JP4114903B2 - Quartz glass tube with tapered groove and optical fiber preform manufacturing method using the same - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a quartz glass tube having a tapered groove and a method for producing an optical fiber preform using the quartz glass tube, more specifically, inserting a core glass rod for an optical fiber preform into the quartz glass tube for an optical fiber preform, A quartz glass tube provided with a tapered groove in the vicinity of the end portion on the holding side of a quartz glass tube for a base material used in manufacturing an optical fiber base material that is integrated by heating and welding or an auxiliary quartz glass tube connected thereto And a method of manufacturing an optical fiber preform using the quartz glass tube.
[0002]
[Prior art]
In recent years, with the practical application of optical fibers, particularly single-mode optical fibers, a large amount of optical fibers have come to be used. However, optical fibers expand the range of use from long-distance trunk lines to general subscriber systems. Therefore, it is expected that a larger amount of optical fiber will be required. In order to expand the range of use, mass production and cost reduction of optical fibers are indispensable. For this purpose, the simplest method is to create a large and long optical fiber preform and draw it. . Such a large and long optical fiber preform has been proposed in JP-A-7-109136. The large optical fiber preform described in the above publication is manufactured by a so-called rod-in-tube method in which a core glass rod for an optical fiber preform is inserted into a quartz glass tube for an optical fiber preform, and is welded and integrated. Yes.
[0003]
[Problems to be solved by the invention]
In the rod-in-tube method, the quartz glass tube for the optical fiber preform and the center of each circle such as the heating heat source are accurately aligned, the optical fiber preform ellipse, the core ellipse, and further the preform and core It is necessary to prevent the optical fiber preform from being bent by aligning the center of the optical fiber preform quartz glass tube and the optical fiber preform on the drawing side. Furthermore, in order to manufacture an optical fiber at a low cost, it is also required to use an expensive optical fiber preform quartz glass tube as efficiently as possible. Although it is important to accurately hold a large and heavy quartz glass tube for centering the circle, a holding jig used in the conventional rod-in-tube method is disclosed in, for example, Japanese Patent Application Laid-Open No. 7-196332. As seen in Kaihei 8-277138, etc., a quartz glass tube for an optical fiber preform or a chuck that sandwiches an auxiliary quartz glass tube connected thereto is generally used, and the optical fiber preform is increased in size and weight. In order to hold the quartz glass tube for use, the size of the chuck itself must be increased and the frictional force between the chuck and the quartz glass tube must be increased. For example, the frictional force can be increased by changing the material of the contact part to a material having a high frictional resistance, increasing the contact area, or increasing the pressing pressure at the chuck. Considering that the frictional resistance cannot be increased so much, and there is a limit to the expansion of the contact area, and further, the increase in pressing pressure may increase the partial compressive stress and break the quartz glass tube, etc. In either case, a sufficient increase in frictional force could not be expected. Therefore, the size of the chuck was increased more than necessary, and the manufacturing cost was high. On the other hand, as described above, it is important to use a quartz glass tube for an optical fiber preform as effectively as possible for cost reduction. However, in the conventional rod-in-tube method, the quartz glass tube and the core glass rod are heated and integrated while the gap between the quartz glass tube and the core glass rod is reduced, so that the airtightness of the connecting portion between the quartz glass tube and the pressure reducing device is maintained. Therefore, an O-ring was used. Since this O-ring is made of rubber or the like, its heat resistance is low, and if the distance between the welded portion of the quartz glass tube and the connecting portion of the O-ring is shortened, the heat resistance limit of the O-ring will be exceeded. In the case where the effective use length of the quartz glass tube for the base material is shortened or the effective use length of the quartz glass tube for the base material is to be secured by using the auxiliary quartz glass tube, the auxiliary quartz glass tube The length had to be significantly increased.
[0004]
In view of the current situation, the present inventors have conducted intensive research, and as a result, provided a tapered groove whose diameter increases toward the outer peripheral side in the vicinity of the end of the holding side of the quartz glass tube, and a holder is provided in the groove. Upon mating, it was found that even a large quartz glass tube can be held accurately and stably by aligning the tapered portion of the groove and the tapered portion of the holding jig by surface contact. Furthermore, the end face on the holding side of the quartz glass tube provided with the tapered groove is mirror-finished, and the end face and the end of the decompression device are connected via a heat-resistant sealing material, so that airtightness is maintained even at high temperatures. It is also found that the effective use length of the quartz glass tube for the base material can be increased, or that the auxiliary quartz glass tube can be shortened when the auxiliary quartz glass tube is used. The invention has been completed. That is,
[0005]
An object of the present invention is to provide a quartz glass tube for an optical fiber preform that can be accurately and stably held in an optical fiber preform manufacturing method, or an auxiliary quartz glass tube connected thereto.
