JP2016075918A - Optical fiber and method for manufacturing the optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multi-core optical fiber having cores of which positions can be easily specified and can be easily fixed, and a method for manufacturing the optical fiber.SOLUTION: An optical fiber 108 includes a plurality of cores 10 and a clad 28 surrounding the cores and having an external shape of Reuleaux polygon in a cross section of the optical fiber.SELECTED DRAWING: Figure 13

Description

  The present invention relates to an optical fiber and a method of manufacturing the same, and more particularly to an optical fiber having a multi-core and a method of manufacturing the same.

  The spread of the Internet and services using the Internet have been rapidly increasing in recent years. Along with this, the amount of communication using optical fibers is rapidly increasing, and there is a demand for an increase in capacity and multiplexing of optical transmission lines. Various methods have been studied for realizing a large capacity and multiplexing of optical transmission lines, and one of them is a method using a multi-core optical fiber in which a plurality of cores are provided in one optical fiber. .

  A multi-core optical fiber is an optical transmission line that performs space division multiplex transmission. By providing a plurality of core regions having a relatively high refractive index in a clad having a relatively low refractive index, a plurality of optical transmissions can be performed simultaneously. An area is provided (for example, Patent Document 1).

JP 2012-32524 A

  When performing communication or the like using optical fibers, it is necessary to connect optical fibers in a communication path and connect optical fibers in a communication device. If a single-core optical fiber has a single core, the cores of both optical fibers may be simply aligned and connected, but in the case of a multi-core optical fiber, there are multiple cores, so alignment Is not easy. Even in a multi-core optical fiber, the positions of the cores of the multi-core optical fibers to be connected are aligned at the connecting portion so as to minimize light transmission loss, and the end faces of the two cores are almost entirely covered. It is necessary to connect to match.

  Regarding the problem of connection between the multi-core optical fibers as described above, in Patent Document 1, when the multi-core optical fibers are connected by making the arrangement of the core group including a plurality of cores symmetrical only with respect to 2π rotation with respect to the optical fiber axis. A technique is disclosed that can uniquely determine the rotation angle.

  The technique disclosed in Patent Document 1 is intended to easily align the two optical fibers by, for example, arranging a position detection core. Only after the rotation around the fiber axis does not occur, the two fibers cannot be aligned properly. In other words, if the optical fiber is not fixed and free, it will rotate around the fiber axis, so even if the position of the position detection core is specified in a certain state, it will be connected to another optical fiber. When the optical fiber is moved, the position of the core for position detection changes due to the rotation of the optical fiber, and as a result, the cores are connected without matching. When connecting optical fibers, the optical fibers are usually placed in the V-groove and the end faces are brought into contact with each other. However, the positions of the cores cannot be specified only by placing them in the V-groove. Since the fiber rotates in the groove and the position of the core changes, it is almost impossible to join the cores without misalignment. Even with the optical fiber of Patent Document 1, it is necessary to first fix the optical fiber in the V-groove and then rotate the optical fiber around the central axis for alignment. take time.

  The present invention has been made in view of such a point, and an object of the present invention is to provide a multi-core optical fiber capable of easily specifying the position of each core and fixing the position easily. It is to provide.

  The first optical fiber of the present invention is a multi-core optical fiber comprising a plurality of cores and a clad surrounding the plurality of cores, and the outer shape of the clad in the cross section of the optical fiber includes: It has a configuration in which at least one straight line portion exists.

  The outer shape of the clad preferably has at least two straight portions.

  In a preferred embodiment, the cladding has a quadrangular outer shape. Preferably, the number of cores is 9, and in the cross section of the optical fiber, one core is disposed at the center, and the core is separated from the line connecting the center and each corner of the outer shape of the cladding. It is preferable that the said core is arrange | positioned.

  In another preferred embodiment, the outer shape of the cladding is hexagonal. Preferably, the number of cores is 7, 13 or 19, and in the cross section of the optical fiber, one core is disposed at the center, and the center and each corner of the outer shape of the cladding are It is preferable that another said core is arrange | positioned on the line to connect.

  In another preferred embodiment, the outer shape of the cladding is a hexagon. Preferably, the number of cores is 10, and in the cross section of the optical fiber, one core is disposed at the center, and is separated on a line connecting the center and each corner of the outer shape of the cladding. It is preferable that the said core is arrange | positioned.

