JP3529149B2 - Large quartz glass tube, large quartz glass preform, and methods for producing them - Google Patents

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-walled large-sized quartz glass tube formed by hot carbon drill press fitting.
Optical fiber preforms with low eccentricity, excellent transmission characteristics, mass productivity, and cost reduction, especially silica glass tube and single mode optical fiber core glass rod are integrated by rod-in-tube method Large-sized quartz glass preforms, and methods for manufacturing them.

[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 the products made by these three manufacturing methods are 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 considered that the method alone has reached the 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. . For example, in a graded index fiber or a single mode fiber, if the clad portion occupying 80% or more of the optical fiber cross-sectional area is manufactured by another method capable of high efficiency and low cost, and combining it with the above three methods, It is considered to be an excellent manufacturing method, for example, it has already been practiced to synthetically adhere the clad portion to the core glass rod manufactured by the VAD method by the OVD method and use it as the material for the optical fiber. In this manufacturing method, since a thin and short core glass rod is used, the synthetic adhesion efficiency of the clad is low, and since each core glass rod is synthesized, mass productivity and cost reduction are limited.

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 concluded that the rod-in-tube method was the most suitable manufacturing method.

However, the conventional rod-in-tube method 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 inserting the core glass rod into such a tube by the rod-in-tube method, a clearance of several mm at least 1-2 mm was required for the purpose of preventing contact with the inner wall of the glass tube, depending on the length, thickness, and skill level. . In this way, the small diameter, large dimensional error of the tube, and the need for a wide clearance overlap each other, causing eccentricity in the preform integrated by the rod-in-tube method, which results in optical A large eccentricity of the fiber appears, and the rod-in-tube method is a manufacturing method with no merit especially when the splice loss of the single-mode fiber in the collective multicore connection work is assumed.

On the other hand, the core glass rod rod-in the quartz glass tube has different characteristics even if it is produced under the same conditions.
The characteristics also change depending on the fiber specifications, user characteristics, and manufacturing method. High-precision quartz glass tubes of various sizes are required to meet these conditions. Although it was excellent in dimensional accuracy to create each of these high-precision quartz glass tubes of various dimensions by mechanical grinding, etc., it took a lot of work time, mass production was difficult, and cost reduction was difficult. When it is produced by the method, mass productivity and cost reduction are possible, but if the dimensional accuracy of the original tube is poor, it is greatly amplified during heating and drawing, and it is difficult to manufacture a quartz glass tube with a target size with high accuracy.

In addition to the above-mentioned 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.

[0010]

DISCLOSURE OF THE INVENTION The inventors of the present invention have made earnest studies on the problems of the present situation, and as a result, in order to improve and enlarge the above-mentioned three methods, which have been used in the current situation, a quartz glass tube having a large diameter and a large wall thickness. To form a large preform by integrating the core glass rod for optical fiber with the rod glass tube method.
It has been found that the quality of the single mode optical fiber such as the eccentricity is good, and the mass productivity and the cost reduction are satisfied at the same time. Then, various problems related to the rod-in-tube method, large quartz glass ingot, especially removing impurities and foreign substances in quartz glass, dehydrated, large high-purity synthetic quartz glass ingot with a controlled refractive index, Grinding and polishing the inner and outer surfaces with a large machine, finishing to exact dimensional accuracy, hydrofluoric acid etching treatment, outer diameter 50 to 3
A large-scale quartz glass tube having a thickness error of 2% or less at 00 mmφ can be solved by combining the large-scale quartz glass tube and the optical fiber core glass rod and integrating them by a rod-in-tube method. It has been made possible, and it has been found that a single high-quality preform can continuously and easily produce a high-quality optical fiber of 3000 km or more.

Precision grinding is possible by the grinding using the above large machine, and the dimensional accuracy is greatly improved.
Various processing damages such as surface roughness, microcracks, cracks, and processing strains occurred on the ground surface due to grinding. This processing damage causes bubbles on the inner boundary surface during integration by the rod-in-tube method, which is brought into the preform, resulting in deterioration of the quality of the optical fiber. It took a long time just to make it smooth.

