KR101117778B1 - Method for Producing Optical Fiber and Preform - Google Patents

Abstract

In the method of manufacturing the optical fiber and the preform of the present invention, the composite base material formed by inserting the core rod into the clad quartz glass tube is disposed in the vertical direction and melted by heating the lower end thereof, thereby integrating the welding of the core rod and the quartz glass tube. In the method of starting the stretching together, the lower end of the quartz glass tube has a circular outer circumference and an inner circumference and a tapered shape whose outer diameter is reduced toward the tip as a whole. The shim deviation of the linear motion part of the glass tube is 1% or less of the outer diameter of the linear motion part, and a quartz glass tube having a maximum thickness and a minimum thickness difference of 1.5% or less of the average thickness at each circular cut surface is used. It is characterized in that the core is fixed.

Quartz, Glass Tube, Fiber Optic, Taper, Core Rod

Description

Manufacturing method of optical fiber and preform {Method for Producing Optical Fiber and Preform}

The present invention relates to a method for producing an optical fiber and a preform by the rod in tube method.

Quartz containing only the core or a part of the clad by VAD method (weather axis method) or MCVD method (internal method) which is the main manufacturing method of a quartz glass optical fiber In the rod-in-tube method in which a glass rod (core rod) is made, and this is inserted into a quartz glass tube to perform heat melting integration, the quartz glass tube is equally circumferentially aligned with the core rod in order to reduce the eccentricity of the core. It is important to make a fusion.

On the other hand, a method of manufacturing an optical fiber at low cost by a rod in tube method using a large tube is disclosed in Japanese Patent Application Laid-Open No. 5-312710. In this way, a large-size quartz glass tube with a core rod inserted into the upper part of a heating furnace is elongated while integrating the hot melt, and a preform is obtained from the lower part of the heating furnace, or the method is performed to achieve good fiber (optical fiberization) while integrating the hot melt. In the present invention, it is preferable to minimize the loss and processing of the quartz glass tube, which increases in cost with the enlargement of the quartz glass tube. Specifically, the core rod is inserted into the quartz glass tube which has only undergone simple cutting, the lower end of the quartz glass tube is held in the heating furnace, and the tip ends wait for the melt to fall (leading), and at the same time the stretching is performed ( Iii) or start an election.

However, when a quartz glass tube having a lower end shape that is simply cut is used, there is a problem that suppression of ECC is difficult.

As disclosed in Japanese Patent Laid-Open No. 63-2826, when the clearance (the difference between the inner diameter of the quartz glass tube and the outer diameter of the core rod) is reduced, the ECC is improved, but the clearance allowed by the tightening of the ECC standard is further reduced. The size and length of the base material make it difficult to insert the core rod without contacting the quartz glass tube.

If the core rod contacts the inner wall of the quartz glass tube when the core rod is inserted, scratches occur on the contact portion, causing bubbles in the weld interface, which causes fiber diameter fluctuations and breakage frequency deterioration.

As for the method of lowering the ECC by uniformly welding the quartz glass tube in the circumferential direction, for example, as shown in Japanese Patent Laid-Open No. 57-118042, the core rod is fixed to the center of the quartz glass tube by a spacer, A partial welding method has been proposed as in Japanese Patent Laid-Open No. 62-59546.

However, since the inner surface of the quartz glass tube is contaminated or roughened by heat, bubbles are generated in the welding interface between the quartz glass tube and the core rod and the fiber diameter fluctuations or the frequency of breakage are deteriorated. do.

Japanese Patent Laid-Open No. 62-59547 discloses a method in which the cores of the quartz glass tube and the core rod are aligned only on the welding end side and the core rod of the welding start end is not brought into contact. This method is easy to carry out and the cost can be reduced since the core rod is inserted only in the clean quartz glass tube and then the core rod is fixed only to the upper part which is not subjected to heat. However, even if the quartz glass tube and the core rod cores were fixed in this manner, there was no ECC suppression effect when a quartz glass tube having a lower cut shape was used.

As a result of investigating the cause of deterioration of ECC, as shown in FIG. 1, when the lead-out lower end of the quartz glass tube 1 melts and starts to increase due to gravity, it is inclined, and an unevenness occurs in the upper thickness and the depth of the inner diameter is shifted. It turned out.

