JPS6096536A - Furnace for producing optical fiber preform - Google Patents

Abstract

PURPOSE:To prevent the deformation and cracking of the quartz glass core tube of a furnace, by inserting a refractory cushioning material between the carbon graphite core tube and the quartz glass core tube of a furnace. CONSTITUTION:A heat-insulating cusioning material 10 made of carbon felt is inserted between the inner surface of the carbon graphite core tube 5 and the outer surface of the quartz glass core tube 4. The cushioning material 10 is furnished with plural perforations to enable the efficient teansmission of the radiant heat from the ring heater 6 and the carbon graphite core tube 5. The porous preform 2 is put into the quartz glass core tube 4, and He gas and Cl2 gas, etc. are passed through the tube. The pressure in the quartz glass core tube 4 is controlled, the temperature is raised, and the preform 2 is converted to transparent glass by moving vertically in the tube under rotation. The life of the quartz glass core tube can be extended, and the conversion of the optical fiber preform to transparent glass can be carried out stably and continuously.

Description

[Detailed Description of the Invention] [Background and Objectives of the Invention] The present invention relates to an improvement of a thermal furnace for manufacturing an optical fiber preform used for dehydrating and transparent vitrifying a porous preform for an optical fiber. It is.

H,-o, 5iCL4. in flame. In the so-called VAD method, a porous base material is obtained by flowing a halide such as GaCl2, synthesizing glass particles such as S i O = 4 and GlloS, and depositing these on a target. This is a method of obtaining an optical fiber base material by forming a transparent glass.

Fig. 1 is a cross-sectional view of an optical fin (heating furnace for producing the base material) used to make a conventional porous base material transparent. Gas N
are arranged in the heating furnace main body 8 which flows as shown by arrow A, and a carbon graphite furnace core tube 5 is arranged in the annular heating element 6 (Ill).

A quartz glass furnace core tube 4 is arranged inside the carbon graphite furnace core tube 5, and the inside of the quartz glass furnace core tube 4 is approximately 180 mm.
While the temperature is maintained at 0°C, Ha gas and Ct gas are indicated by arrow B.
It is flowing like this. Then, inside the quartz glass furnace core tube 4, the porous base material 2 attached to the target 1 is moved up and down while rotating, and the optical fins (base material 6) are turned into transparent glass.
I am getting .

In addition, 9 is a gas curtain.

In the above structure, the quartz glass furnace core tube 4 has a diameter of 1800 mm.
Celsius, it is deformed due to the pressure difference between the inside and outside of the quartz glass furnace core tube 4, its own weight, etc.Furthermore, it adheres closely to the inner wall of the carbon graphite furnace core tube 5, and when the temperature falls, the quartz glass deforms due to the difference in thermal expansion. There was a drawback that the furnace core tube 4 was broken, so that it could only be used once.

Therefore, carbon graphite furnace core f5. ! : Gas was flowed between the quartz glass furnace core tube 4 and the pressure was controlled to prevent deformation, but although quartz glass has a small coefficient of thermal expansion, it also expands greatly at high temperatures, so the quartz glass furnace core Gaps were created between various parts of the surface of the tube 4 and the carbon graphite furnace core g5, making pressure control difficult, easily deforming and cracking, and having a lifespan of only one or two cycles.

The present invention was made in view of the above-mentioned situation, and an object of the present invention is to provide a heating furnace for producing an optical fiber base material that can prevent deformation and cracking of a quartz glass furnace core tube and extend its life. .

[Summary of the invention]

The heating furnace for producing optical fiber preforms of the present invention includes a carbon graphite furnace core tube disposed inside an annular heating element disposed in an inert gas atmosphere, and a carbon graphite furnace core tube disposed inside the carbon graphite furnace core tube. The inside of the tank is maintained at about 1800℃, and gas is flowed to keep the internal pressure higher than atmospheric pressure.
A quartz glass furnace core tube is provided in which an optical fiber base material is manufactured by rotating and vertically moving a porous base material attached to a target, and the inner periphery of the carbon graphite furnace core tube and the quartz glass core tube are provided. A heat-resistant cushioning material is inserted between the furnace core and the outer circumference. .

〔Example〕

Hereinafter, the Carothermal Furnace for manufacturing optical fiber preforms of the present invention will be explained with reference to Examples and FIG. 2, with parts that are the same as those of the conventional art being denoted by the same reference numerals and explanations of the structures of the same parts will be omitted.

FIG. 2 shows a cross-sectional view, and 10 is a heat-resistant cushioning material made of carbon felt with a thickness of 5 mm, which is inserted between the inner periphery of the carbon graphite furnace core tube 5 and the outer periphery of the quartz glass furnace core tube 4. has been done. In addition, since the carbon felt of the cushioning material 1o serves as a heat insulating material, the annular heating element 6
In order to efficiently transmit the secondary radiation heat of the carbon graphite furnace core d5, a plurality of holes (not shown) each having a diameter of 10++o++ are regularly drilled across the width of 60mm.

Then, in this heating furnace, the porous base material 2 is placed inside the quartz glass furnace core tube 4, %Ha gas and Ct2 gas are flowed, and the gas outlet diameter is adjusted so that the internal pressure of the quartz glass furnace core tube 4 is +1 +lll1 from atmospheric pressure. I made it look like a water column. That sickle,
An experiment was conducted in which the temperature inside the quartz glass furnace core tube 4 was raised to about 1800° C., and the porous preform 2 was moved up and down while rotating to make it transparent vitrified to obtain an optical fiber preform 3. As a result of the experiment, no deformation of the quartz glass furnace core tube 4 was observed, and after repeated use several dozen times, it deformed little by little, and a devitrification phenomenon occurred.

However, there was no cracking during lifting and lowering [1'], and it could be used several dozen times for about 100 hours.

In this way, the heating furnace for manufacturing optical fiber base material of this example is
By inserting a carbon felt cushioning material between the inner periphery of the carbon graphite furnace core tube and the outer periphery of the quartz glass furnace core tube, the quartz glass furnace core tube is prevented from deforming and cracking, significantly extending its life, and making transparent glass possible. It is stable and can be performed continuously.

〔Effect of the invention〕

As described above, the heating furnace for producing optical fiber preforms of the present invention has the effect of preventing deformation and cracking of the quartz glass furnace tube and significantly extending its life.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a conventional heating furnace for manufacturing optical fiber base material.
FIG. 2 is a cross-sectional view of an embodiment of a heating furnace for producing an optical fiber preform according to the present invention. Reference Signs List 1: target, 2: porous base material, 6: optical fiber base material, 4: quartz glass furnace core tube, 5: carbon graphite furnace core tube, 6: annular heating element, 10: cushioning material. Child 1 Figure B 2nd Old

Claims (1)

[Claims] (1) A carbon graphite furnace core tube disposed inside an annular heating element disposed in an inert gas atmosphere, and an internal diameter of approximately 18 mm.
The optical fiber base material is produced by keeping the porous base material attached to the target at 00°C and moving it up and down for 6 smym times while keeping the internal pressure close to atmospheric pressure by flowing gas. An optical fiber preform provided with a quartz glass furnace core tube, characterized in that a heat-resistant cushioning material is inserted between the inner periphery of the carbon graphite furnace core tube and the outer periphery of the quartz glass furnace core/U. A hot-mouth furnace for manufacturing.