  A second optical fiber of the present invention is a multi-core optical fiber comprising a plurality of cores and a cladding surrounding the periphery of the plurality of cores, and the outer shape of the cladding in the transverse cross section of the optical fiber is Lulow It has a configuration that is a polygon. And when the Rouleau polygon is Roule heptagon, it is preferable that the number of cores is 7, and in the cross section of the optical fiber, one core is disposed at the center, and the center, It is preferable that another core is disposed on a line connecting each corner of the outer shape of the cladding. In the case where the Rouleau polygon is a Rouro's nine-sided polygon, the number of cores is preferably seven. In the cross-section of the optical fiber, one core is disposed at the center, and the center and the clad It is preferable that another said core is arrange | positioned on the line | wire which connects each corner | angular part of this external shape. It is preferable that the number of cores is 7 when the Rouleau polygon is a Rouleau pentagon.

  A first optical fiber manufacturing method of the present invention is a method of manufacturing a multi-core optical fiber including a plurality of cores and a clad surrounding the plurality of cores, and a plurality of core precursor parts, A step of preparing a preform including a clad precursor portion surrounding the periphery of the plurality of core precursor portions, and a drawing step of forming the optical fiber by heating and stretching the preform, In the preform, at least one straight portion exists in the outer shape of the clad precursor in the cross section, and the shape of the cross section of the optical fiber is similar to that of the preform in the drawing step. It has a configuration that.

  It is preferable that at least two straight portions exist in the outer shape of the cladding precursor. The outer shape of the clad precursor is more preferably a quadrangle, a hexagon or a hexagon.

  A second optical fiber manufacturing method of the present invention is a method of manufacturing a multi-core optical fiber including a plurality of cores and a clad surrounding the plurality of cores, and a plurality of core precursor parts, A step of preparing a preform including a clad precursor portion surrounding the periphery of the plurality of core precursor portions, and a drawing step of forming the optical fiber by heating and stretching the preform, In the preform, the outer shape of the cladding precursor is a Roule heptagon or a nine-sided shape in a cross section, and the optical fiber is formed in a shape similar to that of the preform in the drawing step. It has a configuration.

  In a multi-core optical fiber, there is at least one straight part in the outer shape of the cladding in the cross section of the optical fiber. Therefore, a flat part corresponding to the straight part is created on the stage on which the optical fiber is placed. If so, the position of the core can be easily specified, and the change of the position of the core can be prevented.

3 is a schematic diagram illustrating an end face of an optical fiber according to Embodiment 1. FIG. 6 is a schematic diagram showing an end face of another optical fiber according to Embodiment 1. FIG. 6 is a schematic diagram illustrating an end face of another optical fiber according to Embodiment 1. FIG. It is a schematic diagram which shows the place which mounted the optical fiber which concerns on Embodiment 1 on a stand. It is a schematic diagram which shows the place which mounted the other optical fiber which concerns on Embodiment 1 on the stand. It is a schematic diagram which shows the place which accommodated the other optical fiber which concerns on Embodiment 1 in the ferrule. It is a schematic diagram which shows the place which mounted the other optical fiber which concerns on Embodiment 1 on another stand. It is the figure which showed typically the process of producing the optical fiber which concerns on embodiment. 6 is a schematic diagram showing an end face of an optical fiber according to a modification of Embodiment 1. FIG. 6 is a schematic diagram showing an end face of an optical fiber according to another modification of Embodiment 1. FIG. 6 is a schematic diagram illustrating an end face of an optical fiber according to another modification of the first embodiment. FIG. 6 is a schematic diagram showing an end face of an optical fiber according to still another modification of the first embodiment. FIG. 6 is a schematic diagram showing an end face of an optical fiber according to Embodiment 2. FIG. 6 is a schematic diagram showing an end face of another optical fiber according to Embodiment 2. FIG.

  In the present application, the Roule polygon is a figure that is a common part of a circle having a radius of the longest diagonal line centered on each vertex of the positive / odd square, based on the positive / odd square. Yes, it is a figure that has been replaced with an arc centered at the apex where the line segments of the odd and odd squares face each other.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following drawings, components having substantially the same function are denoted by the same reference numerals for the sake of brevity.

