JPH09328328A - Production of preform for optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a preform for an optical fiber by which the optical fiber good in optical characteristics can be obtained by removing unevennesses on the surface of a preform ingot according to a specific method. SOLUTION: This method for producing a preform for an optical fiber is to carry out the cylindrical grinding of unevennesses produced on the surface of a preform ingot 23 in the method for producing the preform ingot 23 for the optical fiber comprising dehydrating, sintering and vitrifying a soot obtained by depositing a clad part on a starting core member according to an outside vapor deposition method. When the cylindrical grinding of the preform ingot 23 is performed, the position of a core part of the preform ingot 23 is optically measured to determine the central position of the core part 3 and the preform ingot 23 is attached to the center of rotation of the cylindrical grinder machine to carry out the cylindrical grinding in this state. The position of the core part 3 is detected in at least both ends of the preform ingot 23. Concretely, the preform ingot 23 is fixed with ingot gripping chucks 21 supported by chuck supporting parts 24 and then ground with a diamond wheel 22. The setting is performed by aligning the center of the core part 3 with that of the supporting parts 24.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an optical fiber preform capable of obtaining an optical fiber having good optical characteristics even if the surface of the optical fiber preform ingot has irregularities.

[0002]

2. Description of the Related Art An optical fiber preform ingot is manufactured by, for example, dehydrating or sintering soot obtained by depositing a clad portion on the surface of a starting core member by an external attachment method (hereinafter abbreviated as OVD method). Although produced, the soot deposition rate is improved by increasing the generation of glass particles due to flame hydrolysis in an oxyhydrogen flame.Therefore, methods for increasing the diameter of burners and methods for increasing the number of burners are known. .

However, the method of increasing the diameter of the burner has a drawback that the adhesion of glass particles is extremely poor at the initial stage of depositing soot on the surface of the starting core base material, and flame interference occurs when a plurality of burners are used. Therefore, the deposition efficiency of the glass particles is not good, and when the burner is moved in parallel to the starting member and moved left and right, defective parts (tapered parts) are formed at both ends of the deposition soot, especially when the raw material gas is increased. When high-speed deposition is performed, the uneven phenomenon on the surface of the deposited soot becomes remarkable because of the plurality of burners.

[0004]

When manufacturing an optical fiber preform by the OVD method, if a plurality of burners for depositing glass particles are used and the raw material gas is increased to perform high-speed deposition,
The soot deposition rate can be dramatically improved, but in this case, unevenness appears on the surface of the soot and the surface of the ingot obtained by sintering, so it is necessary to remove the unevenness of the ingot surface in advance to make an optical fiber. is there.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a method for manufacturing an optical fiber preform which solves the above problems, in which a soot obtained by depositing a clad portion on a starting core member by an OVD method is used. In the method of manufacturing an optical fiber preform ingot by dehydration / sinter vitrification, the unevenness formed on the surface of the ingot is cylindrically ground.

That is, in the conventional OVD method, when glass particles are deposited on the surface of the starting member, the amount of oxyhydrogen and the amount of raw material gas are controlled at the initial stage of deposition, and the flame is squeezed to adhere the glass particles to the surface of the core member. A method of increasing the amount of gas as the soot diameter increases to increase the deposition rate and smoothing the soot surface while observing the soot surface is used. However, the burner has a larger diameter than that of the conventional one, and glass particles are deposited while traversing the longitudinal direction of the core member as a plurality of burners, and the soot deposited in the target amount is put into a sintering furnace and dehydrated / sintered glass. As a result, irregularities appeared clearly on the surface of the obtained optical fiber preform ingot, but this irregularity can be removed by cylindrical grinding, and it is possible to obtain an ingot with a smooth surface like the one produced by the conventional method. confirmed.

[0007]

If the surface of the ingot obtained by the OVD method has irregularities, the optical characteristics of the optical fiber obtained by drawing the ingot to a desired diameter and drawing the wire will adversely affect the optical characteristics. Therefore, if this ingot is cylindrically ground according to the present invention, the surface becomes smooth, and the optical fiber made from this has good optical characteristics.

