Multicore fiber and method of manufacturing multicore fiber

Abstract

To provide a multi-core fiber that can be reduced in weight and can prevent positional deviation between cores, and a method for manufacturing the multi-core fiber.SOLUTION: A multi-core fiber 1 comprises: a plurality of cores 11; and clads 20 that surround the respective cores 11. The clads 20 have junctions 21 in which parts of outer peripheral surfaces of clad parts 12, in single-core fibers 10 in each of which the core 11 is arranged on the center and the clad part 12 surrounds the core 11, are brought into contact with each other over a width W smaller than the diameter of the clad part 12. The outer peripheral surface of the clad 20 includes the other part of the outer peripheral surface of the clad part 12.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a multi-core fiber and a method for manufacturing the multi-core fiber.

Background Art

[0002] In recent years, the traffic in communication networks has been increasing rapidly. Therefore, in order to meet this demand, a multi-core fiber in which a plurality of cores are arranged in one cladding may be used. In such a multi-core fiber, generally, the shape of the outer peripheral surface in the cross section of the cladding surrounding the plurality of cores is circular.

[0003] As another multi-core fiber, for example, the multi-core fiber described in Non-Patent Document 1 below is known. The multi-core fiber described in this Non-Patent Document 1 has a configuration in which a plurality of single-core fibers each including one core and a cladding surrounding the core are bundled and the bundle is collectively coated with resin. Such a multi-core fiber may be called a multi-element fiber.

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Since the multi-element fiber described in Non-Patent Document 1 above has a structure in which single-core fibers are bundled, the cross-sectional area obtained by combining the claddings of the respective single-core fibers can be smaller than the cross-sectional area of the cladding of a conventional multi-core fiber in which the cross-section of the cladding is circular. Therefore, it is considered that the multi-element fiber can be made lighter than a conventional multi-core fiber in which the outer peripheral surface of the cladding has a circular shape.

[0006] However, in the multi-element fiber described in Non-Patent Document 1 above, the single-core fibers are merely held via resin. Therefore, when an external force acts on the multi-element fiber, for example, when it is cut, the positions of the single-core fibers may shift due to this external force, and there is a risk of misalignment between the cores.

[0007] The present invention has been made in view of the above circumstances, and an object thereof is to provide a multi-core fiber that can be made lighter and suppress misalignment between cores, and a method for manufacturing the multi-core fiber.

Means for Solving the Problems

[0008] To achieve the above object, the multi-core fiber of the present invention includes a plurality of cores and a cladding that surrounds each of the plurality of cores. The cladding has a joint portion in which a part of the outer peripheral surfaces of at least two of the cladding portions in a plurality of single-core fibers, each having a core disposed at the center and a cladding portion surrounding the core, are integrated over a width smaller than the diameter of the cladding portion, and the outer peripheral surface of the cladding includes the other part of the outer peripheral surfaces of the at least two cladding portions.

[0009] According to the above configuration, since a part of the cladding portions of the single-core fibers are integrated, for example, when an external force acts on the multi-core fiber during cutting or the like, the displacement of the positions of the single-core fibers is suppressed. Therefore, the displacement between the cores can be suppressed.

[0010] Further, the width of the joint portion in the cladding of this multi-core fiber is smaller than the diameter of the cladding portion of the single-core fiber. By the way, since the core is arranged at the center of the cladding portion, a part of the outer peripheral surface of the cladding portion other than the joint portion tends to have a substantially constant distance from the center of the core. For this reason, the other parts of the outer peripheral surfaces of the pair of single-core fibers that are integrated at the joint portion are separated from each other. Therefore, there is a constriction in the cladding of this multi-core fiber in the vicinity of the joint portion. Since the cladding of this multi-core fiber has such a constriction, the cross-sectional area can be smaller than, for example, a circular cladding that includes the cladding portions of the single-core fibers inside, and the amount of glass in the cladding can be reduced. For this reason, according to the multi-core fiber of the present invention, weight reduction can be achieved.

[0011] Further, it is preferable that the outer peripheral surface of the cladding at at least one pre-joint portion of the multi-core fiber is recessed in an arc shape toward the center of the joint portion.

[0012] According to such a configuration, since the outer peripheral surface of the cladding at the joint portion is recessed in an arc shape, when an inner coating layer is provided on the outer periphery of the cladding, the starting point of peeling between the cladding and the inner coating layer can be suppressed, and the peeling of the inner coating layer from the cladding can be suppressed. For this reason, the non-uniformity of stress caused by the peeling of the inner coating layer can be suppressed, microbending can be suppressed, and the transmission loss of light propagating through the core can be suppressed.

[0013] Further, the multi-core fiber may have three or more single-core fibers arranged in parallel with each other.

[0014] According to such a configuration, it can be used as a so-called ribbon fiber having three or more cores, and the weight can be reduced while suppressing the displacement between the cores.

[0015] Further, when the multi-core fiber has three or more single-core fibers, it is preferable that the clad has a polygonal void surrounded by the outer peripheral surfaces of the clad portions of the three or more single-core fibers.

[0016] The presence of such a void can make it difficult for the light leaking from the core to be transmitted to other cores, and crosstalk between the cores can be suppressed.

[0017] Further, when the void is present in the clad, it is preferable that each of the portions of the outer peripheral surface of each clad portion that forms the void is curved so as to surround the core closest to the portion.

[0018] Further, when the void is present, it is preferable that each of the widths of the portions of the outer peripheral surface of each clad portion that forms the void is equal to or greater than the diameter of the core closest to the portion.

[0019] In this case, compared with the case where the width of the portion of the outer peripheral surface of the clad portion that forms the void is less than the diameter of the core, the light leaking from the core can be less likely to be transmitted to other cores, and crosstalk between the cores can be suppressed.

[0020] Further, at least one of the single-core fibers has a trench layer that has a refractive index lower than that of the clad portion of the single-core fiber and surrounds the core of the single-core fiber, and it is preferable that the width of the joint portion in the single-core fiber is equal to or less than the diameter of the trench layer.

[0021] In this case, compared with the case where the width of the joint portion exceeds the diameter of the trench layer, the light leaking from the core can be less likely to be transmitted to the adjacent core, and crosstalk between the cores can be suppressed.

[0022] Further, the width of the joint portion may be equal to or less than the diameter of the core of the single-core fiber having the joint portion.

