JP2003201140A - Method of manufacturing multicore optical fiber and optical fiber preform and multicore optical fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a multicore optical fiber which does not give rise to deformation in glass preforms in drawing a plurality of the glass performs across a dummy preform interposed therebetween and facilitates discrimination of cores in connecting the optical fibers to each other and an optical fiber preform and a multicore optical fiber for the same. <P>SOLUTION: The method comprises manufacturing a piece of the multicore optical fiber 11 having a plurality of the cores 15 in a piece of the optical fiber manufactured by disposing the dummy preform 13 in a space segment enclosed by a plurality of the glass preforms 12 for the cores to form the optical fiber preform 10 and heat melting and drawing the optical fiber preform 10, in which the dummy preform 13 is formed of a polygonal shape section having arc surfaces 13a of the curvature equal to the outer circumferential circle of the glass preforms and the drawing is performed by making the arc surfaces 13a of the dummy preform 13 and the outer peripheral surface of the glass preforms congruent with each other. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber used in the field of optical communication, which is a method of manufacturing a multi-optical fiber having a plurality of cores in one optical fiber, an optical fiber preform therefor, and It relates to a multi-core optical fiber.

[0002]

2. Description of the Related Art As an optical fiber for increasing the amount of information transmission, a plurality of multimode optical fibers are used in view of skew characteristics, transmission device cost, crosstalk, and fiber cost in constructing a LAN at a distance of several hundred meters. Attention has been paid to the use of a multi-core optical fiber obtained by melting and integrating the above. This type of multi-core optical fiber is disclosed in, for example, Japanese Patent Laid-Open No. 11-95049, in which cores of a plurality of optical fibers are arranged in a common clad, and one of the cores is formed in an identifiable form. There is disclosed a technique of using a sign when connecting the above.

FIG. 8 is a schematic view showing an example of a conventional method for manufacturing a multicore optical fiber, and FIG. 9 is a view showing a drawn multicore optical fiber. In the figure, 1 is an optical fiber base material, 1a is a glass base material, 1b is a dummy base material, 2 is a multi-core optical fiber, 2a is a core element, 2b is fused glass, 2c is a deformed portion, 3 is a heater, 4 Is a coating die, 5 is a wire drawing guide, 6a, 6b and 6c are guide rollers, 7 is a winding drum, and 8 is a protective coating.

The optical fiber preform 1 comprises a plurality of glass preforms 1a which become core elements of a single mode optical fiber or a multimode optical fiber after drawing. A plurality of glass base materials 1a are bundled at equal intervals around a dummy base material 1b made of the same kind of glass material, held and fixed by an appropriate means, and attached to the drawing furnace.
The dummy base material 1b maintains the arrayed state of the plurality of glass base materials 1a when the optical fiber base material 1 is heated and melted and drawn, and also heats and melts the optical fiber base material 1 to form the glass base material 1a. Fill the inner space surrounded by.
Further, the dummy base material 1b has a function of being fused and integrated with the plurality of core elements 2a after drawing.

The optical fiber preform 1 is heated by a heater 3 in a drawing furnace, drawn into a predetermined glass outer diameter, and a protective coating 8 is applied by a coating die 4.
The multi-core optical fiber 2 provided with the protective coating 8 is wound around the winding drum 7 from the drawing guide 5 through the plurality of guide rollers 6a, 6b, 6c. Although omitted in FIG. 8, an outer diameter measuring device for the drawn multi-core optical fiber 2, a curing device for the protective coating, and the like are used.
It is configured so that a predetermined fiber outer diameter and coating outer diameter can be obtained.

The drawn multi-core optical fiber 2 has the shape shown in FIG. 9, and can be manufactured by a similar method regardless of whether the core element 2a is a single-mode optical fiber or a multi-mode optical fiber. . By heating and melting during drawing, the dummy base material 1b is melted into a molten glass 2b, and the plurality of core elements 2a are
They are fused and integrated by the molten glass 2b and protected by a common protective coating 8. For the protective coating 8, a transparent ultraviolet curable resin or the like is used.

