JPH0324417B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Technical Field The present invention is a method for efficiently reacting a large amount of frit gas fed into a multi-tube burner in the vapor phase axial deposition method (VAD method) for manufacturing preforms for optical fibers. The present invention provides a method for stably and economically manufacturing an optical fiber preform by increasing the deposition rate of glass fine particles laminated in the axial direction.

(b) Background technology VAD using one concentric multi-tube burner
When manufacturing optical fiber preforms by the method, as shown in Fig. 1, glass raw materials such as SiCl ₄ , GeCl ₄ , etc. are usually _injected into the central nozzle of burner B, and combustion gas is injected into the outer _nozzles . As H ₂ ,
Furthermore, a triple-pipe structure burner is used that supplies O ₂ as combustion auxiliary gas to the outermost nozzle n _O.

However, in this method, in order to increase the glass synthesis rate, if the raw material gas supply amount of SiCl ₄ or GeCl ₄ or the amount of H ₂ or O ₂ gas is increased, the flow rate increases and As the diffusion time of H ₂ O generated by combustion decreases, some of the raw material gases SiCl ₄ and GeCl ₄ become unreacted,
The growth of glass particles becomes unstable. Furthermore, since the raw material gas is discharged together with the exhaust gas, the reaction deposition efficiency of the raw material gas is significantly degraded.

Furthermore, as a multi-tube burner structure other than the triple-tube structure burner shown in FIG. In order to obtain a graded index type preform, as shown in Figs. 2 and 3, a plurality of raw material gas supply nozzles n _n are used to supply the raw material gas while gradually changing the concentration, and at the same time supply hydrogen around the raw material gas nozzles. One equipped with a gas supply nozzle n _H and an oxygen gas supply nozzle n _O , or two raw material gas supply nozzles for dispersing the core and cladding as shown in Figure 4.
It has been proposed that an oxygen gas supply nozzle _nO is provided between n and _n (Japanese Patent Application Laid-open No. 30853/1983). However, even with these burner arrangements, the same drawbacks as in the case of FIG. 1 were encountered.

(C) Disclosure of the Invention In the present invention, in order to solve the defect in the conventional method, that is, the reaction deposition efficiency deteriorates when the raw material gases such as SiCl ₄ and GeCl ₄ are increased, the method is as shown in FIG. Raw material gas supply nozzle n _n
An O ₂ gas supply nozzle n _O , an H ₂ gas supply nozzle n _H , and an O ₂ gas supply nozzle n _O are sequentially arranged around the . By supplying O ₂ gas inside this H ₂ gas, the diffusion distance required for the generated high-temperature H ₂ O to react with the source gas ejected from the center nozzle is reduced, and before the source gas adheres to the target. Laminates efficiently in response to Also outside
The O ₂ gas further reacts with the H ₂ gas and serves as a heating source for the generated glass particles and the surface of the growing porous glass base material. Both the inner and outer O ₂ gases of the H ₂ gas must not contain raw material gases such as _{SiCl 4} and GeCl _{4 .}
An example has been shown in which O ₂ gas is ejected from the same nozzle n _{n + O} , but in such an arrangement, the addition of O ₂ gas increases the ejection flow rate of the glass raw material, so improvement in reaction efficiency is not achieved. Further, for the purpose of protecting the nozzle tip of the burner, an inert gas jetting nozzle such as Ar can be provided as a seal gas between the H ₂ gas and O ₂ gas jetting nozzles.

In the present invention, as shown in Fig. 5, the raw material supply nozzle
In addition to the one in which n _n is a single layer, _a multi _- layer _one as shown in Figs. If placed, similar effects can be achieved.

(d) Best Mode for Carrying Out the Invention Example SiCl ₄ 200 in the center nozzle of a quartz quadruple tube burner
cc/min, GeCl ₄ 40c.c./min, and O ₂ to the second layer.
Gas 600c.c./min, _H2 gas 4.2/min in the third layer,
Further, O ₂ gas was supplied at 10/min to the outermost layer to produce a porous glass base material. The diameter of the obtained porous base material was 72 mmφ, and the final growth rate was 81 mm/hour. The adhesion efficiency of the raw material gas was 73%, which is a significant improvement compared to the value of 51% when produced using the conventional method. This porous base material was heated to approximately 1500°C using a resistance furnace heater to make it transparent. The obtained transparent glass rod was placed in a quartz tube with an outer diameter of 26φ and heated in a carbon resistance furnace with an outer diameter/core diameter ratio of 2.5 to a diameter of 125 μm.
A line was drawn on the fiber of the diameter. The transmission loss of this fiber is extremely low, less than 2.5dβ/Km (λ=0.85μm), and the transmission band is wide at 650MHz/Km, giving it excellent characteristics.

[Brief explanation of drawings]

The attached drawings are cross-sectional views of multi-tube burners used in the VAD method. The figure shows one used in the present invention, and FIG. 6 shows a comparative example.

Claims (1)

[Claims] 1 Using a multi-tube burner consisting of a plurality of concentric nozzles, glass raw material gas and combustion gas are mixed and burned to stack glass particles in the axial direction of the starting base material, which is then sintered to produce an optical fiber preform. A method for producing an optical fiber preform in the VAD method, characterized in that an oxygen gas supply nozzle, a hydrogen gas supply nozzle, and an oxygen gas supply nozzle are sequentially arranged around the raw material gas supply nozzle of the multi-tube burner.