JPS6135139B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming an oxide powder layer for optical fibers obtained by flame hydrolysis.

As is known, optical fibers used in the optical communications sector are manufactured by processing an optical fiber base material, also called a preform rod, using a spinning method using heated drawing. The materials were manufactured using CVD and VAD methods.

Incidentally, in the conventional external CVD method, silicon is the main component on the peripheral surface of a glass rod that is supported at both ends and rotated, and halides such as germanium, phosphorus, and boron, or organic metal salts are used as dopants. The blended raw materials are blown in a gas phase together with an oxyhydrogen flame, and the oxide powder (sooting substance) generated by the flame hydrolysis is deposited on the circumferential surface of the glass rod. Also,
In the VAD method, raw material gas and flame are blown onto the plate surface of the rotating bed plate in the same manner as described above, and the resulting oxide powder is deposited on the plate surface in the form of a rod. The base material for optical fibers was obtained by heat-treating the rod-shaped products at high temperatures and vitrifying them. In each of the conventional methods described above, the following problems have arisen.

In other words, in each of the above conventional methods, the liquefied raw material is stored in a vaporization tank equipped with a gas inlet pipe and a gas outlet pipe, and a carrier gas controlled at a stable flow rate by a mass flow controller (MFC) is fed into the gas inlet pipe. Introduced into the vaporization tank and bubbled,
After the raw material was gasified and saturated in the same gas, the carrier gas containing the raw material was fed through the gas introduction pipe to the flame hydrolysis reaction section. Even if an attempt is made to supply a large amount of raw material gas to the reaction section in order to increase the growth rate, the amount of raw material gas is limited by its vapor pressure and ventilation rate, so ready-made vaporizers cannot satisfactorily achieve the intended purpose. For this reason, it was decided to increase the size of the vapor pressure increasing means, which maintains the inside of the vaporization tank and the feed line from the tank to the reaction section at a high temperature, and the oxyhydrogen flame burner through which the raw material gas is injected. Measures were taken to increase the amount of ventilation, but
This requires each of the above measures, making the equipment expensive and difficult to maintain and manage.
In particular, when the amount of ventilation of the raw material gas is increased, it is difficult to achieve proper harmony between the raw material gas and the flame, and there are also problems in that temperature control during flame hydrolysis becomes impossible.

In view of the above problems, the present invention does not supply the raw material in a gaseous state, but instead supplies the raw material in a liquefied state to the position of the flame, and vaporizes the raw material before it comes into contact with the flame. This makes it possible to increase the yield of oxide powder by flame hydrolysis reaction, increase the growth rate of the layer formed by the powder, and simplify the controllability at this time.

The method of the present invention will be explained below with reference to the drawings.

FIG. 1 shows the main parts of the apparatus used in the method of the present invention, and in the figure, 1 is a burner having a multi-tube structure.

This burner 1 has a small-diameter raw material injection pipe 2 at its innermost center, and a flame protection pipe 3, a hydrogen gas pipe 4, and an oxygen gas pipe 5 are successively superposed concentrically around the outer periphery of the pipe 2. Thus, a raw material injection path 6, a flame protection medium injection path 7, a hydrogen gas injection path 8, and an oxygen gas injection path 9 are formed, respectively.

At the base end 2' of the raw material injection pipe 2, which has a tip shape of a concentrated injection type, a diffused injection type, etc., there is a supply pipe 12 having branch pipes 10a, 10b and a valve 11, and a branch pipe 13a. , 13b and a valve 14 are connected to each other, and a heater 16 such as an electric heater for the purpose of vaporizing the raw material is also provided at the base end 2'.
Further, each of the supply pipes 12 and 15 is connected to a raw material supply source (not shown), respectively.

On the other hand, a supply pipe 17 connected to an inert gas (for example, argon, helium, etc.) or oxygen supply source is connected to the above-mentioned flame protection pipe so as to communicate with the flame protection medium supply path 7. , the hydrogen gas pipe 4 and the oxygen gas pipe 5 are connected to supply pipes 18 and 19 that communicate with a hydrogen gas source and an oxygen gas source so as to communicate with the respective gas injection paths 8 and 9.

