JPS62256736A - Production of base material for optical fiber - Google Patents

Abstract

PURPOSE:To enhance the yield of a raw material for a base material in case of producing the base material for optical fiber in a vapor phase axial deposition process (VAD process) by partitioning at least one annular jet port of a multiple combustion burner into two and above and independently controlling the flow rate of gas for partitioned respective flow paths. CONSTITUTION:In case of producing a base material for optical fiber in VAD process, a gaseous raw material such as SiCl4 is jetted through the first layer of an annular multiple combustion burner and gaseous fuel such as H2 and CH4 is jetted through the second layer and inert gas such as Ar and N2 is jetted through the third layer and autocombustion gas such as O2 is jetted through the fourth layer, and fine glass particles are produced by the hydrolysis reaction or the oxidation reaction of the gaseous raw material and the base material for optical fiber is stuck and grown on the tip of a starting rod. In this case, the partitioning pipes of the second layer and the third layer of the burner are eccentrically fitted and a partition is centrally provided to divide respective layers into two ports of A and B. Gases of respective layers are jetted in the optimum flow rate conditions by independently controlling the flow rate of gas of two ports of respective layers and the porous glass base material for optical fiber is produced in good yield of the raw material.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing an optical fiber base material, and more specifically, the OVPO method (external vapor phase oxidation method), AD method. The present invention relates to a method of manufacturing a porous glass preform for optical fibers by a soot generation method such as (vapor phase axial mounting method).

Conventional Technology One method for manufacturing porous glass preforms for optical fibers is to eject a mixture of combustion gas and glass raw material from a combustion burner, generate glass fine particles through a hydrolysis reaction or oxidation reaction in a flame, and then produce glass particles. There is a VAD method in which a porous glass preform is produced by depositing fine particles on the tip of a rotating starting material and moving the starting material relative to a burner as the porous glass preform grows.

In addition, the ○■PO method (Japanese Patent Application Laid-open No. 48-1983) produces a porous glass base material by depositing glass particles generated by a combustion burner on the outer periphery of the starting material and traversing the starting material or the combustion burner one or more times. -73522) is also available.

In the conventional VAD method, the combustion burner shown in Fig. 2 (
A multi-tube burner having a jet nozzle with a round cross section as shown in a) or a multi-tube burner having a jet nozzle with a square cross section as shown in FIG. 2(b) is used. Raw material gas, fuel gas, auxiliary combustion gas, etc. are ejected from each annular injection port, that is, from each layer of the multi-tube burner. For example, in the concentric multi-tube burner shown in FIG. 2, raw material gas is injected from the first layer, fuel gas from the second layer, inert gas from the third layer, and auxiliary combustion gas from the fourth layer. Generally, the raw material gas is 5IC14, and the fuel gas is N2, CH,
Ar -, N2 is used as the inert gas, and 02 is used as the auxiliary combustion gas. Further, GeCl4 or the like may be mixed and supplied as a dopant into the raw material gas.

In manufacturing optical fiber base materials, it is necessary to sufficiently reduce impurities contained in the base material in order to reduce transmission loss.Therefore, burners are made of materials that do not contain such impurities. In addition, since a corrosive raw material is used as the raw material for glass, it is necessary to use a material with excellent corrosion resistance.For this reason, conventionally, quartz burners have been used as combustion burners. However, since quartz has poor workability,
There were limits to improving the manufacturing precision of quartz burners. When a concentric multi-tube burner is used, the gap between the layers often varies in the circumferential direction due to poor concentricity of each layer and variations in the wall thickness of the pipes.

For this reason, the flame formed by the combustion burner and the flow of the generated glass particles do not flow axially symmetrically, resulting in a problem that the adhesion efficiency of the raw material deteriorates. In addition, the manufacturing accuracy of this combustion burner varies depending on the burner.
Since the manufacturing conditions of the porous glass base material change each time the burner is replaced, there is a problem in that the manufacturing conditions of the porous glass base material must be changed each time. Furthermore, even with metal burners that have better dimensional accuracy than quartz burners, it takes a great deal of time and effort to achieve good concentricity, and it is difficult to maintain constant concentricity.

