JPH07109136A - Large-sized quartz glass tube, large-sized quartz glass preform, and methods for producing the same - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a large-scale, high-precision quartz glass tube and a large-scale quartz glass preform capable of mass-producing and reducing the cost of high-quality optical fibers. [Structure] A natural or synthetic quartz glass tube is processed by a non-contact heating processing method to have an outer diameter of 50 to 300 mmφ, an outer diameter / inner diameter ratio of 1.1 to 7, a thickness of 10 mm or more, and a thickness error of 2 % Or less, large-scale quartz glass tube with an inner surface roughness of 20 μm or less,
A large quartz glass preform obtained by integrating a large quartz glass tube and a core glass rod by a rod-in-tube method. The large quartz glass tube has an outer diameter of 50 to 300 mm
φ, ratio of outer diameter to inner diameter is 1.1 to 7, thickness is 10 mm or more,
A quartz glass raw tube having a thickness error of 2% or less is subjected to a heat treatment by a non-contact heating processing method, the ratio (D ₀ / D _i ) of the outer diameter (D ₀ ) to the inner diameter (D _i ) of the quartz glass raw tube. Outer diameter of rear tube (d ₀ )
And the inner diameter (d _i ) ratio (d ₀ / d _i ) is (D ₀ / D _i ) /
It is manufactured by controlling the internal pressure so as to be (d ₀ / d _i ) 1.0 to 1.5 and performing heat treatment, heat stretching or heat pressure stretching at 1600 to 3000 ° C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a large-diameter, thick, high-precision large-sized quartz glass tube processed by a non-contact heating processing method, which has a small eccentricity, excellent transmission characteristics, and mass productivity. A low-cost optical fiber preform, particularly a large silica glass preform in which a silica glass tube and a core glass rod for a single mode optical fiber are integrated by a rod-in-tube method, and a method for manufacturing them Regarding

[0002]

2. Description of the Related Art In recent years, a large amount of optical fibers have come to be used with the practical use of optical fibers, especially single-mode optical fibers. The main manufacturing methods are VAD method (gas phase method), OVD method (external method), and MCVD method (internal method). Only products manufactured by these three manufacturing methods can be used in the world market. Most of them are occupied. However, it has been predicted that the use range of the optical fiber will be expanded from the long-distance trunk line to the general subscriber system, and a larger amount of the optical fiber will be required in the future. It is said that the methods alone have reached their limits in terms of productivity and cost.

It has been 20 years since the research on the silica glass optical fiber, and since the transmission characteristics and the practical reliability have already been examined to the ultimate, mass productivity and cost reduction can be achieved while maintaining these characteristics. The development of possible new manufacturing methods is difficult.

One of the measures to achieve mass productivity and cost reduction is to increase the size of the preform to 300 m / min.
It is considered that mass production and cost reduction can be obtained by drawing at a high speed and increasing productivity per device, and at the same time, evaluation cost and cost reduction by preventing irregular scale can be expected. However, since the above three methods were started from a small laboratory scale and were studied with an emphasis on characteristics, they are excellent in optical fiber characteristics, but have problems in mass productivity and cost reduction. The fiber length that can be produced by reforming is 15 to 30 km by the MCVD method, the VAD method,
The OVD method has a limit of 100 km to 200 km.

Certainly, the above-mentioned 3 manufacturing methods are suitable for manufacturing the transmission part of the optical fiber, but it is not suitable for mass production and cost reduction to manufacture the cladding part at the same time. . Rather, it is considered that if the clad portion occupying 80% or more of the cross-sectional area of the optical fiber for public communication is manufactured by another method that enables high efficiency and low cost, and it is combined with the above three methods, it will be an excellent manufacturing method. For example, it has been already practiced that a cladding portion is synthetically adhered by a OVD method on a core glass rod made by a VAD method, and that it is used as a material for an optical fiber.
However, in this manufacturing method, since a thin and short core glass rod is used, the synthetic adhesion efficiency is low, and since each core glass rod is synthesized, there is a limit to mass productivity and cost reduction.

As a result of studying the above-mentioned conventional method, the present inventors solve the above-mentioned problems by separating the core glass rod and the clad part, efficiently producing only the clad part, and combining them. We thought that it was possible and concluded that the rod-in-tube method was the most suitable.