In the present invention, a required optical fiber base material is manufactured by depositing an oxide powder layer through a device mainly based on the burner 1. At this time, a step index type refractive index distribution is produced. In the case of forming an optical fiber base material having the following by the VAD method, the process is as follows.

First, the liquefied raw material for the core of the optical fiber is fed from the supply pipe 12 into the raw material injection path 6 of the raw material injection pipe 2, and at this time, the heater 16 at the proximal end 2' of the pipe 2 While heating and vaporizing the raw material and injecting it from the tip of the pipe 2, the other supply pipes 17, 18,
Inert gas such as argon, hydrogen gas, and oxygen gas supplied from 19 to each injection of flame protection pipe 3, hydrogen gas pipe 4, and oxygen gas pipe 5 and into supply channels 7, 8, and 9 are ignited and burned to produce the above-mentioned The vaporized raw material is hydrolyzed by the flame at this time, and the oxide powder produced by the reaction is deposited in the axial direction while adhering to the plate surface (powder deposition location) of the rotating base plate, After the oxide powder layer for the core is formed into a predetermined rod-like length, the raw material supply from the supply pipe 12 is cut off, and the liquefied raw material for the cladding is supplied from the other supply pipe 15 to the raw material injection pipe. 2, vaporize it as before, inject it from the tip of the pipe 2, and hydrolyze the vaporized raw material with an oxyhydrogen flame that is combusted in the same manner as above to produce the reaction product. The oxide powder for the barrel cladding is deposited on the outer periphery of the oxide powder layer for the core.

At this time, since the inert gas as a flame protection medium injected from the flame protection pipe 3 is interposed between the raw material and the flame, it prevents raw material powder and oxides from adhering to the tip of the burner 1. Therefore, poor combustion and fire extinguishment due to burner 1 clogging are prevented, and the burner 1 has a strong firepower.
A hydrolysis reaction between the raw material and the flame takes place well ahead of the flame.

In addition, when the reaction is in the above-mentioned state, the heat generated by the reaction flame is also propagated into the raw material injection pipe 2, so that vaporization of the liquid via the heater 16 is promoted in a short time. Become so.

Next, we will explain the case of manufacturing an optical fiber base material having a graded index type refractive index distribution using the external CVD method. In other words, since oxide powder layers with different refractive indexes are formed layer by layer when vitrified, the liquefied raw material is vaporized in the same manner as above, and while it is hydrolyzed by a hydrogen oxide flame, the oxide powder is Each time a layer of powder is formed, the concentration of dopant in the raw material components is changed.

In this case, the liquefied glass raw material is supplied from one supply pipe 12, and the liquefied dopant raw material is supplied from the other supply pipe 15, so that both supply pipes
By adjusting the flow rate of either or both of No. 2 and No. 15, the mixing ratio of the ingredients of the raw materials is changed as specified.

The rod-shaped oxide powder layer obtained by the VAD method or CVD method described above is laminated around the glass rod. The oxide powder layer is treated at high temperature and vitrified. formrod).

In the above-mentioned external CVD method, the raw material for the core and the raw material for the cladding are switched and supplied to one burner 1.
An oxide powder layer for the core and an oxide powder layer for the cladding may be formed by
Alternatively, two or more burners 1 may be used for forming the oxide powder for the core and for forming the oxide powder for the cladding, respectively, to form the desired oxide powder layer.

Next, the method of the present invention and the conventional method will be compared and explained using specific examples.

[Method of the present invention]

At room temperature of 20℃, add 2.91ml of silicon tetrachloride/
The liquids are fed under the conditions of 0.39 ml/min for germanium tetrachloride and 0.065 ml/min for phosphorus oxychloride, and in the burner 1, the vaporization temperature at the base end 2' of the raw material injection pipe 2 is set to 100 to 200°C. Argon 0.5ml/min, hydrogen 3/min, oxygen 6/min for flame protection
When the above raw materials were reacted with a flame of min.
On the substrate as a powder deposition site, 1.26 g of oxide powder (sooted material) was obtained per minute.

