JPH0583501B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a method for manufacturing an optical fiber base material by growing a porous glass body and turning the porous glass body into transparent glass by heating the porous glass body. Regarding
In particular, the present invention relates to a method for producing a new optical fiber base material that can stabilize quality and reduce costs.

[Conventional technology]

The above-mentioned method for manufacturing an optical fiber base material is proposed in, for example, Japanese Patent Application No. 51-38883.
As shown in FIG. 3, this method uses silicon tetrachloride,
Glass materials such as germanium tetrachloride are blown into an oxyhydrogen flame and hydrolyzed, or mixed with high-temperature oxygen gas and subjected to an oxidation reaction to create a diameter of 100 nm.
The front and rear glass particles are synthesized and deposited by spraying from a spray nozzle 21 onto the tip of a rod 22 that moves in the axial direction while rotating, thereby growing a glass particle deposit 23 (hereinafter referred to as a porous glass base material).

Next, fine glass particles for cladding are sprayed around the porous glass base material 23 from the spray nozzle 24 in the same manner. The glass particles not deposited at this time are exhausted from the exhaust pipe 28. Next, this porous glass base material 23 is sequentially fed into a high-temperature furnace 25 provided on its extension, heated, and melted without incorporating air bubbles, thereby converting it into transparent glass, which can be used for optical fibers. It manufactures the base material.

Furthermore, the control of the moving speed in the axial direction in the method described in the above specification is proposed in the specification of Japanese Patent Application No. 52-1775, and the position of the growth end face of the porous glass base material is The detection is performed using a laser or the like shown in Fig. 2, and the moving speed of the sintered body is controlled by this detection output 27 to keep the growth surface of the porous glass base material at a constant position.

[Problem that the invention seeks to solve]

In the above method, the distance between the burner and the porous glass preform is always kept constant, so that a porous preform with uniform dimensions can be obtained. However, the axial movement speed changes depending on the growth rate of the porous glass base material, so the conditions for transparent vitrification are constantly changing. It was difficult to do so. In addition, if you change the conditions for the generation and spraying of glass particles, the pulling speed will also change accordingly.
It was necessary to change the conditions for transparent vitrification each time. Furthermore, when the porous glass base material is turned into transparent vitrification, it bends and contracts, causing the porous glass base material to swing around, or because the rigidity of the porous glass base material is low, the lower end of the porous glass base material vibrates. It was hot too.

The present invention eliminates the instability in transparent vitrification caused by the conventional method, and also prevents whirling and vibration of the surface on which glass fine particles are deposited, thereby making it possible to efficiently produce optical fiber base materials of stable quality. The purpose is to provide a method for

[Means for solving problems]

In order to achieve the above objects, the present invention provides (A)
A step of continuously pulling up a transparent glass rod from a glass melting furnace while rotating, and growing a porous glass body almost uniformly around the outer periphery of the glass rod; a heating step of passing the glass rod and the porous glass body grown on the glass rod through a heating means, thereby turning the porous glass body into transparent vitrification;
The present invention proposes a method for manufacturing an optical fiber base material, which comprises the steps (A) and (B) described above, and is characterized in that the step (B) is performed consecutively to the step (A).

In the above method, it is possible to use a glass melting furnace which rotates on the same axis as the transparent glass rod, but in the opposite direction.

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

FIG. 1 is a diagram illustrating an embodiment of the method of the present invention, in which a glass rod 13 is used as the core of the optical fiber base material, and the glass rod 13 is attached to a rotating and moving rod 12. Spray glass particles for cladding around the nozzle 1
4, and then the base material consisting of the glass rod 13 and the cladding portion 16 is sequentially fed into a high temperature furnace 15 provided on its extension, and is made into transparent glass. Here, 18 is an exhaust pipe for discharging undeposited glass particles, and 17 is a glass melting furnace which will be described later. As the high temperature furnace 15, it is also possible to use one that does not substantially contain moisture.

[Effect]

The first effect of the method of the present invention is that since a glass rod is used as the core part of the optical fiber base material, the moving speed as proposed in the specification of the above-mentioned Japanese Patent Application No. 1775-1980 can be increased. No control is required and it can be moved in the axial direction at a constant speed.
Transparent vitrification can always be performed under constant conditions.

Secondly, in the method of the present invention, since the core portion is made of a glass rod, the glass body does not bend during transparentization, and the porous glass base material underneath does not swing around.

Thirdly, since the glass rod has higher rigidity than porous glass, vibrations of the porous glass base material can also be reduced. The above three points are all
This method is effective in producing optical fiber base materials of stable quality.