[0006]
The present invention also provides a method of manufacturing an optical fiber preform that can increase the effective use length of an optical fiber preform quartz glass tube or shorten an auxiliary quartz glass tube, and is suitable for cost reduction. With the goal.
[0007]
[Means for Solving the Problems]
The present invention that achieves the above object is a quartz glass tube for an optical fiber preform having a tapered groove, or an auxiliary quartz glass tube connected to the quartz glass tube for an optical fiber preform, the end of the holding side thereof The present invention relates to a quartz glass tube characterized in that a tapered groove is provided in the vicinity of the portion, and a method for manufacturing an optical fiber preform using the quartz glass tube.
[0008]
The above-mentioned quartz glass tube for base material is a porous soot body (hereinafter referred to as silica) by depositing silica glass fine particles generated by flame hydrolysis of siloxane compounds such as high-purity silicon tetrachloride and organic silicon compounds in an oxyhydrogen flame. A porous soot body made of fine glass particles is formed as a "porous soot body", dehydrated and converted into a transparent glass, and the resulting quartz glass ingot is molded into a tube by mechanical grinding or the like. It is manufactured by. The auxiliary quartz glass tube connected to the quartz glass tube for a base material is a so-called dummy tube, which contains more impurities and bubbles than the quartz glass tube for the base material, and is an inexpensive quartz glass tube. is there. Although the name of the dummy tube is also given to the quartz glass tube connected to the drawer side, the dummy tube on the holding side is referred to as “auxiliary quartz glass tube” in the present invention in order to distinguish it.
[0009]
A tapered groove is provided in the vicinity of the holding side end of the auxiliary quartz glass tube or the quartz glass tube for the base material of the present invention, and is accurately and stably held by the feed mechanism of the rod-in tube device. . The taper is formed at an angle so that the diameter of the groove gradually increases. Preferably, from the processing of the quartz glass tube or the creation of a holding jig, a groove is provided so that the diameter increases toward the end of the holding side as shown in FIG. Since the taper is formed so that the diameter of the groove gradually increases, the taper part of the groove and the taper part of the holding jig can be brought into surface contact with a wider area, and the quartz glass tube can be accurately It can be fixed and securely held. The taper angle is preferably in the range of 30 to 60 °, and if the taper angle deviates from the above range, the surface contact with the holding jig becomes insufficient and the weight retention is hindered or it is difficult to accurately align the center of the circle. It becomes. This fixing makes it possible to accurately align the center of the circle between the quartz glass tube and the heating source and the center of the circle between the silica glass tube for the optical fiber preform and the optical fiber preform on the drawing side. Further, it is possible to prevent the center of the circle between the core base material and the core from being displaced, and the bending of the optical fiber base material can be eliminated. In the present invention, the vicinity of the end portion on the holding side of the quartz glass tube refers to a range near the end surface of the quartz glass tube and sufficiently withstanding the weight of the quartz glass tube when the quartz glass tube is held.
[0010]
An auxiliary groove can be provided below the tapered groove. By suspending the auxiliary holder in the auxiliary groove, the quartz glass tube does not fall even if breakage occurs in the tapered groove, and an accident or the like can be prevented. Such tapered grooves and auxiliary grooves are formed by grinding using a cylindrical grinder or the like. Further, it is preferable to perform a mirror finish on the holding side end face of the quartz glass tube because the sealing performance is improved. By connecting a heat-resistant sealing material between the end face of the quartz glass tube and the end of the decompression device and connecting to the decompression device, hermeticity is maintained even at high temperatures, and the silica glass tube for optical fiber preform is effective. The use length can be increased, or the auxiliary quartz glass tube can be shortened. Examples of the heat-resistant sealing material include carbon sheets, carbon fibers, metals, ceramics such as silicon dioxide, ceramic fibers, high siliceous glass fibers such as quartz, or composite materials combining these with other materials. It is not particularly limited as long as it has suitable properties as a sealing material by having appropriate elasticity in addition to strength, and those that are usually used industrially are used. The mirror surface treatment may be performed by polishing, and even in the case of a mirror surface treatment with low accuracy depending on the material of the heat-resistant sealing material or the degree of reduced pressure, airtightness that can be used practically can be ensured. This is because, according to the present invention, since the contact area between the quartz glass tube and the end of the decompression device and the heat-resistant sealing material can be widened, the airtightness is superior to the case of a narrow contact area such as an O-ring. Because.
[0011]
On the other hand, examples of the core glass rod for optical fiber include a quartz glass rod which is a light transmission portion and serves as an optical core portion, or a quartz glass rod having an optical cladding portion formed around it. That is, in the present invention, the “core glass rod” is a generic term for a core rod and a clad core rod. A core rod without a clad portion can be produced by a known VAD method, OVD method, or the like. As a means for producing a clad core rod, the core portion and the clad portion are once separated by a VAD method, an OVD method, or the like. And a method of jacketing a quartz glass tube around the core rod, a method of forming a clad portion around the core rod by the OVD method, and a combination of these methods.
