KR100315050B1 - manufacturing method of Qurtz glass preform for optical fiber - Google Patents

Abstract

In the present invention, the gap between the core glass rod for the base material and the quartz glass tube for the base material can be reduced during the production of the quartz glass base material for the optical fiber by the rod-in-tube method. It is an object of the present invention to provide a method for producing a large-scale and high-quality quartz glass base material for optical fibers having no bubbles at the interface. The method of manufacturing includes inserting a core glass rod for an optical fiber base material into a quartz glass tube for an optical fiber base material and heating it. In the method for producing a quartz glass base material for an optical fiber, the quartz glass tube for an optical fiber base material has an average outer diameter difference of 1.0 mm or less in the longitudinal direction, an average inner diameter difference of 0.5 mm or less, and an outer diameter roundness of 0.5 mm. Hereinafter, the roundness of the inner diameter is 0.5 mm or less, and the center deviation of the mean outer diameter is 1 mm or less, and the center deviation of the mean inner diameter with respect to the center of the mean outer diameter is 1 mm or less. One will.

Description

Manufacturing method of Qurtz glass preform for optical fiber

The present invention relates to a method for producing a quartz glass base material for an optical fiber, and more particularly, to a method for manufacturing a large size quartz glass base material for heating and integrating a large sized base fiber quartz glass tube for an optical fiber and a large core fiber rod for an optical fiber base material. It is about.

In recent years, the use of optical fibers, especially single-mode optical fibers, has led to the use of a large number of optical fibers. However, as optical fibers expand their use range from long-distance trunks to general subscriber systems, more and more optical fibers are expected to be required. Mass production and low cost of optical fiber are indispensable for the expansion of such an application range. Therefore, it is the easiest way to prepare a base material for a large and long optical fiber and wiredraw it. However, in the manufacturing method of the optical fiber base material by the shaft attachment method (VAD method) or the external attachment method (DVD method), which have been put to practical use in the past, since both the core part and the clad part are made by the VAD method or the OVD method, it is intended to further increase the size and length. There is a drawback that the production cost is increased due to the relationship between raw materials, combustion gas, and equipment. In addition, in order to create a large and long base material for an optical fiber, a soot body (a porous body in which silica fine particles have been deposited, which is a silica body before projection and vitrification, is called a porous soot body) is used as a precursor of the optical fiber base material. Since the premise of making it large is to make this porous suit itself large, there is a possibility that a crack or the like may occur, or a problem such as falling of the porous suit body may occur, thereby significantly lowering productivity. As a manufacturing method of an optical fiber to solve these defects, a tube for clad parts having 80% or more of the cross-sectional area is made by a high-performance and low-cost method, and the core glass made by the clad parts and the VAD method or the OVD method, etc. Japanese Unexamined Patent Application Publication No. 7-109136 and the like have proposed a method for producing an optical fiber base material by a rod-in-tube method in which a rod is heated to be integrally welded.

In the production method described in the above publication, the inner diameter of the quartz glass tube is opened by mechanical hole drilling, followed by ultra-precision grinding by a honing machine, while the outer circumferential surface is formed by cylindrical grinding. When it becomes elliptical shape with long diameter and short diameter, or it has a lot of very small irregularities or minute cracks on the inner and outer circumferential surfaces, and it is a quartz glass tube for cladding or over cladding, and it is integrated with the core glass rod. If the welding temperature is adjusted to the short diameter part, the welding with the core glass rod on the long diameter side becomes dull, and the cosmetic glass or bubbles are generated. On the contrary, when the long diameter part is matched, the core glass rod and the inner circumference part are sufficiently welded, There was a drawback that the dimensional accuracy deteriorated due to excessive hanging. Therefore, there existed a problem of an optical fiber broken at the time of wire drawing, or the trouble of the connection of the optical fiber after wire drawing.

However, since the manufacturing method described in the above publication is easy to enlarge and lengthen, and is a manufacturing method suitable for mass production and low cost, the present inventors have diligently studied to improve the manufacturing method. The present invention has been completed by discovering that the above defects can be eliminated by the variation in the inner diameter and the roundness of the glass tube in a high precision of a constant value or less. In other words,

An object of this invention is to provide the manufacturing method of the high precision optical fiber base material which has no bubble in the welding interface of the quartz glass tube for an optical fiber base material, and a core glass rod, and there is no deviation of a center of gravity.