However, the rod-in-tube method also has a problem. First, there was a problem with the size of the quartz glass tube. The size of the quartz tube used conventionally has a small diameter (outer diameter 15 to 30 mmφ, thickness 1 to 6 mm),
The dimensional accuracy varied about 10% in outer diameter and 20 to 30% in thickness. When the core glass rod is inserted into such a tube by the rod-in-tube method, a clearance of several mm or at least 1 to 2 mm is required for the purpose of preventing contact with the inner wall of the glass tube, although it depends on the skill of length and thickness. in this way,
The small diameter, large dimensional error of the tube, and the need for a wide clearance overlap to cause eccentricity in the preform integrated by the rod-in-tube method, which results in large deviation of the optical fiber. The rod-in-tube method is a manufacturing method that has no merit when it appears as a core ratio, and particularly when transmission loss is assumed in the construction of single-mode fibers in a batch multi-core connection.

In addition to the above problems, the rod-in-tube method has drawbacks such as inclusion of foreign matter and generation of bubbles on the fused surface between the inner surface of the quartz glass tube and the outer surface of the core glass rod. This depends on the atmosphere at the time of carrying out the rod-in-tube method and the cleaning method, but there is a problem in the inner surface finishing of the quartz glass tube.

[0009]

DISCLOSURE OF THE INVENTION The inventors of the present invention, as a result of diligent examination of these problems in the present situation, have a large diameter and a thick quartz glass tube in order to improve and enlarge the above-mentioned three methods, which have been used in the present situation. If a large preform is formed by integrating the optical fiber core glass rod with the optical fiber core glass rod by the rod incub method, the quality such as the eccentricity of the single mode fiber is good, and the mass productivity and the cost reduction are achieved at the same time. I found that I was satisfied. And, various problems related to the rod-in-tube method, mechanically inside a large high-purity quartz glass ingot or tubular body, the outer surface is ground and polished, with a large diameter,
A thick glass tube was created with accurate dimensional accuracy, and the surface was removed by hydrofluoric acid etching to remove surface contamination, and the roughness of the ground surface and processing strain were alleviated. It can be solved by combining it with the fiber core glass rod by the rod-in-tube method, and it is possible to create a large-scale preform with high accuracy.
It has been discovered that high-quality optical fibers of 000 km or more can be continuously and easily manufactured. In particular, the best characteristics are obtained when a large-sized high-purity synthetic quartz glass ingot or tubular body whose refractive index is controlled by removing impurities and foreign substances in the quartz glass and dehydrating is used.

By the way, the characteristics of the core glass rod rod-in the quartz glass tube vary even if they are produced under the same conditions, and the characteristics vary depending on the fiber specifications, user characteristics, and manufacturing method. Quartz glass tubes of various sizes are required to meet these conditions. It takes a lot of working time to manufacture each of these quartz glass tubes of various sizes by mechanical grinding or the like, which is far from mass production and cost reduction. Further, it is possible to form the quartz glass tube of various sizes by heating and drawing, but the error of the forming tube was greatly amplified during the heating and drawing, and it was difficult to accurately manufacture the quartz glass tube of the target size. . In order to prevent the abnormal deformation of the tube due to the amplification of the error during stretching, it is sufficient to create a tube having an accurate dimension, but it is already known that mechanical grinding, especially precision grinding with a large machine is good for this. It has been proposed by the person. However, although high precision can be obtained by the grinding process using the large-sized machine, various kinds of processing damage such as surface scratches, microcracks, cracks, and processing strains due to grinding are easily given to the ground surface. This processing damage causes bubbles to form on the internal boundary surface during integration by the rod-in-tube method, which results in large quartz glass preforms.
And is a cause of deterioration in the quality of the optical fiber. Therefore, by heating a large quartz glass tube ground by the above-mentioned large machine at a specific temperature and under specific conditions, there is no abnormal deformation of the tube during stretching, and various dimensions in which processing damage is eliminated. The present inventors have discovered that the above quartz glass tube can be accurately manufactured. The present invention has been completed based on these findings.

An object of the present invention is to provide a highly accurate quartz glass tube having a large diameter and a thick wall.

An object of the present invention is to provide a large-scale silica glass preform capable of manufacturing a low-cost optical fiber having excellent mass productivity.

An object of the present invention is to provide a method for producing a highly accurate large-diameter, thick-walled quartz glass tube having a smooth inner surface.

An object of the present invention is to provide a method for efficiently manufacturing large-sized quartz glass tubes of various sizes.

It is an object of the present invention to provide a method for producing a large-sized quartz glass preform using the highly accurate large-diameter, thick-walled quartz glass tube.