When the multi-core optical fiber 2 is composed of a single mode optical fiber, a glass preform composed of a core portion and a clad portion is used, and the core diameter after drawing is 5
Wires are drawn so that the cladding diameter is about 10 μm and the cladding diameter is about 50 μm. In the case of four single mode optical fibers, the diameter of the circle in contact with the cladding outer surface of all the optical fibers is approximately 125 μm. The protective coating 8 formed on the outer periphery of the clad has an outer diameter of 250 as in a normal optical fiber.
It is formed in the order of μm.

When the multi-core optical fiber 2 is composed of a multi-mode optical fiber, a glass base material having only a core portion without a clad glass portion is used, and the drawn core diameter is about 50 μm. To be done. In the case of four multimode optical fibers, the diameter of the circle in contact with the outer surfaces of all cores is approximately 125 μm, as in the case of a single mode optical fiber. The protective coating 8 formed on the outer periphery of the clad has an outer diameter of 250 as in a normal optical fiber.
It is formed in the order of μm.

In the above-mentioned conventional optical fiber preform 1, a dummy preform 1b arranged in a central space surrounded by a plurality of glass preforms 1a is formed in a cylindrical shape. In the heating and melting process during drawing, the dummy base material 1b is softened and melted and fused with each glass base material 1a, but the glass base material 1a is displaced toward the center side by drawing and the inner portion 1 of the glass base material 1a is melted.
In some cases, c is pressed against the cylindrical dummy base material 1b to be deformed. Particularly, in the case where all or most of the core elements are formed of a core portion that serves as an optical transmission line like a multimode optical fiber, when the glass preform 1a for the core is deformed, the mode delay time difference ( Skew) and optical transmission characteristics are deteriorated.

[0010]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above circumstances, and when drawing a plurality of glass preforms with dummy preforms interposed, the glass preforms do not deform. Another object of the present invention is to provide a method of manufacturing a multi-core optical fiber in which the cores can be easily identified when connecting the optical fibers, an optical fiber preform therefor, and a multi-core optical fiber.

[0011]

A method for manufacturing a multi-core optical fiber according to the present invention comprises a dummy base material arranged in a space portion surrounded by a plurality of glass base materials for cores to form an optical fiber base material. A method of manufacturing a multi-core optical fiber having a plurality of cores in one optical fiber, which is manufactured by heating, melting, and drawing a material, wherein a dummy base material has an arc surface having a curvature equal to an outer circumference circle of a glass base material. And a circular arc surface of the dummy base material and the outer peripheral surface of the glass base material are matched with each other.

In the optical fiber preform of the present invention, a dummy preform is arranged in a space portion surrounded by a plurality of glass preforms for cores, and the dummy preform is heated and melted to draw a wire.
An optical fiber preform for producing a multicore optical fiber having a plurality of cores in one optical fiber, wherein a dummy preform is formed in a polygonal cross section having an arc surface having a curvature equal to the outer circumference circle of the glass preform, The circular arc surface of the dummy base material and the outer peripheral surface of the glass base material are matched with each other.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a first embodiment, FIG. 1 (A) is a cross-sectional view of an optical fiber preform made of four glass preforms before drawing, and FIG. 1 (B) is a multicore optical fiber after drawing. FIG. In the figure, 10 is an optical fiber base material, 11 is a multi-core optical fiber, 12 is a glass base material, 13 is an inner dummy base material, 13a is an arc surface, 13b is an edge portion, 15
Is a core element, 16 is an inner fused glass after drawing,
17 indicates a protective coating.

The optical fiber preform 10 has a dummy preform 13 in a central space surrounded by a plurality of glass preforms 12.
(Hereinafter, referred to as an inner dummy base material).
The glass base material 12 forms the core element 15 of the multi-core optical fiber 11, and has an outer diameter of 20 before drawing.
The thing of about mm-36 mm is used. Glass base material 12
Has a core portion doped with germanium at the center and has a clad portion outside thereof, or the glass base material 1
All or most of 2 is used as the core part.

The inner dummy preform 13 holds the arrangement state of the plurality of glass preforms 12, fills the space at the center of the arrangement of the glass preforms 12, and heats and melts the optical fiber preform 10 to draw it. , Prevent the glass base material from being deformed.
In addition, it has a function as a connecting material that fuses and integrates a plurality of drawn core elements 15. Therefore, the inner dummy base material 13 is formed of silica glass or the like having a thermal expansion coefficient and a melting temperature that are substantially the same as those of the glass base material 12.