When performing cylindrical grinding, it is necessary to pay attention to the roundness of the processed ingot and the eccentricity of the core portion. That is, when an ingot is cylindrically ground and drawn from a base material (preform) stretched to a desired diameter to form an optical fiber cable, when the fibers are connected during cable installation, the circularity of the fiber and the deviation of the core The core amount has a great influence on the optical characteristics (connection loss).

Therefore, according to the present invention, when the ingot is cylindrically ground, the position of the core of the ingot is optically measured to determine the center position of the core, and the core is attached to the center of rotation of the cylindrical grinder. By grinding, it is possible to prevent non-circularity when an optical fiber is used and the occurrence of eccentricity defects in the core portion. Therefore, according to the present invention, it becomes possible to rapidly synthesize an optical fiber preform having good optical characteristics. It was

Next, a method of manufacturing an optical fiber preform according to the present invention will be described with reference to the drawings. FIG. 1 is a vertical cross-sectional view of an apparatus for producing a base material soot (porous glass base material) for an optical fiber according to the present invention, FIG. 2 is a vertical cross-sectional view of a cylindrical grinder used in the present invention, and FIG. It is a cross-sectional view of this cylindrical grinding machine. The optical fiber preform soot manufacturing apparatus in FIG. 1 is attached to the burner guide mechanism 9 on the core member welded to the dummy part 1 which is rotated by the core member rotating motor 7 in the closed reactor 10. And a flame from a plurality of oxyhydrogen flame burners 5 traversed by an oxyhydrogen flame burner traverse motor 8 is applied and exhausted from an exhaust hood 6 to form a base metal soot 4 having a tapered portion 2. It is what makes me.

FIG. 2 is a base material soot 4 produced by the apparatus of FIG.
The figure shows a cylindrical grinder for grinding irregularities on the surface of the optical fiber base material ingot 23 obtained by dehydration / sinter vitrification of the ingot 23, which is supported by the chuck support 24. It is fixed by the chuck 21 for gripping the ingot and is ground by the diamond wheel 22. As shown in FIG. 3, the ingot 23 is attached to the ingot.
The position of the core part 3 of 23 is detected from both ends of the ingot by an optical measuring instrument, and the chuck 21 for gripping the ingot is moved so that the center position of the core part 3 becomes the center of the support part 24 which is the rotation center of the cylindrical grinding machine. Set them together and cut with the diamond wheel 22.

[0012]

EXAMPLES Next, examples and comparative examples of the present invention will be described. Example 1 Using the base material soot (porous glass member) manufacturing apparatus for optical fibers shown in FIG. 1, the outer diameter is 25 mmφ and the length is 1,200.
Welded a quartz silica rod for core with a refractive index adjusted for mm single mode optical fiber to a quartz rod for dummy, and attached this to a soot rotating mechanism in a closed reactor,
While rotating at pm, oxygen gas 75L / min, hydrogen gas 150L / min and oxygen gas 9L as carrier gas were supplied to two burners from a raw material supply device (not shown) Per minute accompanied by SiCl of raw material gas
₄ 38 g / min was introduced.

This burner is reciprocated in the range of 1,600 mm at a speed of 150 mm / min by a motor for traversing the burner to deposit glass fine particles generated by flame hydrolysis of SiCl _{4 on} a quartz glass rod for core, and the deposition proceeds. The amount of raw material gas was increased accordingly, and oxygen gas of 150 L /
Min, hydrogen gas 300 L / min, carrier gas 15 L / min, SiCl ₄ 80
When g / min was set, a base metal soot with an outer diameter of 230 mmφ was obtained after 24 hours, but since the average deposition rate was 28 g / min for high-speed synthesis, the surface of the base metal soot had spiral irregularities. It was confirmed that there is.

Next, the base material soot obtained here was put into a sintering furnace, dehydrated and sintered to obtain a transparent base material ingot for an optical fiber having an outer diameter of 130 mm. -Shaped unevenness remains, the maximum depth of unevenness is 1.15
There was mm. Attach the ingot to the cylindrical grinder chuck shown in Fig. 2 and Fig. 3, then measure the position of the core of the ingot with an optical measuring device on both ends of the ingot while rotating the ingot, and move the chuck to the center position of the core. Then, the ingot was set according to the center of rotation of the chuck support. Then, using a diamond wheel with a roughness of # 140, the grinding depth was 0.25 mm, the ingot feed rate was 50 mm / min, and the grinding part was ground 5 times with water cooling. Cylindrical grinding was completed by finishing grinding twice with a depth of 0.05 mm and an ingot feed rate of 50 mm / min.

