JPS6243934B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing an oxide powder rod that serves as the core of an SI type (step index type) optical fiber by a VAD method (vapor deposition method).

There are SI type and GI type (graded index type) optical fibers.The SI type has a refractive index distribution coefficient α of ∞ (in practice, 4≦α), and the GI type has a refractive index distribution coefficient α of ≒≒ It has become 2.

The SI type optical fiber mentioned above has superior light incidence efficiency from a light source compared to the GI type, and is therefore considered important for short-distance communications.

Conventionally, when manufacturing SI type optical fibers, a method has been adopted in which a preform rod is created and manufactured using an internal CVD method or an external CVD method.
However, it has already been pointed out that with these methods, it is difficult to provide a high refractive index difference between the core and the cladding, and there are also problems with mass production and cost reduction.

On the other hand, in the known VAD method, gas phase raw materials such as SiCl ₄ , GeCl ₄ , POCl ₃ , oxyhydrogen flame, and inert gas between the raw materials and the flame are injected from a powder generating burner with a multi-tube structure. Oxide powder (soot) produced by these flame hydrolysis reactions is deposited in a rod shape in a powder depositor to produce an oxide powder rod.

In this way, there are two ways to make an oxide powder rod, one of which is to make a single layer (layer for the core) of an oxide powder rod using a single powder producing burner, and the other is to make a single layer (layer for the core) of an oxide powder rod using a single powder generating burner. The process involves creating two layers of oxide powder (a core layer and a cladding layer) using the primary powder-generating burner.

In the former case, after the oxide powder rod is made into a preform rod for the core by transparent vitrification, a quartz-based glass tube for the cladding is placed on the outer periphery of the rod, and this is spun by heating and drawing to become an optical fiber. .

In the latter case, an oxide powder rod having a core layer and a cladding layer is transparently vitrified to form an optical fiber preform rod, which is spun into an optical fiber in the same manner as described above.

However, even with the optical fiber manufacturing method that uses the VAD method as a starting process, there are problems in manufacturing SI type optical fiber.

First, when producing a single-layer oxide powder rod using a single powder production burner, the temperature distribution at the growth end of the powder rod tends to be high at the center and low at the outer periphery, and the deposition condition of the oxide powder rod is also important. As a result, the concentration of the composition (GeO ₂ ), which is important for forming a predetermined refractive index distribution, is high at the center of the oxide powder rod and low at the outer periphery. A problem arises, especially in the outer periphery of the oxide powder rod, where α≧4, which is required for SI type optical fibers, is considerably lower and α=2-3.

Of course, in such a case, it would be troublesome to shave off the outer periphery of the oxide powder rod after it was made into transparent vitrification.

On the other hand, when producing a two-layer oxide powder rod using two powder-forming burners, the core composition and the cladding composition will mix at the interface between the core layer and the cladding layer. layer,
As a result, the cladding layer cannot be accurately separated and α at the interface becomes less than 4.Also, even if the distance between both burners is set sufficiently large to solve this problem, the core burner cannot be separated as described above. Since the problems of high temperature at the center and low temperature at the outer periphery, and large amount at the center and small amount at the outer periphery remain, this cannot be a fundamental solution.

In order to solve the above-mentioned problems, the present invention manufactures an oxide powder rod that becomes the core of an SI type optical fiber by a VAD method using two burners.The specific method is illustrated below. I will explain it together.

In the figure, 1 indicates a lower exhaust system 2 and an upper exhaust system 3.
Usually, the interior of the reaction vessel 1 is purged with an inert gas such as Ar, He, or _N2 .

Reference numeral 4 denotes a rod-shaped powder depositing device which is rotatably and vertically movable inside the reaction vessel 1 .

5 is a powder generation burner for axial deposition, and 6 is a powder generation burner for circumferential deposition.The tips of both burners 5 and 6 correspond to the tip of the powder depositor 4, which will be described later. It is placed inside the reaction vessel 1 while taking it out.

