JPS6054892B2 - Method for manufacturing optical fiber glass - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method of manufacturing an optical fiber.

Optical fiber manufacturing methods can be broadly classified into the following four types. 1)
Method 2) A glass film with a higher refractive index is formed on the inner wall surface of the starting cylindrical member (usually a quartz pipe is used), and then wire-drawn after heat welding 2) Solid cylindrical member (usually high-purity quartz is used) 3) A method of forming glass with a lower refractive index on the outer wall of the molten glass and drawing it. 3) A method of directly drawing molten glass in multiple crucibles to create a multilayered optical fiber with a high refractive index in the center. 4) There is a method in which a source gas is flame-hydrolyzed to deposit a rod-shaped glass soot on a seed rod, which is then defoamed and vitrified, and drawn to form an optical fiber.

3) is used in the production of optical fibers using low-softening multi-component glass due to the heat-resistant material of the glass melting crucible and the contamination from the crucible when heated to high temperatures.

The conventional technique directly related to the present invention is the above 4), and the features of the method 4) will be described below to provide a detailed explanation of the present invention.

FIG. 1 is a conceptual diagram of an apparatus used in method 4).

Normally, a raw material is mixed into the oxyhydrogen flame emitted from the nozzle 11 to create glass particles, which are deposited on the tip of the starting material that rises while rotating, and are used as the core (light propagation region) when made into an optical fiber. Here, the production time of the sintered body 16 is usually 257! r!
n~35TfrIf1 diameter 50ugly~80W&/Hr
growth rate. Next, fine glass particles for the cladding (the part of the outer periphery of the core with a low refractive index) are blown into a sintered body 17 using the same nozzle 12, and this is degassed in an electric furnace at approximately 1600°C and a carbon heater 15 for local heating. Vitrify. The linear shrinkage rate of this sintered body 17 is 0.3 to 0.
5, the sintered body with a diameter of 257 m, for example, becomes a transparent glass rod 18 of about 10 Tm. The thus produced glass rod for optical fiber (hereinafter referred to as preform) is drawn to produce an optical fiber having an outer diameter of about 130 μm and a core diameter of about 60 pm. Difficulties with the conventional method mentioned above are degassing and long length of the sintered rod. The objective is to reduce the variation in the outer diameter in the direction.

Optical fibers used as optical transmission lines are desired to have low optical transmission loss. If defoaming is not complete, light scattering occurs at the boundary between the bubbles and the glass, resulting in a loss of propagating light. Furthermore, it is clear that variations in the outer diameter have an adverse effect on transmission characteristics. An object of the present invention is to provide a method for manufacturing an optical fiber that facilitates degassing and reduces variation in outer diameter. Conversely, it is possible to produce a preform with a larger diameter for the same defoaming efficiency. Defoaming is carried out through the connected gas phase of the sintered body.

Therefore, the boundary between the transparent vitrified portion and the sintered body portion must be as clear as possible. For example, when transparent vitrification progresses partially, the air bubbles of the shattered sintered body remain inside the glass in contact with the outside air phase.
Defoaming becomes difficult. For this reason, it is desirable that the temperature distribution of the electric furnace for transparent vitrification has a large temperature gradient in the area where the transparent vitrification is to be performed, that is, it is steep so that the boundary between the sintered part and the vitrified part is sharply separated. Furthermore, as the diameter of the sintered body increases, a temperature gradient occurs between the inside and the outer circumference of the rod as the degassing rod moves at a faster speed. That is, it is necessary to match the temperature distribution of the electric furnace and the degassing rate depending on the diameter of the rod, and generally, as the diameter of the sintered rod increases, the difficulty of degassing increases. In order to solve this difficulty, a cylindrical glass sintered body is produced and degassed to form core and cladding glass with few impurities and bubbles, which is then used as an optical fiber. is the main part of the present invention. Defoaming in a rod-shaped sintered body is performed from the outer periphery of the rod, whereas in a cylindrical sintered body, defoaming is possible from both the inside and the outer periphery of the cylinder, and the same defoaming The effectiveness of the present invention is that the volume (outer diameter) of a solid rod-shaped core or clad rod can be arbitrarily increased by increasing the diameter even if the wall thickness of the cylindrical sintered body remains the same. It should be obvious. Hereinafter, the present invention will be explained in detail with reference to Examples.