However, instead of the above-mentioned large-scale mechanical grinding and drilling method, for example, issued by CMC Co., Ltd. (199
March 10, 1st, 1st printing) "Applied technology of high-purity silica" on page 105, Figure 2.1.11, that is, a method of press-fitting a carbon drill under heating (hereinafter referred to as "hot work"). It was found that the quartz glass tube having an inner surface roughness of 20 μm or less can be easily obtained by eliminating the mechanical processing damage described above. Then, it was discovered that by integrating the quartz glass tube and the core glass rod, it is possible to form a highly accurate preform in which no bubbles are generated at the inner boundary surface. The present invention has been completed based on these findings.

It is an object of the present invention to provide a highly accurate quartz glass tube having a large diameter and a thick wall formed by a hot carbon drill press fitting method.

It is an object of the present invention to provide a large silica glass preform capable of manufacturing a low cost optical fiber which is excellent in mass productivity.

An object of the present invention is to provide a method for producing a highly accurate quartz glass tube having a large diameter and a high thickness by a hot carbon drill press-fitting method.

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

[0017]

According to the present invention, which achieves the above object, an outer diameter 50 formed by a hot carbon drill press-fitting method.
~ 300 mmφ, outer diameter / inner diameter ratio = 1.1 to 7, thickness 10
A large-sized quartz glass tube having a thickness of 2 mm or more and a thickness error of 2% or less, and a large-sized quartz glass preform obtained by integrating the large-sized quartz glass tube and a core glass rod for an optical fiber by a rod-in-tube method. The glass tube can be manufactured by punching the center of a large cylindrical quartz glass ingot into a true circular tube by the hot carbon drill press-fitting method, and the large quartz glass preform, the quartz glass tube and the optical fiber core glass rod. It is manufactured by integrating and by the rod-in-tube method.

Here, terms used in this specification are defined. 1) "Quartz glass tube" is made of high-purity natural quartz glass or synthetic quartz glass ingot. In synthetic quartz glass, OH group control and refractive index control are performed according to the purpose. After opening the center of the ingot by a hot carbon drill press fitting method, the outer peripheral surface is mechanically ground with high precision to obtain an outer diameter of 50 to 300 mmφ, an outer diameter / inner diameter ratio = 1.1 to 7, a thickness of 10 mm or more, Thickness error 2
%, A quartz glass tube having an inner surface roughness of 20 μm or less after being formed by etching and having a thickness of 20% or less.

2) "Thickness error" means, for example, 5 or more points or 50 to 10 in a longitudinal direction of a large-sized quartz tube having a predetermined length.
The tube thickness (t) at that position by rotating at 0 mm intervals
The maximum value (t _max. ) And the minimum value (t _min. ) Of the following equation, 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.

3) "Core glass rod for optical fiber"
Is a light transmission part, and for public communication such as single mode and multimode for the purpose of high quality, a clad compounded with a part of the core is attached, and further, the OVD method is used. A glass rod that includes a synthetic clad or / and a quartz glass tube jacketed by the above and 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 satisfying quality characteristics such as purity, OH group and refractive index required for optical fiber clad tubes, and has an outer diameter of 50 to 300 mmφ. A large tube with an outer diameter / inner diameter ratio of about 1.1 to 7. 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. A quartz glass tube having the outer diameter, particularly an outer diameter of 250 to 300 mmφ,
A tube having a length of about 2 to 5 m has already been manufactured.

An optical fiber, such as a single mode fiber, has a cross section having the structure shown in FIG. 1 in FIG.
Is a core, 2 is an optical cladding, 3 is an over cladding, a is an average core diameter (d _core ), b is an optical cladding diameter (d _cladi ), and c is an optical fiber outer diameter (d _clado). ) 12
5 μm is shown. A schematic diagram of the refractive index distribution and the light power distribution of this single mode fiber is shown in FIG. In FIG. 2, the optical cladding portion is located outside the average core diameter (d _core ) and the power distribution of light is broadened.
Therefore, the optical clad diameter (d _cladi ) is combined with the core and the clad at the same time, and its thickness is changed according to the conditions such as the shape of the refractive index distribution of the core, the refractive index difference (Δn), and the usage of the fiber. It is necessary, and usually the value obtained by multiplying the actual performance by the safety factor is 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, the optical fiber according to the present invention is
Since it is formed by drawing a large preform, the ratio of the outer diameter (d _clado ) of the optical fiber to the optical cladding diameter (d _cladi ) d _clado / d _cladi is the large preform.
It is almost proportional to the ratio D _o / D _i of the outer diameter (D _o ) and the inner diameter (D _i ) of the diaphragm. Therefore, in designing an optical fiber, it is necessary to design using the above D _o / D _i as an index. For example, a single mode fiber (for 1.3 μm wavelength) has a core diameter of 9 μm, and a GI type multi-mode fiber has a core diameter of 50.
μm and the outer diameter of the optical fiber is 125 μm, D _o /
D _i has the values shown in Table 1 below.