In the present invention, the inner dummy base material 13
Is formed by an arc surface 13a having a curvature substantially equal to the outer circumference of the glass base material 12 in a portion in contact with the glass base material 12,
It is formed of regular polygonal glass rods corresponding to the number of glass base materials 12. FIG. 1A shows a case where four glass base materials 12 are assembled, and the glass base material 12 includes a core portion 12
It is shown for a single mode optical fiber consisting of a and a clad portion 12b. In this case, the inner dummy base material 1
3 is formed by a regular quadrangular glass rod having a side of an arc surface 13a having a curvature substantially equal to the outer circumference circle of the glass base material 12.

The glass base materials 12 are gathered so as to match the arcuate surface 13a of the inner dummy base material 13, and the ends are bonded together.
They are integrally bundled in an even array using a fusing or binding member. In addition, the glass base material 12 and the inner dummy base material 13
Means that the arcuate surfaces 13a can be matched and densely joined together, so that the glass base material 12 and the inner dummy base material 13 can be integrated beforehand by sintering.

The optical fiber preform 10 in which four glass preforms 12 are gathered around the inner dummy preform 13 is placed in a drawing furnace, heated and melted from the lower end side, and drawn at a predetermined speed. To be done. On the glass fiber immediately after drawing,
The protective coating 17 is applied to form the multi-core optical fiber 11 having the cross-sectional shape shown in FIG. The core element 15 after drawing has, for example, a core diameter of 8 μm and a cladding outer diameter P of 50 μm, and is fused with the side surface of the inner fused glass 16 after drawing (shown by a dotted line) so as to be in close contact with adjacent optical fibers. ) Is integrated.

Two core elements 1 after being integrated
Since the outer dimension Q of 5 is 100 μm, the maximum dimension R of all core elements 15 is about 121 μm, and a multi-core optical fiber having a glass outer diameter of 125 μm which is almost equal to that of a normal single optical fiber can be obtained. The protective coating 17 can be formed by using an ordinary optical fiber having an outer diameter S of 250 μm and a similar coating diameter.

The inner dummy preform 13 before drawing has a circular arc surface 13a in contact with the glass preform 12 having a curvature substantially equal to the outer circumference of the glass preform 12. In addition, the arrangement of the glass base materials 12 can be accurately positioned, and the arrangement positions of the core elements after drawing can be made uniform. Also, the glass base material 12
No unreasonable stress is generated at the joint with the optical fiber preform 10
Since the glass base material is not deformed when it is heated and melted, the optical transmission characteristics of the multicore optical fiber after drawing are not impaired.

FIG. 2 shows a modification of the first embodiment, showing an optical fiber preform before drawing and a multicore optical fiber after drawing. FIG. 2A is a diagram showing an example in which the minimum position of the edge portion of the inner dummy base material is determined, and FIG. 2B is a diagram showing an example in which the maximum position of the edge portion of the inner dummy base material is determined. is there. The reference numerals in the figure are the same as those in FIG.

FIG. 2 shows an example in which a core glass preform for a multimode optical fiber is used as the glass preform 12 and the edge portion 13b of the inner dummy preform 13 has a certain thickness. is there. 2 (A) and FIG.
Any of the optical fiber preforms of (B) is the inner dummy preform 1
It is the same as in the case of FIG. 1 in that each side of 3 is formed by an arc surface 13a which is substantially equal to the outer peripheral circle of the glass base material 12.

By providing the edge portion 13b of the inner dummy base material 13 with a certain thickness, the inner dummy base material 1
It is possible to reduce the occurrence of chipping or damage of the edge portion 13b during the handling of No. 3 described above. Further, since the edge portion 13b has a certain thickness, the core elements 15 in the drawn multi-core optical fiber 11 do not adhere to each other, but are fused and integrated in a form having a slight interval. Therefore, the outer diameter of the core element 15 is 50 μm as in FIG.
m, the two core elements 1 after being integrated
If the outer dimension Q of 5 is 103 μm, the maximum dimension R of all the core elements 15 is about 125 μm, and a multi-core optical fiber having a glass outer diameter of 125 μm of a normal single optical fiber can be obtained.

