Bundle structure, and optical connection structure of bundle structure and multi-core fiber and method for optically connecting the same

Abstract

To provide a bundle structure and the like capable of suppressing a positional deviation of coated optical fibers when being fusion-spliced to a multi-core fiber.SOLUTION: A bundle structure 1 is constituted of two coated optical fibers 3, a capillary 9, and the like. The coated optical fibers 3 each are a single core optical fiber having a cladding 7 covering a core 5 and a core 5. Each of the coated optical fibers 3 has a non-circular outer shape in a cross section perpendicular to an axial direction, and has a straight line part 13 formed on a part of an outer peripheral part. Furthermore, in the respective coated optical fibers 3, the mutual straight line parts 13 are disposed so as to face each other. That is, in the cross section, the coated optical fibers 3 come into line contact with each other. Each of the coated optical fibers 3 is inserted into a hole 11 of the capillary 9.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a bundle structure consisting of a plurality of optical fiber cores, an optical connection structure between the bundle structure and a multi-core fiber, and an optical connection method. [Background technology]

[0002] Due to the recent rapid increase in traffic in optical communications, the transmission capacity of currently used single-core optical fibers is approaching its limit. Therefore, multi-core fibers, in which multiple cores are formed in a single fiber, have been proposed as a means of further expanding communication capacity.

[0003] When a multicore fiber is used as a transmission line, each core of the multicore fiber must be connected to a different optical fiber, optical element, etc. to send and receive transmission signals. In other words, fan-in and fan-out are required to connect the multicore fiber to multiple single-core fibers.

[0004] As a method for connecting such a multi-core fiber and a single-core fiber, a method has been proposed in which a plurality of single-core fibers are inserted into a capillary to form a predetermined arrangement, and the single-core fibers are fixed to the capillary to connect to the multi-core fiber (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-167299 Summary of the Invention [Problem to be solved by the invention]

[0006] 10(a) is a cross-sectional view showing a state in which a multi-core fiber 100 is inserted into a glass capillary 105. The multi-core fiber 100 has a plurality of cores 101 arranged inside a substantially circular cladding 103. For example, in the example shown in the figure, two cores 101 are arranged inside the cladding 103.

[0007] 10(b), a bundle structure 110 is used in which small-diameter optical fiber cores 107 are inserted into a glass capillary 113. Each optical fiber core 107 is a single-core optical fiber having a core 109 disposed in the center of a cladding 111. In the illustrated example, two optical fiber cores 107 are inserted into the capillary 113.

[0008] The outer diameter of the optical fiber 107 matches the pitch between the cores 101 of the multicore fiber 100. For example, if the pitch between the cores 101 of the multicore fiber 100 is 50 μm, the optical fiber 107 to be used also has an outer diameter of 50 μm.

[0009] In this state, the capillaries 105 and 113 are aligned in the XY direction and the rotational direction so that the positions of the cores 101 and 109 are aligned with each other, and then they are bonded together with an adhesive, thereby optically connecting the bundle structure consisting of the optical fiber cores 107 and the multi-core fiber 100.

[0010] On the other hand, in order to improve the reliability of the fan-in / fan-out and to strengthen its high-power durability, fusion splicing is preferable to adhesive splicing. However, in the conventional fan-in / fan-out structure, a small-diameter optical fiber 107 is inserted into the capillary 113, and therefore the gap inside the capillary 113 is large. Furthermore, when attempting to fusion splice such a bundle structure 110 and the multi-core fiber 100, the optical fiber 107 is softened by the heat generated during fusion, because the optical fiber 107 is in only point contact with each other, and the optical fiber 107 is deformed so as to fill the gap between the optical fiber 107 and the capillary 113, which may cause misalignment of the core 109.

[0011] The present invention has been made in view of such problems, and aims to provide a bundle structure or the like that can suppress misalignment of optical fiber cores when fusion splicing to a multi-core fiber. [Means for solving the problem]

[0012] In order to achieve the above-mentioned object, the first invention is a bundle structure consisting of a plurality of optical fiber cores, comprising an optical fiber core consisting of a core and a cladding covering the core, and a capillary into which the plurality of optical fiber cores are inserted, characterized in that the optical fiber cores have straight portions formed on part of their outer periphery in a cross section perpendicular to the axial direction, and the straight portions are arranged so as to face each other.

