JPS582171B2 - Manufacturing method of optical fiber base material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing an optical fiber preform by a VAD method.

Conventionally, optical fibers have been manufactured by various methods, but the VAD method has recently been attracting attention.

In the VAD method (vapor phase attachment method), soot-like glass particles are attached and deposited on one end of a rod-shaped substrate that moves in the direction of the rotation axis while rotating, and the soot-like glass particles grow in the axial direction as the rod-shaped substrate is pulled up. This is a method for making rod-shaped porous glass preforms.

The porous glass preform is then subjected to a predetermined process to form an optical fiber used for optical communications.

By the way, in the conventional method, as a burner for producing a porous glass preform, there are a supply pipe for glass raw materials and Ar gas as a carrier gas, a supply pipe for Ar shield gas, and a large number of pipes outside the Ar shield gas supply pipe. A burner consists of a pipe that supplies flammable gas, combustion O2 gas, or air, a pipe that supplies glass raw material and Ar gas as a carrier gas, a pipe that supplies Ar shield gas, and a combustible A concentric multi-tube burner or the like is used, which is composed of a gas supply pipe and a combustion O2 gas supply pipe.

When the VAD method is carried out using hydrocarbons such as methane, ethane, propane, butane as flammable gases,
Compared to using an oxyhydrogen flame, there are many advantages such as a high temperature flame and a lower gas flow rate.

However, when hydrocarbons are used as the flammable gas in the conventional burner described above, a reducing atmosphere zone such as the O2 band zone is generated over a wide range due to the decomposition of the hydrocarbons due to the initial reaction, and carbon adheres to the generated glass particles. Not only does this cause problems such as darkening, but also the initial temperature reaches 1000° C. or higher, which causes problems such as carbon and glass fine particles adhering to the burner nozzle.

The inventors of the present invention conducted intensive research to eliminate the drawbacks of the conventional method described above, and as a result, they developed a specific supply system for concentric multiple tube burners.
In other words, from the center of the burner outward, the glass raw material, O2 gas as carrier gas, O2 shield gas, hydrocarbon as combustible gas, inert gas, combustion O2
By supplying gas, the drawbacks associated with the above-mentioned conventional methods are substantially eliminated.

In other words, this supply method uses O2 as a carrier gas for the raw material gas and a shield gas between the combustible gas and the raw material gas.
It has two characteristics: (1) the use of an inert shielding gas between the flammable gas and the combustion O2;

As a result of (1) above, the inside of the flame becomes an oxidizing atmosphere, and carbon generated by decomposition of the combustible gas is oxidized from the burner mouth side to the tip of the flame.

Combustion of the flammable gas first occurs between it and the O2 shield gas due to ■■, but since the flow velocity of these gases is slow, both are in a laminar flow state near the crater, and decomposition of hydrocarbons does not occur near the crater.

The combustible gas is then combusted by the combustion O2 gas, but since the inert shielding gas exists between the two, combustion is delayed and carbon and glass particles do not adhere to the burner nozzle.

By the way, in order to obtain a porous glass preform using the above supply method, the oxidation of carbon due to the decomposition of combustible gas and the generation of glass particles must occur at the same time, so it is necessary to wait for the carbon to be completely oxidized. There is.

Therefore, the area near the tip of the flame is applied to the growth point of the preform, but since the tip of the flame is low temperature, the amount of GeO2 doped, which affects the refractive index profile, is slightly reduced, resulting in a graded preform with a small α. You will only get it.

Therefore, in order to meet the demand for a preform close to a step type with a large α, the present inventors oxidized carbon as soon as possible because it was necessary to expose the preform growth point to the high-temperature center part of the flame, where GeO2 is easily doped. Thinking about this, I first investigated the combustion process of hydrocarbons and found that it was as shown in Figure 1.

(The solid line in Figure 1 is the molecular species, the dotted line is the radical species, the diagonal line is the red light emitting part due to carbon excitation light, and the curve A is CO2
, curve B is H2, curve C is O2, curve D is CnH2n+
2. Curve E is OH radical, curve F is H radical) In other words, as is clear from Fig. 1, CnH2n+
2 is decomposed in the initial stage and is very small when the relative scale is 2 or more away from the burner crater, and the same is true for carbon generated in the decomposition stage of CnH2n+2.