[0016]

According to the present invention for achieving the above object, an outer diameter obtained by processing a quartz glass tube by a non-contact heating processing method is 50 to 300 mmφ, and an outer diameter / inner diameter ratio = 1. 1
To a large quartz glass tube having a thickness of 10 mm or more and a thickness error of 2% or less, and a large quartz glass preform obtained by integrating the large quartz glass tube and a core glass rod for an optical fiber by a rod-in-tube method. The large-scale quartz glass tube and the preform include a high-purity quartz glass ingot or a tubular body, particularly a high-purity synthetic quartz glass ingot or a tubular body having a controlled refractive index, which is thermally processed or mechanically ground. Method to grind a quartz glass tube by a grinding method, then heat-treat the quartz glass tube by a non-contact heating processing method, and the quartz glass tube and the optical fiber core glass rod obtained by the heat treatment. It is manufactured by integrating and by the rod-in-tube method.

Here, terms used in this specification will be defined. 1) “Quartz glass base material” means a long cylindrical ingot or large cylindrical quartz glass made of high-purity natural quartz glass or synthetic quartz glass, and the outer circumference is roughly ground if necessary. Quartz glass before being processed to the target dimensions. In particular, synthetic quartz glass includes those in which OH group control and refractive index (n) control are performed in accordance with the quality design of the optical fiber.

2) "Quartz glass raw tube" means a machining method in which a cylindrical quartz glass base material is mechanically ground by a core drilling machine or the like to open a hole, or a carbon drill is press-fitted under heating ( (Hereinafter referred to as "carbon drill press-fitting method"), a large-sized tube or tube-shaped quartz glass preform is created, and the outer surface or inner / outer surface of the tube is mechanically roughly ground to a large target size. Quartz glass tube.

3) “Quartz glass blank tube” means that the inner and outer diameters of the raw quartz glass tube are accurately determined, the thickness error is 2% or less, the inner and outer surfaces are polished and hydrofluoric acid is etched. Quartz glass tube.

4) "Quartz glass heat treatment tube" is a tube obtained by further heat-treating, heat-stretching or heat-pressurizing a quartz glass tube by a non-contact heat processing method,
It refers to a quartz glass tube whose inner and outer surfaces are heat-treated, and / or a quartz glass tube having dimensions different from those of the quartz glass base tube.

5) "Thickness error" means, for example, a large-sized quartz tube having a predetermined length in the longitudinal direction at 5 points or more or 50 to 1
The value of the following equation when the tube thickness (t) at that position is set to the maximum value (t _max. ) And the minimum value (t _min. ), That is, [(t _max.- t _min. ) / {(t _max. + t _min. ) / 2}]
It is calculated by × 100 (%), and it means the value expressed in% of the maximum value in the entire length.

6) "Non-contact type heat processing method (Tool-
"Free Drawing Method""means that a dummy tube is fused to a quartz glass tube, the dummy tube part is held by a processing machine and passed through without contacting the heating zone.
It refers to a processing method in which the quartz glass tube is heat-treated, heat-stretched or heat-pressed.

7) "Core glass rod for optical fiber"
Is a light transmission part, which is composed of a core part and an optical clad part, and for public communication such as single mode and multimode for the purpose of high quality, a synthetic clad is sufficiently attached, and further OVD synthetic cladding or /
And a glass rod that includes a quartz glass tube jacketed, and refers to a glass rod that does not become a fiber suitable for the standard only by drawing it.

The quartz glass tube used in the rod-in-tube method is generally made of quartz glass which satisfies the quality characteristics such as purity, OH group and refractive index required for optical fiber cladding tubes. In the case of the present invention, the outer diameter is particularly 50 to
It is a large tube of about 300 mmφ. Increasing the size is effective for reducing the dimensional error of the quartz glass tube, reducing the eccentricity of the optical fiber, and for mass production and cost reduction. Quartz glass tube having the above outer diameter, especially 250 to 300 mm outer diameter
A pipe having a diameter of φ and a length of 2 to 5 m has already been manufactured.

An optical fiber, for example, a single mode fiber has a structure whose cross section is shown in FIG. In FIG. 1, 1 is a core, 2 is an optical cladding, 3 is an over cladding, a is a core diameter (d _core ), b is an optical cladding diameter (d _cladi ), and c is an optical cladding. Outer Diameter of Fiber (d _clado ) 12
5 μm is shown. A conceptual diagram of the refractive index distribution and power distribution of this single mode fiber is shown in FIG. In FIG. 2, the optical cladding portion is located outside the core diameter (d _core ) and the power distribution of light is broadened. Therefore, the optical clad diameter (d _cladi ) is combined with the clad part at the same time as the core, and its thickness needs to be changed according to conditions such as the shape of the refractive index distribution of the core, the refractive index difference (Δn), and the usage of the fiber. Yes, the value obtained by multiplying the actual performance by the safety factor is usually adopted. The silica glass core rod for optical fibers referred to in the present invention means a silica glass rod including the optical cladding portion shown in FIG.