In FIG. 2A, the edge portion 13b of the inner dummy preform 13 extends outward from the contact point α of the tangent line passing through the center of the optical fiber preform 10 and in contact with the outer periphery of the glass preform 12. This is an example. When the optical fiber preform 10 is heated and melted and drawn, each glass preform 12 is moved toward the center of the inner dummy preform 13. If the edge portion 13b having a certain thickness of the inner dummy base material 13 is inside the contact position α, the edge portion 13b may hit the outer surface of the glass base material 12 and deform the glass base material 12. The edge portion 13b of the inner dummy base material 13 is
If it extends at least outside the contact position α, the edge portion 13b can be prevented from hitting the glass base material 12,
The deformation of the glass base material 12 can also be avoided.

FIG. 2B shows an example in which the edge portion 13b of the inner dummy base material 13 is restricted from extending outward so that the outer exposed portion of the glass base material 12 is at a predetermined angle β or more. The angle β is preferably 180 degrees or more.
When the edge portion 13b extends to the outer side position beyond the angle β, the concave portions between the core elements 15 of the multi-core optical fiber 11 after drawing are filled, and the shape becomes a round quadrangle or a shape close to a circle. It becomes difficult to identify the positional relationship of 15. Therefore, when the protective coating 17 of the multi-core optical fiber 11 is removed to perform optical connection, there is a possibility that the positional relationship of the core element 15 may shift and the connection loss may increase. Therefore, the outer edge portion 13b of the inner dummy base material 13 is limited to a predetermined value or less, and the outer exposed portion of the core element 15 after wire drawing is secured to be 180 degrees or more. It is possible to easily identify the outer shape and the position of the.

FIG. 3 shows the second embodiment, and FIG.
FIG. 3A is a cross-sectional view of an optical fiber preform made of four glass preforms before drawing, and FIG. 3B is a cross-sectional view of a multicore optical fiber after drawing. In the figure, 18 is an outer dummy base material, 18a is an inner circular arc surface, 18b is an outer circular arc surface, 19 is an outer fused glass after drawing, and other reference numerals are the same as those in FIG. To do.

FIG. 3A shows a case where four glass base materials 12 are used, as in the case of FIG.
Shows an example using a core glass preform for a multimode optical fiber. An inner dummy base material 13 having the same shape as that shown in FIG. 1 is arranged in a central space surrounded by the glass base material 12, and another dummy base material 18 is provided in four recesses formed outside the adjacent glass base material 12. (Hereinafter, referred to as outer dummy preforms) are arranged so that the optical fiber preform 10 has a cylindrical shape. The outer dummy base material 18 is
It is made of the same glass material as the inner dummy base material 13.

As shown in the figure, the shape of the outer dummy base material 18 is such that the portion in contact with the glass base material 12 is the glass base material 12.
The outer circular surface is formed by an inner circular arc surface 18a having a curvature substantially equal to that of the outer peripheral circle, and the outer surface is formed by an outer circular arc surface 18b having a curvature approximately equal to the circle in which the four glass base materials 12 are simultaneously in contact. The outer dummy base material 18 has a function of filling the concave portion on the outer side of each glass base material 12 and maintaining the array shape of the glass base materials 12 from the outside together with the inner dummy base material 13 so that the outer shape is a cylindrical shape. Can have Further, colored glass is used for the outer dummy base material, and one or all colors of the four outer dummy base materials are made different from each other, whereby the core element numbers after drawing can be identified. Various substances such as metal ions, non-metal ions, and metal colloids are known as glass colorants, and various identification marks can be formed simultaneously with drawing by appropriately selecting these substances.

The inner dummy base material 13 and the outer dummy base material 18
The optical fiber preform 10 in which four glass preforms 12 are assembled by using is put into a drawing furnace, heated and melted from the lower end side and drawn at a predetermined speed, and a protective coating is provided on the glass fiber immediately after drawing. By applying 17, the multi-core optical fiber 11 having the cross-sectional shape shown in FIG. 3 (B) is formed.
Each core element 15 after being drawn has, for example, a core diameter of 5
At 0 μm, the inner fused glass 16 after drawing and the outer fused glass 19 after drawing are fused and integrated so as to be in close contact with adjacent core elements. The core element dimensions, coating outer dimensions, etc. of the multi-core optical fiber 11 after being integrated are the same as those in FIG. 1 (B).