The time required for the cylindrical grinding in this case was about 200 minutes, but the surface of the ingot thus obtained was smooth and comparable to that produced by the conventional method.
The manufacturing time has been reduced to about 1/2 of that of conventional products, including cylindrical grinding. The ingot obtained here is 45 mm in an electric furnace.
An optical fiber preform was drawn by φ, and then drawn with a drawing machine to give an optical fiber with an outer diameter of 125μ. The optical characteristics of this optical fiber were measured.
The result shown in FIG.

Example 2 A soot synthesized in the same manner as in Example 1 was placed in a sintering furnace and dehydrated and sintered to form a transparent base material ingot for optical fiber. The unevenness remained, and the maximum depth of the unevenness was 1.20 mm. Then, this ingot was set in a cylindrical grinder in the same manner as in Example 1, and the diamond wheel was shaving using a material with a roughness of # 60 to a depth of 0.5 mm and an ingot feed rate of 70 mm / min. While grinding 3 times, then using a # 600 diamond wheel, the grinding depth is 0.1 mm, the ingot feed speed is 50 mm / min, and the grinding depth is 0.05 mm. Cylindrical grinding was completed by grinding once at an ingot feed rate of 50 mm / min.

In this case, the time required for cylindrical grinding was about 110 minutes, but the surface of the obtained ingot was extremely smooth, which was comparable to that produced by the conventional method.
The manufacturing time was reduced to about 1/2 including the cylindrical grinding.
The ingot obtained here was stretched to 45 mmφ in an electric furnace to form an optical fiber preform, which was then drawn by a drawing machine into an optical fiber having an outer diameter of 125 μ, and the optical characteristics of this optical fiber were measured. However, the results shown in Table 1 were obtained.

Comparative Example A base material soot synthesized in the same manner as in Example 1 was dehydrated and sintered into a vitrification in a sintering furnace to prepare a transparent base material ingot for optical fiber. Spiral irregularities were formed on the surface. The remaining depth was 1.15 mm at the maximum. However, this ingot was stretched to 45 mmφ in an electric furnace to form an optical fiber preform without cylindrical grinding, and then drawn with a drawing machine into an optical fiber with an outer diameter of 125 μ, and the optical characteristics of the optical fiber were measured. As a result, the results shown in Table 1 were obtained, showing a large connection loss due to eccentricity in fusion splicing.

[0019]

[Table 1]

[0020]

According to the present invention, from the optical fiber preform manufactured by the high-speed synthesis method, it is possible to manufacture an optical fiber having optical characteristics with smaller splice loss and eccentricity than those of the conventional ones.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of an optical fiber preform soot (porous glass preform) manufacturing apparatus according to the present invention.

FIG. 2 is a vertical cross-sectional view of an optical fiber preform ingot cylindrical grinding machine according to the present invention.

FIG. 3 is a schematic cross-sectional view of an optical fiber preform ingot cylindrical grinding machine according to the present invention.

[Explanation of Codes] 1 ... Dummy part 2 ... Tapered part 3 ... Core part 4 ... Base material soot 5 ... Burner 6 ... Exhaust hood 7 ... Soot rotation mechanism 8 ... Burner traverse motor 9 ... Burner guide mechanism 10 ... Sealed reaction Furnace 21… Ingot gripping chuck 22… Diamond wheel 23… Optical fiber base material ingot 24… Chuck support

Claims (3)

[Claims] 1. A method for producing an optical fiber preform ingot by dehydrating and sintering vitrification of a soot obtained by depositing a clad portion on a starting core member by an external attachment method, and producing unevenness on the surface of the ingot. 1. A method for manufacturing an optical fiber preform, which comprises cylindrically grinding. 2. The method for producing an optical fiber preform according to claim 1, wherein the position of the core portion is detected and the ingot is attached to the center of rotation of a cylindrical grinding machine to prevent eccentricity of the core portion. 3. The method for producing an optical fiber preform according to claim 1, wherein the position of the core portion is detected at least at both ends of the ingot.