[Conventional method]

While supplying raw materials in the gas phase, silicon tetrachloride is kept at 40°C, germanium tetrachloride at 30°C, and phosphorus oxychloride at 15°C, and carrier gas is supplied at 100 ml/min and 100 ml/min into these liquid tanks, respectively. min,
Aeration is performed at a rate of 40 ml/min, and the resulting raw material mixed gas is supplied to the burner, and argon 1 for flame protection is supplied.
When the reaction was carried out using a flame of 2/min, 2/min of hydrogen, and 4/min of oxygen, 0.23 g of oxide powder was obtained per minute at the powder deposited area.

As is clear from both of the above results, the present invention was able to achieve a much higher yield of oxide powder than the conventional method.

In this case, the outer diameter of the burner used in both methods is the same, 20 mm, and in the case of the conventional method, an increase in yield is expected by raising the temperature of the raw material, but the controllability in this case is Taking into account 0.7g/
The yield limit of the burner is approximately 100 min.

On the other hand, in the present invention, it was possible to easily increase the yield of 2 g/min.

Since the present invention is as described above, the following characteristic effects can be obtained.

First, in the present invention, the raw material is fed in a liquefied state, and is then vaporized before the flame for flame hydrolysis, which is different from the conventional method in which the raw material is supplied in a gaseous state from the beginning. In contrast, the yield of oxide powder can be greatly increased and the growth rate of the powder layer can be significantly increased.

Therefore, the productivity in manufacturing the optical fiber base material is improved.

Furthermore, in the present invention, the glass component and the dopant component can be mixed in liquid form at the stage of supplying the raw materials in liquid form. Therefore, when using a variety of dopants, it is possible to mix the glass component and the dopant component in liquid form. , the adjustment and control of these components is extremely simplified.

In addition, compared to conventional methods that use a large amount of carrier gas to supply raw materials to the reaction system, this method has the advantage of being able to omit the gas, and since the presence of the carrier gas restricts the degree of freedom in controlling the temperature of the reaction flame. Therefore, the reaction temperature during flame hydrolysis can be easily controlled.

Furthermore, when using a material with a low vapor pressure near room temperature as a dopant, in the conventional method of supplying raw materials in the gas phase, it is necessary to maintain the raw material feed line up to the reaction flame at a high temperature. There was a problem that these dopants were not used due to the trouble of management, but according to the present invention, the raw material is only heated in the vicinity of the flame, and there is no need to heat the raw material all the way to the burner. Therefore, dopants with low vapor pressure can also be used without the above restrictions.

[Brief explanation of the drawing]

The drawing is a partially cutaway front view showing the main parts of the apparatus used in the method of the present invention. 1... Burner, 2... Raw material injection pipe, 3... Flame protection pipe, 4... Hydrogen gas pipe, 5... Oxygen gas pipe,
6... Raw material injection path, 7... Flame protection medium injection path,
8...Hydrogen gas injection path, 9...Oxygen gas injection path.

Claims (1)

[Claims] 1. A method for obtaining an oxide powder for optical fiber by flame hydrolysis of a raw material containing a glass component, in which a raw material in a liquefied state is fed to a flame position, and the raw material is The material is vaporized in front of the flame, and while the vaporized raw material is blown along with the flame to the powder deposition location, it is flame-hydrolyzed and the oxide powder produced by the reaction is deposited at the deposition location. A method for forming an oxide powder layer for optical fiber. 2. A method for forming an oxide powder layer for an optical fiber according to claim 1, wherein the raw material is blown out from the center of the flame. 3. The method for forming an oxide powder layer for an optical fiber according to claim 2, wherein a flame protection medium is interposed at the boundary between the flame and the raw material.