JPS6222933B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing an optical fiber base material.

A raw material gas for glass formation such as silicon tetrachloride (SiCl ₄ ) and oxygen (O ₂ ) gas are introduced into a reaction tube, and the reaction tube is heated from the outside to oxidize the raw material gas for glass formation to form a fine powder. The method of manufacturing an optical fiber base material by depositing the oxide on the inner wall of a reaction tube and melting it to vitrify it is known as the internal CVD method.

Conventionally, when manufacturing optical fiber base materials using such an internal CVD method, a burner that moves along the reaction tube is used to heat the outer wall of the reaction tube to oxidize the raw material gas, which is then vitrified and removed from the reaction tube. It was attached to the inner wall of the

However, with this method of heating the outer wall of the reaction tube with a burner, heat transfer to the inside of the reaction tube is poor, and in order to bring the temperature inside the reaction tube to the required temperature, it is necessary to adjust the temperature at the heating point on the outer wall of the reaction tube. The temperature had to be higher than that, which caused problems such as shrinkage and deformation of the reaction tube.

In particular, when a reaction tube is made thick or a thick reaction tube is used in order to obtain a large-volume optical fiber preform, the above-mentioned problems are likely to occur.

The present invention eliminates the above-mentioned problems and provides a novel optical fiber that lowers the heating temperature of the reaction tube and prevents shrinkage, deformation, etc. of the reaction tube when producing an optical fiber base material by the internal CVD method. The purpose is to provide a method for manufacturing base materials.

In order to achieve this object, the method for producing an optical fiber preform according to the present invention includes installing a short tubular heater coaxially with the reaction tube and having an outer diameter slightly smaller than the inner diameter of the reaction tube. The heater is movable in the tube axis direction, frit gas and oxidizing gas are introduced into the reaction tube, the introduced gas is heated by the heater to cause a gas phase chemical reaction, and the following steps are carried out. The method is characterized in that glass is produced and the glass is deposited on the inner wall of the reaction tube.

An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a schematic diagram for explaining an embodiment of the method for manufacturing an optical fiber base material of the present invention, and FIG. 2 is a schematic diagram of a heater used in the method of the present invention.

As shown in FIG. 1, a ring-shaped carbon jig 2 for heating is installed inside a quartz reaction tube 1, and the surrounding area is used to prevent impurities in the carbon jig from scattering to the outside. It is covered with a ring-shaped quartz jig 3. Two quartz holders 4 and 5 are attached to the quartz jig 3 that covers the carbon jig 2 and extend along the axial direction of the reaction tube. A high-frequency induction coil 6 is also provided to heat the carbon jig by wrapping around the outer wall of the reaction tube. ing. Here, the quartz holders 4 and 5 are attached to a transfer jig (not shown) that reciprocates in parallel along the tube axis, while the high-frequency induction coil also reciprocates in parallel along the reaction tube. The high-frequency induction coil and the carbon jig are attached to a transfer jig that moves at a constant speed. As shown in FIG. 2, the outer peripheral surface of the ring-shaped carbon jig 2 is a concave surface with a concave lens-like cross section, and the radiant heat is transferred to the reaction tube 1.
It is designed to efficiently concentrate on the inner wall surface.

The raw material gas for glass formation was introduced into the reaction tube equipped with the carbon jig for heating.
SiCl ₄ gas is introduced using O ₂ gas as a carrier gas. Then, by applying a high-frequency voltage to the high-frequency induction coil and reciprocating the coil and a heating carbon jig provided in the reaction tube while moving it along the tube axis direction of the reaction tube, silicon dioxide ( A glass-forming oxide, such as SiO ₂ ), is formed and then melted and deposited as a glass layer on the inner wall of the reaction tube.

In this way, since the heating source for oxidizing the raw material gas for glass formation is inside the reaction tube,
Heat is efficiently conducted to the reaction tube and source gas. Therefore, compared to the conventional method of heating the reaction tube from the outside, the heating temperature of the reaction tube is lower, and shrinkage of the reaction tube is less likely to occur. The advantage is that the base material for optical fiber can be obtained in high yield.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram for explaining the method of manufacturing an optical fiber preform of the present invention, and FIG. 2 is a schematic diagram of a heater used in the method of the present invention. In the figure, 1 is a reaction tube, 2 is a carbon jig, and 3
4 and 5 are quartz holders, and 6 is a high-frequency induction coil.

Claims (1)

[Claims] 1. A short tubular heater whose outer diameter is slightly smaller than the inner diameter of the reaction tube is installed coaxially with the reaction tube, and the heater is movable in the axial direction of the tube. Introducing frit gas and oxidizing gas, heating the introduced gas with the heater to cause a gas phase chemical reaction,
A method for producing an optical fiber preform, comprising the steps of: producing glass and depositing the glass on the inner wall of the reaction tube.