[0012]
1 embodiment of the production method for an optical fiber preform using a quartz glass tube and the optical fiber preform for the core glass rod provided with the tapered over grooved below. That is, the groove 8 of the tapered over a quartz glass tube 1 as shown in FIG. 1 is provided, and篏合the holding jig 3 therein, and a tapered portion of the holding jig tapered portion of the groove to surface contact. On the other hand, the end surface of the holding portion of the quartz glass tube 1 is mirror-finished, and the quartz glass tube 1 and the flange portion 7 of the decompression device end portion 4 are fixed with the fastening bolts 9 through the heat-resistant sheet 6 in order to maintain airtightness. . Next, the quartz glass tube is sucked from the connecting portion 5 to the decompression means provided at the decompression device end 4 to reduce the pressure in the quartz glass tube, and the quartz glass tube and the core glass rod for base material are heated and integrated in a heating furnace. . Since the method of manufacturing the optical fiber preform of the present invention airtightness is maintained through such heat resistance sheet, available preform quartz glass tube to near the heating limit of the heat-resistant sheet, effective The use length can be increased, or the auxiliary quartz glass tube can be shortened, and the manufacturing cost of the optical fiber can be reduced. The holding jig to be used in the manufacturing method for the optical fiber preform of the present invention can bisected shown in jig and 5 for fixing across the tapered over grooved shown in FIG. 4, the tapered grooves each divided piece The jig | tool etc. which are fastened after having been matched are mentioned.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Next, examples of the present invention will be described, but the present invention is not limited thereto.
[0014]
【Example】
Example 1
High-purity silicon tetrachloride is flame-hydrolyzed in an oxyhydrogen flame to produce silica glass fine particles, which are deposited around the substrate, converted into a transparent glass, and then subjected to mechanical grinding to obtain an outer diameter of 160 mm. A 50 mm quartz glass tube for optical fiber preform was prepared. A tapered groove was ground in the vicinity of the upper end of the quartz glass tube for base material with a cylindrical grinder, and the upper end surface thereof was polished with a belt sander using # 1000 diamond paper to make a mirror surface. A core glass rod for an optical fiber preform having an outer diameter of 46 mm was inserted into the obtained quartz glass tube for an optical fiber preform, and held by a holding jig fixed to a feed mechanism of a vertical rod-in-tube apparatus. FIG. 1 is a schematic longitudinal sectional view showing a holding state of the quartz glass tube for base material. In FIG. 1, 1 is a quartz glass tube for a base material, 2 is a core glass rod for a base material, 3 is a holding jig, 4 is an end of a decompression device, 5 is a connection part to decompression means, 6 is a carbon sheet, 7 Is a flange portion at the end of the pressure reducing device, 8 is a tapered groove, and 9 is a fastening bolt. In the holding, the holding jig shown in FIG. 4 was fitted into the tapered groove 8 of the quartz glass tube for base material from the notch side, and fixed with the fastening bolt 9. At that time, a carbon sheet 6 having a thickness of 3 mm was placed between the mirror-finished surface of the end surface of the quartz glass tube for base material and the flange portion 7 at the end of the decompression device in order to maintain airtightness. The fixed quartz glass tube for base material and the core glass rod for base material were heated and stretched to be integrated while being stretched. The obtained optical fiber preform had an outer diameter of 75 mm, a bending accuracy of 0.2 mm / m, and an ellipticity of 0.5%. The ellipticity is obtained by continuously measuring the cross section while rotating the optical fiber preform in the circumferential direction to obtain the maximum value and the minimum value of the outer diameter (maximum value−minimum value) / design value × 100. This is the value obtained by the following formula. Incidentally, in the standard of the optical fiber preform, the bending accuracy is 1 mm / m or less and the ellipticity is 2% or less.
[0015]
When the temperature of the carbon sheet at the time of integration of the quartz glass tube for the base material and the core glass rod was monitored, the heat resistance limit of the used carbon sheet was obtained when the integration of the carbon sheet at the end face was performed by leaving 80 cm. The temperature rose to 650 ° C., and the quartz glass tube for base material could be effectively used leaving only 80 cm from the holding side end face.
[0016]
Comparative Example 1
In Example 1, an optical fiber preform was manufactured in the same manner as in Example 1, except that the flange portion of the tubular body and the end face of the quartz glass tube for optical fiber preform were sealed with an O-ring made of silicon rubber. When the temperature of the O-ring is monitored, the safe temperature of the O-ring reaches 250 ° C. when it is welded and integrated, leaving 190 cm from the end of the quartz glass tube for the base material. Up to a point where 190 cm was left from the holding side end face of the quartz glass tube for base material.