By the way, since the large preform of the present invention is drawn and formed into an optical fiber, the large preform is formed.
The ratio D _o / D _i of the outer diameter (D _o ) to the inner diameter (D _i ) of the optical fiber is the outer diameter (d _clado ) of the optical fiber and the optical cladding diameter (d _cladi ).
_Is substantially proportional to the ratio d _clado / d _cladi . Therefore, in designing an optical fiber, it is necessary to design using the above D _o / D _i as an index. For example, assuming that the core diameter of the single mode fiber (for 1.3 μm wavelength) is 9 μm, the core diameter of the GI type multimode fiber is 50 μm, and the outer diameter of the optical fiber is 125 μm, D _o / D _i is shown in Table 1 below. Is asked.

[0027]

[Table 1] Note) () shows an example of multi-mode

According to Table 1 above, for example, in the case of a multimode fiber shown in parentheses as a typical example, D _o / D _i is 2.
5 or less, usually 5% synthetic clad layer by simultaneous synthesis
If there is a clad layer of 30%, for example 20%, the thickness becomes 60 μm, and D _o / D _i = 2.08. In the case of a single mode fiber, if D _o / D _i is about 7 or less, a practical optical fiber can be obtained. That is, for 1.3 μm band (matched clad type, depressed type), 1.55 μm
Main power for obi, dispersion shift type, etc.
All the distributions are estimated to be about 20 μm or less, and if the safety factor is taken, d _cladi / d _{core ≈3} or more, that is, D _o / D _i ≈
A practical range is 4.63 or less. Further, when the jacket is doubled or tripled, the value of D _o / D _i becomes lower.
Therefore, selecting D _o / D _i in the range of 1.1 to 7 is a condition for manufacturing a practical optical fiber. However, since D _o / D _i is the ratio of the diameter of the preform, in the case of a quartz glass tube for a rod tube, it is necessary to provide a slight gap between the quartz glass tube and the core glass rod. Needless to say.

Various methods known for the case of natural quartz can be used to make large quartz glass tubes. Although the crucible melt drawing method and the mold forming method can be used, it is difficult to increase the diameter of the crucible melting method.In the mold forming method, the heat-resistant material used for the container is in direct contact with the quartz glass for a long time, and Impurities are transferred and diffused to the inner and outer surfaces of the quartz glass base material. Therefore, since the transmission loss of the optical fiber is increased, it is essential to greatly remove the contaminated portion when the jacket is brought close to the core portion.

As a method for producing a large-sized quartz glass tube of the present invention, a cylindrical quartz glass base material is prepared, and the center thereof is mechanically ground, for example, by a core drilling machine such as a drilling machine (trade name, manufactured by Ueda Giken). Opening or columnar quartz glass preform by hot carbon drill press-in method ("Applied technology of high-purity silica" page 105, Figure 2.1.11, CMC, March 10, 1991). (Issued daily) to open the holes by short-time contact, etc., or to deposit the porous silica soot material on the heat-resistant core material, dehydrate and melt vitrify it, or use the direct VAD method to open the holes. It is possible to use a one-step method in which the soot is made, dehydrated, and vitrified.

Generally, the dimensional accuracy of a quartz glass tube is relatively improved due to the increase in size of the tube. To improve the dimensional accuracy, mechanical grinding, particularly precision grinding using a large machine, is preferable, but various kinds of processing damage such as surface scratches due to cutting, microcracks, cracks, and processing distortion are given to the ground surface. According to experiments conducted by the present inventors, it is known that when the inner surface roughness due to grinding exceeds 20 μm, bubbles are generated at the inner boundary surface during integration by the rod-in-tube method. Therefore, the total inner surface roughness of the tube must be at least 20 μm or less.

As the mechanical grinding finishing, the inner peripheral surface of the raw silica glass tube can be precisely machined with precision. For example, the ultra-precision honing method described in the ultra-precision processing technology (edited by the ultra-precision processing research group, Industrial Research Society, p. 421, 1984) is preferable. In this processing method, if the original quartz glass tube has an outer diameter of 50 mmφ or more, the length is 3000 mm.
It is possible to process a simple tube into a tube with a straight length and a perfect circle at all positions. As a result, the clearance with the core glass rod can be narrowed.