[0013] It is desirable that the softening temperature of the capillary be lower than the softening temperature of the optical fiber.

[0014] It is desirable that the distance between the core and the straight portion be 10 μm or more.

[0015] The straight portions may be formed in at least two directions.

[0016] In a cross section perpendicular to the axial direction of the capillary, it is desirable that the ratio of the cross-sectional area of ​​the gap portion of the hole into which the optical fiber is inserted to the total cross-sectional area of ​​the optical fiber be 0.15 or less.

[0017] The optical fiber may have an arcuate portion on its outer periphery excluding the straight portion, and the core may be arranged offset from the center of an imaginary circle formed by extending the arcuate portion.

[0018] The capillary may have seven optical fiber cores, and in a cross section perpendicular to the axial direction of the capillary, the optical fiber core arranged at the center may have six of the straight portions on its outer surface, and six optical fiber cores, each having three of the straight portions, may be arranged around the central optical fiber core, with the straight portions arranged opposite each other.

[0019] The capillary has eight optical fiber cores, and in a cross section perpendicular to the axial direction, four of the optical fiber cores arranged in a 2x2 pattern in the center have three straight sections on their outer surface, and each of the optical fiber cores is arranged so that its straight sections face each other, and on both sides of the optical fiber core in the center, the optical fiber cores on the end sides having two straight sections on their outer surface are arranged so as to sandwich the optical fiber core in the center, and the straight sections of each of the optical fiber cores on the end sides face the straight section of the optical fiber core in the center, and the straight sections of the optical fiber cores on adjacent end sides are arranged so as to face each other.

[0020] According to the first aspect of the present invention, a straight portion is formed on the outer peripheral surface of the cross section of the optical fiber, and multiple optical fibers are arranged so that the straight portions face each other. This makes it possible to suppress misalignment of the optical fibers during fusion splicing, compared to conventional cases where the optical fibers are in point contact with each other. Furthermore, since the void area other than the optical fibers in the capillary hole can be reduced, the heat capacity of the optical fibers can be relatively increased. This makes it possible to suppress softening of the optical fibers due to the discharge heat during fusion splicing, and suppress misalignment of the optical fibers.

[0021] In particular, by setting the softening temperature of the capillary lower than that of the optical fiber, the softening of the optical fiber can be suppressed and the capillary can be softened preferentially, so that the gap between the optical fiber and the capillary can be filled by the softening of the capillary, thereby suppressing misalignment of the optical fiber.

[0022] Furthermore, by making the distance between the core and the straight portion of the optical fiber equal to or greater than 10 μm, optical loss can be suppressed.

[0023] Furthermore, by forming the straight portions in at least two directions, the optical fibers can be arranged to face each other in at least two directions.

[0024] Furthermore, by setting the ratio of the cross-sectional area of ​​the void portion of the hole into which the optical fiber core is inserted to the total cross-sectional area of ​​the optical fiber core in a cross section perpendicular to the axial direction of the capillary to be 0.15 or less, misalignment of the optical fiber core can be efficiently suppressed.

[0025] Furthermore, if the optical fiber has an arcuate portion on the outer periphery excluding the straight portions, and the core arrangement is offset with respect to the center of the imaginary circle formed by extending the arcuate portion, when the straight portions are arranged opposite each other, the overall outer shape can be made to be close to a circle. Therefore, when inserted into the hole of the capillary, the void portion other than the optical fiber can be minimized. Therefore, the positional deviation of the optical fiber can be efficiently suppressed.

[0026] In such a bundle structure, for example, one optical fiber core placed in the center has six straight sections on its outer surface, and six optical fiber cores each having three straight sections are placed around the central optical fiber core, making it possible to optically connect to a seven-core multi-core fiber in which the spacing between adjacent cores is constant.

[0027] Furthermore, for example, four optical fiber cores arranged in two rows and two columns in the center have three straight sections on the outer surface, and two optical fiber cores are arranged vertically and horizontally so that two straight sections face each other, and further, optical fiber cores having two straight sections are arranged so that two on each side sandwich the four optical fiber cores in the center, thereby enabling optical connection to a multi-core fiber with an eight-core lattice arrangement structure.