In the present invention, a glass melting furnace 17 is provided at the bottom of the apparatus for depositing glass particles, and the molten glass is sequentially pulled up and used as a transparent glass rod, so that continuous production of optical fiber preforms is possible. Since the operating time of the equipment increases, the cost of the optical fiber base material can be reduced. In this case, it is important to pull up a straight transparent glass rod from the glass melting furnace, but this is done by rotating the glass melting furnace coaxially with the transparent glass rod, but in the opposite direction, so that the angular velocity of the molten glass at the pulling point of the transparent glass rod is This is achieved by setting 0 to 0. This method will be explained below with reference to FIG.

In FIG. 3, molten glass 33 in a glass melting furnace 32 is pulled up and transferred to a transparent glass rod 31.
is being made. ω ₁ is the angular velocity of the transparent glass rod, ω ₃ is the angular velocity of the glass melting furnace, ω ₂ is the angular velocity of the molten glass at the pulling point of the transparent glass rod, r is the eccentricity of the transparent glass rod at the pulling point, and θ is the stiffness. . Between ω ₁ , ω ₂ , and ω ₃ ω ₁ > ω ₂ >
There is a relationship of ω ₃ or ω ₁ < ω ₂ < ω ₃ .

Force F acting in the radial direction of the molten glass at the pulling point
Considering this, F=mrω ² ₂ −Tsinθ (T is the tension of the glass rod, with the outward force being positive), so F is always negative and the pulling point of the molten glass always exerts a force toward the center. It is necessary that ω ₂ =0 in order to accept and thus form a straight transparent glass rod. In order for ω ₂ =0, ω ₁ and ω ₃ must have different signs.

〔Example〕

Example 1 Using a transparent glass rod with a diameter of 5 mm, a length of 800 mm, and a refractive index difference of 0.29%, which was created by the vapor phase axis method, fine glass particles for the cladding were sprayed using the apparatus shown in Figure 1, and the rod was sequentially made into transparent glass and exposed to light. A base material for fiber was created. The pulling speed was kept constant at 65 mm/hour. As a result, an optical fiber base material was obtained that was uniform in the length direction with a diameter of 33 mm and a length of 760 mm, did not contain bubbles, and was transparent. The porous glass base material did not bend during heating for transparency. Further, no visible vibrations were generated at the point where the glass particles were sprayed. When the glass base material for optical fiber obtained by this method was spun, it was possible to obtain an optical fiber with good characteristics of 0.8 dB/Km (loss at wavelength 1.30 μm).

Example 2 Using the apparatus shown in FIG. 1, 6 GeO ₂
Quartz containing % by weight was melted and a glass rod was pulled up from there at a rate of 2 mm/min, gripped by a chuck 19, and rotated clockwise at 30 rpm. Further, the melting furnace 17 was rotated counterclockwise at 33 rpm. At this time, the angular velocity of the molten glass at the point where the transparent glass rod is pulled up is approximately 0.
The transparent glass rod that was pulled up became straight. The diameter of the transparent glass rod was 3 mm. Fine glass particles were sprayed onto this transparent glass to make it transparent, thereby obtaining a base material for optical fibers with a diameter of 30 mm and a length of 1.5 m. The diameter was uniform in the longitudinal direction, and no bending occurred during heating for transparency.

〔Effect of the invention〕

The present invention eliminates the instability in transparent vitrification of optical fiber preforms with uniform diameters in the longitudinal direction, and can stably produce optical fiber preforms without whirling or vibration, making it possible to efficiently produce high-quality optical fiber preforms. This is a method that can be manufactured in many ways.

[Brief explanation of the drawing]

Figure 1 shows an embodiment of the method of the present invention, and is a diagram illustrating a case in which pulling of molten glass, spraying of glass fine particles for cladding glass, and transparent vitrification are carried out in succession. FIG. 3 is a diagram illustrating a method for pulling up a transparent glass rod from a glass melting furnace in the invention method, and FIG. 3 is a diagram illustrating a method for manufacturing an optical fiber base material by a conventional method.

Claims (1)

[Claims] 1. (A) A step of continuously pulling up a transparent glass rod from a glass melting furnace while rotating, and growing a porous glass body almost uniformly around the outer periphery of the glass rod, (B) While rotating. passing the transparent glass rod continuously moving in the axial direction and the porous glass body grown on the glass rod through a heating means;
A light comprising the above steps (A) and (B) of heating the porous glass body thereby to make the porous glass body transparent vitrified, and performing the step (B) consecutively to the step (A). Method for manufacturing fiber base material. 2. The method for producing an optical fiber base material according to claim 1, wherein a glass melting furnace that rotates on the same axis as the transparent glass rod and in the opposite direction is used as the glass melting furnace. . 3. The method for manufacturing an optical fiber preform according to claim 2, wherein the molten glass furnace is rotated such that the angular velocity of the molten glass at the point of pulling up the transparent glass rod is zero.