Grinding by the above-mentioned ultra-precision honing method and outer circumference grinding are repeated until the thickness error of the raw material pipe becomes 2% or less. Within the above error range, the error is hardly amplified during heating and drawing, and the eccentricity of the fiber is not adversely affected.

In the outer periphery grinding, the grinding surface is heated close to the high temperature portion, and therefore the grinding conditions need not be as severe as in the inner periphery grinding, but since the breaking strength after becoming an optical fiber is affected, hydrofluoric acid etching is performed. Therefore, it is necessary to reduce the sharp stress concentration portion and to make the surface roughness at least 200 μm or less, preferably 100 μm or less. Therefore, for the outer peripheral grinding, for example, a standard outer peripheral grinding or a cylindrical grinder having a proven track record in semiconductor ingot and various ceramics grinding processes can be used.

The quartz glass blank tube whose inner and outer circumferences are ground is integrated with the core glass rod for an optical fiber by the rod-in-tube method. However, even if the core glass rod is manufactured under the same conditions, the characteristics vary, or the fiber specifications, user specifications The characteristics also change depending on the characteristics and manufacturing method. Therefore, in order to fit the quartz glass raw tube to the core glass rod, a heating and drawing process is performed to produce quartz glass tubes of various sizes. For this heating and drawing treatment, a contactless heating processing method that does not allow impurities to adhere to the quartz glass tube is used. A schematic diagram of the non-contact type heat processing method is shown in FIG. In FIG. 3, 4 is a quartz glass tube, 5 is a heating source, 6 is a drawing roll, and 7 is a dummy.
A tube, 8 is a quartz glass heat treatment tube, and 9 is a sensor. It is necessary to pressurize the inside of the tube simultaneously with drawing in order to process the large-sized quartz glass tube to an accurate target size by the non-contact heating processing method. Although the pressure varies depending on the size, thickness, glass viscosity during heating, stretching ratio, etc. of the quartz glass tube, in order to obtain more accurate dimensions, the outside diameter (D ₀ ) and the inside diameter (D _i )) (D ₀ / D _i ), and the ratio of the outer diameter (d _o ) to the inner diameter (d _i ) of the heat-treated quartz glass heat treatment tube (d _o /
d _i ) is (D ₀ / D _i ) / (d _o / d _i ) = 1.0 to 1.
It is preferable to process it within the range of 5. When the ratio is 1.0 or less, the shape of the pipe is deformed, and when it exceeds 1.5, the thickness error of the pipe becomes large, and the pipe bursts depending on the temperature condition. As described above, it is not possible to manufacture a quartz glass tube having an accurate size outside the above processing range. Particularly, when the ratio is close to 1.5, it is absolutely necessary to reduce the thickness error to 2% or less. Further, the temperature of the heat processing is an outer diameter of 50 to 300.
1600 ° C. to 3000 ° C., preferably 2000 ° C. to 2800 ° C. are required as mmφ. Below the temperature range, it becomes difficult to heat-soften the quartz glass tube, and above the temperature range, the quartz glass tube is deformed or cast with deterioration and maintains accurate dimensional accuracy. Is difficult. D _o / D _i or d _o / d _i represents the overclad portion of the single mode optical fiber, and the ratio is 2 to 7 in the case of single jacketing, and 1.1 in the case of jacketing twice or more. Combine those with a degree of ~ 3.

Since the heat-treated quartz glass heat-treated tube is heat-treated at a high temperature of 1600 ° C. to 3000 ° C., various processing damages such as roughness of the ground surface and processing strain due to mechanical grinding are relaxed or reduced. To be released. In particular, as the degree of deformation of heat drawing is larger, surface scratches, cracks, pits, etc. are greatly deformed and expanded, the groove becomes shallower, the acute angle part disappears, and it has been conventionally required for a quartz glass tube for a rod-in tube. Further, it is possible to omit process treatments unsuitable for mass production, such as high-precision mechanical polishing treatment, inner surface fire polishing treatment, or treatment for forming a special glass layer on the inner surface. Therefore, it is advantageous to manufacture a large-sized quartz glass tube with high accuracy and utilize thermal deformation to obtain the desired large-sized quartz glass tube.