Even if the core of the quartz glass tube 1 and the core of the core rod 2 are matched in advance, if the lower end molten portion of the quartz glass tube is displaced as shown in Fig. 1, welding starts with the core of the quartz glass tube and the core rod displaced. The difference in the thickness of the quartz glass tube around the core rod is generated, which causes deterioration of ECC. In addition, in FIG. 1, the code | symbol 1a, 2a shows the shape before melt deformation of the quartz glass tube 1 and the core rod 2. As shown in FIG.

When the lower surface starts to incline at least at the start of melting, the upper thickness of the portion where the lower surface is lowered becomes thinner than other portions, and the force supporting the lower weight is weakened. In addition, the thinner thickness makes it easier to conduct heat in the furnace, so the viscosity is lowered, and the force supporting the weight of the lower portion is weaker than that of other portions, and the lower side of the lower surface is further lowered. That is, this phenomenon has inherent instability toward the more inclined direction once the bottom surface starts to tilt, and thus improves the heat balance of the furnace, the dimensional accuracy of each part, the ellipse of the quartz glass tube, It is difficult to prevent disturbances such as thickness deviation, right angle of the lower end cut surface, seam between the quartz glass tube and the heating furnace, and vibration.

With respect to such a phenomenon, the present invention inserts a composite base material in which a core rod is inserted into a quartz glass tube from the upper part of the heating furnace, draws it while integrating the hot melt, and obtains a preform at the lower part of the heating furnace, or further performs heating or melting. In the method of manufacturing the optical fiber by integrating it at the same time while integrating, the optical fiber and the preform which can obtain a good ECC while providing a wide clearance which reduces the difficulty in inserting the core rod by minimizing the lower end of the quartz glass tube. An object of the present invention is to provide a method for producing the same.

The said objective is following 1.-12. It can be achieved by the configuration of either.

1. The core rod containing only the core or a part of the clad is inserted into the quartz glass tube for cladding, and the composite base material formed is vertically arranged and melted by heating the lower end thereof, and the core rod and the quartz glass tube are heated. In the optical fiber manufacturing method which starts extending | stretching with the unification of welding, the lower end part containing the part which melt | dissolves first of a quartz glass tube is a taper whose outer periphery and inner periphery are substantially circular shape, and the outer diameter is reduced toward the front end as a whole. In all circular cut surfaces that are shaped and have a circular center of average outer diameter at each circular cut face of the tapered portion and the linear motion portion of the linear motion portion of the quartz glass tube is 1% or less of the outer diameter of the quartz glass tube straight portion, and each tapered portion includes a tapered portion. The quartz glass tube has a shape in which the difference between the maximum thickness and the minimum thickness in each section is 1.5% or less of the average thickness. And a core of at least the lower end of the quartz glass tube and the core rod is fixed to each other.

2. The internal diameter of the tapered portion of the quartz glass tube to be used is also reduced in shape toward the tip.

3. The tapered tip of the quartz glass tube to be used is sealed, The manufacturing method of the optical fiber of said 1. or 2. characterized by the above-mentioned.

4. The taper-shaped tip of the quartz glass tube to be used is opened, The manufacturing method of the optical fiber of said 1. or 2. characterized by the above-mentioned.

5. The outer diameter or the inner diameter of the tapered portion of the quartz glass tube to be used, or the diameter change of both of them is stepped, or part of the stepped, characterized in that 1.-4. The manufacturing method of the optical fiber in any one of Claims.

6. The method for producing an optical fiber according to any one of items 1 to 5 above, wherein the core rod and the quartz glass tube are integrally melted and simultaneously stretched to a desired optical fiber diameter to directly obtain an optical fiber.

7. Fabrication of the optical fiber according to any one of 1 to 5 above, wherein the core rod and the quartz glass tube are stretched and melted at the same time to form a preform, and the optical fiber is obtained by a precuring machine from the preform. Way.

8. The core rod including only the core or a part of the clad is inserted into the quartz glass tube for cladding to dispose the composite base material formed in the vertical direction and melted by heating the lower end thereof, thereby integrating the welding of the core rod and the quartz glass tube. In the method for manufacturing a preform for an optical fiber which starts drawing together with the tape, the lower end portion including the first molten portion of the quartz glass tube is substantially tapered in its outer circumference and inner circumference and whose outer diameter is reduced toward the tip as a whole. In all circular cut surfaces including the tapered portion, the center of the outer diameter of the average outer diameter at each circular cut face of the tapered portion, and the amount of seam deviation of the linear motion portion of the quartz glass tube is 1% or less of the outer diameter of the quartz glass tube straight portion, Quartz oil having a shape where the difference between the maximum thickness and the minimum thickness in each cross section is 1.5% or less of the average thickness Using a tube, and further method of manufacturing a preform for optical fibers, characterized in that keep at least a lower end fixed to match plant of the quartz glass tube and the core rod.

