JPS6034504B2 - Optical fiber manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Field of Application of the Invention The present invention relates to an improvement in a method for manufacturing an optical fiber, particularly in a method for depositing a layer to become a core glass on the inner wall of a glass tube.

[2] Conventional technology As a method for manufacturing optical fibers, a gas (or vapor) of a silicon compound (or a silicon compound containing a doping substance for controlling the refractive index), an oxidizing gas, an inert gas, etc. is passed between high-frequency electrodes. He proposed a method in which the glass film was deposited on the inner wall surface of a hollow glass tube heated to a high temperature after plasmacytinization was achieved. 10783
4).

In this method, the plasma stability conditions were investigated by changing the gas type, gas flow rate, electrode shape, oscillation frequency, high-frequency power, etc. As a result, as the supply amount of the silicon compound (or the silicon compound containing the doping substance for controlling the refractive index) increases, the plasma flame gradually cools down, becomes unstable, and eventually disappears. I understand. For this reason, it was found that the supply of the above gas had to be restricted, resulting in low productivity. lake
OBJECTS OF THE INVENTION The present invention aims to improve the optical fiber manufacturing method previously proposed by the present inventor.

In other words, in a method in which a silicon compound gas, an oxidizing gas, or an inert gas is passed through a glass tube and a glass film is formed on the inner wall of the tube by utilizing the high temperature generated by plasma ionization inside the tube, the east concentration of the plasma flame is , improve stability,
The purpose is to quickly cause a vapor phase growth reaction of a large amount of raw material gas. '4} General description of the invention The present invention has a structure in which the tip of a carbon rod is inserted into the inner glass tube of a closed double glass tube, and the gap between the outer glass tube and the inner glass tube is cooled with water. The tube was inserted into the glass tube in which the glass film was to be deposited, and plasma was generated in the gap between the glass tube and the inserted double glass tube using a coil placed around the outer periphery of the glass tube. It is something.

Then, a glass film is deposited on the inner wall of the glass tube by plasma gas, raw material gas, and oxygen gas sent into this gap.

The difference from the conventional method is that since the carbon rod is always inserted, the plasma flame does not disappear and continues to be transferred to the carbon rod. Therefore, it is possible to cause a large amount of raw material gas to undergo a vapor phase growth reaction and increase productivity. Note that the carbon rods are placed in the same manner inside the glass tube on which the glass film is to be deposited, and their length is made longer than the area on which the glass film is to be deposited. '5' Example The present invention will now be described in detail with reference to examples.

FIG. 1 is a diagram illustrating an embodiment of the present invention.

In the figure, a glass tube 1 is used to deposit a glass film 7 on its inner wall. A coil 3 is wound around the outside of the glass tube 1 so that it can move in the direction of arrow 5 or 5' at a desired speed. High frequency power generated by an oscillator (not shown in the drawing) is applied to the coil 3. In the glass tube 1, carbon rods 4 are installed in the same position. The length of the carbon shank 4 is approximately the same as that of the glass tube 1. The carbon rod 4 is sealed inside a glass tube 9 to prevent oxidation.] This glass tube 9 is inserted into a glass tube 8. Further, water 10 is placed between the outer circumference of the glass tube 9 and the inner wall of the quartz glass tube 8 as indicated by the arrow 11.
11' to prevent the temperature of the glass tubes 8 and 9 from rising. In this state, argon gas is flowed from the two directions of the arrows to induce high frequency power to the carbon blade 4 and generate a plasma flame 6. After that, the raw material gas for glass waist formation (for example, SI
A glass film 7 (Si02 or Si0
2 containing at least one type of oxide such as P24, Ge02, &03 as a dopant) is deposited.

Compared to the conventional method, in order to allow the vapor growth reaction to occur with the carbon rod 4 always inserted, the plasma flame 6 is less likely to disappear even when a large amount of raw material gas is fed, and the gas is kept at a higher temperature. It is possible to induce a vapor phase growth reaction. Next, specific examples of the present invention will be described.

A coil 3 was wound 5 turns around a quartz tube 1 (outer diameter 2 mm), and high-frequency power (1 VA) with an oscillation frequency of about MHz was applied. Then, argon gas was fed from the arrow 2 at a flow rate of 4/min to induce high-frequency power to the carbon blade 4 and generate a plasma flame 6. Next, the SI held at about 2000
Oxygen in C14 and POC13 at 200cc/min
The steam was then sent into the quartz tube 1 from the arrow 2 along with oxygen at 400 cc/min. SIC from this state
The stability of the plasma flame was investigated by increasing the amount of oxygen fed into the 14 chamber. As a result, it was found that the plasma flame was stable and the vapor phase growth reaction proceeded until the amount of oxygen fed into the SIC 14 was about several som/min. By the way, in the conventional method in which carbon rod 4 is removed, the above oxygen amount is 40
The plasma flame disappeared at about 0 cc/min.
(6) Effects of the Invention As explained above, according to the present invention, a carbon rod is always inserted in the flow path of the raw material gas, and high frequency power is induced to generate a plasma flame to cause a vapor growth reaction. Even if a large amount of gas is fed, the plasma flame is not easily extinguished, and the vapor phase growth reaction can be carried out while the gas is kept at a high temperature, which has the effect of increasing productivity.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating a method of manufacturing an optical fiber according to the present invention. Figure 1

Claims (1)

[Claims] 1. In the pre-processing process for manufacturing an optical fiber, in which a raw material gas for forming a glass film is flowed into a glass tube to form a glass film on the inner wall of the glass tube, a carbon rod is inserted into the glass tube, and high frequency power is applied to the carbon rod. 1. A method for manufacturing an optical fiber, characterized in that the glass film is formed by a vapor growth reaction by inducing a plasma flame and generating a plasma flame.