The inner dummy base material 13 and the outer dummy base material 18 before drawing are arcuate surfaces 13 in contact with the glass base material 12.
Since a and 18a are formed with a curvature almost equal to the outer circumference circle of the glass base material 12, no unreasonable stress is generated in the joining with the glass base material 12, and the outer surface of the glass base material 12 is similarly pressed with an unreasonable pressing force. Do not receive Therefore, the optical fiber preform 10
When the glass is heated and melted, the glass base material is not deformed, and the arrayed shape can be maintained and drawn. Further, by using colored glass of different colors for the outer dummy base material 18, the core number can be identified.

FIG. 4 is a view showing a modification of the second embodiment explained in FIG. 3, FIG. 4 (A) shows an example in which the outer dummy base material is arranged at one place, and FIG. 4 (B). FIG. 4 is a diagram showing an example in which outer dummy base materials are arranged at three locations. The reference numerals in the figure are the same as those used in FIG.

Similar to the case of FIG. 3, FIG. 4A shows a central space surrounded by the glass preforms 12 by assembling four glass preforms 12 made of a core glass preform for a multimode optical fiber. The inner dummy base material 13 is arranged in the portion. The outer dummy base material 18 is arranged in one of four recesses formed outside the adjacent glass base material 12. in this case,
By using colored glass for the outer dummy base material 18,
It is possible to identify the core element number after drawing.

In FIG. 4B, the outer dummy base material 18 is arranged in three of the four recesses formed outside the adjacent glass base material 12, and one recess is left. In this case, the outer dummy base material 18 may be colored glass, but may be uncolored. Outer dummy base material 1
One concave portion in which 8 is not arranged serves as an index to identify the core element number after drawing.

FIG. 5 shows a third embodiment, and FIG.
FIG. 5A is a cross-sectional view of an optical fiber preform made of three glass preforms before drawing, and FIG. 5B is a cross-sectional view of a multicore optical fiber after drawing. The reference numerals in the figure are the same as those in FIG.

In this example, as shown in FIG. 5A, three glass preforms 12 for the core are used. The glass base material 12 having an outer diameter of about 20 mm to 36 mm is used, and the glass base material 12 has a core portion doped with germanium at the center thereof and the outside thereof as a clad portion, or the glass base material 12 Is formed of a core glass having no clad portion. In the figure, it is shown as a glass base material having only a core glass without a clad portion.

This embodiment has substantially the same structure as that of the first embodiment except that the inner dummy base material 13 is formed in a regular triangular cross section. The inner dummy base material 13 is made of the glass base material 12. It has three arcuate surfaces 13a having a curvature substantially equal to the outer circumference circle. Further, although the edge portion 13b is shown as having a certain thickness as in the example of FIG. 2, it may be a shape having no thickness. The glass base materials 12 are assembled so as to contact the circular arc surface 13a of the inner dummy base material 13, and end portions thereof are bonded, fused, or bundled together in an even array using a binding member. Further, the circular arc surface 13a of the inner dummy base material 13 and the glass base material 12 may be integrated by sintering.

The multi-core optical fiber 11 after drawing is
As shown in FIG. 5 (B), the inner fused glass 1 after drawing is so drawn that the adjacent core elements 15 are almost in close contact with each other.
6 is fused with the side surface of 6 (indicated by a dotted line) to form a protective coating 1.
7 is given. In this example, since the number of cores is smaller than that in the case of four cores, the outer diameter of the core element 15 after drawing can be made large, and in the case of a multimode optical fiber,
The core diameter can be 62.5 μm. In the case of a single mode optical fiber, the core diameter is 8 μm and the cladding diameter is 62.
It becomes 5 μm.

Also in the example of FIG. 5, the glass base material 12 is deformed by regulating the position of the edge portion 13b of the inner dummy base material 13 as described with reference to FIGS. 2 (A) and 2 (B). Also avoiding each core element 15 at the time of connection
It is possible to easily identify the outer shape and the position of the. Further, as described with reference to FIGS. 3 and 4, by using the outer dummy base material, the core number can be identified.