9. The internal diameter of the tapered portion of the quartz glass tube to be used is also reduced toward the tip of the quartz glass tube.

10. The taper-shaped tip of the quartz glass tube used is sealed, The manufacturing method of the optical fiber preform of said 8. or 9. characterized by the above-mentioned.

11. The taper-shaped tip of the quartz glass tube used is opened, The manufacturing method of the preform for optical fibers of said 8. or 9. characterized by the above-mentioned.

12. The manufacturing method of the preform for optical fibers in any one of said 8. to 11 characterized by the step shape of a taper-shaped part of the quartz glass tube used, or the diameter change of both of them, being stepped, or partly stepped.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows an example of the melting start state of a quartz glass tube at the time of manufacturing an optical fiber by the manufacturing method of a conventional optical fiber.

(A), (b), (c) is a figure which shows the example which processed the front end of the quartz glass tube in accordance with embodiment of this invention.

3 is a view showing another example in which the tip of the quartz glass tube is processed according to the embodiment of the present invention.

4 is a view showing another example in which the tip of the quartz glass tube is processed according to the embodiment of the present invention.

FIG. 5 is a diagram for explaining the amount of seam shift between the center of the center of the average outer diameter at each circular cut surface of the tapered portion and the linear motion portion of the quartz glass tube.

FIG. 6 is a diagram for explaining the difference between the maximum thickness and the minimum thickness for each cross section in all circular cut surfaces including tapered portions of quartz glass tubes.

FIG. 7: is explanatory drawing for demonstrating the aspect at the time of manufacturing a preform which concerns on embodiment of this invention. FIG.

In the manufacturing method of the optical fiber and the preform of the present invention, in the manufacture of actual predecessors or preforms, a composite base material formed by inserting a core rod containing only a core or a part of a clad in a quartz glass tube for cladding is arranged in a vertical direction. And the conventional one of manufacturing the optical fiber and the preform which melt | dissolve by heating the lower end part, and start extending | stretching with integral welding of a core rod and a quartz glass tube can be used. As a manufacturing method of a quartz glass tube, what is disclosed by Unexamined-Japanese-Patent No. 07-109141 which the applicant of this application is one of the applicant can be used.

In the present invention, the lower end portion including the first molten portion of the quartz glass tube is substantially tapered in its outer circumference and inner circumference, and its outer diameter is reduced toward its tip, and the average at each circular cut surface of the taper. A quartz glass tube having a shape in which the amount of misalignment between the circle center of the outer diameter and the linear motion portion of the quartz glass tube is 1% or less of the outer diameter of the quartz glass tube direct movement portion is used.

If the amount of seam shift exceeds the value, ECC reduction, which is the intended purpose of the present invention, cannot be achieved. The smaller the amount of seam shifting is, the better it is, but it may be less than or equal to the straightness of the quartz tube itself.

In practice, as shown in Fig. 2A, the outer periphery of the quartz glass tube is preferably machined into a tapered shape to form a tapered shape. This processing can be easily performed by an NC lathe or the like. 2, the code | symbol 2 represents a core rod.

Moreover, you may seal in a taper shape as shown in FIG.2 (b) by heat processing. This process can be easily produced by setting an elongated quartz glass tube on a glass shelf, melting the processed portion by heat of a burner or an electric furnace, and melting. Also in this case, since the core of a tapered sealing part needs to be made so that it may not shift with the core of a quartz glass tube, it is good to use a graphite coat etc. auxiliary.

In the case of sealing, in order to facilitate the cleaning of the inner surface of the quartz glass tube, an opening may be provided at the tip as shown in Fig. 2C. 2 (b) and 2 (c) are examples of shapes in which the inner diameter of the tapered portion of the quartz glass tube is reduced toward the tip.

If the inclined surface is difficult to process, even if the tapered portion is ground in fine steps as shown in Fig. 3, there is no problem in the effect of the present invention such as reduction of ECC. Adverse effects and the like, and preferably smooth.