As a method for producing natural quartz glass according to the present invention, a good quality portion is selected from naturally occurring crystal ingots, the outer shell of each crystal ingot is removed, and the central portion is taken out and crushed. The impurities are removed by chemical treatment after removing foreign matters. Using this as a raw material, it is manufactured by a method known from old times, such as a crucible melt drawing method and a molding method, which is still used for general purposes. However, the method of forming a large-scale cylindrical quartz glass preform by the Bernoulli method using oxyhydrogen has the least impurities, so it can be recommended as a method of producing a quartz glass material for optical fibers.

As a method for producing the synthetic quartz glass ingot or tubular body used in the present invention, there is a conventionally known method for applying high-purity silica, Nos. 100 to 104.
Although various production methods described in pages etc. are conceivable, the high temperature vapor phase Bernoulli method is a method of directly obtaining a glass ingot by a gaseous silicon compound, for example, SiCl ₄ and an oxyhydrogen flame, and an OH group in synthetic quartz glass. Since it is contained in a large amount of 800 ppm or more (for low OH), it is unsuitable as a material for optical fibers, and is used exclusively for photomask substrates for semiconductors and optical members of exposure apparatuses. Further, the improved plasma method, which has a low OH group, requires a large amount of electric power and is high in cost. Therefore, the plasma method is only used for producing special products such as high-purity core glass for optical fibers. In contrast,
Lower the flame temperature than the direct vitrification method, wipe the raw material gas on the rotating base material (target), form a porous soot material and then perform dehydration treatment, etc., and then vitrify, It is suitable as the manufacturing method of the base material of the present invention without the above-mentioned drawbacks. The VAD method mainly manufactures a solid cylindrical quartz glass base material, and the OVD method directly produces a tubular quartz glass base material.

In the synthetic quartz glass tube adopting the manufacturing method by the soot method, the OH group and the refractive index can be accurately adjusted according to the clad portion of the core glass rod used. The large quartz glass preform of the present invention is 75
For large diameter preforms of mmφ or less, a preform is made by using a quartz glass tube of about 75 mmφ, a large preform is re-stretched, or a quartz glass tube and a core glass rod are combined and stretched in a rod-in-tube process. It is preferable that the preform having the target outer diameter is directly obtained by simultaneously performing the same steps.

In the single mode core glass rod, it is important to select the characteristics such as the mode field diameter, the cutoff wavelength and the dispersion. In recent years, the characteristics have become much higher, so if the core glass rod produced is used as it is, the characteristics often vary slightly. Therefore, the clad thickness of the core glass rod is adjusted once with the quartz glass tube, the characteristics are checked, and then the large-sized quartz glass tube is rejacketed or the outer diameter is adjusted by combining etching and the like. The large quartz glass preform has a wide adjustment range, so that it has a feature that higher accuracy can be obtained.

[0041]

Example 1 Using a shaft-attached method (VAD method), SiCl ₄ was vaporized, subjected to flame hydrolysis in an oxyhydrogen flame burner, and sprayed on a rotating quartz glass rod to prepare a large quartz porous soot material. This soot material was put into an electric furnace, heated and dehydrated with a mixed gas of He and Cl ₂ in consideration of the clad portion of the core glass rod, and made into transparent glass at 1550 ° C. by a zone melting method to obtain a large quartz glass base material ingot. In this quartz glass ingot, first, the center part was opened with a core drilling machine of # 80 grindstone, and then the outer circumference was also # 80.
Rough grinding was performed with an outer peripheral grinder of a No. whetstone.

The inner surface of the above synthetic quartz glass raw tube is processed by a long automatic honing machine for ultra-precision finishing to make a straight and perfectly circular hole, and then an NC outer circumference grinder is used for inner diameter. The outer circumference is ground so that the center and the outer diameter center coincide with each other, and the thickness error is alternately processed until the thickness error becomes 2% or less. After confirming the thickness error, the inner circumference is # 800 and the outer circumference is # 14.
Finished with 0. Then, in order to remove surface contamination and to alleviate surface processing strains, the surface of the quartz glass is checked and finished with etching while checking the surface with hydrofluoric acid at a concentration of 30% to 5%, ultrasonic cleaning, pure water cleaning, and synthetic quartz It was a glass tube. This synthetic quartz glass tube has an outer diameter of 93.5 mm
φ, inner diameter (D _i ) 31.6 mm φ (D _o / D _i 2.9
6), the thickness 30.95Mm, thickness error (t _max. Over _{t min.) 0.42mm (1.36%} ), length 700m
m, and the weight was 9.3 kg. Examination and 8mm moved longitudinally further the surface with a stylus type simple roughness tester, the inner surface roughness (R _max.) 8.5μm, an outer surface roughness (R _max.) 68μm
Met.

