JPH1072230A - Production of optical fiber preform - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a preform at an increased deposition rate and in an in creased shape yield(a ratio (%) of (effective length)/((effective length)+(ineffective length)) of a preform) by arranging burners for forming fine glass particles in a specific direction, in a production that is composed by comprises subjecting a glass raw material to a flame hydrolysis or an oxida tion to form fine glass particles, depositing a resulting fine glass particle on a starting material and growing a deposited fine glass particle to produce an optical fiber preform. SOLUTION: This production is composed by subjecting a glass raw material to the flame hydrolysis or oxidation to form fine glass particles, depositing the resulting fine glass particles on a starting material and growing the deposited fine glass particles to produce an optical fiber preform. In the production, burners for forming fine glass particles are arranged in a circumferential direction of a preform to be produced so that central axes of the burners are directed toward a starting material in at last three direction. At this time, the angle between central axes of every adjacent two of the burners is preferably 45 to 120 deg.C and the angle between the central axis of each of the burners and the axis of the starting material is more desirably 60 to 100 deg..

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an aggregate of glass fine particles on an outer peripheral portion of a cylindrical starting material, and is particularly suitable as an intermediate product in manufacturing a preform for an optical fiber requiring high purity. The present invention relates to a method for forming an aggregate of glass fine particles deposited on the outer peripheral portion of a starting material at a high deposition rate.

[0002]

2. Description of the Related Art In a method of forming a deposit of glass fine particles in an axial direction on an outer peripheral portion of a cylindrical starting material, an angle between a central axis of a burner and an axis of the starting material is in a range of 20 to 70 °. (Japanese Patent Application Laid-Open No. 61-18624)
No. 0). Also, burners of multiple soot spraying mechanisms are attached at different angles toward the target member,
Depositing glass fine particles (Japanese Patent Laid-Open No. Hei 4-16002)
Japanese Patent Application Laid-Open No. Hei 5-58652 discloses a method in which adjacent burners are shifted in the circumferential direction as well as in the axial direction of the starting material to deposit glass particles (Japanese Patent Laid-Open No. 5-58652).

However, it is difficult for these known methods to form a deposit of fine glass particles at a sufficient deposition rate. In order to efficiently produce a porous base material, the deposition efficiency [the weight of the glass fine particles that can be synthesized per unit time, or the ratio of glass fine particles adhered to the raw material gas supply amount (deposition yield)] is increased, It is necessary to make the outer diameter uniform portion as long as possible. The above-mentioned known technique discloses a method of supplying a glass raw material from a plurality of burners in order to increase the deposition efficiency. However, there is a problem that the deposition efficiency is reduced due to interference between the burners due to a flame. That is, when the burner interval is reduced, adjacent flames interfere with each other, so that the flow of the glass fine particle flow is disturbed, and the deposition efficiency on the deposition surface is reduced. On the other hand, if the burner interval is increased, soot is not uniformly deposited at the end portion by the burner interval, so that the ineffective portion (tapered portion) at the end portion becomes longer and the obtained good portion becomes shorter.

[0004]

DISCLOSURE OF THE INVENTION The present inventors have proposed a method for producing a base material for an optical fiber in which a glass raw material is subjected to flame hydrolysis or oxidation to deposit and grow glass fine particles on a starting material. As a result of intensive studies to improve the temperature, it was found that an excellent effect could be obtained by specifying the arrangement of the burners, and the present invention was reached. That is,
An object of the present invention is to increase the deposition rate and shape yield when depositing glass microparticles on a starting material by flame hydrolysis or oxidation of a glass raw material in a method of manufacturing a preform for an optical fiber.

[0005]

The above object can be achieved by the following manufacturing methods. (1) In a method for producing a base material for an optical fiber, in which a glass raw material is subjected to flame hydrolysis or oxidation and glass fine particles are deposited and grown on a starting material, burners for generating glass fine particles are arranged in a circumferential direction of the base material, and three directions are provided. A method for producing a preform for an optical fiber, characterized by being arranged as described above. (2) The angle between adjacent burners arranged in the circumferential direction is 45
The method for producing a preform for an optical fiber according to the above (1), wherein the angle is set to 120 °.

(3) The method for manufacturing a preform for an optical fiber according to the above (1) or (2), wherein the angle between the central axis of the burner and the axis of the starting material is 60 to 100 °. . (4) The method for producing a preform for an optical fiber according to any one of the above (1) to (3), wherein the deposition and generation of the glass particles are performed by a VAD method. (5) The method for producing a preform for an optical fiber according to any one of the above (1) to (3), wherein the deposition and generation of the glass particles are performed by an OVD method.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the above-mentioned method (1), glass particles are deposited by disposing burners for generating glass particles from three directions in the circumferential direction of a base material, thereby preventing interference of a flame and improving a deposition rate. Can be done. Further, since the burner interval in the axial direction can be reduced, the shape yield as shown in FIG. 1 can be improved. In the present invention, the burners are arranged from three or more directions in the circumferential direction. However, the number of burners in the same axial direction is not limited. Here, the shape yield is obtained by expressing the effective portion length / (effective portion length + ineffective portion length) in%. 2 and 3 show an embodiment for carrying out the method of the present invention. FIG. 2 is a schematic diagram showing the three-way arrangement of the VAD method according to the present invention, and FIG. FIG.