Problems to be Solved by the Invention As mentioned above, in the conventional method of manufacturing a porous glass base material for optical fiber by the soot method using an annular multi-tube combustion burner, the gaps between each layer of the combustion burner are narrowed in the circumferential direction. Since the flow is not constant, the flame that is formed and the flow of the glass particles that are generated are not axially symmetrical, resulting in a problem that the adhesion efficiency of the raw material deteriorates.

SUMMARY OF THE INVENTION Therefore, the present invention aims to provide a method for producing an optical fiber preform in which the flame flow formed by the combustion burner and the glass particle flow generated in the flame are axially symmetrical, and the raw material yield is high. It is something.

According to the present invention, gaseous frit is injected from a multi-tube combustion burner in which a plurality of annular injection ports are concentrically provided and subjected to flame hydrolysis to generate granular particles. A method of manufacturing a porous glass preform by depositing glass on a rotating starting material and growing the granular glass in the direction of the rotation axis, wherein at least one annular injection port of the multi-tube combustion burner is partitioned into two or more. , independently controlling the flow rate of each partitioned flow path.

Operation Before detailed explanation of the present invention described above, the above-mentioned problem will be explained with reference to the drawings.

FIG. 3(a) shows a cross section of a jet outlet of a quadruple tube burner in which partition pipes of the second layer and the third layer are eccentrically attached.

In the illustrated burner, the second layer has a narrow gap on the left side and a wide gap on the right side. On the other hand, the third layer is wider on the left side and narrower on the right side.

When such an eccentric burner is used, the gas flows in the second and third layers are biased towards the wider gap due to the pressure drop within the burner.

Therefore, in a combustion burner having a cross section of the jet nozzle as shown in Fig. 3(a), the raw material gas is placed in the first layer, the fuel gas is placed in the second layer, the inert gas is placed in the third layer, and the auxiliary gas is placed in the fourth layer. If it flows, the combustion gas in the second layer will mostly flow to the right side where the gap is wide, and the inert gas in the third layer will mostly flow to the left side where the gap is wide. As a result, the flame formed on the right side of the burner is large and the flame formed on the left side is small. Further, on the right side where the flow rate of the inert gas is low, the combustion gas and the heat-assisting gas are mixed quickly, and a flame is formed very close to the burner outlet, resulting in an increase in the temperature at the burner tip.

Conventionally, in such cases, the gas flow rate in the third layer was increased to avoid damage to the burner, which made it impossible to achieve the optimal gas flow conditions for glass particle generation. could not be synthesized.

However, in the method according to the present invention, as shown in the cross-sectional view of the jet port in the third case (b), a partition is provided in the center, for example, and each seat is divided into two ports A and B. Then, the flow rates of the two ports of each layer are adjusted independently. At that time, so that the flame is formed symmetrically,
'If the flow rates of the A boat and the B port are adjusted, it is possible to synthesize a porous glass preform under conditions close to the optimal flow rate for any burner with any eccentricity.

For the sake of simplicity, an example in which each layer is partitioned into two ports has been described for a quadruple tube burner, but any case can be applied to the case of concentric multiple tubes. The same applies to the square annular multi-tube burner shown in FIG.

Furthermore, it is not necessary to include partitions in all layers of the burner, and even if partitions are provided only in specific layers that play an important role in forming the porous base material, the effects of the present invention will not be impaired.

Furthermore, this method is applicable not only to the VAD method described above but also to any manufacturing method that includes a process of forming a porous glass base material.

EXAMPLES Hereinafter, examples of the method for manufacturing an optical fiber preform according to the present invention will be described with reference to the accompanying drawings.

A porous base material was synthesized using a quartz eight-tube burner having a spout as shown in FIG.

Each of the four layers from the center of this eight-layer burner outlet is equally divided into four boats. Table 1 shows the results of measuring the eccentricity of the layers.

Table 1 The definition of eccentricity here is explained for the eccentricity of the second layer. FIG. 4 schematically shows the second layer formed by two pipes. The second layer is defined by the outer circumference 3 of the pipe 1 and the inner circumference 4 of the pipe 2.