When the multi-core optical fiber 11 formed in the various embodiments described above is used by being bent in one direction, a time difference (skew) occurs in the speed of light propagating through each core element. In order to reduce this, it is advisable to twist the multi-core optical fiber 11 when the multi-core optical fiber is drawn and wound.

FIGS. 6 and 7 show an example in which the multi-core optical fiber 11 is twisted at the time of drawing, FIG. 6 is a diagram showing the outline of the drawing, and FIG. 7 is a diagram showing the details of the twisting. In the figure, 20 is a heater, 21 is a coating die, 22 is a wire drawing guide, 23 is a swing guide roller, and 24a and 24a.
Reference numerals b and 24c denote fixed guide rollers, and 25 denotes a winding drum. Since the other reference numerals are the same as those used in FIG. 1, the description thereof will be omitted.

As shown in FIG. 6, the optical fiber preform 10
Is heated by a heater 20 in a drawing furnace, drawn into a predetermined glass outer diameter, and covered with a coating die 21. The multi-core optical fiber 11 provided with the protective coating passes through the drawing guide 22, is twisted by the swing guide roller 23, and passes through the plurality of fixed guide rollers 24a, 24b, 24c and the winding drum 25.
It is wound up in. Although omitted in FIG. 6, in addition,
An apparatus for measuring the outer diameter of the drawn multi-core optical fiber 11, a curing apparatus for the protective coating, and the like are used, and are configured to obtain a predetermined fiber outer diameter and coating outer diameter.

In FIG. 7, when the rotation axis y of the rocking guide roller 23 rotates by + θ about the drawing direction axis z, a lateral force is applied to the multi-core optical fiber 11 by this rotation, and the rocking guide is rotated. The multi-core optical fiber 11 rolls on the surface of the roller 23. The rolling imparts a twist to the multi-core optical fiber 11. Then, when the swing guide roller 23 is rotated by −θ in the opposite direction, the multicore optical fiber 11 rolls on the surface of the swing guide roller 23 in the opposite direction. In this way, by repeatedly giving the swing guide roller 23 a rotation from + θ to −θ, it is possible to alternately impart clockwise and counterclockwise twists with respect to the moving direction of the multicore optical fiber 11. it can.

The fixed guide roller 24a next to the swing guide roller 23 is installed right next to the swing guide roller 23.
After contacting the circumferential surface of No. 3 at an angle of about 90 °, it moves to the fixed guide roller 24a. Fixed guide roller 24a
Has a V-shaped narrow groove so that the multi-core optical fiber 11 does not roll on the roller surface. By suppressing the rolling of the multicore optical fiber 11 on the surface of the fixed guide roller 24a, the swing guide roller 22
A twist can be imparted to the coated optical fiber 20 with high efficiency with respect to the rotation of the.

In the above first to third embodiments, the case where the number of cores of the core element is 3 and 4 has been described, but the present invention can be applied to a multi-core optical fiber having more cores. it can. In this case, the inner dummy base material according to the present invention may be used in combination with a rectangular shape or a triangular shape, and may be formed by appropriately changing the thickness of the glass base material and the outer diameter dimension of the core element.

[0045]

As is apparent from the above description, by forming the portion of the dummy base material which is in contact with the glass base material with an arc surface having a curvature substantially equal to the outer circumferential circle of the glass base material, The arrangement can be accurately positioned, and the arrangement position of the core elements after drawing can be made uniform. In addition, no undue stress is generated in the joint between the glass preform and the dummy preform, and when the optical fiber preform is heated and melted, the glass preform is not deformed and the optical transmission characteristics are impaired. Absent.

The position of the core element is identified by restricting the position of the edge portion of the inner dummy base material,
The positioning of the optical fiber connection can be facilitated. Further, by selectively providing the outer dummy base material or using a colored one, it is possible to easily identify the array element number of the core element, etc. and surely perform the optical fiber connection.

Further, when the multi-core optical fiber is bent and used in one direction by swinging the multi-core optical fiber at the time of drawing, there is a time difference in the speed of light propagating through each core element. It is possible to reduce the occurrence of (skew).

[Brief description of drawings]

FIG. 1 is a diagram illustrating a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a modified example of the first embodiment of the present invention.

FIG. 3 is a diagram illustrating a second embodiment of the present invention.

FIG. 4 is a diagram illustrating a modified example of the second embodiment of the present invention.