(Embodiment 1)
FIG. 1 shows an end face (a plane perpendicular to the fiber axis) of the multi-core optical fiber according to the first embodiment. In the optical fiber 101 of this embodiment, in the clad 21 made of quartz, the core 10 has one core 10 at the center axis portion, and the six cores 10, 10,... (Peripheral core) around the center axis are regular hexagons. Placed in place. That is, each core 10, 10,... Is surrounded by the clad 21. The clad 21 has a so-called D-shaped outer shape in which a part of a circle is cut off in a cross section (cross section perpendicular to the fiber axis) of the optical fiber 101 to form one chord and one arc. The central angle with respect to the arc is about 290 degrees. The peripheral cores 10, 10,... Are arranged at symmetrical positions in which the fiber center axis is a six-fold rotation axis. One of the peripheral cores 10 is disposed on a vertical line extending from the fiber central axis to the chord of the clad 21.

  The seven cores 10, 10,... Extend along the center axis of the fiber, and quartz or the like is doped with quartz to make the refractive index higher than that of quartz, and each propagates an optical signal as a single mode fiber. Let

  Since the optical fiber 101 of the present embodiment has the above-described arrangement of the cores 10, 10,... And the characteristics of the outer shape of the cladding 21, the chord portion of the cladding 21 is placed on the table 60 as shown in FIG. When the optical fiber 101 is placed so as to be in contact with the mounting surface 60a of the base 60, the position and arrangement of the cores 10, 10,... Are specified with respect to the mounting surface 60a. That is, three cores 10, 10, 10 are arranged on one line perpendicular to the mounting surface 60a, and the middle core 10 is a core on the central axis, and the remaining four cores 10, 10 are arranged. ,... Are located at the apexes of the regular hexagon together with the cores 10 and 10 at both ends arranged on one line perpendicular to the mounting surface 60a.

  When two optical fibers 101 according to the present embodiment are prepared and the end faces are connected to each other, it is necessary to match the arrangement and positions of the seven cores 10, 10,. This is because a connection loss occurs if the position of the core 10 is shifted at the joint. In this embodiment, the positions and arrangements of the respective cores 10, 10,. Since the surfaces are in contact with each other, the optical fiber 101 does not rotate around the central axis, and the positions and positions of the cores 10, 10,... Are fixed as they are. For this reason, only the end faces of the optical fibers 101 placed on the table 60 are brought into contact with each other, so that there is no deviation in the rotational direction around the central axis, and if the positions of the cores 10 at the central axis position are aligned, 10, all connected so that there is almost no connection loss. As described above, in the optical fiber 101 of the present embodiment, when the chord portion of the clad 21 is placed on the mounting surface 60a of the base 60, the core position in the rotational direction around the central axis is eliminated, and the cores 10 and 10 of the optical fiber 101 are eliminated. , ... The position can be easily identified. In particular, it is possible to eliminate the shift due to the rotation of the core position around the central axis.

  This embodiment also includes a multi-core optical fiber having two or more planar portions in the fiber outer shape. In such a case, there are two or more strings in the cross section of the optical fiber. For example, as shown in FIG. 2, an optical fiber 102 whose outer shape is a square in the cross section of the fiber is also an optical fiber of this embodiment. The optical fiber 102 is a multi-core fiber having nine cores 10, 10,..., And the cores 10, 10,. That is, one core 10 is placed at the position of the fiber center axis, and three cores 10 are arranged at both ends and the center of each of the four sides around the core. Each side of the square formed by the cores 10, 10,... Is parallel to each side of the outer shape of the cladding 22, and each corner (each vertex) of the core 10 and the cladding 22 located on the fiber central axis. The core 10 which hits the corner | angular part of square arrangement | positioning exists on the line which connects.

  Further, an optical fiber 103 whose outer shape is a regular hexagon in the cross section of the fiber as shown in FIG. 3 is also an optical fiber of this embodiment. The optical fiber 103 is a multi-core fiber having seven cores 10, 10,..., And the cores 10, 10,. That is, one core 10 is placed at the position of the fiber central axis, and the cores 10, 10,. Each side of the regular hexagon formed by the cores 10, 10,... Is parallel to each regular hexagonal side of the outer shape of the cladding 23, and each corner portion (each vertex) of the core 10 and the cladding 23 located on the fiber central axis. ), The core 10 located at each vertex of the regular hexagon exists.