[0024]

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

According to Table 1 above, for example, in the case of a multimode fiber, D _o / D _i is 2.5 or less, and when the composite clad is about 20%, d _cladi = 60 μm, 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, the power distributions for the 1.3 μm band (matched clad type, depressed type), 1.55 μm band, dispersion shift type, etc. are all about 20 μm or less, and d _cladi / D
_The practical range is _core ≈3 or more, that is, D _o / D _i ≦ 4.63 or less. Further, when the jacket is doubled or tripled, the value of D _o / D _i becomes lower. Therefore, D _o /
Selecting 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, it goes without saying that it is necessary to provide a gap between the core rod and the tube in the case of the tube for the rod intub. .

Generally, the dimensional accuracy of a quartz glass tube is improved by mechanical grinding, particularly precision grinding by a large machine. In particular, when a hot carbon drill press fitting method is adopted as a large-scale drilling machine, the outer diameter is 50 to 300 mmφ, the outer diameter / inner diameter ratio is 1.1 to 7, the length is 2000 to 3000 mm, and the thickness is 10.
It is possible to easily form a large-sized quartz glass tube having an inner surface roughness of 20 μm or less, actually several μm or less without grinding and polishing the inner surface of the quartz glass tube of mm or more. According to the experiments conducted by the present inventors, no grinding scratches, microcracks, cracks, and processing distortions caused by mechanical perforation are generated, and at the maximum diameter of the holes left open, smooth without heat processing. It has been found that an inner surface is obtained and no bubbles are generated at the interface with the core glass rod after the rod incubation.

By accurately grinding the outer peripheral surface of the large-sized quartz glass tube while measuring the shape, the thickness error of the large-sized quartz glass tube can be accurately set to 2% or less. By setting the thickness within this error range, the error is hardly amplified during heating and drawing, and the eccentricity of the fiber is not adversely affected.

In addition to the above advantages, the hot carbon drill press-fitting method has a feature that when the outer diameter of the ingot to be ground is 50 mmφ or more, the accuracy of the roundness and straightness of the opening is remarkably improved. Therefore, in the case of a quartz glass ingot having an outer diameter of 50 mmφ or more, the outer diameter is 300 mmφ or more by opening by the hot carbon drill press fitting method,
A large-diameter tube with a length of about 3000 mm can be made into a tube with a straight length and a perfect circle at all positions, and it has already been put to practical use in natural quartz glass.

Due to the low internal impurities of the tube according to the method of the invention, mechanical removal of the contaminated part is almost unnecessary. This is because the contact time between the quartz glass and the heat-resistant molding material is overwhelmingly shorter than that of the mold method or the crucible melting method, so that the adhesion and residual transfer of impurities from the heat-resistant molding material hardly occur. Even when the inner surface is cleaned, strong etching is not required, and there are no defects such as mechanical scratches, cracks, chipping, and distortion, so the surface deterioration after etching is much less than that due to machining. There are features. As the drill material for the hot press carbon drill method, heat resistant materials such as alumina and tungsten can be used in addition to carbon.

In the outer peripheral grinding process, the outer peripheral ground surface is heated close to the high temperature portion, so that the grinding conditions do not have to be as severe as in the above inner peripheral grinding, but the breaking strength after the optical fiber is formed. As the sharp stress concentration part is relaxed by hydrofluoric acid etching, the surface roughness should be at least 2.
It is necessary to set the thickness to 00 μm or less, preferably 100 μm or less. For such surface roughness, for example, a standard outer peripheral grinder or a cylindrical grinder, which has a proven record in grinding semiconductor ingots and various ceramics, can be used.

As a method for producing the synthetic quartz glass ingot used in the present invention, various conventionally known production methods can be used. In the high-temperature vapor phase Bernoulli method, synthetic quartz glass contains a large amount of OH groups of about 800 to 1200 ppm. The plasma method can adjust the OH group content, but requires a large amount of power and is costly, so it is only used for manufacturing special products such as high-purity core glass for optical fibers.