FIG. 5 is a diagram illustrating a third embodiment of the present invention.

FIG. 6 is a schematic diagram illustrating a method of drawing a multi-core optical fiber according to the present invention.

FIG. 7 is a diagram showing an example of applying a twist to the multicore optical fiber of the present invention.

FIG. 8 is a schematic diagram illustrating a conventional method of drawing a multi-core optical fiber.

FIG. 9 is a diagram illustrating a conventional multicore optical fiber.

[Explanation of symbols]

10 ... Optical fiber base material, 11 ... Multi-core optical fiber,
12 ... Glass base material, 13 ... Inner dummy base material, 13a ... Arc surface, 13b ... Edge part, 15 ... Core element, 16
... Inner fused glass after drawing, 17 ... Protective coating, 18 ...
Outer dummy base material, 18a ... Inner arc surface, 18b ... Outer arc surface, 19 ... Outer fused glass after drawing, 20 ... Heater, 21 ... Coating die, 22 ... Wire drawing guide, 23 ... Swing guide roller, 24a , 24b, 24c ... Fixed guide rollers, 25 ... Winding drum.

Claims (12)

[Claims] 1. An optical fiber preform by arranging a dummy preform in a space portion surrounded by a plurality of core glass preforms,
A method for manufacturing a multi-core optical fiber having a plurality of cores in one optical fiber, which is manufactured by heating and melting the optical fiber base material, and drawing the dummy base material on the outer periphery of the glass base material. A method of manufacturing a multi-core optical fiber, which is formed by a polygonal cross section having an arc surface having a curvature equal to a circle, and the arc surface of the dummy base material and the outer peripheral surface of the glass base material are matched with each other. 2. An edge portion of the dummy base material extends outward from a contact point of a tangent line passing through the center of the optical fiber base material and in contact with the outer periphery of the glass base material. A method for manufacturing a multi-core optical fiber according to. 3. The edge portion of the dummy base material is restricted from extending outward so that an externally exposed portion of each core element of the drawn multi-core optical fiber is 180 ° or more. The method for manufacturing a multicore optical fiber according to claim 2. 4. An outer dummy base material is arranged in a concave portion on the outer side of the plurality of glass base materials, and a portion of the outer dummy base material in contact with the glass base material has a curvature equal to an outer circumference circle of the glass base material. The method of manufacturing a multi-core optical fiber according to claim 1, wherein the outer dummy base material is formed into an arc surface, and the arc surface of the outer dummy base material and the outer peripheral surface of the glass base material are matched with each other. 5. The method of manufacturing a multi-core optical fiber according to claim 4, wherein the outer dummy preform is selectively disposed in a concave portion outside the plurality of glass preforms. 6. The method of manufacturing a multi-core optical fiber according to claim 4, wherein colored glass is used for the outer dummy base material. 7. The method of manufacturing a multi-core optical fiber according to claim 1, wherein twisting is applied during drawing of the optical fiber preform. 8. A multi-core light having a plurality of cores in one optical fiber by arranging a dummy base material in a space portion surrounded by a plurality of glass base materials for cores, heating and melting the dummy base material, and drawing the same. An optical fiber preform for producing a fiber, wherein the dummy preform is formed with a polygonal cross section having an arc surface having a curvature equal to the outer circumference circle of the glass preform, and the arc preform of the dummy preform and the glass preform. An optical fiber preform characterized by matching the outer peripheral surface of the material. 9. An outer dummy base material is arranged in a concave portion on the outer side of the plurality of glass base materials, and a portion of the outer dummy base material in contact with the glass base material has a curvature equal to an outer circumference circle of the glass base material. The optical fiber preform according to claim 8, wherein the optical fiber preform is formed by an arcuate surface, and the arcuate surface of the outer dummy preform and the outer peripheral surface of the glass preform are matched with each other. 10. The optical fiber preform according to claim 9, wherein the outer dummy preforms are arranged in all the concave portions on the outer sides of the plurality of glass preforms to have a circular outer shape. 11. The optical fiber preform according to claim 9, wherein the glass preform and the dummy preform are integrated by sintering. 12. A multi-core optical fiber manufactured by the method for manufacturing a multi-core optical fiber according to any one of claims 1 to 7.