[0028] The second invention is a connection structure between the bundle structure and the multi-core fiber according to the first invention, characterized in that the core of the multi-core fiber and the core of the optical fiber core are aligned and fusion-spliced ​​to each other.

[0029] According to the second invention, it is possible to obtain an optical connection structure in which a plurality of optical fibers and a multi-core fiber are fusion-spliced ​​with high precision.

[0030] The third invention is an optical connection method for a bundle structure and a multi-core fiber according to the first invention, characterized in that it comprises a step of temporarily fusing the capillary and the optical fiber core, and a step of arranging the optical fiber core and the multi-core fiber opposite each other and aligning them, and then fusion splicing them.

[0031] According to the third aspect of the present invention, a plurality of optical fibers and a multi-core fiber can be fusion-spliced ​​with high accuracy. [Effects of the Invention]

[0032] According to the present invention, it is possible to provide a bundle structure or the like that can suppress misalignment of optical fiber cores when fusion splicing to a multi-core fiber. [Brief explanation of the drawings]

[0033] [Figure 1] 1(a) is a cross-sectional view showing the bundle structure 1, FIG. 1(b) is a diagram showing the cross-sectional area of ​​the optical fiber core 3, and FIG. 1(c) is a diagram showing the cross-sectional area of ​​the void portion in the hole 11 of the capillary 9. FIG. [Figure 2] 4(a) to 4(c) are diagrams showing a method of installing an optical fiber 3 in a bundle structure 1. FIG. [Figure 3] FIG. 2(a) is a cross-sectional view showing a multi-core fiber 20, and FIG. 2(b) is a cross-sectional view showing a bundle structure 1a. [Figure 4] 1(a) to 1(c) are diagrams showing a method of installing an optical fiber 3 in a bundle structure 1a. [Figure 5] 1(a) to 1(c) are diagrams showing a method of installing the optical fiber 3 in the bundle structure 1b, and FIG. 1(d) is a cross-sectional view of the bundle structure 1b. [Figure 6] 10(a) to 10(c) are diagrams showing a method of installing the optical fiber 3 in the bundle structure 1c, and FIG. 10(d) is a cross-sectional view of the bundle structure 1c. [Figure 7] 1(a) is a cross-sectional view of a bundle structure 1d, and FIG. 1(b) is a diagram showing an optical fiber core 3a before processing. [Figure 8]1(a) is a cross-sectional view of a bundle structure 1e, FIG. 1(b) is a diagram showing an optical fiber 3 before processing, and FIG. 1(c) is a diagram showing an optical fiber 3a before processing. [Figure 9] 1(a) is a cross-sectional view of the bundle structure 1f, and (b) and (c) are diagrams showing the optical fiber core 3 before processing. [Figure 10] 1A is a cross-sectional view of a multi-core fiber 100, and FIG. 1B is a cross-sectional view of a bundle structure 110. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0034] The bundle structure according to this embodiment will be described below. Fig. 1 is a diagram showing a bundle structure 1 made up of a plurality of optical fiber cores 3, and is a cross-sectional view perpendicular to the axial direction of a capillary 9. The bundle structure 1 will be described as being connected to the above-mentioned multi-core fiber 100 (Fig. 10(a)).

[0035] The bundle structure 1 is composed of two optical fiber cores 3, a capillary 9, and the like. The optical fiber core 3 is a single-core optical fiber having a core 5 and a cladding 7 covering the core 5. The outer shape of each optical fiber core 3 in a cross section perpendicular to the axial direction is not circular, and a straight portion 13 is formed in part of the outer periphery. Furthermore, each optical fiber core 3 is arranged so that the straight portions 13 face each other. In other words, the optical fiber cores 3 are in line contact with each other in the cross section.

[0036] Each optical fiber 3 is inserted into a hole 11 of the capillary 9. Both the optical fiber 3 and the capillary 9 are made of glass, but by changing the material, the softening temperature of the capillary 9 can be made lower than the softening temperature of the optical fiber 3. For example, borosilicate glass can be used for the capillary 9, and quartz glass can be used for the optical fiber 3.