[0023] In this case, compared with the case where the width of the joint portion exceeds the diameter of the core, the light leaking from the core can be less likely to be transmitted to the cores of the single-core fibers joined to each other, and crosstalk between the cores can be suppressed.

[0024] Further, at least one of the cores may be elliptical.

[0025] By making the core elliptical in this way, it may become easier to maintain the polarization mode of the light propagating through the core.

[0026] Further, to achieve the above object, a method for manufacturing a multi-core fiber according to the present invention includes a bundling step of bundling single-core fiber rods including a core glass body disposed at the center and a clad glass body surrounding the core glass body, and a drawing step of drawing the bundled single-core fiber rods so that a part of the outer peripheral surfaces of the clad glass bodies in a molten state are in contact with each other over a width smaller than the diameter of the clad glass body.

[0027] According to this method for manufacturing a multi-core fiber, a part of the outer peripheral surfaces of the clad glass bodies in contact with each other in a molten state can become a joint portion where a part of the outer peripheral surfaces of the respective clad portions in the single-core fiber are integrated over a width smaller than the diameter of the clad portion. Also, another part of the outer peripheral surface of each clad glass body is a part of the outer peripheral surface of the clad portion in the single-core fiber where the distance from the center of the core has a certain tendency. Therefore, according to this method for manufacturing a multi-core fiber, any of the above multi-core fibers can be manufactured.

[0028] Further, in the method for manufacturing a multi-core fiber, in the bundling step, it is preferable to bundle a plurality of the single-core fiber rods so that adjacent single-core fiber rods are in contact with each other.

[0029] In this case, since the rods for single-core fibers are drawn while being in contact with each other, a part of the outer peripheral surfaces of the respective rods for single-core fibers can be more effectively integrated with each other.

[0030] Further, in the method for manufacturing the multi-core fiber, in the bundling step, it is preferable to weld the outer peripheral surfaces of the clad glass bodies of the adjacent rods for single-core fibers to each other.

[0031] In this case, displacement between adjacent rods for single-core fibers can be suppressed. In particular, when the welded portion includes an end portion at which drawing of the rod for single-core fiber is started, it is preferable because it serves as a trigger for bringing a part of the outer peripheral surfaces of the clad glass bodies into contact with each other in the drawing step.

Advantages of the Invention

[0032] As described above, according to the present invention, it is possible to provide a multi-core fiber that can be lightweight and suppress displacement between cores, and a method for manufacturing a multi-core fiber capable of manufacturing the multi-core fiber.

Brief Description of the Drawings

[0033]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Embodiments for Carrying Out the Invention

[0034] Hereinafter, embodiments for carrying out the multi-core fiber and the method for manufacturing the multi-core fiber according to the present invention are illustrated together with the accompanying drawings. The embodiments illustrated below are for facilitating the understanding of the present invention and are not for limiting the interpretation of the present invention. The present invention can be changed and improved from the following embodiments without departing from the gist thereof. Also, in this specification, for ease of understanding, the dimensions of each member may be exaggerated.

[0035] (First Embodiment) FIG. 1 is a diagram showing the structure of a cross section perpendicular to the longitudinal direction of a multi-core fiber according to the first embodiment. In FIG. 1, hatching is omitted in order to avoid complication of the figure. As shown in FIG. 1, the multi-core fiber 1 of the present embodiment mainly includes a plurality of single-core fibers 10, a single inner coating layer 30 that coats each of the single-core fibers 10, and an outer coating layer 40 that coats the inner coating layer 30. In FIG. 1, an example in which there are three single-core fibers 10 is shown.

[0036] The inner coating layer 30 and the outer coating layer 40 are formed of resin. Examples of such resin include thermosetting resin, ultraviolet curable resin, and the like. Further, when the inner coating layer 30 and the outer coating layer 40 are formed of thermosetting resin, the outer coating layer 40 may be formed of a different type of thermosetting resin from the inner coating layer 30. Also, when the inner coating layer 30 and the outer coating layer 40 are formed of ultraviolet curable resin, the outer coating layer 40 may be formed of a different type of ultraviolet curable resin from the inner coating layer 30.

[0037] Note that the inner coating layer 30 and the outer coating layer 40 are not essential as the configuration of the multi-core fiber 1. The multi-core fiber 1 having no inner coating layer 30 and outer coating layer 40 is also called a multi-core fiber bare wire.

[0038] Each single-core fiber 10 includes a circular core 11 disposed at the center, an inner cladding layer 13 surrounding the core 11, a trench layer 14 surrounding the inner cladding layer 13, and a cladding portion 12 surrounding the trench layer 14. This can be understood as the cores 11 of the respective single-core fibers 10 being separated from each other. Thus, in the present embodiment, the cladding portion 12 surrounds the core 11 via the inner cladding layer 13 and the trench layer 14, and has a circular outer shape. Therefore, the outer peripheral surface of the cladding portion 12 tends to have a substantially constant distance from the center of the core 11. The core 11, the inner cladding layer 13, and the trench layer 14 may be collectively referred to as a core element. Note that the trench layer 14 may directly surround the core 11 without providing the inner cladding layer 13.

[0039] The inner clad layer 13 and the clad portion 12 have a refractive index lower than that of the core 11, and the trench layer 14 has a refractive index lower than that of the inner clad layer 13 and the clad portion 12. By having such a trench layer 14 in the multi-core fiber 1, crosstalk between the cores 11 of the adjacent single-core fibers 10 can be suppressed as compared with the case where the trench layer 14 is not provided.

[0040] As shown in FIG. 1, a part of the outer peripheral surfaces of the respective clad portions 12 in a pair of adjacent single-core fibers 10 are integrated at the joint portion 21. Therefore, the multi-core fiber 1 of the present embodiment has three joint portions 21. Thus, in the multi-core fiber 1 of the present embodiment, one clad 20 composed of the clad portions 12 of the respective single-core fibers 10 is formed. Here, the clad 20 includes the clad portion 12 and the joint portion 21. For this reason, the clad 20 surrounds the respective cores 11 of the respective single-core fibers 10. Therefore, the inner coating layer 30 is a single coating layer that surrounds the outer peripheral surface of the clad 20.