Both burners 5 and 6 in this case are quadruple tubes,
A multi-tube structure such as a quintuple tube is used.
In the case of a quadruple tube structure, a gas phase raw material injection channel, an inert gas injection channel, a hydrogen injection channel, and an oxygen injection channel are provided concentrically from the center to the outer periphery. In the case of the five-pipe structure, there is an injection channel for the gas-phase raw material containing the dopant at the center, and an injection channel for the gas-phase raw material not containing the dopant, an injection channel for the hydrogen, and an injection channel for the gas-phase raw material not containing the dopant are located at the outer periphery. active gas injection channel;
Oxygen injection channels are sequentially provided.

In the above, when the axis of the powder depositor 4 is L, the center line of the powder generating burner 5 is O ₁ , and the center line of the powder generating burner 6 is O ₂ , the intersection angle between L and O ₁ is θ ₁ is set as 0°≦ _θ1 <45°, and the intersection angle _θ2 between L and _O2 is 45°< _θ2 <≦90
It is set like ゜.

In the present invention, after the powder depositor 4 is rotated in the reaction vessel 1, predetermined raw material gas, combustion gas, and inert gas are injected from both burners 5 and 6, and oxidation is caused by a flame hydrolysis reaction by the combustion gas. The powder is generated and deposited on the tip of the powder depositor 4, and the powder depositor 4 is moved upward in the direction of its axis L in accordance with the deposition rate (growth rate) of the powder. In this way, an oxide powder rod 7 of a desired length is produced.

At this time, one powder generating burner 5 particularly promotes the growth of the oxide powder rod 7 in the axial direction, and the other powder generating burner 6 promotes the growth of the same rod 7 in the circumferential direction.

When producing the oxide powder rod 7 in this way, if only one of the powder generating burners 5 is used, there will be a tendency for the powder to accumulate with a large amount at the center and a small amount at the outer periphery, and a tendency for the hot cloth distribution to be high at the center and low at the outer periphery. α at the outer periphery of the rod 7 will be less than 4, but in the above case, the other powder generating burner 6 will eliminate the situation where the outer periphery is small and the outer periphery is low temperature. Uniform the overall powder deposition situation and temperature distribution situation.

Therefore, according to the present invention, a core oxide powder rod 7 having a uniform refractive index distribution in the radial direction and α of 4 or more can be obtained for an SI type optical fiber.

In addition, by adjusting the relative spacing between the burners 5 and 6, the temperature at the growth end of the oxide powder rod ₇ can be maintained appropriately. Since it is also possible to prevent the dopant from reacting unreacted, a predetermined refractive index distribution can be obtained in this respect as well.

In the present invention, as the gas phase raw material, a silicon compound is used as the main component and a germanium compound is used as the dopant, but phosphorus compounds and others are also effective as the dopant.

Examples of the silicon compounds, germanium compounds, and phosphorus compounds mentioned above include halides, hydrides, and oxychlorides.
Examples include SiCl ₄ , GeCl ₄ , POCl ₃ , SiHCl ₃ and SiH ₄ .

In addition, when producing the oxide powder rod 7 for the core as described above, the dopant concentration from the powder production burner 5 for axial deposition is the same as that from the powder production burner 6 for circumferential deposition. It is best to have the same or higher dopant concentration.
In such a case, it is easier to obtain a predetermined refractive index distribution.

Furthermore, the cross-sectional shape of both burners 5 and 6 may be circular or square, and the combustion gas injected from them may also be natural gas, city gas, propane gas, etc. in addition to oxyhydrogen.

Furthermore, the oxide powder rod 7 produced as described above is made transparent by heat treatment, resulting in SI
This is the preform rod for the core of the type optical fiber, and the outer periphery of this preform rod is covered with a glass tube for the cladding made of quartz glass, Vycor glass, etc., and both are heated and drawn and spun to form the SI type. optical fiber.