In addition, depending on the processing method, there is no problem even if a straight portion as shown in FIG. 4 remains at the tip portion. 3 and 4, reference numeral 10 denotes a quartz glass tube, reference numeral 12 denotes a foil-shaped grindstone, and reference numeral 14 denotes an aspect of the movement of the grindstone.

In the case of melt processing, there is no problem in the effect of the present invention even if a tapered shape of graphite is used or a quartz glass tube or a quartz glass rod that is thinned to the tip of the tapered shape is not a problem. The method which is not lifted is preferable.

The amount of seam shift between the circle center of the average outer diameter at each circular cut face of the tapered portion and the linear motion portion of the quartz glass tube is defined as follows.

As shown in the right drawing of Fig. 5, for example, three centers (at least two places) a, b and c of the quartz glass tube linear part are obtained, and the center of the garden having the average outer diameter as the outer diameter is obtained for each cross section. Let it be the center of each cross section. If the cross section is two places, the straight line passing through the centers of the two cross sections is regarded as the center line 30 of the quartz glass tube direct moving portion. If the cross section is three places or more as shown in the drawing, a straight line with a minimum difference between the centers of all the cross sections is obtained by using the least square method or the like, and this may be the center line 30. In the tapered shape, for example, at several cross sections as shown in d1 to d3 in FIG. 5, the center of each cross section is obtained by the same method, and the amount of deviation from the centerline 30 of the quartz glass tube direct drive section obtained above is calculated. This shift amount is expressed as a percentage of the average outer diameter of the quartz glass tube straight part, and the maximum value is referred to as the shift amount.

What is necessary is just to increase and decrease the number of actual measurement cross sections, the number of measurements in each measurement cross section, etc. so that the required precision may be acquired according to a processing precision or a measurement precision.

Meanwhile, in the right view of FIG. 5, reference numeral 32 denotes an actual outer diameter shape, for example, in a cross section d1 of the left figure, reference numeral 34 denotes a garden having an average outer diameter obtained from the external diameter shape 32, and reference numeral 36 denotes a garden 34. The center and reference numeral 38 each indicate an amount of shift in the core from the center line 30 of the quartz glass tube direct moving portion in this cross section.

In the present invention, in all the circular cut surfaces including the tapered portions of the quartz glass tube to be used, the difference between the maximum thickness and the minimum thickness in each cross section must be 1.5% or less of the average thickness.

If the difference between the maximum thickness and the minimum thickness in each cross section exceeds the above value, it may not be possible to achieve the intended purpose of the present invention, which is ECC reduction as described above.

In all circular cut surfaces including the tapered portion of the quartz glass tube, the difference between the maximum thickness and the minimum thickness in each cross section is obtained by subtracting the minimum thickness Mn from the maximum thickness Mx as shown in FIG. 6.

As described above, the outer diameter or the inner diameter of the tapered portion of the quartz glass tube to be used or the diameter change of both thereof may be stepped or partly stepped.

 In the present invention, in the case of manufacturing a direct optical fiber, at the same time as the integral melting of the core rod and the quartz glass tube, it may be stretched to the desired optical fiber diameter to obtain a direct optical fiber, or the melting of the core rod and the quartz glass tube is integrated. The preform may be drawn at the same time as a single piece to obtain a preform, and optical fibers may be obtained using a preselected machine from the preform.

According to the optical fiber manufacturing method of this invention, ECC of 0.2 micrometer or less can be achieved even if it uses the core rod of the outer diameter whose clearance is about 4 mm-20 mm to the quartz glass tube of outer diameter 100-250 mm and inner diameter 40-70 mm. .

In the case of the base material of this size, it is difficult to achieve an ECC of 0.2 µm or less unless the clearance is set to 4 mm or less, and it is difficult to prevent the core rod from contacting the inner surface of the quartz glass tube when the core rod is inserted. .

Japanese Unexamined Patent Application Publication No. 2003-327440 relates to the stretching of the quartz glass tube and the core rod simultaneously by thinning the tip of the optical fiber base material. In addition, Japanese Patent Laid-Open No. 2002-80238 relating to a preform defines the shape in the longitudinal direction. However, this invention aims at reducing the start loss and the loss time, and the object is completely different from the present invention.

This invention aims at reducing ECC by taper shape, and the dimensional precision of the taper-shaped part circumferential direction is important.