[0041] FIG. 2 is an enlarged view showing the state of the joint portion 21. Note that, in FIG. 2, only one joint portion 21 is shown. The outer peripheral surface of the clad 20 at each joint portion 21 is recessed in an arc shape toward the center of the joint portion 21. That is, the bottom 21B of the valley, which is the outer surface of the joint portion 21, is recessed in a rounded arc shape. The width W of each joint portion 21 is smaller than the diameter of the clad portion 12. Note that the width W of each joint portion 21 is the length along the direction perpendicular to the line connecting the centers of the cores 11 of the pair of single-core fibers 10. In the present embodiment, the widths W of the respective joint portions 21 are generally the same size. However, at least one of these may have a different size. Also, the number of joint portions 21 in which the outer peripheral surface of the clad 20 is recessed in an arc shape is not particularly limited, and one or more are sufficient.

[0042] In addition, the diameter of the circumscribed circle Co of the clad 20 indicated by the dashed line in FIG. 1 is not particularly limited, and may be, for example, 125 μm.

[0043] In the present embodiment, the width W of each joint portion 21 is smaller than the diameter of the trench layer 14 of each single-core fiber 10, and further smaller than the diameter of the core 11 of each single-core fiber 10. By making the width W of the joint portion 21 smaller than the diameter of the trench layer 14 and the diameter of the core 11 in this way, light leaking from the core 11 is less likely to be transmitted to the adjacent core 11 through the joint portion 21, and crosstalk between the cores 11 can be more effectively suppressed. However, the width W of the joint portion 21 may be equal to or greater than the diameter of the core 11, or may be equal to or greater than the diameter of the trench layer 14.

[0044] As described above, a part of the clad portion 12 of each single-core fiber 10 is used as the joint portion 21. In the present embodiment, the other part of the outer peripheral surface of each clad portion 12 is divided by two joint portions 21 into a surface 12F1 located between the two joint portions 21 and a surface 12F2 other than the surface 12F1. The surfaces 12F1 and 12F2 generally maintain the shape of the outer peripheral surface of the single-core fiber 10 and are surfaces having a constant distance from the center of the core 11. Note that the constant distance from the core includes deviations due to manufacturing errors and the like. The surfaces 12F2 of a pair of adjacent single-core fibers 10 are separated from each other while drawing arcs from the joint portion 21. Therefore, a constriction is formed in the clad 20. Here, the joint portion 21 is provided over the entire longitudinal direction of the multi-core fiber 1.

[0045] In the center of the multi-core fiber 1 of the present embodiment, a polygonal void G surrounded by the surface 12F1 of the clad portion 12 of each single-core fiber 10 is formed. This void G is not filled with resin, glass, or the like. In the present embodiment, since there are three single-core fibers, the outer shape of the void G is an equilateral triangle.

[0046] In this embodiment, among the outer peripheral surfaces of the cladding portions 12 of the respective single-core fibers 10, the surface 12F1, which is the portion where the gap G is formed, is curved so as to surround the core 11 closest to the surface 12F1. According to such a configuration, it is considered that the light leaking from the core 11 is likely to be blocked by the gap G, and crosstalk between the cores can be suppressed.

[0047] Here, in FIG. 1, a line segment L connecting two joint portions 21 at the shortest distance is shown by a broken line. If the length of this line segment L is taken as the width of the surface 12F1, in this embodiment, the width of the surface 12F1 is larger than the diameter of the core 11 of the single-core fiber 10 closest to the surface 12F1 and the diameter of the trench layer 14. According to such a configuration, compared with the case where the width of the surface 12F1, which is the portion where the gap G is formed, is equal to or less than the diameter of the core 11, the light leaking from the core 11 is less likely to be transmitted to other cores 11, and crosstalk between the cores can be suppressed. However, the width of the surface 12F1 may be equal to or less than the diameter of the core 11, or may be equal to or less than the diameter of the trench layer 14.

[0048] As described above, the multi-core fiber 1 of this embodiment includes a plurality of cores 11 and a cladding 20 surrounding the plurality of cores 11 respectively. The cladding 20 has joint portions 21 in which a part of the outer peripheral surfaces of the respective cladding portions 12 in a plurality of single-core fibers 10, each having a core 11 disposed at the center and the cladding portion 12 surrounding the core 11, are integrated over a width smaller than the diameter of the cladding portion 12. The outer peripheral surface of the cladding 20 includes a surface 12F1 and a surface 12F2, which are other parts of the outer peripheral surfaces of the respective cladding portions 12.

[0049] According to such a configuration, since the cladding portions 12 of the single-core fibers 10 are integrated, when an external force acts on the multi-core fiber 1, for example, during cutting, the displacement of the positions of the single-core fibers relative to each other is suppressed. Therefore, the displacement between the cores can be suppressed.

[0050] In addition, the width of the joint 21 in the cladding 20 of this multi-core fiber 1 is smaller than the diameter of the cladding portion 12 of the single-core fiber 10. By the way, since the core 11 is arranged at the center of the cladding portion 12, a surface 12F2, which is a part of the outer peripheral surface of the cladding portion 12 excluding the joint 21, tends to have a constant distance from the center of the core 11. For this reason, as described above, the surfaces 12F2 of the pair of single-core fibers 10 that are integrated at the joint 21 are separated from each other while drawing arcs from the joint 21. Therefore, the cladding 20 of this multi-core fiber 1 has a constriction formed by a pair of surfaces 12F2 in the vicinity of the joint 21. Since the cladding 20 of this multi-core fiber 1 has such a constriction, the cross-sectional area can be smaller than that of a cladding having an outer circumferential surface shape in a cross section that is, for example, the circumscribed circle Co shown in FIG. 1 including the cladding portions 12 of the single-core fibers 10 on the inside as the outer circumferential surface, and the amount of glass in the cladding 20 can be reduced. Note that the glass forming the core 11 and the cladding 20 is generally covered with a coating, but the resin for the coating is generally lighter than glass. For this reason, according to the multi-core fiber 1 of the present embodiment, weight reduction can be achieved. Further, in the multi-core fiber 1 of the present embodiment, since the outer circumferential surface of the cladding 20 includes at least a part of the outer circumferential surfaces of the two or more cladding portions 12, compared with a case where the outer circumferential surface of the cladding 20 does not include at least a part of the outer circumferential surfaces of the two or more cladding portions 12, in the above-mentioned part, it is possible to make the thickness of the cladding 20 the minimum necessary thickness, and a multi-core fiber 1 that can more effectively contribute to weight reduction can be realized.