Example After two powder generating burners 5 and 6 having a quadruple pipe structure with a circular cross section are arranged in the reaction vessel 1 as shown in the figure, SiCl ₄ =5.5 m is emitted from each burner 5 and 6.
mol/min, GeCl ₄ = 1.1 mmol/min, POCl ₃ =
0.03 mmol/min, H ₂ = 3.5/min, Ar = 0.75
/min, and O ₂ =8.0/min, these were subjected to a flame hydrolysis reaction, and the resulting oxide powder was deposited in the powder depositor 4 in the form of a rod.

The oxide powder rod 7 thus obtained was heated to 1500°C.
It was made into transparent glass in a He atmosphere and made into a preform rod for the core.

When this preform rod was measured using an interference microscope, it was found that α=11, confirming that it is effective as a glass for the core of SI type optical fiber.

Note that the relative refractive index difference was able to be 2.1%.

For comparison, one powder producing burner 5 was used to produce an oxide powder bar for the core, and two powder producing burners 5 and 6 were used to produce an oxide powder bar having a core layer and a cladding layer. When powder rods were made and made into transparent glass, α remained at ≈3 in all cases, making them unsuitable for use as SI type optical fibers.

In addition, in the former (burner 5 only) in this comparative example, SiCl ₄ = 5.5 mmol/min, GeCl ₄ = 1.1 m
mol/min, POCl ₃ = 0.03 mmol/min, H ₂ = 3.5
/min, Ar = 0.75/min, _{O 2} = 8.0/min, and in the latter (burners 5 and 6), gas phase raw materials, inert gas, hydrogen, and oxygen are injected from one burner 5 under the same conditions as above. from the other burner 6.
SiCl ₄ = 5.5 mmol/min, H ₂ = 3.5/min, Ar =
0.75/min, O ₂ =8.0/min was injected.

As explained above, the present invention relates to a method for manufacturing an oxide powder rod, which is the core of an SI type optical fiber, by a vapor phase axial method. The powder generation burner for axial deposition is arranged so that the intersection angle θ ₁ with respect to the axis of the powder depositor satisfies 0°≦θ ₁ <45°, and The powder generating burners used for deposition are arranged so that the intersection angle θ ₂ with respect to the above-mentioned axis is 45° < θ ₂ ≦90°. The method is characterized in that the oxide powder produced by supplying is deposited and grown in a rod shape in a powder depositor.

In the present invention, since the oxide powder rod for the core is produced through both powder producing burners arranged under the above conditions, a large amount of powder at the center and a large amount at the outer periphery which are observed when only one powder producing burner is used are produced. The negative effects of a small amount of powder accumulation and a temperature distribution tendency of high temperature at the center and low temperature at the outer periphery are eliminated, and as a result, the oxide powder is desirable for the core of SI type optical fiber. A rod, that is, an oxide powder rod with a refractive index distribution coefficient α of 4≦α is obtained.

Moreover, in the present invention, since the oxide powder is produced by each of the above-mentioned powder producing burners to produce a predetermined oxide powder bar, the manufacturing speed can be increased even when producing a large oxide powder bar. Therefore, high quality oxide powder rods can be efficiently produced.

[Brief explanation of the drawing]

The drawing is a schematic cross-sectional view showing one embodiment of the method of the present invention. 4... Powder depositor, 5, 6... Burner for powder generation, 7... Oxide powder rod, θ ₁ , θ ₂ …… Intersection angle.

Claims (1)

[Claims] 1 In a method for manufacturing an oxide powder rod, which is the core of an SI type optical fiber, by a vapor phase axial method, a powder generation burner for axial deposition and a powder generation burner for circumferential deposition are prepared. The powder generation burner for axial deposition is arranged so that the intersection angle θ ₁ with respect to the axis of the powder depositor is 0°≦θ ₁ <45°. The burner has an intersection angle _θ2 of 45°<θ with respect to the above-mentioned axis.
₂ ≦90°, and the oxide powder produced by supplying a glass vapor phase raw material and a dopant to both powder generation burners is deposited and grown in a rod shape in a powder depositor. A method for producing an optical fiber oxide powder rod.