On the other hand, dehydration treatment was performed after the raw material gas was blown onto the rotating base material (target) to form a porous soot material, which was lower than the above-mentioned direct vitrification method. In addition, when the VAD method of vitrification is used, a solid ingot can be satisfactorily manufactured, and the OH group and the refractive index can be accurately adjusted according to the clad portion of the core glass rod used. The most preferable method for producing the synthetic quartz glass base material ingot of the present invention.

The large quartz glass preform of the present invention comprises:
A large-sized quartz glass preform for an optical fiber can be manufactured by combining a quartz glass tube and a core glass rod and integrating them by a rod-in-tube method. However, in the case of a large-diameter preform of about 75 mmφ, a preform is directly formed by directly using a 75 mmφ quartz glass tube, the large-scale quartz glass preform is re-stretched, or a quartz glass tube and a core glass are used in a rod-in-tube process. It is preferable that the preform having the target outer diameter is directly obtained by simultaneously performing the combination with the rod and the stretching in the same step.

In the single mode core glass rod, it is important to select the core diameter (a), the cutoff wavelength (λ _c ), and the dispersion (λ _o ). However, in recent years, the properties required have become much higher, and therefore, if the core glass rod produced is used as it is, some variations in the properties often occur. Therefore, the clad thickness of the core glass rod should be directly synthesized, or adjusted once with a relatively thin quartz glass tube and then jacketed with a large quartz glass tube to form a preform, and then fine adjustment such as etching. I do.

[0035]

[Example 1] A large-scale porous soot material was prepared by a shaft attachment method (VAD method), and this large-scale porous soot material was put into an electric furnace to obtain V
Taking the dehydration condition of the core glass into consideration by the AD method, the dehydration by heating with a mixed gas of He and Cl ₂ was performed,
Vitrified into transparent glass at 550 ° C, rough-ground it to an outer diameter of 96
A quartz glass ingot having a diameter of mmφ and a length of about 820 mm was obtained.

In order to make a hole in the center of this ingot by using the hot carbon drill press-fitting method and further improve the dimensional accuracy,
The outer periphery was ground, treated with hydrofluoric acid, and washed. The synthetic quartz glass tube at this point has an outer diameter of 101 mmφ and an inner diameter of 40 m.
mφ, outer diameter / inner diameter ratio = 2.525, length 775 mm, and weight about 11.5 kg. The thickness error (t _max. Over t _min.) Was 0.525mm (1.72%). No mechanical impact, cracks due to cutting, cracking, processing strain, etc. were observed on the inner surface of this pipe, and the inner surface roughness (R
_Max. ) was 1.2 μm or less when examined by a stylus type simple roughness meter.

On the other hand, a 1.3 μm single mode core glass rod having a refractive index (Δn) of 0.36% and a cladding layer partially welded by the VAD method was prepared. The rod was heat-stretched to an outer diameter of about 38 mmφ by a precision automatic stretching machine with outer diameter control, and after slightly etching the outer surface of the rod, the rod was blown with a length of 775 mm. After carefully inserting the core glass rod into the synthetic quartz glass tube, align the centers of the synthetic quartz glass tube and the core glass rod with each other, and contact both ends with the dummy quartz material. I corrected it. Insert this into the vertical electric furnace from above and
The tip was melted at 0 ° C., and the pressure was reduced by a vacuum pump. Temperature (2000-2800 ° C) and vacuum degree (20
The moving speed was changed while adjusting each of 0 to 1000 mmAq), the interfacial bubble condition was examined, and the entire length was slowly moved at 2 mm / min under the condition of no bubble to prepare a preform. No bubbles were generated at the internal interface of the obtained preform. Part of this preform has an outer diameter of approximately 50 mm
As a result of heat drawing to φ and examination with a preform analyzer, no step in refractive index was found at the interface between the quartz tube and the core glass. This preform is 125 μm with a wire drawing machine.
As a result of examining the characteristics as an optical fiber of, the eccentricity is 0.3μ.
m, 1.3 μm Transmission loss was 0.344 dB / km, which was an excellent fiber.