  When the optical fiber 103 having a regular hexagonal fiber cross section is placed on a table 62 provided with two mounting surfaces 62a and 62b as shown in FIG. 5, the angle formed by the two mounting surfaces 62a and 62b is 120 degrees. Therefore, a set of adjacent planar portions of the clad outer shape is in close contact with the two mounting surfaces 62a and 62b, respectively, and is kept in a stable state. As described above, when there is the base 62 having the mounting surfaces 62a and 62b that are in contact with the two plane portions in the outer shape of the clad of the optical fiber, the optical fiber 103 is sandwiched between the two mounting surfaces and is almost fixed. Therefore, the rotational movement around the center axis of the fiber is more reliably prevented as compared with the optical fiber having only one plane portion like the optical fiber 101 having the D-shaped cross section, and the two mounting surfaces 62a and 62b can be prevented. The position and arrangement of each of the cores 10, 10,. The same applies to the optical fiber 102 having a square cross section, and the optical fiber 102 may be a table having two mounting surfaces that intersect at 90 degrees.

  In addition, when using a ferrule for fiber connection, the ferrule serves as the bases 60 and 62 if the shape of the hole in the ferrule that houses the fiber is the same as the outer shape of the fiber (cladding outer shape). FIG. 6 schematically shows an end portion of a ferrule 70 that houses an optical fiber 103 having a regular hexagonal cross section. The inside of the ferrule 70 is a hole having a regular hexagonal cross section, and the optical fiber 103 is accommodated in the hole. The outer surface of the optical fiber 103 is in contact with the inner wall of the ferrule hole, and the position of the cores 10, 10,... Is specified and the optical fiber 103 is fixed so that the position does not change. If a mark corresponding to the shape and position of the regular hexagon of the internal hole, for example, a mark corresponding to one corner of the regular hexagon, is attached to the outer surface side of the ferrule 70, the optical fiber 103 is bonded using the mark. Sometimes it is easy to align the core.

  In FIG. 7, four optical fibers 103, 103,... Are sandwiched and fixed by a pair of bases 64, 65. The optical fiber 103 is the same as that shown in FIG. This is an example applied to the connection of a 4-core fiber tape. A pair of bases 64 and 65 shown in FIG. 7 are used when connecting four optical fibers 103, 103,... Arranged in parallel and covered to form a tape (ribbon). Note that when connecting, the coating is peeled off to expose the optical fiber 103. By sandwiching the four optical fibers 103, 103,... From above and below, it is possible to securely fix the four optical fibers 103, 103,. It can be connected easily with minimum.

  There are various methods for manufacturing the multi-core optical fiber of this embodiment. For example, as a fiber preform made of cylindrical quartz, a plurality of holes having a circular cross section are formed along the central axis of the cylinder. There is a method using a perforated pipe. For example, when creating an optical fiber 103 having a regular hexagonal cross section, a cylindrical core provided with a core portion having a high refractive index at the center of each hole of a perforated pipe having a regular hexagonal arrangement and a hole at the center position thereof. After inserting the base material, heating and stretching are performed to prepare a preform precursor, and the outer surface of this preform precursor is ground to prepare a hexagonal column preform. The preform is heated and drawn to produce an optical fiber. The cross section of the preform has the same shape and core arrangement as the optical fiber.

  A process for producing an optical fiber from a preform is schematically shown in FIG. A preform 200 is prepared in which a plurality of core precursor parts (parts having a relatively high refractive index) are surrounded by a clad precursor parts (parts having a relatively low refractive index). The outer shape of the clad precursor part is a regular hexagon, and the core precursor part is disposed in the regular hexagon in the cross section therein. The preform 200 is softened by heating in the electric furnace 300. When the end of the preform 200 is stretched in this state, the outer shape is stretched while maintaining a hexagonal shape, and the optical fiber 100 is obtained. The optical fiber 100 is drawn while the outer diameter is measured by the outer diameter measuring device 400. The feed speed of the preform 200 and the take-up speed of the optical fiber 100 are adjusted by the output of the outer diameter measuring device 400 so that the fiber diameter is constant. Then, a resin coating for protecting the outer surface is applied by the die 500, and the optical fiber 100 is wound on the winding bobbin 600.