[0037] Here, in a cross section perpendicular to the axial direction of the capillary 9, it is desirable that the ratio of the cross-sectional area of ​​the gap portion of the hole 11 into which the optical fiber 3 is inserted (B in FIG. 1(c)) to the total cross-sectional area of ​​the optical fiber 3 (A in FIG. 1(b)) be 0.15 or less. As shown in FIG. 10(b), in a conventional bundle structure, the optical fiber 107 are in point contact with each other in the cross section, the cross-sectional area of ​​the gap portion is large, and the total cross-sectional area of ​​the optical fiber 107 and the total cross-sectional area of ​​the gap portion are approximately 1:1. However, by forming and arranging straight portions 13 opposite each other as shown in FIG. 1(a), the total cross-sectional area of ​​the optical fiber 3 can be made seven times or more the total cross-sectional area of ​​the gap portion.

[0038] Next, we will explain the manufacturing method of the bundle structure 1. First, as shown in Fig. 2(a), a single-core optical fiber 3 with a circular outer shape is prepared. For example, to accommodate a multi-core fiber with a core pitch of 50 µm, an optical fiber 3 with a diameter of 125 µm can be used.

[0039] Next, as shown in Fig. 2(b), a straight portion 13 is formed on a part of the outer surface of the optical fiber 3. To form the straight portion 13 in this manner, for example, a part of the circular optical fiber may be cut with a laser, or a part of the side surface may be removed by polishing, etching, or the like. Note that instead of forming a circular optical fiber, the cladding 7 may be processed into a shape that has the straight portion 13 from the beginning and then drawn. In this way, the method for forming the straight portion 13 is not particularly limited.

[0040] 2(b), the distance (C in the figure) between the core 5 and the straight portion 13 is preferably 10 μm or more. If the core 5 and the outer peripheral surface of the cladding 7 are too close, there is a risk of loss due to light leakage.

[0041] 2(c), the pair of optical fiber cores 3 with the straight portions 13 formed thereon are arranged facing each other so that the straight portions 13 are in contact with each other, and are inserted into the capillary 9 to form the bundle structure 1. After the optical fiber cores 3 are inserted into the hole 11 of the capillary 9, the capillary 9 and the optical fiber cores 3 may be pre-fused (the optical fiber cores 3 and the capillary 9 are fixed with a lower amount of heat than that used in the main fusion).

[0042] Next, a method for optically connecting the bundle structure 1 and the multi-core fiber 100 will be described. As described above, for example, the bundle structure 1 that has been temporarily fused and the multi-core fiber 100 inserted into the capillary 105 (see FIG. 10(a)) are arranged facing each other, and the positions of the core 5 and the core 101 in the XY directions and the rotational direction are aligned. Thereafter, the multi-core fiber 100 and the bundle structure 1 are fusion-spliced ​​to obtain a connection structure between the bundle structure 1 and the multi-core fiber 100.

[0043] Here, when fusion splicing the multi-core fiber 100 and the bundle structure 1, it is desirable that the capillaries 9 and 105 have approximately the same outer diameter. By doing so, when heated from the outside with an arc, the internal multi-core fiber 100 and the bundle structure (coated optical fiber 3) can be heated approximately uniformly.

[0044] On the other hand, in the conventional bundle structure 110 (see FIG. 10(b)), the inner diameter of the hole (for example, 100 μm+α (for example, α=0.3 μm to 1.0 μm)) is small to insert the thin-diameter optical fiber 107 (for example, 50 μm×2). Therefore, if the outer diameter of the capillary 113 is made substantially the same as the outer diameter of the capillary 105 of the multi-core fiber 100, the wall thickness of the capillary 113 needs to be increased. As a result, during fusion splicing, the heat capacity of the capillary 113 is too large, so the optical fiber 107 softens before the entire capillary 113 softens, which may cause the optical fiber 107 to be displaced.

