JP2022128317A - Multi-core fiber and method for manufacturing multi-core fiber - Google Patents

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

The present invention relates to a multi-core fiber and a method for manufacturing a multi-core fiber.

In recent years, the amount of communication in communication networks tends to increase rapidly. Therefore, in order to meet this demand, multi-core fibers in which a plurality of cores are arranged in one clad are sometimes used. In such a multi-core fiber, generally, the cross-section of the clad surrounding the cores has a circular outer peripheral surface.

Also, as another multi-core fiber, for example, a multi-core fiber described in Non-Patent Document 1 below is known. The multi-core fiber described in Non-Patent Document 1 has a configuration in which a plurality of single-core fibers each having one core and a clad surrounding the core are bundled and the bundles are collectively coated with resin. Such multi-core fibers are sometimes called multi-element fibers.

S. Jain et al., “Multi-Element Fiber Technology for Space-Division Multiplexing Applications,” Opt. Express, vol. 22, issue 4, pp. 3787-3796, 2014.

Since the multi-element fiber described in Non-Patent Document 1 has a configuration in which single-core fibers are bundled, the cross-sectional area of the combined clad of each single-core fiber is the same as that of a conventional multi-core fiber having a circular clad cross-section. It can be small compared to the cross-sectional area of the cladding. Therefore, it is considered that the multi-element fiber can be made lighter than the conventional multi-core fiber in which the outer peripheral surface of the clad has a circular shape.

However, in the multi-element fiber described in Non-Patent Document 1, the single-core fibers are simply held together via resin. Therefore, when the multi-element fiber is cut, for example, if an external force acts on the multi-element fiber, the position of the single-core fibers may shift due to the external force, resulting in a positional shift between the cores.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to provide a multi-core fiber capable of reducing weight and suppressing misalignment between cores, and a method of manufacturing the multi-core fiber.

In order to achieve the above object, the multicore fiber of the present invention includes a plurality of cores and clads surrounding the plurality of cores, the clads having cores arranged in the center and clad portions corresponding to the cores. At least two portions of the outer peripheral surfaces of the cladding portions of the plurality of single-core fibers surrounding the core have a joint portion that is integrated over a width smaller than the diameter of the cladding portions, and the outer peripheral surfaces of the cladding portions includes other parts of the outer peripheral surfaces of the at least two cladding portions.

According to the configuration described above, since the cladding portions of the single-core fibers are partially integrated with each other, the position of the single-core fibers does not shift when an external force acts on the multi-core fiber during cutting, for example. is suppressed. Therefore, misalignment between cores can be suppressed.

Also, the width of the junction in the clad of this multi-core fiber is smaller than the diameter of the clad of the single-core fiber. By the way, since the core is arranged at the center of the clad portion, the distance from the center of the core tends to be substantially constant in a portion of the outer peripheral surface of the clad portion other than the joint portion. Therefore, other parts of the outer peripheral surfaces of the pair of single-core fibers that are integrated at the joint are spaced apart from each other. Therefore, the cladding of this multi-core fiber has a constriction in the vicinity of the joint. Since the cladding of this multi-core fiber has such a constriction, the cross-sectional area of the cladding can be smaller than that of a cladding having an outer peripheral surface in cross section that includes, for example, the cladding portion of each single-core fiber inside. The amount of glass can be less. Therefore, according to the multi-core fiber of the present invention, the weight can be reduced.

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

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

Also, the multi-core fiber may have three or more single-core fibers arranged in parallel.

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

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

Due to the presence of such voids, light leaking from a core may be less likely to be transmitted to other cores, and crosstalk between cores may be suppressed.

In addition, when the gap exists in the clad, it is preferable that each part of the outer peripheral surface of the clad part forming the gap is curved so as to surround the core closest to the part.

Further, when the gap exists, it is preferable that the width of each of the portions forming the gap in the outer peripheral surface of each of the clad portions is equal to or larger than the diameter of the core closest to the portion.

In this case, light leaking from the core may be less likely to be transmitted to other cores, and crosstalk between cores may be suppressed, compared to the case where the width of the portion forming the gap on the outer peripheral surface of the cladding is less than the diameter of the core. can be

At least one of the single-core fibers has a trench layer surrounding the core of the single-core fiber and having a lower refractive index than the cladding of the single-core fiber, Preferably, the width of the junction is less than or equal to the diameter of the trench layer.

In this case, compared to the case where the width of the junction is larger than the diameter of the trench layer, light leaking from the core may be less likely to be transmitted to adjacent cores, and crosstalk between cores may be suppressed.

Also, the width of the joint may be equal to or less than the diameter of the core of the single-core fiber having the joint.

In this case, compared to the case where the width of the spliced portion is larger than the diameter of the core, light leaking from the core may be less likely to be transmitted to the spliced single-core fiber cores, and crosstalk between the cores may be suppressed.

Also, at least one of the cores may be elliptical.

Making the core elliptical in this way can help maintain the polarization mode of light propagating through the core.