  By adjusting the temperature in the electric furnace 300, the cross-sectional shape of the preform 200 (including the core arrangement) and the cross-sectional shape of the optical fiber 100 are similar. In this way, the optical fiber 100 of this embodiment is manufactured.

  In order to fabricate the preform 200 described above, a stack-and-draw method using a single-hole pipe in which a cylindrical core base material and a quartz rod are packed in a hexagonal quartz pipe with a cross-sectional outer shape is adopted. May be.

  Next, a modification of the number of cores and arrangement will be shown. FIG. 9 shows an optical fiber 104 in which the outer shape of the clad 24 is a regular hexagon, and 13 cores 10, 10,. The cores 10, 10,... Are the vertices of an equilateral triangle with each side of the regular hexagon formed by the cores 10, 10,... In addition to the seven cores 10, 10,. (It is not a central axis but an apex outside the regular hexagon). In this case, the same effect as described above can be obtained by using the table 62, the tables 64 and 65, the ferrule 70, and the like. Further, since the number of cores of the optical fiber 104 is slightly less than twice that of the optical fiber 103, more information can be transmitted / received through one fiber.

  FIG. 10 shows an optical fiber 105 in which the outer shape of the clad 25 is a regular hexagon, in which 19 cores 10, 10,. The cores 10, 10,... Are in addition to the 13 cores 10, 10,... Of the optical fiber 104 shown in FIG. 9, and the outer regular hexagons so that the cores 10, 10,. It is arranged at each vertex part. This optical fiber 105 also has the above effects.

  FIG. 11 shows an optical fiber 106 in which the outer shape of the clad 26 is a regular hexagon, and 37 cores 10, 10,. The cores 10, 10,... Are the outermost regular hexagons so that the cores 10, 10,... Are arranged in a triple regular hexagonal arrangement in addition to the 19 cores 10, 10,. Are arranged at points that divide each vertex part and each side into three equal parts. This optical fiber 106 also has the above effects.

  Next, modifications of the clad outer shape, the number of cores, and the arrangement will be shown. FIG. 12 shows an optical fiber 107 in which the outer shape of the cladding 27 is a regular hexagon, and ten cores 10, 10,. The cores 10, 10,... Are arranged on a line connecting the fiber center axis and each corner portion (each vertex) of the outer shape of the cladding 27, respectively. This optical fiber 107 also has the above effects.

(Embodiment 2)
The optical fiber of the second embodiment is a multi-core optical fiber having a polygonal shape in which the clad outer shape in the fiber cross section is a rouleau. The optical fiber 108 shown in FIG. 13 is a heptagon with a cross-sectional outer shape of the cladding 28, and the optical fiber 109 shown in FIG.

  The optical fiber 108 in FIG. 13 has seven cores 10, 10,..., One on the central axis, and six on each apex of a regular hexagon around the center axis. Of the cores 10, 10,..., Only one of the regular hexagonal vertices is on a line connecting the fiber center axis and the heptagonal corner of the outer shape of the cladding 28. For this reason, it turns out that the core is a specific core of seven, and other six cores are also specified in the positional relationship with the core. That is, it is possible to specify all the cores by using the core on the line connecting the central axis and the corner as a marker.

  The optical fiber 108 in FIG. 14 is the same as the optical fiber 107 except that the clad outer shape of the optical fiber 107 shown in FIG.

  Since the optical fibers 108 and 109 of the second embodiment are polygonal with a clau outer shape, when the fiber diameter is observed from a direction perpendicular to the fiber central axis, the optical fiber rotates around the fiber central axis. The same diameter is always observed. When the optical fiber according to the first embodiment is observed in the same manner, for example, when the clad outer shape is a regular hexagon, the maximum diameter and the minimum diameter are 2: 1.73. When the optical fiber is manufactured by the apparatus shown in FIG. 8, the optical fiber 100 is drawn while the outer diameter is measured by the outer diameter measuring device 400, and the outer diameter measuring device 400 has a constant fiber diameter. Since the feeding speed of the preform 200 and the take-up speed of the optical fiber 100 are adjusted by the output, if the optical fiber of the first embodiment rotates around the central axis, the thickness of the optical fiber becomes uneven. However, if the optical fiber of the second embodiment is rotated around the central axis, the fiber diameter does not change, so the thickness of the optical fiber is kept constant. The optical fiber according to the second embodiment has the same effect as the optical fiber according to the first embodiment.