[0045] In contrast, in the bundle structure 1, for example, when optical fibers 3 having a diameter of 125 μm are processed, even if the core pitch is 50 μm, the inner diameter of the hole 11 can be 175 μm+α (for example, α=0.3 μm to 1.0 μm). Therefore, the wall thickness of the capillary 9 can be made relatively thin, and the heat capacity can be made smaller than conventional ones. As a result, the entire capillary 9 can be softened before the optical fibers 3 are softened, and at the beginning of discharge, the softened capillary 9 can fill the gaps around the optical fibers 3. Therefore, misalignment of the optical fibers 3 can be suppressed, and then the optical fibers 3 and the multi-core fiber 100 can be fusion-spliced. In order to obtain such effects, it is desirable that the outer diameter of the capillary 9 be, for example, 0.3 mm or less.

[0046] As described above, according to this embodiment, optical fiber cores 3 having straight portions 13 are arranged opposite each other to form a bundle structure 1, so that positional deviation between the optical fiber cores 3 can be suppressed compared to the conventional case where the optical fiber cores are in point contact with each other in the cross section.

[0047] In particular, since the total cross-sectional area of ​​the optical fiber 3 can be increased, the heat capacity of the optical fiber 3 relative to the capillary 9 increases, allowing the capillary 9 to be softened preferentially. For example, compared to the case where a small-diameter fiber with a diameter of 50 μm is used (FIG. 10(b)), if optical fiber cores with a diameter of 125 μm are processed and arranged opposite each other so that the core pitch is 50 μm, the total cross-sectional area of ​​the optical fiber cores can be more than five times larger, and the heat capacity can also be more than five times larger. Therefore, the start of softening of the optical fiber cores 3 at the beginning of discharge can be delayed, and positional displacement can be suppressed.

[0048] Furthermore, compared to the conventional case, the area of ​​the voids other than those of the optical fiber 3 inside the capillary 9 can be made smaller. For example, the cross-sectional area of ​​the voids can be made 0.15 or less relative to the total cross-sectional area of ​​the optical fiber 3. Therefore, by softening the capillary 9, the voids around the optical fiber 3 can be efficiently filled. Therefore, the positional deviation of the optical fiber 3 can be suppressed.

[0049] Furthermore, as mentioned above, by setting the softening temperature of the capillary 9 lower than that of the optical fiber 3, it is possible to more efficiently soften the capillary 9 preferentially in the initial stage to fill the voids, and then fusion-splicing the optical fiber 3 to the multi-core fiber 100.

[0050] In the above-described embodiment, the bundle structure 1 for connecting with two multi-core fibers 100 has been described, but the number of fibers in the bundle structure is not limited to this. For example, Fig. 3(a) is a cross-sectional view of a state in which four multi-core fibers 20 are inserted into a capillary 25. In the following description, the same reference numerals will be used to designate components that exhibit the same effects as the components shown in Figs. 1 and 2, and duplicated description will be omitted.

[0051] The multicore fiber 20 also has a structure in which the cores 21 are covered with the cladding 23, and the four cores 21 are arranged at equal intervals so as to be at the vertices of a square. That is, the intervals between adjacent cores 21 are the same, and the core pitch is, for example, 40 μm.

[0052] 3(b) is a diagram showing a bundle structure 1a for connection to such a multi-core fiber 20. In this embodiment, four optical fiber cores 3 are arranged with their straight portions 13 facing each other. In this case, while in the above-mentioned embodiment, there is only one straight portion 13 for one optical fiber core 3, in this embodiment, the straight portions 13 are formed in two directions. More specifically, the straight portions 13 are formed so as to be perpendicular to each other.

[0053] Figures 4(a) to 4(c) are diagrams showing the steps of manufacturing such a bundle structure 1a. First, as shown in Figure 4(a), a single-core optical fiber 3 having a core 5 at its center is prepared, and as shown in Figure 4(b), part of the outer periphery is removed to form straight sections 13 that are perpendicular to each other. The lengths of the straight sections 13 in each direction are the same.

[0054] In this way, four optical fibers 3 each having the straight portion 13 formed thereon are fabricated, and as shown in Fig. 4(c), they are arranged so that the straight portions 13 face each other, and are then inserted into the capillary 9, thereby forming the bundle structure 1a. In this case, the optical fibers 3 and the capillary 9 may also be temporarily fused together.

[0055] In this way, the straight sections 13 can be formed in two or more directions, not just one direction, and the number of optical fiber cores 3 and the positions at which the straight sections 13 are formed can be set appropriately depending on the number of cores in the multi-core fiber to be connected.