In order to achieve the above objects, the method for manufacturing a multi-core fiber of the present invention includes a bundling step of bundling single-core fiber rods each including a core glass body arranged in the center and a clad glass body surrounding the core glass body. a drawing step of drawing the bundled single-core fiber rod so that parts 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 bodies in a molten state; It is characterized by comprising

According to this method of manufacturing a multi-core fiber, the portions of the outer peripheral surfaces of the clad glass bodies that are in contact with each other in the molten state are larger than the diameter of the clad portions in the single-core fiber. It can be a joint that is brought together over a small width. Another portion of the outer peripheral surface of each clad glass body is a portion of the outer peripheral surface of the clad portion of the single-core fiber that tends to have a constant distance from the center of the core. Therefore, according to this method of manufacturing a multicore fiber, any one of the above multicore fibers can be manufactured.

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

In this case, the adjacent single-core fiber rods are drawn in a state of being in contact with each other, so that the portions of the outer peripheral surfaces of the single-core fiber rods can be more effectively integrated.

Further, in the method for manufacturing a multi-core fiber, it is preferable that the outer peripheral surfaces of the clad glass bodies of the adjacent single-core fiber rods are welded together in the bundling step.

In this case, it is possible to suppress misalignment between adjacent single-core fiber rods. In particular, when the portion to be welded includes the end of the rod for single-core fiber where drawing is started, this is preferable because it serves as a trigger for bringing the outer peripheral surfaces of the clad glass bodies into contact with each other in the drawing step.

As described above, according to the present invention, it is possible to provide a multi-core fiber capable of reducing weight and suppressing misalignment between cores, and a method of manufacturing a multi-core fiber capable of manufacturing the multi-core fiber.

1 is a diagram showing the structure of a cross section perpendicular to the longitudinal direction of a multi-core fiber according to a first embodiment of the present invention; FIG. It is an enlarged view which shows the state of a joint part. 1. It is a figure which shows the process of the manufacturing method of the multi-core fiber shown in FIG. It is a figure which shows the state of the first half of a bundling process. It is a figure which shows the latter half of a bundling process, and the appearance of a pretreatment process. FIG. 3 is a side view of the preform for multi-core fiber after the pretreatment step; FIG. 7 is a view of the preform for multi-core fiber shown in FIG. 6 as viewed from the fused tip side; It is a figure which shows the mode of a wire-drawing process. FIG. 2 is a diagram showing a multi-core fiber according to a second embodiment of the present invention from the same viewpoint as in FIG. 1; FIG. 3 is a diagram showing a multi-core fiber according to a third embodiment of the present invention from the same viewpoint as in FIG. 1; FIG. 4 is a diagram showing a multi-core fiber according to a fourth embodiment of the present invention from the same viewpoint as in FIG. 1; It is a figure which shows the modification of this invention from the viewpoint similar to FIG. FIG. 3 is a diagram showing another modification of the present invention from the same viewpoint as in FIG. 1; FIG. 3 is a diagram showing still another modified example of the present invention from a viewpoint similar to that of FIG. 2;

Embodiments for carrying out the multi-core fiber and the method for manufacturing the multi-core fiber according to the present invention will be exemplified below with reference to the accompanying drawings. The embodiments illustrated below are intended to facilitate understanding of the present invention, and are not intended to limit and interpret the present invention. The present invention can be modified and improved from the following embodiments without departing from its gist. In addition, in this specification, the dimensions of each member may be exaggerated to facilitate understanding.

(First embodiment)
FIG. 1 is a diagram showing the structure of a cross section perpendicular to the longitudinal direction of the multicore fiber according to the first embodiment. Note that hatching is omitted in FIG. 1 to avoid complicating the drawing. As shown in FIG. 1, the multi-core fiber 1 of this embodiment includes a plurality of single-core fibers 10, a single inner coating layer 30 covering each of the single-core fibers 10, and the inner coating layer 30. and an outer coating layer 40 to be provided as a main configuration. Note that FIG. 1 shows an example of three single-core fibers 10 .

The inner coating layer 30 and the outer coating layer 40 are made of resin. Examples of such resins include thermosetting resins and ultraviolet curable resins. Moreover, when the inner coating layer 30 and the outer coating layer 40 are formed from a thermosetting resin, the outer coating layer 40 may be formed from a different type of thermosetting resin from the inner coating layer 30 . Moreover, when the inner coating layer 30 and the outer coating layer 40 are formed from an ultraviolet curable resin, the outer coating layer 40 may be formed from a different type of ultraviolet curable resin from the inner coating layer 30 .

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 multicore fiber 1 without the inner coating layer 30 and the outer coating layer 40 is also called multicore fiber bare wire.