(Other embodiments)
The above-described embodiment is an exemplification of the present invention, and the present invention is not limited to these examples, and these examples may be combined or partially replaced with known techniques, common techniques, and known techniques. Also, modified inventions easily conceived by those skilled in the art are included in the present invention.

  The material configuration of the cladding and the core is not limited to the configuration of the above-described embodiment, and may be any configuration as long as it functions as an optical fiber. In addition, the clad outer shape in the cross section is not limited to D shape, square, regular hexagon, regular hexagon, roule's heptagon / nagon, other polygons, roule's pentagon, circle notched with two or more strings The shape may be different. Any number of cores may be used. In the case where the clad outer shape in the cross section is a Louro pentagon, seven cores are preferable, and one core is preferably arranged at the center axis and one at each apex of the regular hexagon around the center axis. In this case, one core may be arranged on a line connecting the central axis and one of the corners of the clad.

  Another base having the same shape may be prepared with respect to the base 62 shown in FIG. 5, and the optical fiber 103 may be sandwiched and fixed from above and below.

  The shape of the hole in the ferrule is not limited to a hexagon, and may be a D shape, a square, a regular hexagon, or a Roule polygon.

  In order to prevent the corners of the clad of the optical fiber from being chipped, the corners can be rounded down.

  As for the arrangement of the cores, the other cores may not be arranged on the line connecting the central axis and the corners of the cladding outer shape. However, in an arrangement in which no other core is placed on the line connecting the central axis and the corner of the cladding outer shape, the cladding diameter is adjusted to sufficiently reduce the leakage of the electric field distribution of the light propagating through the core to the cladding. It is necessary to enlarge compared with the core arrangement of the form, and in that case, the fiber diameter becomes large. When the fiber diameter is increased, it is necessary to increase the amount of quartz serving as a material, and since the strain when the fiber is bent increases, it is easy to break.

  Rare earth elements may be added to the core.

  As described above, the optical fiber according to the present invention is useful for optical communication and the like.

10 core 21 clad 22 clad 23, 24, 25, 26 clad 27 clad 28 clad 29 clad 101 optical fiber 102 optical fiber 103, 104, 105, 106 optical fiber 107 optical fiber 108 optical fiber 109 optical fiber 200 preform

Claims (7)

A multi-core optical fiber comprising a plurality of cores and a clad surrounding the plurality of cores,
An optical fiber in which the outer shape of the clad is a Roule polygon in a cross section of the optical fiber.   2. The optical fiber according to claim 1, wherein the Rouleau polygon is a Roule heptagon and the number of the cores is 7. In the cross section of the optical fiber, one core is disposed at the center,
The optical fiber according to claim 2, wherein another core is disposed on a line connecting the central portion and one corner of the outer shape of the clad.   2. The optical fiber according to claim 1, wherein the polygon of the rouleau is a roule pentagon and the number of the cores is seven.   2. The optical fiber according to claim 1, wherein the rouleau polygon is a rouleaux hexagon and the number of cores is ten. In the cross section of the optical fiber, one core is disposed at the center,
The optical fiber according to claim 5, wherein another core is disposed on a line connecting the center portion and each corner portion of the outer shape of the clad. A method of manufacturing a multi-core optical fiber comprising a plurality of cores and a clad surrounding the plurality of cores,
Preparing a preform comprising a plurality of core precursor parts and a clad precursor part surrounding the periphery of the plurality of core precursor parts;
A drawing step of heating and preforming the preform to form an optical fiber,
The preform has a roule's heptagon or nine-sided shape in cross section in the cross section,
The method of manufacturing an optical fiber, wherein the optical fiber has a cross-sectional shape similar to the preform in the drawing step.

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