[0056] Furthermore, the optical fiber 3 used to form the straight portion 13 was a single-core optical fiber with the core 5 located at the center, but this is not limited to this. Fig. 5(a) is a diagram showing an optical fiber 3a. The single-core optical fiber 3a has a circular outer shape like the optical fiber 3, but the core 5 is located not in the center of the cladding 7 but at a position offset from the center.

[0057] As shown in Figure 5(b), for such an optical fiber 3a, the cladding 7 is removed on the opposite side to the eccentricity direction of the core 5. For example, by removing half of the outer diameter of the optical fiber 3a so that it passes through the center of the cladding 7, the length of the straight portion 13 can be made to approximately match the outer diameter of the optical fiber 3a. In this case, to make the distance between the core 5 and the straight portion 13 10 µm or more, the core 5 needs to be eccentric from the center of the optical fiber 3a by (10 µm + radius of the core 5) or more.

[0058] As shown in Fig. 5(c), the straight portions 13 of the optical fiber cores 3a obtained in this manner are arranged so as to face each other, and the cores 5 are inserted into a capillary 9 to obtain a bundle structure 1b as shown in Fig. 5(d). That is, the optical fiber cores 3a in the bundle structure 1b have arc portions on the outer periphery excluding the straight portions 13, and the arrangement of the cores 5 is shifted and eccentric with respect to the center of a virtual circle formed by extending the arc portions (i.e., the outer shape of the cladding 7 in Fig. 5(a)).

[0059] By using such optical fiber 3a, for example, when two optical fibers 3a are arranged facing each other, the combined outer shape can be made approximately circular. This makes it possible to minimize the gap in the circular hole 11 of the capillary 9. Here, when two optical fibers 3a are arranged facing each other and have a diameter of 100 μm, if the inner diameter of the capillary 9 is 100.2 μm or less, the optical fibers 3a cannot be inserted. If the inner diameter exceeds 101 μm, the position of the optical fiber becomes unstable within the capillary 9, and the connection loss with the opposing multi-core fiber tends to increase when splicing. For this reason, it is preferable that the inner diameter be approximately 100 + 0.3 to 1.0 μm. When the inner diameter of capillary 9 is D and an optical fiber core 3a with a diameter of 100 μm is inserted, the ratio X of the total cross-sectional area of ​​the optical fiber core 3a to the cross-sectional area of ​​the gap is: X=249.8 when D=100.2 μm; X=166.4 when D=100.3 μm; X=124.8 when D=100.4 μm; and X=99.8 when D=100.5 μm. 8, when D=100.6 μm, X=83.1, when D=100.7 μm, X=71.2, when D=100.8 μm, X=62.3, when D=100.9 μm, X=55.3, when D=101.0 μm, X=49.8, when D=101.1 μm, X=45.2, and when D=101.2 μm, X=41.4. In this way, by increasing the ratio of the total cross-sectional area of ​​the optical fiber cores 3 a to the cross-sectional area of ​​the gap portion, it is possible to suppress misalignment between the optical fiber cores 3 a.

[0060] It is also possible to obtain a four-core bundle structure using such an eccentric optical fiber 3a. In this case, as shown in Fig. 6(a), for the optical fiber 3a whose core 5 is eccentric, parts of the cladding 7 are removed in two mutually orthogonal directions as shown in Fig. 6(b). In this case, straight sections 13 are formed that are orthogonal to each other and have approximately the same length, so that the angles with respect to the eccentric direction of the core 5 (the lower right direction in the figure) are ±45° when viewed from the center of the optical fiber 3a.

[0061] As shown in Fig. 6(c), the straight portions 13 of the optical fibers 3a obtained in this manner are arranged facing each other, and as shown in Fig. 6(d), by inserting them into a capillary 9, a bundle structure 1c can be formed in which the cores 5 are arranged at equal intervals. Even in this case, when four optical fibers 3a are arranged facing each other, the outer shape can be made approximately circular. This makes it possible to minimize the void portion in the hole 11 of the capillary 9. This makes it possible to suppress misalignment between the optical fibers 3a.

