another method is to flow oxygen and argon into a quartz tube, wrap a coil connected to a 4-10 MHz high-frequency oscillator around the quartz tube, and supply 10-30 kW of high-frequency power to this coil to generate a high-frequency discharge. A known method is to create plasma and use the heat of this plasma to heat a mixture of raw material gas and argon gas flowing through a tube placed concentrically in the center of a quartz tube, causing an oxidation reaction. .

(See % Open/Close 48-26208) Since these methods do not contain hydrogen or its compounds in the reaction system, they are effective as methods for producing anhydrous glass bodies, but they have several drawbacks in practice.

That is, the former method uses poisonous and relatively expensive gas, resulting in high production costs.

In the latter method, the reaction system is separated from the outside by a quartz tube, etc., and there is less contamination from the heating source, but the high-frequency plasma is unstable and it is not easy to maintain the desired temperature state. do not have.

In order to solve these drawbacks, the present invention is characterized by synthesizing glass by heating with stable DC discharge plasma and by a method that does not introduce impurities into the glass from discharge electrodes or the like.

The present invention will be explained in detail below with reference to the drawings.

In addition to the method described above, attempts have been made to generate high-temperature gas by passing a large current through a resistor such as carbon to generate heat, and then passing an inert gas through this to generate high-temperature gas (especially Application No. 51-30844 Japanese Patent Publication No. 52-1143
35-), in practice, the heat exchange rate is poor, and 1 of the input power
Only less than 0% of the energy is available, and it is not easy to improve this efficiency.

The present invention aims to improve this heat exchange rate and efficiently produce a glass body.

When creating plasma by direct current discharge, the biggest problem is that electrode materials get mixed into the plasma due to evaporation or sputtering, and when such plasma is used as a heat source for glass synthesis, Metal ions are dispersed in the liquid, resulting in large absorption losses.

Therefore, the main point of the present invention is to generate high-temperature gas that does not contain impurities by a simple method.

Figure 1 is a diagram showing the concept of the present invention, in which two carbon rods 1
is hermetically sealed and fixed in the quartz tube 2, and argon gas is flowed into the quartz tube 2.

A voltage of 60V is applied to both ends of carbon rod 1, and 1
When a pulsed voltage of 00 OV was applied to start discharge, a current of about 10 OA flowed, and gas at a temperature of 1400°C was obtained near the gas outlet 3, with a heat exchange efficiency of 65%.
It was about.

FIG. 2 is a cross-sectional view of one embodiment of the present invention, showing an example of the cross-section of a discharge nozzle that is actually used to generate glass soot.

In Fig. 2, 21° and 22 are cylindrical carbon electrodes with a cross section as shown in the figure, and are placed in a refractory container 2 such as quartz.
It is fixed within 3.

Argon gas is flowed into the quartz container 23 from the argon inlet 24 at a rate of 10 to 157 per minute.

A double-walled refractory pipe is pushed inside the carbon electrode 22, and oxygen gas is supplied from the oxygen inlet 25 at 101/min, and from the inlet 26, argon gas, 2091/min of silicon tetrachloride, and 2 g/min of germanium tetrachloride are supplied. Both components flow in gaseous form, and 60 V is applied between electrodes 21 and 22.
, 80 A of direct current is passed to generate plasma in the shortest gap 27 between the electrodes 21 and 22.

The argon gas heated by the plasma and the oxygen, silicon tetrachloride, and germanium tetrachloride gases blown out from the center of the electrode 22 are mixed at the reaction outlet 28 to cause an oxidation reaction, resulting in the doping of germanium oxide. A fine powder of silicon oxide was synthesized.

These glass soots are stacked on a quartz starting material 29 that is installed above the discharge nozzle and rotates (once per second) while moving upward at a speed of 3 times per minute. was formed.

This glass soot sintered body 30 is sprayed with glass soot to a thickness of 10 mm using a similar discharge nozzle to send only oxygen and silicon tetrachloride from the inlet 26 and keeping the other conditions the same. A fiber base material was made.

Next, this was placed in an electric furnace at 1700℃ for a heating length of 30 minutes.
As a result of zone melting by feeding at a speed of 4 times per minute, the refractive index of the peripheral part was 1.458 and the refractive index of the central part was 1.468.
A transparent optical fiber base material having an outer diameter of 20 mm was obtained.

One end of this base material was heated and drawn into a thread, and the spectral characteristics of the obtained fiber were measured, and as a result, the water content was 11] pm or less.

The most problematic aspect of the method of the present invention is the possibility of the discharge electrode material being mixed into the glass.

Since the method of the present invention uses carbon as an electrode,
Impurity metals contained in carbon or carbon fine particles sputtered by discharge may be mixed into the glass.

The carbon electrode used was heated to 3000'C in vacuum before use.
The mixture was heated for 10 minutes to remove impurities.

No absorption was observed at all due to the removal of impurities by this treatment.

Further, the carbon fine particles sputtered by the discharge were oxidized in the area of the air outlet 28 by the oxygen blown in from the oxygen inlet 25, and turned into CO2 gas, which prevented them from being mixed into the glass as particulate carbon.

As explained above, the glass synthesized by reaction using an inert gas heated by DC discharge plasma has the same quality as the conventionally used high-frequency plasma method, and has improved thermal efficiency.

Furthermore, compared to high-frequency plasma, it has the advantage that the plasma is stable and homogeneous glass can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram of the present invention, and FIG. 2 is a sectional view of an embodiment of the present invention. 1... Carbon electrode, 2... Quartz tube,
3... Gas outlet, 21, 22... Carbon electrode, 23... Quartz container, 24...
...Argon inlet, 25...Oxygen inlet, 2
6...Argon and glass raw material inlet, 27.
...Shortest gap between electrodes 21 and 22, 28...
...Reaction part outlet, 29...Quartz starting material, 3
0...Glass soot sintered body,

Claims (1)

[Claims] 1. After making a soot-like glass sintered body by heating silicon tetrachloride, at least one doping additive vapor, and oxygen gas to high temperature and oxidizing it, this glass sintered body is heated to make it transparent. In a method for producing a glass fiber base material to be vitrified, a high-temperature inert gas is produced by direct current discharge using carbon as an electrode in an inert gas flow, and the silicon tetrachloride and at least one doping additive vapor are produced. 1. A method for producing a base material for glass fiber, which comprises mixing and oxygen gas to cause an oxidation reaction.