Moreover, an object of this invention is to provide the manufacturing method of the large sized optical fiber base material suitable for mass production and low cost.

In the present invention achieving the above object, in the method of manufacturing a quartz glass base material for an optical fiber in which a core glass rod for an optical fiber base material is inserted into a quartz glass tube for an optical fiber base material and welded integrally, the quartz glass tube for an optical fiber base material is in a longitudinal direction thereof. The average outer diameter difference is 1.0 mm or less, the average inner diameter difference is 0.5 mm or less, the outer diameter roundness is 0.5 mm or less, and the inner diameter roundness is 0.5 mm or less. It relates to a method for producing a quartz glass base material for an optical fiber, wherein the center-of-center deviation of the average inner diameter is 1 mm or less.

As mentioned above, the manufacturing method of this invention uses the method of manufacturing the optical fiber quartz glass base material by what is called rod-in-tube method which inserts the core glass rod for optical fiber base material into the quartz glass tube for optical fiber base material, and welds together. The base glass quartz glass tube has an average outer diameter difference of 1.0 mm or less in its longitudinal direction, an average inner diameter difference of 0.5 mm or less, an outer diameter roundness of 0.5 mm or less, an inner diameter roundness of 0.5 mm or less, and an average outer diameter deviation of 1 mm or less. , The center deviation of the mean inner diameter is less than or equal to 1 mm from the center of the mean outer diameter If the quartz glass tube is outside the numerical range, the inner and outer circumferences of the core glass rod and the quartz glass tube are not evenly heated, and the inner circumferential surface of the core glass rod is in contact with the quartz glass tube when the core glass rod is inserted to damage the inner circumferential surface. This causes inconvenience such as the presence of a. In addition, the gap between the core glass rod and the quartz glass tube cannot be reduced, which makes it difficult to manufacture a quartz glass base material for optical fibers with high accuracy.

The average outer diameter difference is a quartz glass tube of a predetermined length, and the outer diameter of the circumference is determined by measuring the outer diameter of the tube by a laser type external diameter measuring instrument at 360 points of 4 points or more at intervals of 50 to 100 mm, and averaging them. The average inner diameter difference is a pipe thickness measured by a laser thickness meter at 360 points of 4 points or more at intervals of 50 to 100 mm in the same manner as described above, and calculated on the circumference by the calculation with the outer diameter. It is the value obtained by calculating the inner diameter and averaging them. Further, the roundness is measured by measuring the outer diameter and the thickness of the tube by a laser type diameter gauge and a thickness gauge at 360 points of 4 points or more at intervals of 50 to 100 mm for a quartz glass tube of a predetermined length. Calculate the maximum, minimum, and average values of the outer and inner diameters on the circumference thereof, and determine the maximum value of their [maximum outer diameter (inner diameter)-average outer diameter (inner diameter) or [average outer diameter (inner diameter)-minimum outer diameter (inner diameter)]. The deviation of the center of gravity is based on the mean center diameter of the end face of the quartz glass tube and the plane center of the mean inner diameter. The deviation from the axis of the straightening in the longitudinal direction.

The high-precision quartz glass tube for optical fibers is a cylindrical grinding device provided with diamond abrasive grains. The outer circumferential surface of a cylindrical or cylindrical quartz glass ingot is first ground, and then polished by a polishing apparatus to an outer diameter. The center of gravity of this outer diameter is obtained, and it is manufactured by opening with a core drill perforation device equipped with diamond abrasive grains according to the center of gravity, and polishing by a polishing apparatus equipped with cerium oxide abrasive grains. Preferably, the polished quartz glass tube is further heated and melted so as to have a mirror surface having a maximum roughness Rmax of 1 or less on the inner and outer surfaces. Since the outer circumferential surface is formed with high precision as described above, even when there are small irregularities on the outer surface when measuring the outer diameter by the laser measuring instrument, the outer circumferential surface can be accurately measured and the inner circumferential surface with high precision can be ground. In forming the inner peripheral surface of the quartz glass tube, a method of press-fitting a carbon drill under heating may be used. This method is particularly suitable for the grinding of the inner circumferential surface of a large quartz glass tube, and by this grinding, the inner circumferential surface becomes a mirror surface, and polishing can be omitted.