The eccentricity of the second layer referred to here indicates the deviation of the center of the circle on the inner circumference 4 from the center of the circle on the outer circumference 3.

From this measurement result, the layer with relatively large eccentricity, that is, the layer where the gap changes relatively greatly in the circumferential direction, is the second layer.
It can be seen that there are 4.5 and 6 layers.

First, for comparison, a porous base material was manufactured by flowing gas at the same flow rate from each of the four partitioned ports.

5IC14 is supplied from the first layer as a raw material, and hydrogen is supplied as a combustion gas from the second and sixth layers, oxygen is supplied as a combustion assisting gas from the fourth and eighth layers, and argon is used as an inert gas. were supplied from the third, fifth and seventh layers, respectively. The flow rate of each gas is SIC]4=1700cc/
m1nSH2=21A/min, 02=25β/mi
n.

8r=15j2/min.

When the flame and glass particle flow formed by the burner were observed, it was found that the glass particle flow was not axially symmetrical, and the flow was non-uniform, with some turbulence occurring. The raw material yield for porous matrix synthesis was as low as 52%. The raw material yield indicates the ratio of the raw material attached to the porous base material to the raw material input amount supplied from the burner.

A flame was formed using the same burner and the same gas flow rate, and while observing the flame, the flow rate of each of the four partitioned boats was adjusted so that the flow of the glass particles was axially symmetrical and no turbulence occurred. Adjustment of the flow rate of each partitioned port can be easily realized, for example, by connecting each boat to a supply source through independent flow rate adjustment valves and adjusting the flow rate adjustment valves independently.

In the case of this example, the gas flow rate of each port in the second layer and the gas flow rate of each boat in the fourth layer were adjusted. As a result, the flame could be made to flow nearly axially symmetrically, and as a result, the raw material yield of the produced porous base material could be increased to 61%.

As described in detail, the method for manufacturing an optical fiber preform according to the present invention involves dividing the non-uniform flow of gas flowing from each eccentric layer of a concentric multi-tube burner into two or more layers for each layer. By adjusting the flow rate of gas from each port, a uniform flow is achieved, and an axially symmetrical flame flow and glass particle flow are realized.

In other words, it is possible to prevent the deterioration of the adhesion efficiency of raw materials and to produce a porous glass preform for optical fibers with a high raw material yield.

Therefore, the method for manufacturing an optical fiber preform according to the present invention can be utilized over a wide range of applications.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of the jet nozzle of a combustion burner used in one embodiment of the method for manufacturing an optical fiber preform according to the present invention, and FIG. FIGS. 3(a) and 3(b) are schematic cross-sectional views of the jet nozzle of a combustion burner used in the present invention; FIGS. FIG. 4 is a schematic cross-sectional view of a combustion burner nozzle for explaining. FIG. 4 is a diagram for explaining the definition of eccentricity in a concentric multi-tube combustion burner. (Main reference numbers) 1... Pipe that separates the first and second layers, 2... Pipe that separates the second and third layers, 3... Outer circumference of vibe 1, 4... Inside of vibe 2 circumference

Claims (3)

[Claims] (1) A gaseous glass raw material is ejected from a multi-tube combustion burner with a plurality of concentric injection ports, subjected to flame hydrolysis, and the resulting granular glass is deposited on a rotating starting material. In a method for manufacturing a porous glass preform by growing it in the direction of the rotation axis, at least one annular injection port of the multi-tube combustion burner is partitioned into two or more, and the flow rate of each partitioned flow path is independently controlled. 1. A method for manufacturing an optical fiber base material, the method comprising controlling the manufacturing method. (2) The method for manufacturing an optical fiber preform according to claim 1, wherein the same type of gas is flowed out from the same annular injection port divided into two or more. (3) Adjust the gas flow rate of each flow path of each annular injection port partitioned into two or more so that the flame and granular glass flow formed by the combustion burner are formed axially or plane symmetrically. A method for manufacturing an optical fiber preform according to claim 1 or 2.