[0051] In addition, according to this multi-core fiber 1, since the cladding portions 12 are integrated, when the multi-core fiber 1 is cut, the splitting force easily propagates to the respective single-core fibers 10 through the joint 21 starting from the portion where the cutting blade is inserted, and the cut surface can be made closer to being flat.

[0052] In addition, in the multi-core fiber 1 of the present embodiment, the outer peripheral surface of the cladding 20 at the joint portion 21 is recessed in an arc shape toward the center of the joint portion 21. In this way, when the inner coating layer 30 is provided on the outer periphery of the cladding 20, the starting point of peeling between the cladding 20 and the inner coating layer 30 can be suppressed, and the peeling of the inner coating layer 30 from the cladding 20 can be suppressed. Therefore, the non-uniformity of stress caused by the peeling of the inner coating layer 30 can be suppressed, microbending can be suppressed, and the transmission loss of the light propagating through the core 11 can be suppressed.

[0053] Further, according to the multi-core fiber 1 of the present embodiment, the cladding 20 has a polygonal void G surrounded by the outer peripheral surfaces of the cladding portions 12 of the respective single-core fibers 10. According to such a configuration, the multi-core fiber can be made lighter than the case where there is no void G and the portion of the void G is filled with, for example, glass. Further, the existence of such a void G can suppress crosstalk between the cores.

[0054] In addition, the multi-core fiber 1 of the present embodiment has a configuration in which the centers of the cores 11 of the three single-core fibers 10 are arranged on the vertices of an equilateral triangle as described above. Therefore, when fusing and connecting the multi-core fibers 1 to each other, for example, by arranging the ends of a pair of multi-core fibers 1 to face each other in a V-shaped groove having two non-parallel surfaces, one surface in contact with both of a pair of single-core fibers 10 and the other surface in contact with both of the other pair of single-core fibers 10, the positions of the respective cores 11 of the multi-core fiber 1 on one side and the positions of the respective cores 11 of the multi-core fiber 1 on the other side can be made to generally coincide. Therefore, according to this multi-core fiber 1, when fusing and connecting the multi-core fibers 1 to each other, the process of aligning the multi-core fiber 1 on one side and the multi-core fiber 1 on the other side can be simplified.

[0055] Next, a method for manufacturing the multi-core fiber 1 will be described.

[0056] FIG. 3 is a diagram showing the steps of a method for manufacturing the multi-core fiber 1. As shown in FIG. 3, the method for manufacturing the multi-core fiber 1 includes a bundling step SP1, a pretreatment step SP2, and a wire drawing step SP3.

[0057] (Bundling Step SP1) FIG. 4 is a diagram showing the state of the first half of this step. In this step, first, as shown in FIG. 4, a plurality of single-core fiber rods 10R including a core glass body 11R that is arranged at the center and serves as a core and a cladding glass body 12R that surrounds the core glass body 11R and serves as a cladding portion are prepared. In the present embodiment, as shown in FIG. 1, since the number of cores 11 is three, three single-core fiber rods 10R are prepared. Further, in the present embodiment, each single-core fiber rod 10R has the same size and the same configuration as each other. In the present embodiment, since each single-core fiber 10 has an inner cladding layer 13 and a trench layer 14, each single-core fiber rod 10R has an inner cladding glass body 13R that surrounds the core glass body 11R and serves as the inner cladding layer 13, and a trench glass body 14R that surrounds the inner cladding glass body 13R and serves as the trench layer 14.

[0058] Next, as shown in FIG. 4, they are arranged at a position where a plurality of single-core fiber rods 10R are bundled. In the present embodiment, they are arranged such that the centers of the three single-core fiber rods 10R are located on the vertices of an equilateral triangle. Next, the arranged single-core fiber rods 10R are bundled with, for example, a binding band 51. In this way, the single-core fiber rods 10R are bundled with each other in a state where a plurality of single-core fiber rods 10R are bundled. In the present embodiment, the three single-core fiber rods 10R are bundled such that adjacent single-core fiber rods 10R are in contact with each other. Note that, different from the example in FIG. 4, in a state where the single-core fiber rods 10R are bundled with each other, the single-core fiber rods 10R do not necessarily have to be in contact with each other.

[0059] FIG. 5 is a diagram showing the state of the latter half of this process and the pretreatment process SP2. As shown in FIG. 5, dummy glass rods 52 are fixed to both ends of the bundled single-core fiber rods 10R to form a multi-core fiber base material 1P. By fixing such dummy glass rods 52, the state in which the single-core fiber rods 10R are bundled is maintained even when a fixing jig such as a binding band 51 is removed, and the displacement between the single-core fiber rods 10R is suppressed. It is preferable to fix the dummy glass rod 52 by welding. In the case of fixing by welding, it is possible to effectively suppress the adhesion of impurities to the single-core fiber rod 10R. Further, the dummy glass rod 52 may be fixed only to one end of the bundled single-core fiber rods 10R. Further, a plurality of single-core fiber rods 10R may be bundled without using the binding band 51. In this case, for example, each single-core fiber rod 10R is fixed to a dummy glass rod 52 one by one, and as a result, a plurality of single-core fiber rods 10R may be bundled by being fixed to the dummy glass rod 52.

[0060] (Pretreatment process SP2) Next, this step is performed. FIG. 6 is a side view of the base material for a multi-core fiber after this step. In this step, after removing the binding band 51, as shown in FIG. 5, while heating a part of the side surface of the bundled single-core fiber rods 10R, one dummy glass rod 52 is pulled toward the side opposite to the other dummy glass rod 52. As a result, as shown in FIG. 6, the part of the one dummy glass rod 52 and the single-core fiber rod 10R on the side of the dummy glass rod 52 are melted and removed, and the vicinity of the melted part in the base material 1P for a multi-core fiber becomes a tapered shape. FIG. 7 is a view of the base material 1P for a multi-core fiber shown in FIG. 6 as seen from the melted tip side. As shown in FIG. 7, by being melted as described above, on the tip portion 1PF of the base material 1P for a multi-core fiber, the outer peripheral surfaces of the respective clad glass bodies 12R of the adjacent single-core fiber rods 10R are welded to form three joint portions 21R. The base material 1P for a multi-core fiber is marked off from the tapered side. Therefore, in the present embodiment, the outer peripheral surfaces of the clad glass bodies 12R are welded including the end portion where the marking off of the single-core fiber rod 10R starts.