Therefore, the present inventors developed a burner structure in which the tubes for supplying the glass raw material and O2 gas as a carrier gas and the tube for supplying O2 shield gas were made to protrude beyond other tubes provided outside of them. The carbon is first oxidized,
After that, glass fine particles are generated, and even if the preform growth point is placed in the high-temperature region at the center of the flame, a preform with a large α containing sufficient GeO2 can be freely obtained without being affected by carbon at all. I made it possible.

The present invention will be described below with reference to FIGS. 2 to 5.

First, the concentric multiple tube burner used in the present invention will be explained.

The concentric multi-tube burner 1 shown in FIG. 2 is an example of a burner that can be used in the present invention. , a pipe 3 that supplies O2 shielding gas, a pipe 4 that supplies hydrocarbons such as methane, ethane, propane, butane, etc., a pipe 5 that supplies shielding gas such as He, N2, Ar, etc., and a combustion The outermost tube 6 supplies O2 gas.

Further, the concentric multi-tube burner 1 shown in FIG. 3 is another example of a burner that can be used in the present invention, and this burner 1 has a small-diameter tube 2a and a large-diameter tube for supplying the glass raw material and O2 gas as a carrier gas. The structure is the same as that of the burner shown in FIG. 2 above, except that it is composed of two tubes, the diameter tube 2b.

According to the configurations shown in FIGS. 2 and 3, glass fine particles and carbon are prevented from adhering to the crater.

However, in this case, in order to completely oxidize the carbon within the flame, the flame is made long and the vicinity of the flame tip is applied to the preform growth point, thereby obtaining a preform with a small α in which the GeO2 doping amount is small in the peripheral area. .

Furthermore, each of FIGS. 4 and 5 is an improved example of a burner that can be used in the present invention, and these burners 1 include a tube 2 that supplies a glass raw material and O2 gas as a carrier gas.
Or 2a, 2b and the pipe 3 that supplies O2 shield gas
2 to 4 from other pipes 4, 5, and 6 provided on the outside thereof.
The structure is the same as that of the burner 1 shown in FIG. 2 and FIG. 3, respectively, except that it protrudes by about mm.

According to this configuration, carbon is completely oxidized before the raw material gas reacts and becomes glass particles, so the high temperature part of the flame can be applied to the preform growth point, and the Ge02
It is possible to obtain a preform with a large α that includes a sufficient amount of α.

Using the concentric multi-tube burner 1 shown in Figs. 2 to 5 above, the glass raw material and O2 as carrier gas, O2 shield gas,
Hydrocarbons as combustible gases, inert gas, and combustion O2 gas in the outermost layer are supplied through predetermined pipes, and then flame hydrolysis is performed using the VAD method to attach soot-like glass particles to one end of the rod-shaped base material. The soot-like glass particles are deposited and grown in the axial direction while pulling up the rod-shaped base material to form a rod-shaped porous glass preform.

A porous glass preform consisting of a core and a cladding can be formed by various methods.

For example, SiCl4, GeCl4, PO is added to the tubes 2 or 2a, 2b of the concentric multi-tube burner 1 shown in FIGS. 2 to 5 above.
After a suitable combination of Cl3 is supplied and subjected to flame hydrolysis treatment to form a porous glass preform core, SiCl4 alone or SiCl4 alone or in a predetermined tube of the burner shown in FIGS. SiCl4,BBr
The porous glass preform core can be coated with a porous glass preform cladding by supplying and flame treating the porous glass preform core, thereby forming a porous glass preform consisting of the core and the cladding.

Alternatively, after forming a porous glass preform core as described above, it is heated in a high-temperature furnace such as an electric furnace to make it transparent and vitrified to form a stretched rod, and then this stretched rod is inserted into a SiO2 tube. After that, an optical fiber base material consisting of a core and a cladding may be formed by heating and fusing.

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples.