Next, this synthetic quartz glass tube was placed in a vertical electric furnace and heated to 2200 ° C., an inert gas was caused to flow inside and outside the tube to weld the lower end, and then pressure drawing was carried out. The five types of synthetic quartz glass tubes shown in Figure 3 were prepared. The inner surface roughness R _max. After the heat treatment is low as shown in Table 2.

On the other hand, the refractive index difference (Δn) is 0.3 by the VAD method.
A 35% single mode core glass rod was prepared. The core glass rod shown in Table 1 was obtained by hot drawing and calculating the synthetic quartz glass tube shown in Table 2 as a clad layer and etching the outer periphery of the core glass rod. Insert each core glass rod into each synthetic quartz glass tube,
When integrated by heating in an electric furnace and measured by a preform analyzer, no difference in refractive index was observed between the clad layers.

[0045]

[Table 2]

No. 2 in Table 2 Using a preform of 3 (62 mmφ), an optical fiber strand of 125 μm was prepared,
When the fiber characteristics of the strand were investigated, the cutoff wavelength (λ _c ) was 1.245 μm, and the transmission loss of 1.3 μm was 0.3.
It was a high-quality optical fiber with 34 dB / km and an eccentricity rate of 0.32 μm.

[0047]

Example 2 A large-scale porous soot material was prepared by the external method (OVD method), dehydrated, and subjected to a refractive index adjustment treatment to be vitrified to prepare four original synthetic quartz glass tubes in a tubular form.
After finishing the inner diameter with an ultra-precision honing machine, the center line of the inner diameter and the outer diameter was artificially removed to make it eccentric, the outer peripheral surface was ground, and hydrofluoric acid treatment was performed for cleaning and finishing. This synthetic quartz glass tube has an outer diameter of 100 mmφ, an inner diameter of 32 mmφ, and D _o
/ D _i = 3.125 Table 3 shows the measured errors.

The above synthetic quartz glass tube was placed in an electric furnace,
Drawing under heat and pressure at 2200 ° C (pressing: 0 mm to 100 mm water column)
mm) and the dimensions after processing were examined. The results are shown in Table 3.

[0059]

[Table 3] _{However, α: d o / d i} β: (D 0 / D i) / (d 0 / d i) condition A was the internal pressure of the raw tube and the outside pressure approximately equal.

As shown in Table 3 above, in a quartz glass tube having a large error, the error after drawing increases as the pressure ratio and the drawing ratio increase. In particular, the pressurization ratio greatly changes the thickness error of the quartz glass tube, and a tube of 3.9% or more deforms asymmetrically under the unstable condition at the start, and then expands rapidly in the furnace. Ruptured.

Among the above synthetic quartz glass tubes, No. 8 and B
Using a tube under the conditions of (that is, a tube made with an error of 1.8% of a raw tube and having an error of 2% or less in thickness after heating and pressurizing drawing),
An optical fiber core glass rod was inserted and a preform was prepared by the rod-in-tube method. When examined with a preform analyzer, the refractive index difference in the clad is 0.0
It was 1% or less, and the eccentricity after drawing was 0.45 μm, and there was no problem as a single mode fiber.

[0052]

Example 3 A center of a quartz glass ingot made of high-purity natural quartz glass was punched by a hot carbon drill press-fitting method. Then, the outer periphery was ground to match the center of the inner diameter, and hydrofluoric acid etching, water washing, and drying were performed. The finished blank has an outer diameter of 150 mmφ, an inner diameter of 62 mmφ, D ₀ / D _i = 2.
42, the length is 2500 mm, and the thickness error of the total length measured at intervals of 50 mm is 0.35 mm (0.79%).
Inner surface roughness (R _max. ) Is 1 μm or less, outer surface roughness (R _max.
max. ) was 85 μm. In addition, when this quartz glass was examined for an absorption band of 2.7 μm with an infrared spectrophotometer, the average value was 1
It contained 66 ppm of OH groups.

Next, the above quartz glass tube was placed in a vertical electric furnace and the temperature was raised to 2250 ° C. to seal the lower end. The outer diameter, inner diameter, and thickness are checked while adjusting the pressure from the upper end with air, and the outer diameter, inner diameter, and thickness are checked.
A quartz glass tube having mφ and 125 mmφ was prepared. Table 4 shows the dimensions of each quartz glass tube.

