JPS6186440A - Manufacture of preform for optical fiber - Google Patents

Abstract

PURPOSE:To increase the adhesion efficiency of fine particles and to obtain efficiently a high-quality preform by laminating the glass particles while cooling the porous base material in case of manufacturing the preform for an optical fiber by a gas phase axial accumulation method. CONSTITUTION:The raw material for glass and the combustion gas are mixed and burned by a burner 31 and the produced fine glass particles 33 are stuck and accumulated on the lower end of a rod-shaped base material 35 which is moved in the upper direction while rotating and a porous glass base material 34 is formed by growing them in the axial direction. In this case, a blow-off port 36 of gas for cooling is provided to the part upper than the burner 31 in approximating to the porous glass base material 34 and a gas 37 for cooling such as N2 gasified from liquid nitrogen is blown on the porous base material 34 to cool it. Thereby the adhesion efficiency of the fine glass particles 33 is increased by the thermo phoresis effect. Then the porous base material 34 is sintered and vitrified to obtain the aimed preform for an optical fiber.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention provides a new method for manufacturing optical fiber preforms using the VAD method (vapor deposition method).

[Conventional technology]

In the VAD method, as shown in FIG. 1, soot-like glass particles 3T are deposited on the end of a rod-shaped substrate 5 that rotates and moves upward, and as the rod-shaped substrate 5 is pulled up, the soot-like glass particles are deposited. In this method, a rod-shaped porous glass preform 65r is grown in the 3t-axis direction, and then subjected to a predetermined treatment to produce an optical fiber preform. Then, this optical fiber preform is spun to produce an optical fiber. The above-mentioned VAD method is said to be a method with excellent mass productivity. In FIG. 1, 1 is a glass particle synthesis burner, 2 is an oxyhydrogen flame, and 4 is an unreacted point of the raw material appearing at the center of the flame.

[Problem that the invention attempts to solve] By the way, the VAD method has a high synthesis rate.

When manufacturing a porous glass base material, it is necessary to increase the amount of raw material input per unit time, but because the adhesion efficiency of sooty glass particles on the porous glass base material decreases, the amount of raw material input is proportional to the amount of raw material input. The problem was that it was not possible to increase the deposition rate on the porous matrix. In the past, efforts have been made to appropriately select parameters such as burner shape, windshield diameter, and oxyhydrogen flow rate in order to prevent the above-mentioned drop in adhesion efficiency. However, changing these parameters also changes the flame shape and stability, as well as particle generation and growth, making it impossible to significantly improve the deposition rate.

Figure 2 shows the deposition rate Cf1 min) and the 81014 input amount C1.
7 minutes).

In view of the above-mentioned current situation, an object of the present invention is to provide a method for improving the adhesion efficiency of sooty glass particles onto a porous glass base material.

[Means for solving problems]

The Thermo-7 Oretus effect is known as one of the forces that contributes to improving the adhesion efficiency of sooty glass particles.In the case of the VAD method, the Thermo-7 Oretus effect is also used to improve the adhesion efficiency of sooty glass particles. It is thought that this has a great effect on the deposition on the wood [Reference: J, pp1. Fhyg,
535920-5925 (1982)]. Due to the above-mentioned thermophoresis effect, the soot-like glass particles have a velocity component that moves toward the sooty-like glass particle deposition surface on the surface of the porous glass base material, and in order to adhere to the deposition surface, it is necessary to There must be a negative temperature gradient towards the surface. Traditionally, this temperature gradient is.

They were left to form naturally due to the oxyhydrogen flame and porous glass matrix.

The present inventors investigated various methods of increasing the temperature gradient and came to the conclusion that the most appropriate method was to spray cooling gas onto the porous glass base material from a source other than the glass particle synthesis burner. Using this method, f! ! The temperature gradient around the deposition surface can be increased while minimizing hydrogen flame and feedstock flow turbulence, thereby increasing the deposition efficiency of sooty glass particles onto the porous glass matrix. .