In addition, the method of providing a large number of portions that are not melt-deformed at the tip portion, that is, when the upper portion is sufficiently melt-started at the tip portion, reduces the inclination effect of the melt-deformed portion at the lower end, and the tip portion can be processed as in the present invention. There is no need. However, since the loss of the quartz glass tube in the portion of the distal end portion that is not melted is increased, the cost increases, and the waste quartz glass also increases.

In addition, if the tip of the core rod is brought into contact with the inner diameter of the tapered portion having a reduced inner diameter in advance, the ECC is improved regardless of the circumferential dimensional accuracy of the tapered portion, but this method is substantially fixed at the distal end. It is the same as the conventional method.

Moreover, in this method, it is difficult to adjust the lengths of the core rod and the quartz glass tube, and the quartz glass powder generated by the tip of the core rod rubbing the inner wall of the quartz glass tube is blown upwards, and thus the welding interface after the clasps is formed. It causes bubbles and increases the fiber diameter variation and the frequency of breaking the fiber.

In the case of using the present invention, the cores of the quartz glass tube and the core rod need to be precisely aligned at least at the lower end portion, but there is little influence even if the cores are properly aligned except at the lower end portion.

(Example 1)

The lower end of the quartz glass tube having an outer diameter of 180 mm and an inner diameter of 52 mm was subjected to mechanical grinding in a shape where the tip was thin at an angle of 40 ° with respect to the outer surface.

The deviation of the core of the tapered portion after grinding and the core of the quartz glass tube was 0.5% of the outer diameter in all cross sections, and the difference between the maximum thickness and the minimum thickness in each cross section of the tapered portion was 0.8% of the average thickness. A core rod having an outer diameter of 40 mm made by the VAD method was inserted therein.

The clearance between the core rod and the quartz glass tube was 12 mm (one 6 mm), and when the quartz glass tube was inserted into the core rod, the outer surface of the core rod could be inserted without rubbing on the inner surface of the quartz glass tube.

After the insertion, the core rod 2 and the core of the quartz glass tube were correctly aligned as shown in FIG. 7 and fixed at the two upper portions 40a and 40b of the quartz glass tube 1 by the metal jig 40.

In Fig. 7, the lower end of the composite base material was held in the electric furnace, and the lower end was allowed to melt, and the lead was stretched out and stretched simultaneously with the clarity of the quartz glass tube and the core rod to obtain a preform having an outer diameter of 90 mm. When the optical fiber of 125 micrometers of outer diameters was produced by the preselection machine in this preform, ECC was 0.14 micrometers and was a favorable value.

(Example 2)

The lower end of the quartz glass tube having an outer diameter of 200 mm and an inner diameter of 50 mm was melted using an oxyhydrogen burner, and sealing was performed in a tapered shape.

The gap between the core of the tapered portion and the quartz glass tube after encapsulation was 0.9% of the outer diameter in all sections, and the difference between the maximum thickness and the minimum thickness in all the sections except the blocked portion of the tapered portion was 1.3% of the average thickness. .

A core rod having an outer diameter of 35 mm made by the VAD method was inserted therein. The clearance between the core rod and the quartz glass tube was 15 mm (7.5 mm on one side). When the quartz glass tube was inserted into the core rod, the outer surface of the core rod could be inserted without touching the inner surface of the quartz glass tube. As in Example 1, the core rod and the core of the quartz glass tube are precisely aligned and fixed at the two upper portions of the quartz glass tube, the lower end of the quartz glass tube is kept in the electric furnace, and the lead is waited for melting. Simultaneous stretching was performed with the laps of the rod to directly manufacture an optical fiber having an outer diameter of 125 µm. The ECC of the obtained optical fiber was a good value of 0.19 m.

(Example 3)

The lower end of the quartz glass tube having an outer diameter of 160 mm and an inner diameter of 50 mm was melted using an oxyhydrogen burner, and sealing was performed in a tapered shape. Furthermore, this tip was cut so that a hole having a diameter of 10 mm could be drilled and used as a water draining hole during the cleaning of the quartz glass tube.

The deviation of the core of the tapered portion after grinding and the core of the quartz glass tube was 0.5% of the outer diameter in all cross sections, and the difference between the maximum thickness and the minimum thickness in each cross section of the tapered portion was 0.8% of the average thickness.

