JPS6168340A - Production of parent glass material for optical fiber - Google Patents

Abstract

PURPOSE:To enable to use hydrocarbon gas as fuel for flame to be used for hydrolysis of a starting material for the glass by flowing each starting material gas with a specified arrangement to each port using a multilayered tube. CONSTITUTION:Gas streams are arranged in such a manner that fuel hydrocarbon gas is flowed out from a burner interposed between flows of gaseous oxygen. Namely, a concentric cylindrical six layered tubular burner is used, and (i) gaseous starting material and carrier gas are flowed through a central port 5, gaseous oxygen is flowed through a second port 6 and a sixth port 10, seal- gas is flowed through a third port 7 and a fifth port 9, and hydrocarbon gas is flowed through a fourth port 8. The hydrocarbon gas is burnt completely by the above-described process, thus, deterioration of quality due to deposition and entanglement of fine carbon particles to a porous glass body to be generated by the incomplete combustion is avoided.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a method for producing a glass base material for optical fibers by hydrolyzing glass raw materials to synthesize glass particles, and particularly relates to a method for producing a glass base material for optical fibers by hydrolyzing a glass raw material and synthesizing glass particles. Suitable for fiber manufacturing.

[Conventional technology]

Conventionally, one of the methods for manufacturing a glass base material for optical fibers is to put a glass raw material such as AXCT4 into a flame, synthesize Shigawas fine particles through a hydrolysis reaction, and then transfer the glass fine particles to a starting material, that is, on a mandrel or A method of manufacturing an optical fiber base material in which the base material is deposited on the tip of a glass rod and then heated to become transparent has been widely used, and an oxyhydrogen flame has been mainly used as the flame.

By the way, recently, the use of hydrocarbon gas as a flame fuel instead of oxyhydrogen flame has been considered. Hydrocarbon gases generally have a higher heat of combustion per unit volume than hydrogen gas. For example, methane gas is 212 KCJ&L/n
o 1. Acetylene gas has a heat of combustion of 310Kcat/mol, while hydrogen gas has a heat of combustion of 68Kcat/mol.
It is l. For this reason, when depositing glass particles, it is easy to increase the surface temperature of the porous glass body to be deposited, so the bulk density of the porous glass body can be increased, and the porous glass body is difficult to break. , it has the advantage of being easy to create.

By the way, when synthesizing glass particles using a multi-tube burner using H3, which has a large diffusion coefficient, as a fuel gas, the multi-tube burner should have a simple cross-sectional structure (with a central part) as shown in Figure 4, for example. A concentric multi-tube with 1 to 4 layers can be used.

In FIG. 4, 1 is a glass raw material, 2 is a mountain, 3 is an inert gas, and 4 is 0. Shows the part where gas flows. The inert gas flowing in step 3 is necessary to prevent the tip of the burner from being heated and worn out due to combustion reaction near the burner outlet. It is also desirable to make the generated glass particle stream as narrowly focused as possible to ensure that the glass particle stream deposits the glass particles accurately and efficiently on the desired deposition surface. Therefore, the frit is flowed into the center boat 1 of the burner so that the frit stream can be placed in the center of the flame. Furthermore, 03 with a small diffusion coefficient is added to the outermost M
4, and by focusing the flame, it has the effect of increasing the degree of convergence of the glass raw material. When using a burner with a large diffusion coefficient, even if a burner with such a simple structure is used, H1 will be sufficiently diffused in the inert gas and 0. It reacts quickly.

However, in a burner having a simple structure as shown in FIG. 4, when a hydrocarbon gas having a large molecular weight and a small diffusion coefficient is used instead of '12 as a fuel gas, the following problems occur.

That is, when hydrocarbon gas is flowed into the hydrogen gas boat 2 of the quadruple tube burner for oxyhydrogen flame shown in FIG. A long, carbon-containing flame forms from the tip. If glass particles are deposited using such a flame, carbon particles will be mixed into the porous glass body, deteriorating the transmission characteristics.

In order to avoid such carbon contamination, there is a method of increasing the distance between the burner and the porous glass body to promote mixing with oxygen gas, but in this method, as the porous glass body is moved away from the burner, the tip of the flame If the porous glass body is heated only by heating, the temperature in the deposition region cannot be maintained high. For this reason, it is difficult to create a porous glass body that is difficult to break by increasing the bulk density with the regular gas flow method of a quadruple tube burner. Obtaining the body was difficult.