[0017]
Comparative Example 2
In Example 1, an optical fiber preform was manufactured in the same manner as in Example 1 except that a quartz glass tube for optical fiber provided with a groove without a taper was used as shown in FIG. The bending accuracy of the obtained optical fiber preform was 0.8 mm / m, and the ellipticity was 2.2%.
[0018]
Example 2
In the first embodiment, the holding jig shown in FIG. 5 is used instead of the holding jig shown in FIG. 4, and the auxiliary quartz glass tube is welded to the quartz glass tube for optical fiber, and the vicinity of the holding side end of the auxiliary quartz glass tube is used. Were provided with a tapered groove and an auxiliary groove at the bottom. A holding jig was fixed to the tapered groove, and an auxiliary holding tool was fixed to the auxiliary groove. A schematic cross-sectional view of this holding state is shown in FIG. In FIG. 2, 1 is a quartz glass tube for a base material, 2 is a core glass rod for a base material, 3 is a holding jig, 4 is an end of a decompression device, 5 is a connection portion to decompression means, and 6 is a plate ceramic. A composite material sandwiched between iron plate materials, 7 is a flange portion at the end of the decompression device, 8 is a tapered groove, 9 is a fastening bolt, 10 is an auxiliary quartz glass tube, 11 is an auxiliary groove, and 12 is an auxiliary holder. The quartz glass tube and the core glass rod for base material were heated and integrated in the same manner as in Example 1 to manufacture an optical fiber base material. The bending accuracy of the obtained optical fiber preform was 0.18 mm / m, and the ellipticity was 0.5%.
[0019]
【The invention's effect】
The quartz glass tube of the present invention is provided with a tapered groove at its end, and the center of the circle with the heating source or the like can be aligned by mating the tapered portion and the tapered portion of the holding jig. Accurate and stable. Furthermore, the end surface of the quartz glass tube is mirror-finished, and by placing a heat-resistant sheet there, the hermeticity inside the tube can be maintained even at high temperatures, and the effective use length of the quartz glass tube for optical fiber preforms In addition, when an auxiliary quartz glass tube is used, the quartz glass tube can be shortened, and the manufacturing cost of the optical fiber can be reduced.
[Brief description of the drawings]
FIG. 1 is a schematic longitudinal sectional view when a quartz glass tube for an optical fiber preform provided with a tapered groove of the present invention is fixed by a holding jig.
FIG. 2 is a schematic longitudinal sectional view when a quartz glass tube is fixed with the holding jig of FIG.
FIG. 3 is a schematic longitudinal sectional view when a quartz glass tube for an optical fiber preform having a non-tapered groove is fixed with a holding jig.
4 is a plan view of a holding jig according to Embodiment 1. FIG.
5 is a plan view of a holding jig according to Embodiment 2. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Quartz glass tube 2 Core glass rod for optical fiber base materials 3 Holding jig 4 Pressure-reducing device end part 5 Connection part to pressure-reducing means 6 Heat-resistant sheet 7 Flange part of pressure-reducing device end part 8 Tapered groove 9 Tightening bolt 10 Auxiliary Quartz glass tube 11 Auxiliary groove 12 Auxiliary holder

Claims (6)

A quartz glass tube used for manufacturing an optical fiber preform using a vertical rod-in-tube device in which a core glass rod for an optical fiber preform is inserted into a quartz glass tube for an optical fiber preform, and then heated and integrated. The quartz glass tube is a quartz glass tube for an optical fiber preform or an auxiliary quartz glass tube connected to the quartz glass tube for an optical fiber preform, and grinding is performed on the outer surface near the end portion on the upper holding side thereof A quartz glass tube, characterized by being provided with a tapered groove. 2. The quartz glass tube according to claim 1, wherein the taper is formed so that a diameter of the groove increases toward an end portion side of the holding side of the quartz glass tube. The quartz glass tube according to claim 2, wherein the taper angle is in the range of 30 to 60 °. The quartz glass tube according to any one of claims 1 to 3, wherein the end surface on the holding side of the quartz glass tube is mirror-finished. In the method of manufacturing an optical fiber preform using a vertical rod-in-tube apparatus in which a core glass rod for an optical fiber preform is inserted into a quartz glass tube for an optical fiber preform and heated and integrated, the quartz glass The tube is a quartz glass tube for an optical fiber preform or an auxiliary quartz glass tube connected to the quartz glass tube for an optical fiber preform, with a taper formed on the outer surface near the end on the upper holding side by grinding A method for producing a preform for an optical fiber, wherein a groove is provided, and the tapered portion of the holder of the vertical rod-in-tube device is mated and fixed to the tapered portion of the groove by surface contact. 6. The method of manufacturing an optical fiber preform according to claim 5, wherein the holding end face of the quartz glass tube is mirror-finished, and the end face and the end of the decompression device are connected via a heat resistant sheet.

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