A core rod having an outer diameter of 35 mm made by the VAD method was inserted therein. The clearance between the core rod and the quartz glass tube was 15 mm (7.5 mm on one side). When the quartz glass tube was inserted into the core rod, the outer surface of the core rod could be inserted without touching the inner surface of the quartz glass tube. As in Example 1, the core of the core rod and the quartz glass tube are precisely aligned and fixed at the two upper portions of the quartz glass tube, and the lower end of the quartz glass tube is kept in the electric furnace, waiting to be melted, and the quartz glass tube and the core rod are opened. Stretching simultaneously with the overlap of to form a preform having an outer diameter of 60 mm, and an optical fiber having an outer diameter of 125 µm was obtained by a preponder, and ECC was a good value of 0.12 µm.

(Comparative Example 1)

A quartz glass tube having an outer diameter of 180 mm and an inner diameter of 52 mm having the same dimensions as in Example 1 was prepared, and a core rod having an outer diameter of 40 mm prepared by the VAD method was inserted therein while the lower end was a simple cut surface.

The clearance between the core rod and the quartz glass tube was also 12 mm (6 mm on one side) as in Example 1. As in Example 1, the core rod and the core of the quartz glass tube are precisely aligned to fix the core rod at the two upper portions of the quartz glass tube, the lower end of the quartz glass tube is kept in the electric furnace, and the lower end is waited for melting. At the same time as stretching of the quartz glass tube and the core rod, the preform having an outer diameter of 90 mm was obtained. In this preform, an optical fiber having an outer diameter of 125 µm was manufactured by an optical fiber precipitator, and ECC was measured.

(Comparative Example 2)

A quartz glass tube having an outer diameter of 180 mm and an inner diameter of 52 mm having the same dimensions as in Example 1 was prepared, and a core rod having an outer diameter of 50 mm prepared by the VAD method was inserted therein while the lower end was a simple cut surface.

Since the clearance between the core rod and the quartz glass tube was as small as 1 mm on one side, when the core rod was inserted into the quartz glass tube, the outer surface of the core rod contacted the inner surface of the quartz glass tube to cause scratches.

The core rod is fixed with the core of the quartz glass tube, and the core rod is fixed at the two upper portions of the quartz glass tube, the lower end of the quartz glass tube is kept in the electric furnace, and the lead is waited for melting, and the curb of the quartz glass tube and the core rod is fixed. Stretching was carried out simultaneously, and a preform having an outer diameter of 90 mm was obtained.

As a result of observing this preform, a large number of bubbles were observed at the welding interface between the core rod and the quartz glass tube due to the scratches generated when the core rod was inserted.

In this preform, an optical fiber having an outer diameter of 125 µm was manufactured using an optical fiber pretractor, and ECC was measured. As a result, it was a good value of 0.18 µm. However, a large variation in the diameter of the fiber, which was caused by bubbles at the interface, was observed, and fracture occurred.

(Comparative Example 3)

In the same manner as in Example 3, the lower end of the quartz glass tube having an outer diameter of 160 mm and an inner diameter of 50 mm was melted using an oxyhydrogen burner, and sealing was performed in a tapered shape.

Furthermore, this tip was cut so that a hole having a diameter of 10 mm could be drilled and used as a water draining hole during the cleaning of the quartz glass tube.

The discrepancy between the core of the tapered portion after grinding and the core of the quartz glass tube was 1.2% of the outer diameter in all cross sections, and the difference between the maximum thickness and the minimum thickness in each cross section of the thin end portion was 0.7% of the average thickness.

The core rod of the outer diameter 35mm created by the VAD method was inserted in the inside. The clearance between the core rod and the quartz glass tube is 15 mm (7.5 mm on one side). The cores of the core rods and the quartz glass tube are precisely aligned and fixed at the two upper portions of the quartz glass tube, the lower end of the quartz glass tube is kept in the electric furnace, waiting to be melted, and drawn out and drawn together with the curb of the quartz glass tube and the core rod. To produce a preform having an outer diameter of 60 mm, and an optical fiber having an outer diameter of 125 µm was obtained using a preselected machine. However, ECC was difficult to be seen as good at 0.28㎛.

(Comparative Example 4)

In the same manner as in Example 2, the lower end of the quartz glass tube having an outer diameter of 200 mm and an inner diameter of 50 mm was melted using an oxyhydrogen burner, and sealing was performed in a tapered shape.

The gap between the core of the tapered portion and the quartz glass tube after encapsulation was 0.8% of the outer diameter in all sections, and the difference between the maximum thickness and the minimum thickness in all the sections except the blocked portion of the tapered portion was 1.7% of the average thickness. .