[0061] In the above description, an example in which the joint portion 21R is formed only at the tip portion 1PF of the base material 1P for a multi-core fiber has been described. However, by heating the entire length of the base material 1P for a multi-core fiber in the longitudinal direction, the joint portion 21R may be formed over the entire length of the base material 1P for a multi-core fiber in the longitudinal direction.

[0062] Also, in the present embodiment, an example in which one dummy glass rod 52 is removed as described above has been described. However, only the one dummy glass rod 52 may be heated to make it conical. In this way, a base material 1P for a multi-core fiber in which a conical dummy glass rod 52 is fixed on one side and a cylindrical dummy glass rod 52 is fixed on the other side may be formed.

[0063] (Marking-off Step SP3) Next, this step is performed. FIG. 8 is a diagram showing the state of this step. As shown in FIG. 8, first, as a preparation stage for performing this step, the multi-core fiber base material 1P after the pre-treatment step SP2 is installed in the spinning furnace 110 so that the tip 1PF of the multi-core fiber base material 1P faces downward in the vertical direction. Then, the heating part 111 of the spinning furnace 110 is heated, and the multi-core fiber base material 1P is inserted into the heating part 111 from the tip 1PF side to heat it. At this time, the part of the multi-core fiber base material 1P located in the heating part 111 is heated to, for example, 1900°C to 2300°C and becomes in a molten state. In this step, in this molten state, the multi-core fiber base material 1P is drawn so that a part of the outer peripheral surfaces of the clad glass bodies 12R are in contact with each other over a width smaller than the diameter of the clad glass body 12R. By being drawn at such a temperature, the adjacent clad glass bodies 12R are integrated with each other through the surface tension while melting at the parts other than the tip 1PF. Thus, three joint parts 21R are formed along the longitudinal direction of the multi-core fiber base material 1P.

[0064] The part of the multi-core fiber base material 1P that exits the spinning furnace 110 solidifies immediately. Thus, in each single-core fiber rod 10R, the core glass body 11R becomes the above-mentioned core element, and the clad glass body 12R becomes the clad part 12. As a result, each single-core fiber rod 10R becomes three single-core fibers 10 having an outer peripheral surface with a tendency that the distance from the center of the core 11 is constant. Also, the joint part 21R in the molten state solidifies immediately and becomes three joint parts 21. Thus, the multi-core fiber bare wire shown in FIG. 1 is formed. Then, as shown in FIG. 8, this multi-core fiber bare wire 1N passes through the cooling device 120 and is cooled to an appropriate temperature. For example, it is cooled to 40°C to 50°C.

[0065] Next, the multi-core fiber bare wire 1N passes through a first coating device 131 containing a first thermosetting resin that becomes the inner coating layer 30, and the cladding 20 is coated with the first thermosetting resin. The multi-core fiber bare wire 1N coated with the first thermosetting resin passes through a first heating furnace 132 and is heated inside the first heating furnace 132. By this heating, the material forming the first thermosetting resin crosslinks and the first thermosetting resin hardens, forming the inner coating layer 30.

[0066] In addition, when the inner coating layer 30 is formed from an ultraviolet curable resin, after the cladding 20 is coated by a first coating device 131 containing the first ultraviolet curable resin, the resin is cured.

[0067] Next, the multi-core fiber bare wire 1N covered with the inner coating layer 30 passes through a second coating device 133 containing a second thermosetting resin that becomes the outer coating layer 40, and the inner coating layer 30 is coated with the second thermosetting resin. The multi-core fiber bare wire 1N coated with the second thermosetting resin passes through a second heating furnace 134 and is heated inside the second heating furnace 134. By this heating, the material forming the second thermosetting resin crosslinks and the second thermosetting resin hardens, forming the outer coating layer 40.

[0068] In addition, when the inner coating layer 30 is formed from an ultraviolet curable resin, after the cladding 20 is coated by a second coating device 133 containing the second ultraviolet curable resin, the resin is cured.

[0069] In this way, the multi-core fiber 1 shown in FIG. 1 is formed.

[0070] Thereafter, the direction of the multi-core fiber 1 is changed by a turn pulley 141 and it is wound by a reel 142.

[0071] According to the manufacturing method of the multi-core fiber 1 of this embodiment, a part of the outer peripheral surfaces of the clad glass bodies 12R in contact in a molten state can become a joint part where a part of the outer peripheral surfaces of the respective clad parts 12 in the respective single-core fibers 10 are integrated over a width smaller than the diameter of the clad part 12. Also, another part of the outer peripheral surface of each clad glass body 12R is a part where the distance from the center of the core 11 tends to be constant among the outer peripheral surfaces of the respective clad parts 12 in the single-core fiber 10. Therefore, according to this manufacturing method of the multi-core fiber, the above multi-core fiber 1 can be manufactured.

[0072] Also, according to this manufacturing method of the multi-core fiber, since the multi-core fiber can be manufactured only by wire-drawing the bundled plurality of single-core fiber rods 10R, a process of making holes in the glass member serving as the clad and inserting the glass member serving as the core into the holes can be omitted. Therefore, reduction in the number of processes and reduction in manufacturing cost can be achieved.

[0073] Also, in this manufacturing method of the multi-core fiber, since the single-core fiber rods are assembled so that the adjacent single-core fiber rods are in contact with each other during the bundling process SP1, the clad glass bodies are more likely to be welded compared to the case where the single-core fiber rods are close but not in contact. Therefore, the joint part can be formed more effectively.

[0074] Also, in this embodiment, in the bundling process SP1, the outer peripheral surfaces of the clad glass bodies 12R of the adjacent single-core fiber rods 10R are welded to each other. For this reason, displacement between the adjacent single-core fiber rods 10R can be suppressed. In particular, in this embodiment, since the outer peripheral surfaces of the clad glass bodies 12R are welded on the side where wire-drawing of the single-core fiber rod 10R starts, it can be used as a trigger for bringing a part of the outer peripheral surfaces of the clad glass bodies 12R into contact with each other in the wire-drawing process SP3.

[0075] (Second Embodiment) Next, the second embodiment will be described. For components that are the same as or equivalent to those in the first embodiment, the same reference numerals will be given and redundant descriptions will be omitted, unless otherwise specifically described.