[0062] Furthermore, it can also accommodate multi-core fibers with even more cores. FIG. 7(a) is a diagram showing a bundle structure 1d, and FIG. 7(b) is a diagram showing the outer shape of the optical fiber 3a before processing. As described above, the arrangement of the cores 5 is shifted from the center of the optical fiber 3a. Straight sections 13 (straight sections 13 passing through the center of the original optical fiber 3a) are formed in two directions at a predetermined angle so as to sandwich the cores 5 of the optical fiber 3a. For example, by setting the interior angle between the straight sections 13 to 45°, it is possible to obtain an eight-core bundle structure 1d in which the cores 5 are arranged at equal intervals in the circumferential direction. In this way, the number of optical fibers 3a can be set according to the number of cores in the multi-core fiber to be spliced.

[0063] Also, a multi-core bundle structure may be formed by mixing the optical fibers 3 and 3a. Fig. 8(a) is a diagram showing bundle structure 1e, Fig. 8(b) is a diagram showing the outer shape of the optical fiber 3 before processing, and Fig. 8(c) is a diagram showing the outer shape of the optical fiber 3a before processing. Bundle structure 1e consists of one optical fiber 3 and six optical fiber 3a, for a total of seven optical fibers 3 and 3a.

[0064] In a cross section perpendicular to the axial direction of the capillary 9, an optical fiber 3 is arranged at the center of the bundle structure 1e. The optical fiber 3 arranged at the center is formed in a substantially regular hexagon with six straight portions 13 on its outer circumferential surface. Six optical fibers 3a are arranged around the central optical fiber 3. Each of the optical fibers 3a has three straight portions 13 in a portion other than the arc portions. More specifically, straight portions 13 are formed in three directions on both sides of the central straight portion 13 so as to form an interior angle of 120°. The six straight portions 13 of the central optical fiber 3 and the three straight portions 13 of the surrounding optical fibers 3a are all the same length.

[0065] In this way, the central straight portions 13 of the surrounding optical fiber cores 3a are arranged so that they face each straight portion 13 of the central optical fiber core 3, and the straight portions 13 of adjacent optical fiber cores 3a face each other. In this way, the cores 5 can be arranged so that the distances between adjacent cores 5 are all the same, and optical connection can be made to the corresponding 7-core multi-core fiber.

[0066] Furthermore, the hole 11 of the capillary does not have to be circular. Fig. 9(a) is a diagram showing a bundle structure 1f, and Figs. 9(b) and 9(c) are diagrams showing the outer shape of the optical fiber 3 before processing. The bundle structure 1f consists of eight optical fiber 3. Furthermore, in this embodiment, the hole 11 of the capillary 9 is approximately rectangular, and the optical fiber 3 is inserted through the hole 11.

[0067] In a cross section perpendicular to the axial direction of the capillary 9, the optical fibers 3 are arranged in 2 rows and 4 columns (sometimes in the vertical and horizontal directions). That is, two rows of optical fibers 3 are arranged on each side of the central 2 rows and 2 columns of four optical fibers 3, sandwiching the central optical fibers 3.

[0068] As shown in Fig. 9(b), the four optical fiber cores 3 arranged in the center of the bundle structure 1f have three straight portions 13 on their outer circumferential surface so that adjacent straight portions 13 are perpendicular to each other. More specifically, a short straight portion 13 is formed on the opposite side of the arc portion across the core 5, and long straight portions 13 are formed on both sides of this straight portion 13. The four optical fiber cores 3 in the center are arranged in two rows and two columns (vertically and horizontally) so that two straight portions 13 face each other (short straight portions 13 face each other in the vertical direction, and long straight portions 13 face each other in the horizontal direction).

[0069] The optical fiber 3 at the center of the bundle structure 1f is sandwiched horizontally from both sides by the optical fiber 3 at the end portions of the two vertical rows of optical fiber 3 at the center. As shown in Fig. 9(c), the optical fiber 3 at the end portions has two straight portions 13 of the same length that are perpendicular to each other on the outer surface. One straight portion 13 of each optical fiber 3 at the end portions faces the longer straight portion 13 of the optical fiber 3 at the center, and the straight portions 13 of the optical fiber 3 adjacent vertically at the end portions face each other.