As a method for producing a cylindrical or cylindrical quartz glass ingot for forming a quartz glass tube used in the present invention, silica fine particles produced by flame hydrolysis of siloxane compounds such as silicon tetrachloride and organosilicon compounds in a hydrogen oxyhydrogen salt are deposited. And a Bernoullis method using an oxyhydrogen flame, for example, a method of dehydration, projection vitrification, or crystals naturally produced to be pulverized and purified by chemical treatment.

On the other hand, as a core glass rod for optical fibers, a quartz glass rod or the quartz glass rod in which the optical clad part was formed in the circumference | surroundings of light is mentioned. That is, in the present invention, "core glass rod" refers to the core rod and the clad core rod. The core rod which does not have a clad part can be formed by a well-known VAD method, an OVD method, etc. Moreover, as a means of producing a cladding core rod, it is a method of jacketing a quartz glass tube to a core rod, and around a core rod. The method of forming a clad part by OVD method etc. is mentioned.

In the production of an optical fiber glass base material using the optical fiber base material core glass rod and the optical fiber base material quartz glass tube, the core glass rod for base material is carefully inserted in the quartz glass tube for base material so as not to come into contact with the inner circumferential surface of the core fiber rod. The centers of the glass rod and the quartz glass tube are fixed to each other, and preferably, both ends are connected to the dummy quartz material, and the bends and distortions caused by the connecting process are corrected while rotating the whole, and the bottom is inserted from the top of the vertical electric furnace. The method of integrally welding by heating to a belt shape at the temperature of 1900-2800 degreeC sequentially is employ | adopted. In particular, in the production of a large-scale optical fiber base material, it is preferable to perform welding integrally while stretching. Incidentally, heating in the form of a belt is also referred to as so-called john melt, and refers to heating in which the heating zone gradually moves.

Next, although an Example of this invention is described, this invention is not limited at all.

(Example 1)

Using the VAD method, silicon tetrachloride was evaporated, flame hydrolyzed in an oxyhydrogen flame, and silica glass fine particles were deposited on a rotating quartz glass rod to prepare a porous suit body. Into the porous soot body into an electric furnace, considering the conditions such as the refractive index of the core glass rod, and He, Cl ₂ to vitrification thermal dehydration to 1100 ℃ by the mixed gas, and still transparent in the He atmosphere at 1600 ℃ cylindrical quartz A glass ingot was obtained. Both ends of the cylindrical quartz glass ingot are cut, the outer periphery of which is precisely ground to a predetermined size by a cylindrical grinding device equipped with diamond abrasive grains, and then polished by a cerium oxide polishing device, and subjected to dimensional measurement by a laser outside diameter measuring device. , Saved the center of outer diameter. The hole is drilled by a core drill perforator equipped with diamond abrasive grains in accordance with the original center, polished by a precision honing machine equipped with cerium oxide abrasive grains, etched with hydrofluoric acid, washed with pure water, and dried. Was performed to prepare a quartz glass tube. The dimensions of the obtained quartz glass tube were measured by a laser outer diameter gauge and a thickness gauge at a distance of 50 mm. The length was 1000 mm, the outer diameter was 60 mm, the average difference in the radial direction was 0.4 mm, and the roundness was 0.08 mm. , The inner diameter is 20mm, the average inner diameter difference in the longitudinal direction is 0.02mm, the roundness is 0.05mm at the maximum, the deviation from the center of the mean outer diameter is 0.1mm at the maximum, and the circle of the average inner diameter with respect to the center of the outer diameter The deviation of the center was at most 0.1 mm.