[0076] FIG. 9 is a diagram showing the multi-core fiber 1 of this embodiment from the same perspective as FIG. 1. As shown in FIG. 9, the multi-core fiber 1 of this embodiment is mainly different from the multi-core fiber 1 of the first embodiment in that it has four single-core fibers 10. In this embodiment, the four single-core fibers 10 are arranged such that the centers of their respective cores 11 are located on the vertices of a square.

[0077] The multi-core fiber 1 of this embodiment has four joints 21. At each joint 21, a part of the outer peripheral surfaces of the clad portions 12 of a pair of adjacent single-core fibers 10 are integrated over a width smaller than the diameter of the clad portion 12. Therefore, the cladding 20 of the multi-core fiber 1 of this embodiment is composed of the clad portions 12 of the respective single-core fibers 10. The outer peripheral surface of the cladding 20 is a surface where the distance from the center of the core 11 is constant for the other part of the outer peripheral surface of each clad portion 12 except for the joint 21.

[0078] Also in this embodiment, the other parts of a pair of adjacent single-core fibers 10 are separated from each other while drawing an arc from the joint 21, and a constriction is formed in the cladding 20. Further, in the cladding 20, there is a polygonal void G surrounded by the outer peripheral surfaces of the four single-core fibers 10, and in this embodiment, there is a square void G.

[0079] According to such a configuration, similar to the first embodiment, since the clad portions 12 of the single-core fibers 10 are integrated with each other, displacement between the cores 11 can be suppressed. Further, since the clad 20 of this multi-core fiber 1 has a constriction similar to that of the first embodiment, the amount of glass used as the clad can be reduced, and weight reduction can be achieved. Further, since the void G as described above exists, further weight reduction can be achieved.

[0080] (Third Embodiment) Next, the third embodiment will be described. For components that are the same as or equivalent to those of the first embodiment, the same reference numerals will be given and redundant descriptions will be omitted, unless otherwise specifically described.

[0081] FIG. 10 is a diagram showing the multi-core fiber 1 of the present embodiment from the same perspective as FIG. 1. As shown in FIG. 10, the multi-core fiber 1 of the present embodiment is mainly different from the multi-core fiber 1 of the first embodiment in that it has six single-core fibers 10. In the present embodiment, the six single-core fibers 10 are arranged such that the centers of their respective cores 11 are located on the vertices of a regular hexagon. Further, in the multi-core fiber 1 of the present embodiment, one dummy fiber 90 is arranged in the space surrounded by the six single-core fibers 10. This dummy fiber 90 does not have a core or a trench layer and is made of the same material as the clad portion 12. Further, this dummy fiber 90 may have a portion with a lower refractive index than the clad portion 12. In this case, crosstalk to the cores existing diagonally to the dummy fiber 90 can be suppressed. In that the multi-core fiber 1 of the present embodiment has such a dummy fiber 90, it is different from the multi-core fiber 1 of the first embodiment that does not have a dummy fiber.

[0082] The multi-core fiber 1 of the present embodiment has six joints 21 and six joints 22. In each joint 21, a part of the outer peripheral surfaces of the clad portions 12 of a pair of adjacent single-core fibers 10 are integrated over a width smaller than the diameter of the clad portion 12. Further, in each joint 22, a part of the outer peripheral surface of each single-core fiber 10 and a part of the outer peripheral surface of the dummy fiber 90 are integrated over a width smaller than the diameter of the clad portion 12 and the diameter of the dummy fiber. Therefore, the clad 20 of the multi-core fiber 1 of the present embodiment is composed of the clad portions 12 of the respective single-core fibers 10 and the dummy fiber 90.

[0083] The outer peripheral surface of the clad 20 of the multi-core fiber 1 includes a part other than the joints 21 and 22 on the outer peripheral surface of each clad portion 12, and this other part is a surface having a constant distance from the core 11. Also in the present embodiment, the respective other parts of a pair of adjacent single-core fibers 10 are separated from each other while drawing an arc from the joint 21, and a constriction is formed in the clad 20. Further, six voids G exist in the clad 20 of the present embodiment. Each void G is surrounded by the outer peripheral surfaces of a pair of adjacent single-core fibers 10 and the outer peripheral surface of the dummy fiber 90.

[0084] The multi-core fiber 1 of the present embodiment having such a dummy fiber 90 is produced by arranging six single-core fiber rods 10R in a regular hexagonal shape around a dummy fiber rod that becomes the dummy fiber 90 in the bundling step SP1 and bundling them in the same manner as in the first embodiment. Then, each bundled single-core fiber rod can be produced by drawing it together with the dummy fiber rod in the same manner as in the wire-drawing step SP3.

[0085] According to the configuration of the multi-core fiber 1 of the present embodiment, similar to the first embodiment, since the clad portions 12 of the single-core fibers 10 are integrated, displacement between the cores 11 can be suppressed. Further, since the clad 20 of this multi-core fiber 1 has a constriction similar to that of the first embodiment, the amount of glass used as the clad can be reduced, and weight reduction can be achieved. Further, since the void G as described above exists, further weight reduction can be achieved.

[0086] Further, in the multi-core fiber 1 of the present embodiment, a dummy fiber 90 is disposed in the space surrounded by the six single-core fibers 10, and since there is a joint portion 22 with this dummy fiber 90, the number of joint portions is larger than when the dummy fiber 90 does not exist. Therefore, when the multi-core fiber 1 is cut, the splitting force is likely to propagate to the multi-core fiber 1 starting from the portion where the cutting blade is inserted, and the cut surface can be made flatter. Further, this multi-core fiber 1 is stronger than the case where there is no dummy fiber and can suppress breakage.

[0087] (Fourth Embodiment) Next, the fourth embodiment will be described. For components that are the same as or equivalent to those of the first embodiment, the same reference numerals will be given and redundant descriptions will be omitted, unless otherwise specifically described.

[0088] FIG. 11 is a view showing the multi-core fiber 1 of the present embodiment from the same perspective as FIG. 1. The multi-core fiber 1 of the present embodiment has one dummy fiber 91 and three dummy fibers 92. The dummy fibers 91 and 92 do not have a core or a trench layer, are made of the same material as the clad portion 12, and have a diameter smaller than the diameter of each single-core fiber 10.