[Problem that the invention seeks to solve]

In view of the above knowledge, the present invention aims to solve the problems.
By improving the conventional method and using hydrocarbon gas as a fuel gas, we have synthesized a porous glass body that suppresses the precipitation of carbon particles and has a high bulk density that is difficult to break, thereby creating an optical fiber with excellent transmission loss. The purpose was to provide a method for stably producing .

[Means to solve problems]

As a means of achieving the above objects, the present invention uses a multi-tube burner to form a flame.1. A method for producing a glass preform for optical fibers, which includes a step of introducing raw materials for glass synthesis into the flame, synthesizing glass fine powder, depositing it on the starting material, and then heating and transparentizing the deposited body. A hydrocarbon gas is used as the flame fuel, and the gas arrangement for flowing from multiple pipes is such that seal gas is arranged on both sides of the hydrocarbon gas, and oxygen gas is arranged on both sides of the gas. The present invention provides a method for manufacturing a glass preform for optical fibers.

A particularly preferred embodiment of the present invention includes the above-mentioned method using a gas containing argon gas, nitrogen gas, or helium gas as the sealing gas, and a further preferred embodiment includes the method using a gas containing argon gas, nitrogen gas, or helium gas as the sealing gas, and in a further preferred embodiment, methane gas or The above method uses a gas containing acetylene gas as a main component.

Basically, the present invention is implemented by arranging the gas in the boat of the multi-tube burner so that when a hydrocarbon gas is used as the fuel for the flame used in the hydrolysis reaction of glass raw materials, the fuel is sandwiched between oxygen gas. Then, oxygen gas is inserted between the porous glass body being deposited and the flow of hydrocarbon gas, and the carbon particles generated by incomplete combustion are completely burned in this oxygen gas flow, resulting in a polycarbonate gas. The method is characterized by a multi-tube burner boat gas arrangement that prevents the gas from reaching the glass body.

In the method of the present invention, the central boat of the multi-tube is for the glass raw material, and the carrier gas is, for example, argon gas,
Helium gas, nitrogen gas.

Oxygen gas or a mixture thereof is used.

Additionally, if necessary, hydrogen gas or the gases listed as carrier gases may be flowed from the raw material boat.The number of glass raw material boats is not necessarily limited to one boat; for example, the raw material composition may be changed and flowed from multiple boats. A flame gas boat is placed outside the frit boat.

The flame gas port is filled with oxygen gas, seal gas e, hydrocarbon scum, seal-tj, x, from inside to outside.

Oxygen gas is used as the sealing gas, and an inert gas such as argon gas or helium gas, nitrogen gas, or a mixture thereof is used as the sealing gas. Moreover, you may further add a gas boat in the above order as needed.

Examples of the hydrocarbon gas used in the present invention include methane,
Examples include ethane, propane, butane, ethylene, and acetylene.

FIG. 1 shows the simplest embodiment of the present invention.
It is a figure explaining the case where a concentric cylindrical six-tube burner is used. The center boat 5 allows glass raw materials, carrier gas, or hydrogen gas to flow as required, as described above. 2nd boat 6
Oxygen gas is supplied to the E6 boat 10, seal gas is supplied to the third boat 7 and fifth boat 9, and hydrocarbon gas is supplied to the fourth boat 8. In other words, oxygen gas and seal gas are supplied to the second and subsequent boats. , hydrocarbon gas, seal gas, and oxygen gas in that order.

The multi-tube burner used in the present invention is not limited to a concentric cylindrical shape, but may have a tapered shape, a rectangular shape, or a non-axisymmetric shape, and a flame-forming gas boat is arranged to surround a frit boat. It is acceptable as long as it is

The manufacturing process according to the method of the present invention is characterized in that the present invention essentially uses a hydrocarbon gas as a combustion gas and the method of gas flow in the process of depositing glass particles. Any method may be used for the steps up to this point.

〔Example〕

The present invention will be described in detail below with reference to Examples and Comparative Examples.