On the other hand, by the VAD method, a core rod for the cladding optical fiber base material having a refractive index difference (Δn) of the core and the clad was 0.343%, and the outer diameter was adjusted to 19 mm with respect to the inner diameter of the quartz glass tube for the optical fiber base, and was 2000 ° C. It was heated and stretched by the vertical type electric furnace of. Carefully insert this core glass rod into the quartz glass tube so that it does not come into contact with the inner circumferential surface of the core glass rod, and fix the core glass rod and the center of each circle of the quartz glass tube, and fix both ends to a dummy tube made of quartz glass. The substrate was placed from the upper side of the vertical electric furnace at 0 ° C., and the lower end was welded. Then, the inside of the quartz glass tube was decompressed by a vacuum pump, sequentially heated to a belt shape, and integrally welded to prepare a base material for the optical fiber. The obtained base material was measured by a laser outer diameter gauge at an interval of 50 mm, and it was ± 0.2 mm or less with respect to the set outer diameter. In addition, when the quartz glass base material for the optical fiber was measured by a preform analyzer, no variation in the center of gravity was seen.

(Example 2)

After crushing naturally produced crystals to adjust the particle size, a cylindrical natural quartz glass ingot was prepared by the Bernoulli method with an oxyhydrogen salt using a crystal powder purified by chemical treatment. About the obtained cylindrical quartz glass ingot, the quartz glass tube for an optical fiber base material was produced similarly to Example 1, The length is 2000 mm, the outer diameter is 120 mm, the average outer-diameter difference with respect to the longitudinal direction is 0.3 mm, and roundness is the maximum. 0.15mm, inner diameter is 60mm, average inner diameter difference in the longitudinal direction is 0.02mm, roundness is maximum 0.03mm, deviation from the center of the mean outer diameter is 0.1mm at the maximum, mean inner diameter to the center of the center The maximum deviation of the center of gravity was 0.2 mm.

A quartz glass for optical fibers was inserted into the quartz glass tube in the same manner as in Example 1, and a core glass rod whose outer diameter was adjusted to 59 mm with respect to the inner diameter of the quartz glass tube was inserted so as not to contact the inner circumferential surface thereof. The base material was manufactured. The outer circumference of the obtained base material was measured at 50 mm intervals by a laser outer diameter measuring instrument, and the result was less than ± 0.2 mm with respect to the set outer diameter. Moreover, when the said quartz glass base material for optical fibers was measured with the preform analyzer, the dispersion | variation of the center of gravity was not seen.

(Example 3)

The porous soot body was prepared by the OVD method, placed in an electric furnace, and dehydrated at 1100 ° C. in a furnace of N ₂ , Cl ₂ mixed gas in consideration of the conditions such as the refractive index of the core glass rod, and then kept in a vacuum atmosphere. It heated to 1600 degreeC and made the cylindrical quartz glass ingot. A quartz glass tube was manufactured in the same manner as in Example 1 from the obtained cylindrical quartz glass ingot. The obtained quartz glass tube had a length of 3500 mm, an outer diameter of 200 mm, an average outer diameter difference of 0.8 mm in the longitudinal direction of the quartz glass tube, a maximum roundness of 0.09 mm, an inner diameter of 40 mm, and an average of the quartz glass tube in the longitudinal direction. The inner diameter difference was 0.12 mm, the roundness was 0.1 mm at the maximum, the deviation from the center of the mean outer diameter was 0.6 mm at the maximum, and the deviation of the center of the mean inner diameter with respect to the center of the mean outer diameter was 0.7 mm at the maximum.

By the method similar to Example 1, it extended | stretched with the vertical type electric furnace of 2000 degreeC with the outer diameter to 39 mm with respect to the inner diameter of the quartz glass tube, and created the core glass rod. The core glass rod was inserted in the same manner as in Example 1 so as not to contact the inner circumferential surface of the tube, and the core glass rod and the quartz glass tube were fitted in the center of each circle, and both ends were connected to the dummy tube made of quartz glass. The quartz glass base material for the optical fiber was produced by placing the lower end part from the upper part from the lower end part to the upper part of the vertical electric furnace and welding the lower part part, and then decompressing the inside of the quartz glass tube by a vacuum pump, and heating it in a belt shape sequentially while stretching. did. The obtained base material was measured with respect to the outer periphery at 50 mm intervals by a laser outer diameter measuring instrument, and it was less than +/- 0.2 mm with respect to the set outer diameter. Moreover, when the said quartz glass base material for optical fibers was measured with the preform analyzer, the dispersion | variation of the center of gravity was not seen.