In the above method (2), the angle (interval) between adjacent burners arranged in the circumferential direction, for example, the angle α between the starting central axis shown in FIG. To 120 °, preferably 60 to 120 °,
Interference between adjacent flames is prevented, and at the same time, a uniform outer diameter portion is appropriately maintained to increase the deposition rate.
When α <45 °, the flames interfere with each other, so that the deposition rate cannot be increased. When three burners are arranged, α _MAX
= 120 ° (α _MAX = 90 ° for four lines).

In the above method (3), the angle between the burner center axis and the axis of the starting material, for example, the angle θ shown in FIG. 5 is set to 60 to 100 °, preferably 75 to 90 °. 60
If it is less than °, the bulk velocity of the deposited soot has a radial distribution, and soot cracks are likely to occur. On the other hand, if it exceeds 100 °, there is a disadvantage that the deposition efficiency is reduced.

The present invention can be applied to the VAD method or the OVD method as in the above method (4) or (5). Further, in the present invention, adjacent burners of at least three glass fine particle generation burners can be separated at appropriate intervals in the axial direction to suppress interference between flames.
For example, 1 shown in FIG.
It is preferable to set it to 0 to 200 mm. If the burners are moved in the circumferential direction, the burner interval is increased, so that flame interference can be suppressed as compared with the case where the burners are arranged linearly.

[0011]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto. (Example 1) In the VAD method, the angle between the central axis of each burner and the axis of the starting material was 60 °, and three burners were arranged at intervals of 45 ° in the circumferential direction. Each burner uses a concentric octuple-tube burner, and sequentially from the center port, 6 liters / minute of SiCl _{4 and} 10 liters / minute of H _2.
Min, Ar ₃ l / min, O ₂ 20 l / min, Ar
5 L / min, H ₂ 80 L / min, Ar 5 L / min, O ₂ 40 L / min, 90 mm / hr
At the speed described above, the starting material was pulled up in the axial direction. As a starting material, a glass rod having a core of GeO ₂ —SiO ₂ and a cladding of SiO _{2 having} an outer diameter of 30 mmφ and a length of 700 mm is used, and dummy rods (outer diameter of 30 m) are provided at both ends of the glass rod.
mφ, length 400 mm). The outer diameter of the obtained porous base material was 250 mmφ, the deposition rate was 30 g / min, and the shape yield [effective part length / (effective part length + non-effective part length)] was 80%.

(Embodiment 2) In the OVD method, Embodiment 1
A starting material similar to the above was prepared, and the rod was arranged in the vertical direction.
The arrangement of the three burners is set as shown in Table 1 and the porous base material
Was manufactured. The burner structure used was the same as in Example 1.
The gas flow condition is 6 port H _TwoOnly flow rate 1
The same settings were used except that the volume was increased to 20 liters / minute. Ma
The starting material was reciprocated at a speed of 500 mm / min.
Glass particles were laminated until the diameter became 230 mm.

[0013]

[Table 1]

FIG. 7 is a graph summarizing the above experimental results.
And 8. That is, the burner angle adjacent in the circumferential direction is preferably 45 to 120 °, and the angle between the burner center axis and the starting material axis is preferably 60 to 90 °.

[0015]

According to the present invention, a glass raw material is flame-hydrolyzed or oxidized, and glass fine particles are deposited and grown on a starting material to produce a glass fiber preform. Specific location, ie at least 3
By performing deposition and growth while arranging the substrate toward the base material from the direction, the deposition rate and the shape yield can be significantly increased.

[Brief description of the drawings]

FIG. 1 is a model diagram showing an effective portion length and an ineffective portion length of an optical fiber preform obtained by depositing glass fine particles on a starting material.

FIG. 2 is a conceptual diagram showing a method according to a VAD method in a three-way arrangement showing one embodiment of implementing the method of the present invention.

FIG. 3 is a conceptual diagram showing an OVD method in a three-way arrangement showing one embodiment of implementing the method of the present invention.

FIG. 4 is a conceptual diagram showing an angle α between adjacent burner central axes arranged in the circumferential direction according to the present invention.

FIG. 5 is a conceptual diagram showing an angle θ between a central axis of a burner arranged in a circumferential direction and an axis of a starting material according to the present invention.

FIG. 6 is a conceptual diagram showing an axial interval l of burners arranged at an angle α in the circumferential direction when θ = 90 °.

FIG. 7 is a graph showing the relationship between the burner angle α adjacent to the circumferential direction, the deposition rate, and the yield obtained in the example of the present invention.

FIG. 8 is a graph showing the relationship between the angle θ between the burner center axis and the starting material, the deposition rate, and the yield obtained in the example of the present invention.

Claims (5)

[Claims] 1. A method for producing a base material for an optical fiber in which a glass raw material is subjected to flame hydrolysis or oxidation to deposit and grow glass fine particles on a starting material, wherein a burner for producing glass fine particles is arranged in a circumferential direction of the base material; A method for manufacturing a preform for an optical fiber, wherein the preform is arranged from three or more directions. 2. The method of manufacturing an optical fiber preform according to claim 1, wherein an angle between adjacent burners arranged in the circumferential direction is 45 to 120 °. 3. The method according to claim 1, wherein the angle between the central axis of the burner and the axis of the starting material is 60 to 100 °. 4. The method for producing a preform for an optical fiber according to claim 1, wherein the deposition and generation of the glass fine particles are performed by a VAD method. 5. The method for producing a preform for an optical fiber according to claim 1, wherein the deposition and generation of the glass particles are performed by an OVD method.