[0089] The dummy fiber 91 is disposed within the space surrounded by the three single-core fibers 10. A part of the outer peripheral surface of the dummy fiber 91 is integrally formed with a part of the outer peripheral surface of the cladding portion 12 of each single-core fiber 10 over a width smaller than the diameter of the cladding portion 12 and the diameter of the dummy fiber 91 at each joint portion 22. Thus, three gaps G1 surrounded by a part of the outer peripheral surface of the cladding portion 12 of each single-core fiber 10 and a part of the outer peripheral surface of the dummy fiber 91 are formed in the cladding 20 of the multi-core fiber 1. The gaps G1 are not filled with resin, glass, or the like.

[0090] Each dummy fiber 92 is disposed within the space surrounded by the outer peripheral surface of each single-core fiber 10 and the circumscribed triangle LA shown by the broken line that contacts the outer peripheral surface of each of the three single-core fibers 10. A part of the outer peripheral surface of the dummy fiber 92 is integrally formed with a part of the outer peripheral surface of the cladding portion 12 of a pair of adjacent single-core fibers 10 over a width smaller than the diameter of the cladding portion 12 and the diameter of the dummy fiber 92 at each joint portion 23. Thus, three gaps G2 surrounded by a part of the outer peripheral surface of each of a pair of adjacent single-core fibers 10 and a part of the outer peripheral surface of the dummy fiber 92 are formed in the cladding 20 of the multi-core fiber 1. The gaps G2 are not filled with resin, glass, or the like.

[0091] The cladding 20 of the multi-core fiber 1 of the present embodiment is composed of the cladding portions 12 of the respective single-core fibers 10 and the dummy fibers 91 and 92. The outer peripheral surface of this cladding 20 includes a part other than the joint portions 21, 22, and 23 on the outer peripheral surface of each cladding portion 12. This other part is a surface having a constant distance from the core 11. Also, the respective other parts of a pair of adjacent single-core fibers 10 are separated from each other while drawing an arc from the joint portion 23. Therefore, a constriction is formed in the cladding 20.

[0092] The multi-core fiber 1 of the present embodiment having such dummy fibers 91 and 92 can be manufactured by arranging dummy fiber rods that become the dummy fibers 91 and 92 between the single-core fiber rods 10R bundled in an equilateral triangle in the bundling step SP1, binding each single-core fiber rod and each dummy fiber rod, and drawing each single-core fiber rod together with each dummy fiber rod as in the wire drawing step SP3.

[0093] According to such a configuration, as in the first embodiment, since the clad portions 12 of the single-core fibers are integrated, displacement between the cores 11 can be suppressed. Further, since the clad 20 of this multi-core fiber 1 has a constriction similar to that of the first embodiment, the amount of glass used as the clad can be reduced, and weight reduction can be achieved.

[0094] Further, in the multi-core fiber 1 of the present embodiment, since the dummy fibers 91 and 92 are arranged and joints 22 and 23 with the dummy fibers 91 and 92 exist, the number of joints is larger than when the dummy fiber 90 does not exist. Therefore, when the multi-core fiber 1 is cut, the splitting force is more likely to propagate through the multi-core fiber 1 starting from the portion where the cutting blade is inserted, and the cut surface can be made flatter. Further, this multi-core fiber 1 is stronger than the case where there is no dummy fiber and can suppress breakage.

[0095] As described above, the present invention has been described by taking the above embodiments as examples, but the present invention is not limited thereto.

[0096] For example, in the above embodiment, an example was described in which there is a gap surrounded by the claddings of three or more single-core fibers or dummy fibers in the cladding of the multi-core fiber. However, the presence of such a gap is not essential. FIG. 12 is a diagram showing a modified example of the multi-core fiber from the same viewpoint as FIG. 1. In this modified example, for components that are the same as or equivalent to those in the first embodiment, the same reference numerals are given and redundant explanations are omitted unless otherwise specifically described.

[0097] As shown in FIG. 12, in the multi-core fiber 1 according to this modified example, three single-core fibers 10 are arranged in parallel. In this modified example, at each joint 21, a part of the outer peripheral surfaces of the clad portions 12 of a pair of adjacent single-core fibers 10 are integrated over a width smaller than the diameter of the clad portion 12, forming the joint 21. Therefore, the cladding 20 of this multi-core fiber 1 is composed of the clad portions 12 of the plurality of single-core fibers 10. The outer peripheral surface of the cladding 20 of the multi-core fiber 1 includes a part other than the joint 21 on the outer peripheral surface of each clad portion 12. This other part is a surface with a constant distance from the center of the core 11. The respective other parts of a pair of adjacent single-core fibers 10 are separated from each other while drawing an arc from the joint 21, and a constriction is formed in the cladding 20.

[0098] According to such a configuration, similar to the first embodiment, since the cladding portions of the single-core fibers are integrated, displacement between the cores can be suppressed. Further, since the cladding 20 of this multi-core fiber 1 has a constriction similar to that of the first embodiment, the amount of glass used as the cladding can be reduced, and weight reduction can be achieved. Further, according to this modification, since the three single-core fibers 10 are arranged in parallel, it can be used as a so-called ribbon fiber. In this modification, an example in which the multi-core fiber 1 is composed of three single-core fibers has been described. However, a multi-core fiber may be configured by arranging two single-core fibers in parallel, or a multi-core fiber may be configured by arranging four or more single-core fibers in parallel.

[0099] Further, in the above embodiment, an example in which the core 11 is circular has been described. However, for example, as shown in FIG. 13, the core 11 may be elliptical. FIG. 13 is a view showing another modification of such a multi-core fiber from the same viewpoint as FIG. 1. In FIG. 13, the illustration of the inner cladding layer 13 and the trench layer 14 is omitted. The modification shown in FIG. 13 has the same configuration as the multi-core fiber 1 of the first embodiment except that the core 11 is elliptical.