Example 1 Using the six-tube burner shown in Fig. M1, five oxygen gases were supplied from the second port9. Argon gas 4t/min from the third boat,
Natural gas whose main component is methane gas from the 4th boat
t/min, nitrogen gas S t/min from the 5th boat, and oxygen gas 10 t/min from the 6th boat to form a flame, and 16 sand was flowed from the center boat using argon gas as a carrier gas to produce tetrachloride. Silicon α was charged at 36 t/min.

The root of the flame was probed with a glass rod and confirmed that no carbon particles were observed.

The starting material was a pure silica glass rod with an outer diameter of 5 mm.
A flame was passed back and forth over this to deposit glass particles. In order to suppress radial variation in the bulk density of the porous glass body, the carrier gas was gradually lowered to α4 t/min depending on the outer diameter of the porous glass body. Deposition was carried out until the outer diameter of the porous glass body was 80III+.
No inclusion of carbon particles was observed. The composite structure of the starting material and the porous glass body was heated with helium gas at 5 t/min, chlorine gas Q at 0.5 t/min, and sulfur hexafluoride gas at 11.2 t/min.
Dehydration and fluorine doping were performed in an atmosphere of 1,300° C. and a descending rate of 5 dew/min. Next, transparent vitrification was performed in an atmosphere of helium gas at 10 t/min under conditions of a temperature of 116 soC and a descending speed of 37 mIn. Furthermore, the transparent glass body is stretched to obtain an outer diameter of ? fl and the first
Glass particles were deposited under the same conditions as the first time until the outer diameter reached 70 mm, and then dehydration, fluorine doping, and transparent vitrification were performed under the same conditions as above.

Through the above steps, an optical fiber intermediate having a refractive index structure as shown in FIG. 2 was obtained. The relative refractive index difference 11 of this optical fiber intermediate is 0.3X.

The ratio of core diameter 12 to cladding diameter 13 was 9 times.

After covering this with a quartz glass tube for a jacket, a fiber with a refractive index structure as shown in FIG. 3 is drawn with an outer diameter of 14
is 125μm, cladding diameter 15 is 65pm, core diameter is 16
An optical fiber with a diameter of 7 pm was obtained. The transmission characteristics of this optical fiber are a loss of 14B/@ at a wavelength of 1.3pm.
In the following, it was found to be good as a single mode fiber.

Comparative Example 1 Using a quadruple tube burner as shown in Fig. 4, silicon tetrachloride was fed from the center boat 1 at α36t/min, argon gas was used as a carrier gas for 1617 minutes, and methane was the main component from the second boat 2. 2.1 t/min of natural gas, 1.3 t/min of argon gas from 5th port 3, 4th boat 4
Oxygen gas was flowed at 15 t/min from each, and the outer diameter was 6.
Glass fine particles were deposited on a pure silica glass rod with an outer diameter of 20. Around this time, the porous vitrification became grayish, and carbon fine particles were observed to be mixed in.

When the above method was carried out with the carrier gas being oxygen IIL 6 t/min and the other conditions being the same, contamination of carbon fine particles was observed from around the time when the outer diameter reached 50 mm.

Furthermore, when the burner was moved away from the oxygen carrier by 5α to prevent the carbon-containing portion of the flame from reaching the porous glass body until the outer diameter of the porous glass body became 70 mm, the outer diameter was 50 mm. The porous glass body burst when it grew to -.

When the bulk density of this glass body was measured, α21/d
It was below.

Example 2 Using the six-tube burner shown in Fig. 1, oxygen gas 7 t/min, argon gas 317 min, acetylene gas 7 L/min, nitrogen gas 2,217 min, and oxygen gas 12 t/min were supplied to the second to sixth boats. /min in this order to form a flame, and silicon tetrachloride vapor α42 is released from the center port along with oxygen gas 17.
t/min was input. The flame thus formed was reciprocated on a rotating pure silica glass rod having an outer diameter of 8 mφ to deposit glass particles. In this way, the outer diameter? A composite structure of O■ porous glass and glass rod was obtained, but no inclusion of carbon particles was observed.

The composite structure was heated with helium gas 5t/min, chlorine gas α05
Dehydration and fluorine doping were performed in an atmosphere of 67 sulfur fluoride gas α2 t/min at a temperature of 1300° C. and a descending rate of 3 times. Next, the temperature was 1650°C in an atmosphere of helium gas at 10 t/min.