Example 1 The burner of Figure 2 with the diameters shown in the table below was used.

SiC14250cc is added to the pipe 2 having the diameter shown in the table above.
/min, GeCl4 40cc/min, O2280cc/min, POCl3 3cc/min, and tube 3,
O2 1200cc/min for tubes 4, 5, and 6, C3
H8 560cc/min, He600cc/min, O2
The flow rate was 6000 cc/min, and the distance between the burner mouthpiece and the rod-shaped base material was 7 cm.

After 10 hours of continuous flame hydrolysis treatment, α was approximately 18.
A porous glass preform core was formed.

Soot and carbon were not attached to the burner crater.

Example 2 The burner of Figure 4 having the diameter shown in the table below was used.

Note that the tubes 2 and 3 protrude 2 mm from the tubes 4, 5, and 6.

SiCl4250cc was added to the pipe 2 having the diameter shown in the table above.
/min, GeCl4 40cc/min, O2280cc/min, POCl3 3cc/min, and tube 3,
O2 1200cc/min for 4, 5, and 6, C3
H8 560cc/min, He600cc/min, O260
The flow rate was 00 cc/min, and the distance between the burner nozzle and the rod-shaped base material was 4 cm.

After continuous flame hydrolysis treatment for 10 hours, α was approximately 10.
A porous glass preform core was formed.

Soot and carbon were not attached to the burner crater.

As explained above, in the present invention, from the center to the periphery, (a) O2 gas as a glass raw material and carrier gas, (b) O2 shield gas, (c) hydrocarbons as combustible gas, (ni) ) inert gas, (e)
Combustion O2 gas is separately supplied to each tube of a concentric multi-tube burner for flame hydrolysis, thereby forming a porous glass preform.

Therefore, the inside of the flame becomes an oxidizing atmosphere, and the carbon generated by the decomposition of the combustible gas is oxidized from the crater side to the flame tip, so that the glass particles do not darken.

In addition, combustible gases are first burned by O2 shielding gas, but due to the low flow rate of these gases, there is a laminar flow near the crater, so hydrocarbon decomposition does not occur near the crater, and the gas is combusted away from the crater. Since combustion takes place completely in one part, and the combustion of combustible gas by O2 is delayed due to the presence of inert gas in between, there is virtually no inconvenience such as carbon and glass particles adhering to the burner nozzle. A porous preform with a small α can be obtained by applying the vicinity of the flame tip where carbon has been completely oxidized to the preform growth point.

However, if a concentric multi-tube burner is used, in which the tubes for supplying the glass raw material and the O2 gas as a carrier gas and the tube for supplying the O2 shielding gas are provided so as to protrude from other tubes provided on the outside thereof, Since there are already very few hydrocarbons and carbon in the area where the glass raw material is injected, there is no effect of carbon at all during the reaction of the glass raw material, and the high temperature part of the flame can be applied to the preform growth point. Therefore, a sufficient amount of GeO2 can be contained, and a preform with a large α can be obtained.

[Brief explanation of drawings]

Figure 1 shows the distribution of molecular species and radical species generated when hydrocarbons are burned in a concentric multi-tube burner.
5 to 5 are schematic perspective views of burners used in the present invention, respectively. 1...Concentric multiple tube burner, 2, 2a, 2b, 3
, 4, 5, 6... tube.

Claims (1)

[Claims] 1. One or more tubes that sequentially supply glass raw material and O2 gas as a carrier gas from the center toward the outside when manufacturing an optical fiber preform by the VAD method; A concentric multiplex system consisting of a pipe that supplies O2 shielding gas, a pipe that supplies hydrocarbons as combustible gas, a pipe that supplies inert shielding gas, and an outermost pipe that supplies combustion O2 gas. A method for producing an optical fiber base material, which comprises subjecting it to flame hydrolysis using a tube burner. 2. The above patent claim uses a concentric multi-tube burner in which a tube for supplying glass raw material and O2 gas as a carrier gas and a tube for supplying O2 shield gas are provided so as to protrude from other tubes provided outside the burner. A method for manufacturing an optical fiber preform according to scope 1.