JPH0986948A - Production of porous glass base material for optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a producing condition stably producing a porous glass base material in a short time at newly starting a VAD(vapor-phase axial deposition) device without cracking a clad layer by specifying a ratio of hydrogen supplying to a burner for cladding to a gas for a raw material of glass. SOLUTION: In a producing device of a porous glass base material for an optical fiber by a VAD method, an H2 /SiCl4 ratio supplying to a burner B2 forming a clad layer 2 is decided to, e.g. 8-10 and the surface maximum temperature of the formed clad layer 2 is adjusted to 650-900 deg.C. An H2 /SiCl4 ratio of a burner B3 forming a clad layer 3 is set to e.g. 1.2-2.0 times of the ratio of H2 /SiCl4 for the clad burner B2 and the surface maximum temperature of the formed clad layer 3 is made to 650-900 deg.C. As a burner 4 forming a clad layer 4 is set to the same condition. Thus, glass fine granules to be a core are accumulated at the top end of a starting material in a rod-like.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a so-called VAD.
The present invention relates to a method for producing a porous glass preform for an optical fiber by a method, and provides a method suitable for producing a large preform and early starting when a VAD device is newly introduced.

[0002]

2. Description of the Related Art The VAD method is well known as a method for producing a porous glass preform for optical fibers. This method
For example, as shown in FIG. 1, a core burner B1 and a plurality of cladding burners B2, B3, B4 are used, and a cylindrical columnar shape is formed at the tip of a starting member S which is rotatable about its axis and is movable in the axial direction. This is a method of forming a porous optical fiber preform 10 having a two-layer structure composed of a core 1 and clad layers (2, 3, 4). The core burner B1 may have, for example, SiCl
₄ and GeCl ₄ and O _2, H ₂ is supplied, GeO ₂ -Si produced by flame hydrolysis and thermal oxidation reactions
O ₂ glass fine particles are deposited on the tip of the starting member S to form the core 1. Also, clad burners B2, B3, B
4, for example, SiCl ₄ and O ₂ and H ₂ are supplied to deposit similarly produced SiO ₂ glass fine particles as clad layers 2, 3 and 4 around the core 1 in sequence. The respective gas amounts supplied to B2, B3 and B4 are made equal.

The obtained porous optical fiber preform 10 is
It is dehydrated in a chlorine-based gas and He atmosphere and made into vitrified glass to form an optical fiber preform. At this time, when the core-clad diameter ratio of the obtained optical fiber preform has a predetermined value, the fiber is drawn as it is to be made into a fiber, but when the core-clad diameter ratio does not reach the predetermined value, This preform is stretched, a SiO ₂ glass fine particle layer is deposited on the outside thereof to form a transparent glass, and this process is repeated until the core-clad diameter ratio reaches a predetermined value to form an optical fiber preform, which is drawn into a fiber. And

[0004]

However, the demand for optical fibers for the spread of optical communication and multimedia in recent years is remarkable, and the introduction of such optical fibers requires further cost reduction of optical fibers. In the manufacture of optical fibers, the size and speed of the optical fiber preform have been increased, and at the time, when new equipment is introduced, it is desired to start it up early. In the above-mentioned conventional method for producing an optical fiber preform, a plurality of burners are used, and when an attempt is made to produce a large-sized porous optical fiber preform under conventional conditions, the preform sometimes breaks. In particular, this phenomenon often occurs in the clad layer, and the greater the number of burners, the more difficult it is to balance the hardness of each glass fine particle layer and the more easily it breaks. Since it takes a long time to manufacture a porous optical fiber preform, if it breaks on the way, the operating rate of the device will significantly decrease. Moreover, when the VAD device is newly started up, it takes a great deal of time to determine the conditions under which the glass fine particle layer is not cracked.

[0005]

SUMMARY OF THE INVENTION The present invention is intended to solve the above problems, and the invention according to claim 1 is characterized in that a starting member using a burner for a core and a plurality of burners for a clad is used. When a glass optical particle is laminated at the tip of the to prepare a porous optical fiber preform composed of a core and a clad, the ratio of hydrogen to be supplied to the clad burner and the glass raw material gas is set to the innermost layer of the clad. The method for producing a porous glass preform for optical fibers is sequentially increased from the burner to the outer burner. The invention according to claim 2 is characterized in that in the invention according to claim 1,
The ratio of hydrogen supplied to the outer cladding burner to the glass raw material gas / the ratio of hydrogen supplied to the inner cladding burner to the glass raw material is 1.2 to 2.0. Further, the invention according to claim 3 is characterized in that, in the invention according to claim 2, the maximum surface temperature of each glass particle layer laminated by each cladding burner is 650 to 900.
℃.