Transparent vitrification was achieved at a descending speed of 5.

Further, the transparent glass body was stretched to an outer diameter of 10 cm, and the deposition was carried out under the same conditions as the first time until the outer diameter became 40 m.
Dehydration, fluorine doping, and transparent vitrification were performed under the same conditions as the first time.

The optical fiber intermediate obtained through the above steps has a refractive index structure as shown in FIG. 2, with a relative refractive index difference 11 of α3X and a ratio of core diameter 12 to cladding diameter 13 of 10 times. Ta. After covering this with a quartz glass tube for jacket,
When drawn, the fiber has a refractive index structure as shown in FIG. 5, with an outer diameter 14 of 125 μm and a cladding diameter 15 of 70 μm.

An optical fiber with a core diameter of 16 7 μm was obtained.

The transmission characteristics of this optical fiber were good as a single mode fiber, with a loss of 1 dB/&jl or less at a wavelength of t3 μm.

Comparative Example 2 Only oxygen gas [1 L/min] was supplied from the center boat 1 of the quadruple tube as shown in Fig. 4, and acetylene gas IO 1/min and argon gas IO/min from the second boat 2 to fourth boat 4.
17 t/min of oxygen gas were flowed in this order to form a flame. In order to observe the adhesion of carbon particles within the flame, a quartz rod was inserted into the flame and observed.It is expected that the porous glass body will be touched after it has grown to an outer diameter of approximately 50 m. Significant adhesion of carbon particles was observed at the flame site.

Furthermore, the generation of carbon fine particles was suppressed by setting the oxygen gas flow rates of the center boat 1 and the fourth boat 4 to t5t/min and 191/min, respectively, and after moving the burner 2cm away,
4 was injected from the center boat 1 at 42 L/min of IIL together with the above oxygen, a quartz rod with an outer diameter of 61III was rotated, and the flame was reciprocated over it to perform deposition.
When the cod had grown to zero, carbon fine particles were observed on the surface of the glass porous body, and cracks occurred at an outer diameter of 80 m. When this glass porous body was disassembled and the inside was observed, it was found that carbon fine particles were mixed in at a portion having an outer diameter of about 40 mm or more.

〔Effect of the invention〕

As is clear from the above description and examples, the method of the present invention involves introducing a glass raw material into a flame fueled by a hydrocarbon gas, and subjecting it to flame hydrolysis to synthesize glass fine particles to create a glass base material. This method still has the advantages of increasing the bulk density of the porous glass body and creating a porous glass body that is difficult to break, and there is no contamination of carbon particles into the porous glass body, which was a drawback of the conventional method. Therefore, it is possible to stably produce a porous glass body, the resulting optical fiber base material and optical fiber have excellent transmission loss characteristics, and there is no cracking during production, so it is an economically superior method.

The method of the present invention also has the advantage that it can be carried out with a burner of simple construction.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a six-tube burner used in a practical embodiment of the present invention, and FIG. 2 shows a refractive index distribution of an optical fiber intermediate produced according to an embodiment of the present invention. 5 is a refractive index distribution 1rrriaa,i of an optical fiber made from the optical fiber intermediate shown in FIG. 2, and FIG. 4 is a sectional view of a quadruple tube burner used in the conventional method (comparative example).

Claims (3)

[Claims] (1) A flame is formed using a multi-tube burner, raw materials for glass synthesis are introduced into the flame to synthesize glass fine powder, and after being deposited on the starting material, the deposited body is heated to make it transparent. A method for manufacturing a glass base material for optical fibers, which includes using a hydrocarbon gas as the flame fuel, arranging seal gas on both sides of the hydrocarbon gas as a gas arrangement for flowing from multiple pipes, and A method for producing a glass base material for optical fibers, further comprising arranging oxygen gas on both sides thereof. (2) The method for manufacturing a glass preform for optical fibers according to claim (1), wherein a gas containing argon gas, nitrogen gas, or helium gas is used as the sealing gas. (3) The method for producing a glass preform for an optical fiber according to claim (1), wherein the hydrocarbon gas is a gas whose main component is methane gas or acetylene gas.