That is, in the method of the present invention, raw materials for glass and combustion gas are mixed and burned in a burner, fine glass particles are laminated in the axial direction to create a porous base material, and this is later sintered to make it transparent to produce an optical fiber preform. The present invention relates to a method for producing an optical fiber preform, the method comprising cooling the porous base material (and then layering fine glass particles thereon).

A preferred embodiment of the present invention includes the method for manufacturing an optical fiber preform described above, in which the porous base material is cooled by blowing low-temperature N, gas, or Ar gas.

The present invention will be explained in detail below.

FIG. 3 is a diagram explaining one embodiment of the present invention, and in the figure 31
32 is a glass particle synthesis burner, 32 is an oxyhydrogen flame, 33 is a flow of glass particles, 34 is a porous glass base material, 35 is a starting base material 36 is a cooling gas outlet, and 37 is a flow of cooling gas.

The cooling gas outlet 36 is disposed above the burner 31, close to the porous glass base material, and is directed toward the surface on which the glass fine particles are deposited. As the cooling gas, for example, 00 tkW of liquid nitrogen, vaporized nitrogen, or sublimated dry ice is used. The flow rate of the cooling gas is adjusted to the minimum amount within the range where the cooling gas separates the flame into both sides and directly hits the porous glass base material. In this way, by adjusting the cooling gas outlet and the cooling gas, the shape and stability of the flame can be improved.
The surface of the porous glass base material that is exposed to the cooling gas can be cooled while minimizing the influence on the generation and growth of particles. As the porous glass base material rotates, the cooled surface is directly exposed to the flow of high-temperature glass particles, and a large amount of glass particles are deposited due to the Thermo7 Oretus effect, improving the adhesion efficiency of glass particles. can be done.

〔Example〕

An embodiment of the present invention will be described below. In the arrangement shown in Figure @3, a quadruple tube with an outer diameter of 20 m was used as the glass particle synthesis burner. A cooling gas outlet with a diameter of 20 mm was used, and the distance from the porous glass base material was maintained at 2 mm. The flow rate of the cooling gas was 1 t/min. The glass raw materials, combustible gas, and combustion assisting gas were flowed at the flow rates shown in Table 1.

Table 1 Porous glass base materials were prepared for cases in which cooling gas was not flowed at the above flow rates and cases in which it was flowed.

When the temperature of the porous glass base material deposition surface was measured using a spot sensor, it was 780°C without flowing cooling gas and 730°C with flowing cooling gas, and the temperature of the top surface was lowered by 50°C due to cooling gas. hole.

In addition, the adhesion rate of glass particles onto the porous glass base material was 63% when no cooling gas was flowing, and 7% when it was flowing.
7%, and the method according to the present invention was found to be effective in improving adhesion efficiency. When the porous glass base material created under the above conditions while flowing a cooling gas was made into transparent glass and made into a fiber, the loss (L 6 dB/km (λ=1.
3μ).

An optical fiber with a bandwidth of 690 KHg (λ=t3μ) was obtained. In this way, by blowing the cooling gas onto the deposition surface of the porous glass base material to cool it, it was possible to increase the adhesion efficiency and obtain a high-quality glass fiber for optical communication.

〔Effect of the invention〕

As is clear from the above explanation and the data of the examples, the method of the present invention can improve the adhesion efficiency of sooty glass particles onto the porous base material, so it can efficiently produce high-quality optical fiber preforms. Can be manufactured well.

[Brief explanation of drawings]

Fig. 1 is a schematic explanatory diagram of the conventional WAD method, Fig. 2 is a graph showing the relationship between 8 i Ct4 input amount and deposition rate in the case of the conventional method, and Fig. 3 is an example of an embodiment of the method of the present invention. FIG. 2 is a schematic diagram. S; ('/d Length quantity (9/?)

Claims (2)

[Claims] (1) A method for producing a preform for optical fiber by mixing raw materials for glass and combustion gas in a burner, stacking glass particles in the axial direction to create a porous base material, and later sintering this to make it transparent. , characterized in that glass fine particles are laminated while cooling the porous base material,
A method for manufacturing an optical fiber preform. (2) The method for manufacturing an optical fiber preform according to claim (1), wherein the porous base material is cooled by blowing low-temperature N_2 gas or Ar gas.