[0054]

[Table 4]

Outer diameter 100 mmφ from the quartz glass tube
The tube was selected, an optical fiber core rod for a single mode by the VAD method was attached, and the tube was integrated by the rod tube method.

Similar to the tube drawing conditions, the first drawing start outer diameter is 50 mmφ, then 75 mmφ, 9
Three types of 6 mmφ were prepared. The preforms of each size were each ground into pieces and visually inspected the fused surface between the inside of the quartz glass tube and the outer surface of the core rod, but almost no bubbles were found.

A wire was drawn using a 50 mmφ preform,
As a result of examining the fiber characteristics, the eccentricity is 0.27 μm,
The transmission loss of 1.3 μm was 0.347 dB / km.

[0058]

INDUSTRIAL APPLICABILITY The large-scale quartz glass tube of the present invention is excellent in high precision because it reduces the generation of bubbles at the boundary surface between the rod and the tube of the large-scale preform manufactured using the same, and has a low eccentricity. It is a large-scale quartz glass tube that can provide large-scale preforms. These large quartz glass tubes and large preforms can be easily manufactured by simple means such as machining and heat treatment, and by drawing them, high-quality optical fibers can be manufactured with a low disconnection rate, mass production, and low cost. It can be made much more.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a single mode fiber.

FIG. 2 is a conceptual diagram of a refractive index distribution and a light power distribution of a single mode fiber.

FIG. 3 is a schematic view of a method for producing a large-sized quartz glass heat-treated tube by subjecting a large-sized quartz glass tube to heat treatment by a non-contact heating method.

[Explanation of symbols]

 1 Core 2 Optical Clad 3 Overclad 4 Quartz Glass Tube 5 Heating Source 6 Stretch Roll 7 Damper Tube 8 Quartz Glass Heat Treatment Tube 9 Sensor-a Core Diameter b Optical Cladding Diameter c Optical Fiber Outer Diameter

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kiyoshi Yokokawa Kiyoshi Kawamura, Kanayama, Tamura-cho, Koriyama-shi, Fukushima 88 Koriyama Plant, Shin-Etsu Quartz Co., Ltd. Koriyama Plant Co., Ltd. (72) Masanori Suzuki, Inventor Masanori Kawamura, Kanayama, Koriyama City, Fukushima 88 Shin-Etsu Quartz Co., Ltd.Koriyama Plant (72) Toshiyuki Kato Kawakubo, Kanayama, Koriyama City, Fukushima Prefecture 88 Shinetsu Quartz Co. Koriyama Factory (72) Inventor Yutaka Watanabe Kanayama, Tamura-cho, Fukushima Prefecture Kawakubo 88 Shin-Etsu Quartz Co., Ltd.Koriyama Factory (72) Inventor Gerhard Filsmeier Germany 8750 Asiyafemburg Bussadweg 42

Claims (5)

[Claims] 1. An outer diameter obtained by processing a quartz glass tube by a non-contact heating processing method is 50 to 300 mmφ, an outer diameter / inner diameter ratio = 1.1 to 7, a thickness of 10 mm or more, and a thickness error of 2%. Less than,
A large quartz glass tube with an inner surface roughness of 20 μm or less. 2. The large quartz glass tube according to claim 1, wherein the quartz glass is high-purity natural quartz glass or synthetic quartz glass. 3. A large-sized quartz glass preform obtained by integrating the large-sized quartz glass tube according to claim 1 and a core glass rod for an optical fiber by a rod-incubation method.
Mu. 4. A quartz glass base tube is prepared by mechanically grinding the outer surface or the inner and outer surfaces of a high-purity quartz glass base material to form a raw quartz glass tube, followed by polishing and hydrofluoric acid etching. Then, the ratio of the outer diameter (D ₀ ) to the inner diameter (D _i ) of the quartz glass raw tube (D
₀ / D _i ) and the ratio (d ₀ / d _i ) of the outer diameter (d ₀ ) to the inner diameter (d _i ) of the heat-treated pipe are (D ₀ / D _i ) / (d ₀ / d
The large-scale quartz according to claim 1 or 2, wherein the internal pressure is controlled so that _i ) = 1.0 to 1.5, and heat treatment, heat stretching or heat and pressure stretching is performed at 1600 to 3000 ° C. Glass tube manufacturing method. 5. A method for manufacturing a large-sized quartz glass preform, characterized in that the large-sized quartz glass tube according to claim 1 and the core glass rod for an optical fiber are integrated by a rod-in-tube method.