[0006]

In the present invention, the structure of the apparatus is the same as that of a typical VAD apparatus shown in FIG. 1, but the amount of gas supplied to the cladding burners B2, B3, B4 is adjusted. There is. That is, first, H ₂ / SiCl ₄ is applied to the burner B2 that forms the cladding layer 2, for example, from 8 to 8
The burner position, angle, etc. are set so that the maximum surface temperature of the clad layer 2 to be formed is 650 to 900 ° C. If the temperature does not fall within the above range, SiCl
Readjust by increasing or decreasing the supply amount of ₄ . O ₂ with H ₂ when without changing the supply amount of SiCl ₄ achieving adjustment of temperature
Increase or decrease. Next, the burner B for forming the clad layer 3
3 is H ₂ / SiCl _4, for example, clad burner B
2 H ₂ / SiCl ₄ of 1.2 to 2.0, and the maximum surface temperature of the cladding layer 3 formed in the same manner is 650 to 9
Set to 00 ° C. The same applies to the burner B4 forming the clad layer 4. The number of clad burners is two or more, and the number is not particularly limited.

When a porous glass preform for optical fibers was produced by making the above adjustments, cracks did not occur in the cladding layer. Further, since H ₂ / SiCl ₄ is specified, the manufacturing conditions can be narrowed down and, for example, the burner position, the burner angle and the like can be easily adjusted.
The reason why H ₂ / SiCl ₄ is made larger toward the outside of the cladding layer is because the base material diameter is larger and the surface area is larger toward the outside, so a large amount of heat is required. By setting the ratio in the range of 1.2 to 2.0, the hardness of each clad glass fine particle layer can be balanced and cracks can be almost eliminated. If the maximum surface temperature of each clad layer is out of the range of 650 to 900 ° C., the hardness of each layer and the hardness of the adjacent layer are not well balanced, and sometimes cracks may occur. Production in the range is preferable.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION

Example 1 A base material was produced by setting the gas supply conditions to the burner as shown in Table 1 with the configuration shown in FIG. The obtained porous glass preform for optical fibers has a core diameter of 30 mmφ and a cladding diameter of 150.
With a diameter of mmφ and a length of 800 mm, the clad layer did not crack anywhere. In addition, the maximum surface temperature of each clad layer was measured with a radiation thermometer.
It was 800 ° C.

[0009]

[Table 1]

Example 2 A base material was prepared under the conditions shown in Table 2. The obtained porous glass preform for optical fibers had a core diameter of 30 mmφ and a cladding diameter of 17
No crack was generated in the cladding layer at 0 mmφ and a length of 900 mm. The maximum surface temperature of each clad layer was measured with a radiation thermometer and found to be 650, 690, 740 from the inside.
° C.

[0011]

[Table 2]

Example 3 A base material was prepared under the conditions shown in Table 3. The obtained porous glass preform for optical fibers had a core diameter of 30 mmφ and a cladding diameter of 14
No crack was generated in the clad layer at 0 mmφ and a length of 800 mm. The maximum surface temperature of each clad layer was measured with a radiation thermometer, and it was 800, 840, 880 from the inside.
° C.

[0013]

[Table 3]

Comparative Example 1 A base material was prepared under the conditions shown in Table 4. When the base material was manufactured to a length of 400 mm, the clad 3 cracked. The maximum surface temperature of each clad layer is 700, 720, 62 from the inside.
It was 0 ° C.

[0015]

[Table 4]

Comparative Example 2 A base material was prepared under the conditions shown in Table 5. When the base material was manufactured to a length of 200 mm, cracks occurred between the clads 3 and 4. The maximum surface temperature of each clad layer is 700, 7 from the inside.
It was 20,620 degreeC.

[0017]

[Table 5]

[0018]

According to the method of the present invention, when a large-sized core / clad type porous glass preform for an optical fiber is manufactured by the VAD method, the clad layer uses a plurality of burners and is supplied to the clad burner. Since the ratio of hydrogen to the glass raw material gas is gradually increased from the burner forming the innermost layer of the clad toward the outer burner, the clad layer can be manufactured without cracking. Further, according to this method, cracking of the cladding layer can be suppressed, so that a stable production condition can be found in a short time when a new VAD device is started up.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view of a typical VAD method.

[Explanation of symbols]

 B1 burner for core B2, B3, B4 burner for clad 1 core 2, 3, 4 clad layer 10 porous glass preform for optical fiber

Claims (3)

[Claims] 1. A clad burner for producing a porous optical fiber preform composed of a core and a clad by laminating glass particles on the tip of a starting member using a core burner and a plurality of clad burners. A method for producing a porous glass preform for optical fibers, characterized in that the ratio of hydrogen to glass raw material gas supplied to the glass is gradually increased from the burner forming the innermost layer of the clad toward the outer burner. 2. The ratio of hydrogen to the glass raw material gas supplied to the outer cladding burner / the ratio of hydrogen to the glass raw material gas supplied to the inner cladding burner = 1.2 to 2.0. The method for producing a porous glass preform for an optical fiber according to claim 1. 3. The method for producing a porous glass preform for an optical fiber according to claim 2, wherein the maximum surface temperature of each glass fine particle layer laminated by each clad burner is 650 to 900 ° C.