Example 1 FIG. 2 is a sectional view showing an outline of the apparatus used in the present invention.

A mixed gas of SiCI4 and source gas POCl3 as a dopant for controlling the refractive index is ejected from 21 with an oxyhydrogen burner, and SiO2-P2O formed by a flame hydration reaction is produced.
．． Glass particles were sintered deposited on the end of a rotating cylindrical starting material.

This sintered body 25 is moved upward by a rotating roll 23 and degassed in an electric furnace 22 to form a transparent cylindrical glass 26, which is then heated and welded in an electric furnace 24 to form a high-purity glass 26 for the core.
7 was produced. Rare gas 02 flowing from the nozzle 28. N2 helps defoaming and is effective in controlling the shape of the end of the cylindrical sintered body. The sintered body at this time had an outer diameter of 14φ and an inner diameter of 10Wr.
1! 1, and the outer diameter of the glass rod after being made into transparent glass and further welded is 7.1T! It was n. A solid rod-shaped sintered body with an outer diameter of about 10 w0n is defoamed and vitrified (outer diameter after vitrification is ~7
Tfr! Ft) is approximately 2.5 wft/min, whereas the degassing rate of the sintered body produced by this method is approximately 6 wft/min.
It was possible to increase the speed by 2 to 4 times to 1 Cyrfr1n/Min. The rod-in-tube method (
When fabricated using the method of inserting a solid core rod into a quartz vibrator and heating and melting it to form a free form, the optical transmission loss at the GaAs laser light wavelength (8300A) was approximately 5 dB.
/-, which was a fairly low loss, but absorption due to 0H harmonic vibration at a wavelength of around 9500A was observed. This is thought to be caused by the incorporation of H from the oxyhydrogen burner. Example 2 FIG. 3 is an outline of a high-purity glass tube manufacturing apparatus.

A combustible gas not containing hydrogen (for example, NO, CO, etc.) is introduced from 35 through the starting circular pipe 31, while a source gas is introduced from 36 along with oxygen (into the outer peripheral part of the starting circular pipe 31).
Send it in.

A sintered gas 33 was grown at the end of the circular tube 31 by burning combustible gas at the end of the tube 31 and decomposing and oxidizing the source gas using the combustion heat.

The sintered glass 33 thus formed is a white porous sintered glass tube, and as it grows, it is pulled downward together with the starting material, defoamed and vitrified in an electric furnace 37, and high-purity glass tubes 32 are successively grown. Ta. The flow rate of the combustible gas, that is, the magnitude of the firepower when it is combusted, depends on the sinterability and formation speed of the glass sintered body 33, and the amount of source gas depends on the formation speed of the glass sintered body 33. The balance between the flow rate and the flow rate of (source gas +02) introduced from 36 is an important factor in controlling the shape of 33 (outer and inner diameter). High-purity glass tubes made using this method are welded,
When it was made into a bar-like rod, its volume was 5 to 1@ compared to the conventional rod manufacturing method shown in FIG. Therefore, by forming the rod into a tube shape, defoaming becomes very easy and the effective growth rate of the rod can be increased. Furthermore, according to this method, Ge, B, P, Sn
A quartz-based glass tube containing one or more oxides such as oxides can be manufactured. In Example 1, by arranging multiple burners as soot sources, a preform having an arbitrary refractive index distribution can be produced, as in the case of FIG. 1 showing the conventional method.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of a conventional optical fiber rod manufacturing apparatus;
FIG. 2 is a cross-sectional view showing an overview of an optical fiber rod manufacturing apparatus in one embodiment of the present invention, and FIG. 3 is a cross-sectional view showing an overview of a high-purity glass tube manufacturing apparatus in another embodiment of the present invention. .

Claims (1)

[Claims] 1. In the step of producing optical fiber glass using a flame hydrolysis method or a CVD method using a thermal decomposition reaction,
A method for manufacturing optical fiber glass, characterized in that the step includes a step of forming a soot-like hollow cylindrical member composed only of soot deposition. 2 The soot-like hollow cylindrical member is degassed by heating.
2. The method of manufacturing optical fiber glass according to claim 1, wherein the glass member is vitrified to produce a hollow cylindrical glass member. 3. The optical fiber according to claim 1, wherein the soot-like hollow cylindrical member is degassed by heating to form an optical fiber, and then heated and welded to produce a solid cylindrical glass member. A method of manufacturing glass for use.