[0038]

Example 2 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 pipe has an outer diameter of 150 mmφ, an inner diameter of 62 mmφ, and an outer diameter / inner diameter ratio =
2.42, length 2500mm, 50m in the length direction
Thickness error measured every m is 0.35 mm (0.79%)
The inner surface roughness (R _max. ) Was 1 μm or less, and the outer surface roughness (R _max. ) Was 85 μm. In addition, when this quartz glass was examined for an absorption band of 2.7 μm with an infrared spectrophotometer,
It contained on average 166 ppm of OH groups.

Next, the 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,
Check thickness and outer diameter 50mmφ, 75mmφ, 100mm
A φ, 125 mmφ quartz glass tube was prepared. Table 2 shows the dimensions of each quartz glass tube.

[0040]

[Table 2]

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. Preforms of each size were each cut into pieces and polished, and the fused surface between the inside of the quartz glass tube and the outer surface of the core rod was visually inspected, but almost no bubbles were found.

As a result of drawing the fiber using a 50 mmφ preform and examining the fiber characteristics, the eccentricity was 0.27 μm.
The transmission loss at m and 1.3 μm was 0.347 dB / km.

[0044]

The large quartz glass tube of the present invention can generate bubbles at the interface between the rod and the tube even if it is integrated with the core glass rod for an optical fiber while being opened by the hot carbon drilling method. It is a quartz glass tube that can provide a high-quality large preform that does not have a low eccentricity.
By drawing a large preform made from the high quality quartz glass tube, a high-quality optical fiber can be mass-produced and the cost can be reduced.

[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 of imagining a large quartz glass tube by a hot carbon drill press fitting method.

[Explanation of symbols] 1 core 2 Optical cladding 3 overclad 4 Cylindrical quartz glass ingot 5 carbon drill 12 Quartz glass tube 13 heating heater a Core diameter b Optical cladding diameter c Optical fiber outer diameter

   ─────────────────────────────────────────────────── ─── Continued front page    (73) Patent holder 599089712               Heraeus Quartz Grasse Gezersi               Yaft Mitt Beschlenktel Ha               Houtung und Company Company               Dit Gezelshaft               Heraeus Quarzglas               GmbH & Co. KG               Germany, D-63450 Hanau,               Quartz Strasse 8 (72) Inventor Kiyoshi Yokokawa               Fukushima Prefecture Koriyama City Tamura Town Kanaya character Kawakubo 88 Shin               Koshi quartz Co., Ltd. Koriyama factory (72) Inventor Masaaki Aoyama               Fukushima Prefecture Koriyama City Tamura Town Kanaya character Kawakubo 88 Shin               Koshi quartz Co., Ltd. Koriyama factory (72) Inventor Masanori Suzuki               Fukushima Prefecture Koriyama City Tamura Town Kanaya character Kawakubo 88 Shin               Koshi quartz Co., Ltd. Koriyama factory (72) Inventor Toshiyuki Kato               Fukushima Prefecture Koriyama City Tamura Town Kanaya character Kawakubo 88 Shin               Koshi quartz Co., Ltd. Koriyama factory (72) Inventor Yutaka Watanabe               Fukushima Prefecture Koriyama City Tamura Town Kanaya character Kawakubo 88 Shin               Koshi quartz Co., Ltd. Koriyama factory (72) Inventor Gerhard Vilsmeier               Federal Republic of Germany 8750 Asiayafen               Burg Bussadeuegg 42                (56) References JP-A-62-41732 (JP, A)                 JP-A-1-160838 (JP, A)                 JP-A-3-247525 (JP, A)                 JP 60-176941 (JP, A)                 "Applied technology of high-purity silica", Co., Ltd.               CMC, March 10, 1991, P102               −105

Claims (2)

(57) [Claims] 1. The center of a large quartz glass ingot is perforated by a hot carbon drill press fitting method, and then the outer diameter is 50 to 300.
mm, outer diameter to inner diameter ratio 1.1 to 7, thickness 10 mm or more,
A large-scale quartz glass preform characterized by accurately grinding the outer periphery to a thickness error of 2% or less and a surface roughness of 200 μm or less on the outer periphery, and integrally welding the obtained quartz glass tube and a core glass rod for optical fiber. Manufacturing method. 2. The large-scale quartz glass preform according to claim 1, wherein in the step of welding and integrating the large-scale quartz glass tube and the core glass rod for optical fiber, the integration and the stretching are performed at the same time. Manufacturing method.