The core rod of the outer diameter 35mm created by the VAD method was inserted in the inside. The clearance between the core rod and the quartz glass tube is 15 mm (7.5 mm on one side).

As in Example 1, the lower end of the core rod and the quartz glass tube were kept in the electric furnace and waited for melting. The lead was stretched at the same time as the quartz glass tube and the core rod collapsing to prepare an optical fiber having an outer diameter of 125 μm. . ECC of the obtained optical fiber was 0.24 micrometers, and it was hard to say that it was favorable.

According to the present invention described above, an optical fiber and a preform capable of obtaining good ECC while minimizing cost increase can be obtained by making the leading end of the quartz glass tube tapered.

Claims (12)

The core rod including only the core or a part of the clad is inserted into the quartz glass tube for cladding, and the composite base material formed is melted by vertically arranging the lower end of the core rod, and the core rod and the quartz glass tube are stretched together. The optical fiber manufacturing method which discloses the optical fiber manufacturing method WHEREIN: The lower end part which comprises the part which melt | dissolved for the first time of a quartz glass tube is a taper shape whose outer periphery and inner periphery are circular shape, and the outer diameter is reduced toward the front end as a whole, and each circular shape of a tapered shape part is carried out. The maximum thickness in each cross section of all circular cut surfaces including a tapered portion of 1 mm or less of the outer diameter of the quartz glass tube linear motion part and the center deviation of the mean center diameter of the cut surface and the linear motion part of the quartz glass tube. Use a quartz glass tube having a shape in which the difference in minimum thickness is 1.5% or less of the average thickness. Method for producing an optical fiber, characterized in that positioning at least according to a fixed plant of the lower end of the glass tube and the core rod. The method of claim 1, An inner diameter of the tapered portion of a quartz glass tube to be used is also reduced toward the tip. The method of claim 1, The tapered tip of the quartz glass tube used is sealed, The manufacturing method of the optical fiber characterized by the above-mentioned. The method of claim 1, A tapered tip of the quartz glass tube to be used is opened. The method of claim 1, A method of manufacturing an optical fiber, characterized in that the outer diameter or the inner diameter of the tapered portion of the quartz glass tube to be used or the diameter change of both thereof is stepped or partly stepped. The method of claim 1, A method of manufacturing an optical fiber, wherein the core rod and the quartz glass tube are melt-integrated and simultaneously stretched to a desired optical fiber diameter to directly obtain an optical fiber. 6. The method according to any one of claims 1 to 5, A method of manufacturing an optical fiber, characterized in that the core rod and the quartz glass tube are integrally melted and stretched at the same time to form a preform, and the optical fiber is obtained from a preform with the preform. The core rod including only the core or a part of the clad is inserted into the clad quartz glass tube, and the composite base material formed is melted by vertically arranging the lower end of the core rod, and the core rod and the quartz glass tube are melted together. In the manufacturing method of the preform for optical fibers which starts extending | stretching, the lower end part containing the part which melt | dissolved first of a quartz glass tube is a taper shape in which the outer periphery and the inner periphery are original states, and the outer diameter is reduced toward the front end as a whole, and taper For each circular cross section of all circular cut surfaces including tapered portions, the amount of core deviation between the circular center of the average outer diameter at each circular cut face of the shaped portion and the linear motion portion of the quartz glass tube is 1% or less of the outer diameter of the quartz glass tube straight portion. The quartz glass tube has a shape where the difference between the maximum thickness and the minimum thickness is 1.5% or less of the average thickness. And fixing at least the lower end seam of the quartz glass tube and the core rod to fix the preform for the optical fiber. The method of claim 8, The inner diameter of the tapered portion of the quartz glass tube to be used is also reduced toward the tip of the quartz glass tube. The method of claim 8, The tapered tip of the quartz glass tube used is sealed, The manufacturing method of the preform for optical fibers characterized by the above-mentioned. The method of claim 8, The tapered tip of the quartz glass tube to be used is opened, The manufacturing method of the preform for optical fibers characterized by the above-mentioned. The method according to any one of claims 8 to 11, A method of manufacturing a preform for an optical fiber, characterized in that the outer diameter or the inner diameter of the tapered portion of the quartz glass tube to be used or the diameter change of both thereof is stepped or partly stepped.

Images