[0100] Such an elliptical core 11 can be formed, for example, during the above-described wire drawing process SP3. For example, as shown in FIG. 3, the multi-core fiber 1 of the first embodiment is manufactured by arranging the centers of three single-core fiber rods 10R at the vertices of an equilateral triangle and drawing them in a bundled state. During this wire drawing, the single-core fiber rod 10R receives surface tension from both of the other two single-core fiber rods 10R that are welded to it. This surface tension is a force that pulls the core glass body 11R in the direction of the joint 21R. In this example, since surface tension is applied in the direction of two joints 21R to one core glass body 11R, as a result of the synthesis of this surface tension, at least one of the plurality of cores 11 may be deformed into an elliptical shape as shown in FIG. 13. Deforming the core 11 into an elliptical shape in this way can be achieved by adjusting the temperature of the spinning furnace 110 in the wire drawing process SP3 to adjust the magnitude of the surface tension. If the core 11 is elliptical in this way, the polarization mode of the light propagating through the core 11 can be maintained.

[0101] Also, in the above embodiment, an example in which the outer peripheral surface of the cladding 20 at the joint 21 is recessed in an arc shape has been described. However, the outer peripheral surface of the cladding 20 at the joint 21 does not have to be recessed in an arc shape. FIG. 14 is a view showing still another modification example of such a multi-core fiber 1 from the same viewpoint as FIG. 2. As shown in FIG. 14, in this example, there is a portion where the width W of the joint 21 is constant. That is, in this example, when moving the joint 21 along the line connecting the cores 11 adjacent to each other, the width of the joint 21 is constant. For this reason, at least a part of the outer peripheral surface of the cladding 20 at the joint 21 becomes planar. Having such a shape of the outer peripheral surface of the cladding 20 at the joint 21 can facilitate peeling of the inner coating layer 30.

[0102] In the above embodiment, the example in which the joint portion 21 is provided over the entire longitudinal direction of the multi-core fiber 1 has been described. However, the joint portion 21 may be provided only at a part of the longitudinal direction of the multi-core fiber 1. In this case, at the part, the multi-core fiber 1 can be lightened and the displacement between the cores can be suppressed.

[0103] In the above embodiment, the example in which a part of the outer peripheral surfaces of at least two clad portions 12 are integrated with each other over a width smaller than the diameter of the clad portion 12 has been described. However, the joint portion 21 may be such that a part of the outer peripheral surfaces of at least two clad portions 12 are integrated with each other over a width larger than the diameter of the clad portion 12. In this case, at the location where the joint portion 21 is directed, the displacement between the cores in the multi-core fiber 1 can be suppressed. Further, even when an external force is applied to the clad 20, the joint portion 21 integrated over a width larger than the diameter of the clad portion 12 can protect the clad portion 12 and reduce damage to the clad portion 12. Further, since the cross-sectional area of the joint portion 21 becomes large, when the multi-core fiber 1 is cut, the splitting force can easily propagate to each single-core fiber 10 through the joint portion 21 having a large cross-sectional area starting from the portion where the cutting blade is inserted, and the cut surface can be made closer to being flat.

[0104] In the above embodiment, when three or more single-core fibers 10 are provided, the joint portion 21 is not limited to being provided such that a part of the outer peripheral surfaces of the respective clad portions 12 are integrated with each other, and a part of the outer peripheral surfaces of at least two clad portions 12 may be integrated with each other. In this case, the outer peripheral surface of the clad 20 includes the other part of the outer peripheral surfaces of the at least two clad portions 12.

[0105] In the above embodiment, the light propagating through at least two cores 11 of the multi-core fiber 1 may have a mode non-coupling region with each other, or the light propagating through at least two cores 11 of the multi-core fiber 1 may have a mode coupling possible region with each other.

[0106] In the above-described embodiment, an example in which the trench layer is included in the cladding portion of the single-core fiber has been described, but such a trench layer is not an essential configuration.

Industrial Applicability

[0107] According to the present invention, a multi-core fiber capable of reducing weight and suppressing displacement between cores and a method for manufacturing the multi-core fiber are provided, and can be used, for example, in fields such as communication.

Explanation of Reference Numerals

[0108] 1 ··· Multi-core fiber 10 ··· Single-core fiber 10R ··· Rod for single-core fiber 11 ··· Core 12 ··· Cladding portion 14 ··· Trench layer 20 ··· Cladding 21 ··· Joint portion G ··· Gap

Claims

1. A plurality of cores; a clad surrounding each of the plurality of cores; and comprising the clad has a joint portion where a part of the outer peripheral surfaces of at least two of the clad portions in a plurality of single-core fibers in which each core is disposed at the center and the clad portion surrounds the core are integrated over a width smaller than the diameter of the clad portion, the outer peripheral surface of the clad includes another part of the outer peripheral surfaces of the at least two clad portions, the plurality of single-core fibers are three or more, the clad has a polygonal void surrounded by the outer peripheral surfaces of the clad portions of three or more of the single-core fibers, at least one width of a part of the outer peripheral surface of each clad portion that forms the void is equal to or greater than the diameter of the core closest to the part, the width of the joint portion is smaller than the diameter of the core of the single-core fiber having the joint portion A multi-core fiber characterized by the above.

2. The outer peripheral surface of the clad at at least one of the joint portions is recessed in an arc shape toward the center of the joint portion The multi-core fiber according to claim 1, characterized by the above.

3. Having three or more of the single-core fibers arranged in parallel to each other The multi-core fiber according to claim 1 or 2, characterized by the above.

4. At least one of the parts of the outer peripheral surface of each clad portion that forms the void is curved so as to surround the core closest to the part The multi-core fiber according to claim 1, characterized by the above.

5. At least one of the single-core fibers has a trench layer having a refractive index lower than that of the clad portion of the single-core fiber and surrounding the core of the single-core fiber, the width of the joint portion in the single-core fiber is smaller than the diameter of the trench layer The multi-core fiber according to any one of claims 1 to 4, characterized by the above.

6. At least one of the cores is elliptical The multi-core fiber according to any one of claims 1 to 5, characterized by the above.

7. A bundling step of bundling single-core fiber rods including a core glass body disposed at the center and a clad glass body surrounding the core glass body; A pretreatment step of welding the outer peripheral surfaces of adjacent single-core fiber rods outside the spinning furnace; A wire drawing step of wire drawing the bundled single-core fiber rods so that a part of the outer peripheral surfaces of the clad glass bodies are in contact with each other over a width smaller than the diameter of the clad glass body in a molten state; comprising; In a preparation stage for performing the wire drawing step, a multi-core fiber base material in which the outer peripheral surfaces of the adjacent single-core fiber rods are welded to each other is installed in the spinning furnace A method for manufacturing a multi-core fiber, characterized by the above.

Images