[0070] The distance between the cores 5 of the vertically and horizontally adjacent coated optical fibers 3 is the same. In this way, optical connection can be made to a multi-core fiber having a lattice-like core arrangement of 2 rows x 4 columns.

[0071] In this way, by forming straight sections 13 at desired positions of the optical fiber cores 3, 3a according to the arrangement of the cores 5 and arranging the straight sections 13 opposite each other, it is possible to obtain a bundle structure in which the total cross-sectional area of ​​the optical fiber cores is increased compared to the conventional method and the voids in the holes 11 of the capillaries 9 are reduced.

[0072] Although the embodiments of the present invention have been described above with reference to the accompanying drawings, the technical scope of the present invention is not limited to the above-described embodiments. It is clear that those skilled in the art can conceive of various modifications and alterations within the scope of the technical ideas described in the claims, and it is understood that these modifications and alterations also fall within the technical scope of the present invention. [Explanation of symbols]

[0073] 1, 1a, 1b, 1c, 1d, 1e, 1f...Bundle structure 3, 3a....Optical fiber core 5...Core 7. Clad 9...Capillary 11……hole 13...Straight section 20...Multicore fiber 21...Core 23...Clad 25...Capillary 100...Multicore fiber 101...Core 103...Clad 105...Capillary 107....Optical fiber core 109...Core 110...Bundle structure 111...Clad 113...Capillary

Claims

1. A bundle structure consisting of a plurality of optical fiber cores, an optical fiber comprising a core and a cladding covering the core; a capillary into which a plurality of the optical fiber cores are inserted; Equipped with A bundle structure characterized in that the optical fiber core wires have straight portions formed on part of their outer peripheries in a cross section perpendicular to the axial direction, and the straight portions are arranged so as to face each other.

2. 2. The bundle structure according to claim 1, wherein the softening temperature of said capillary is lower than the softening temperature of said optical fiber.

3. 2. The bundle structure according to claim 1, wherein the distance between the core and the straight portion is 10 μm or more.

4. 2. The bundle structure according to claim 1, wherein the straight portions are formed in at least two directions.

5. The bundle structure according to claim 1, characterized in that in a cross section perpendicular to the axial direction of the capillary, the ratio of the cross-sectional area of ​​the void portion of the hole into which the optical fiber core is inserted to the total cross-sectional area of ​​the optical fiber core is 0.15 or less.

6. 2. The bundle structure according to claim 1, wherein the optical fiber core has an arc portion on the outer periphery excluding the straight portion, and the cores are arranged offset from the center of a virtual circle formed by extending the arc portion.

7. Seven of the optical fiber core wires are included, The bundle structure described in claim 1, characterized in that in a cross section perpendicular to the axial direction of the capillary, the optical fiber core wire arranged at the center has six of the straight portions on its outer surface, and six of the optical fiber core wires, each having three of the straight portions, are arranged around the central optical fiber core wire, and each of the straight portions is arranged opposite each other.

8. The optical fiber cable includes eight of the optical fibers, In a cross section perpendicular to the axial direction of the capillary, the four optical fiber cores arranged in a 2x2 pattern in the center have three of the straight portions on the outer circumferential surface, and the optical fiber cores are arranged so that the straight portions face each other, The bundle structure described in claim 1, characterized in that the optical fiber core wires at the end sides, each having two of the straight portions on its outer surface, are arranged on both sides of the optical fiber core wire at the center so as to sandwich the optical fiber core wire at the center, and the straight portions of each of the optical fiber core wires at the end sides are opposite to the straight portion of the optical fiber core wire at the center, and the straight portions of each of the optical fiber core wires at adjacent end sides are arranged opposite to each other.

9. A connection structure between the bundle structure and a multi-core fiber according to any one of claims 1 to 8, An optical connection structure characterized in that the cores of the multicore fiber and the cores of the optical fiber coated wire are aligned and fusion-spliced ​​to each other.

10. A method for optically connecting the bundle structure according to any one of claims 1 to 8 to a multi-core fiber, comprising: a step of temporarily fusing the capillary and the optical fiber; a step of arranging the optical fiber core and the multi-core fiber opposite to each other, aligning them, and then fusion splicing them; An optical connection method comprising:

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