(Example 4)

After producing a cylindrical quartz glass ingot by the OVD method similar to that of the manufacture of Example 3, the both ends thereof were cut, and the outer periphery thereof was accurately ground to a predetermined dimension by a cylindrical grinding device equipped with diamond abrasive grains, followed by cerium oxide. Grinding with a polishing device and dimensional measurement with a laser outside diameter measuring machine to determine the center of the outer diameter, and the hole is drilled by a core drill drilling device equipped with diamond grains in accordance with the center of gravity, and fine honing with cerium oxide grains After polishing by a processing apparatus, a quartz glass tube was placed in a vertical electric furnace heated to 2000 ° C., and the surface was subjected to melt mirroring treatment while flowing inert gas therein. Subsequently, hydrofluoric acid etching, washing with pure water, and drying were used to obtain a quartz glass tube having a surface roughness Rmaqx of 0.3 m on the inner circumferential surface and a 0.35 µm surface roughness Rmax on the outer circumferential surface. Dimensions of the quartz glass tube were measured at intervals of 50 mm by a laser outer diameter gauge and a thickness gauge. The length was 3500 mm, the outer diameter was 200 mm, and the average outer diameter difference in the longitudinal direction of the quartz glass tube was 0.5 mm, and the roundness was maximum. 0.05mm, inner diameter is 40mm, the average inner diameter difference in the longitudinal direction of the quartz glass tube is 0.1mm, the roundness is 0.07mm at the maximum, and the deviation of the center of the outer diameter is 0.3mm at the maximum, The maximum deviation of the center of gravity of the mean inner diameter was 0.4 mm. In addition, the maximum roughness Rmax is the value measured with the contact simplified illuminometer (Tokyo Seimitsu Co., Ltd., Surfcom 300B) based on the definition of Japanese Industrial Standard (JIS) B0601.

In the quartz glass tube, a core glass rod having an outer diameter of 39 mm with respect to the inner diameter of the quartz glass tube was inserted so as not to contact the inner circumferential surface of the quartz glass tube, and the belt was sequentially stretched as in Example 3. A quartz glass base material for an optical fiber was prepared by heating to a shape and integrating welding. The obtained base material was measured at 50 mm intervals by a laser outer diameter measuring instrument, and found to be ± 0.2 mm or less with respect to the set outer diameter. Moreover, when the said quartz glass base material for optical fibers was measured with the preform analyzer, the dispersion | variation of the center of gravity was not seen.

The quartz glass base material for the optical fiber obtained by the manufacturing method of the present invention uses a quartz glass tube with high dimensional accuracy, so that the core glass rod and the quartz in the base material at the time of manufacturing the quartz glass base material for the optical fiber by the rod in tube method. It is a high-precision and high-quality quartz glass base material for optical fibers, which can reduce the gap with the glass tube and has no bubble in the adhesion interface between the quartz glass tube for the base material and the core glass rod. By using the quartz glass base material for the optical fiber, a high quality optical fiber can be produced with high productivity and low cost.

Claims (4)

In the manufacturing method of the quartz glass base material for optical fibers in which the core glass rod for an optical fiber base material is inserted in the quartz glass tube for an optical fiber base material, and the welding is integrated, the said quartz glass tube for an optical fiber base material has an average outer diameter difference of 1.0 mm or less in the longitudinal direction, and averages The inner diameter difference is 0.5 mm or less, the outer diameter roundness is 0.5 mm or less, and the inner diameter roundness is 0.5 mm or less, and the center deviation of the mean outer diameter is 1 mm or less, and the mean center diameter deviation of the mean inner diameter is 1 mm Method for producing a quartz glass base material for an optical fiber, characterized in that the following. The method of manufacturing a quartz glass base material for an optical fiber according to claim 1, wherein the quartz glass tube for an optical fiber base material is a high purity synthetic quartz glass tube or a natural quartz glass tube. The method for producing a quartz glass base material for an optical fiber according to claim 1 or 2, wherein the quartz glass tube for an optical fiber base material is a quartz glass tube having an inner surface which is heated and melted and mirrored. The method of manufacturing a quartz glass base material for an optical fiber according to claim 3, wherein the maximum roughness Rmax of the inner and outer surfaces of the quartz glass tube is 1 µm or less.