Each single-core fiber 10 includes a circular core 11 arranged at the center, an inner clad layer 13 surrounding the core 11, a trench layer 14 surrounding the inner clad layer 13, and a clad portion 12 surrounding the trench layer 14. contains. This can be understood as the cores 11 of each single-core fiber 10 being spaced apart from each other. Thus, in this embodiment, the clad part 12 surrounds the core 11 via the inner clad layer 13 and the trench layer 14, and has a circular outer shape. Therefore, the distance from the center of the core 11 to the outer peripheral surface of the clad portion 12 tends to be approximately constant. Core 11, inner cladding layer 13, and trench layer 14 are sometimes collectively referred to as a core element. Note that the trench layer 14 may directly surround the core 11 without providing the inner clad layer 13 .

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

As shown in FIG. 1 , portions of the outer peripheral surfaces of the clad portions 12 of the pair of single-core fibers 10 adjacent to each other are integrated at the joint portion 21 . Therefore, the multicore fiber 1 of this embodiment has three joints 21 . Thus, in the multi-core fiber 1 of the present embodiment, one clad 20 made up of the clad portions 12 of the single-core fibers 10 is formed. Here, clad 20 includes clad portion 12 and joint portion 21 . Thus, the cladding 20 surrounds each core 11 of each single-core fiber 10 . Therefore, the inner coating layer 30 is a single coating layer surrounding the outer peripheral surface of the clad 20 .

FIG. 2 is an enlarged view showing the appearance of the joint 21. As shown in FIG. Note that only one joint 21 is shown in FIG. The outer peripheral surface of the clad 20 at each joint 21 is recessed in an arc shape toward the center of the joint 21 . That is, the bottom 21B of the valley, which is the outer surface of the joint 21, is recessed in a rounded arc shape. The width W of each joint 21 is smaller than the diameter of the cladding portion 12 . The width W of each joint 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 addition, in this embodiment, the width W of each joint portion 21 is approximately the same size. However, at least one of these may be of different size. Also, the number of joints 21 in which the outer peripheral surface of the clad 20 is arcuately recessed is not particularly limited, and the number may be one or more.

Also, the diameter of the circumscribed circle Co of the clad 20 indicated by the dashed line in FIG. 1 is not particularly limited, but may be, for example, 125 μm.

In this embodiment, the width W of each junction 21 is smaller than the diameter of the trench layer 14 of each single-core fiber 10 and smaller than the diameter of the core 11 of each single-core fiber 10 . By making the width W of the junction 21 smaller than the diameter of the trench layer 14 and the diameter of the core 11 in this way, the light leaking from the core 11 is less likely to be transmitted to the adjacent core 11 via the junction 21 . 11 can be more effectively suppressed. However, the width W of the junction 21 may be equal to or greater than the diameter of the core 11 or equal to or greater than the diameter of the trench layer 14 .

A portion of the clad portion 12 of each single core fiber 10 is used as the joint portion 21 as described above. Further, in the present embodiment, the other part of the outer peripheral surface of each cladding portion 12 is formed by the two joint portions 21 such that the surface 12F1 positioned between the two joint portions 21 and the surface 12F2 other than the surface 12F1 are formed. is divided into The surface 12F1 and the surface 12F2 generally keep the shape of the outer peripheral surface of the single-core fiber 10, and are surfaces at a constant distance from the center of the core 11. As shown in FIG. Note that the constant distance from the core includes deviation due to manufacturing errors and the like. The surfaces 12F2 of the pair of single-core fibers 10 adjacent to each other are separated from each other while drawing an arc from the joint 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 .

A polygonal gap G surrounded by the surfaces 12F1 of the cladding portions 12 of the single-core fibers 10 is formed in the center of the multi-core fiber 1 of this embodiment. This gap G is not filled with resin, glass, or the like. In this embodiment, since there are three single-core fibers, the outer shape of the gap G is an equilateral triangle.

In this embodiment, the surface 12F1, which is the portion forming the gap G, of the outer peripheral surface of the cladding portion 12 of each single-core fiber 10 is curved so as to surround the core 11 closest to the surface 12F1. According to such a configuration, light leaking from the core 11 is likely to be blocked by the gap G, and crosstalk between the cores can be suppressed.

Here, in FIG. 1, the line segment L connecting the two joints 21 at the shortest distance is indicated by a dashed line. Assuming that the length of this line segment L is the width of the surface 12F1, in this embodiment the width of the surface 12F1 is greater than the diameter of the core 11 and the diameter of the trench layer 14 of the single-core fiber 10 closest to the surface 12F1. . With such a configuration, light leaking from the core 11 can be less likely to be transmitted to the other cores 11 than when the width of the surface 12F1, which forms the gap G, is equal to or less than the diameter of the core 11. crosstalk between 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 .

As described above, the multi-core fiber 1 of this embodiment includes a plurality of cores 11 and clads 20 surrounding the plurality of cores 11. The clads 20 are arranged in the center of the cores 11. 12 has a joint portion 21 in which parts of the outer peripheral surface of each of the clad portions 12 of the plurality of single-core fibers 10 surrounding the core 11 are integrated over a width smaller than the diameter of the clad portion 12. , the outer peripheral surface of the clad 20 includes a surface 12F1 and a surface 12F2, which are other portions of the outer peripheral surface of each clad portion 12 .

According to such a configuration, since the cladding portions 12 of the single-core fibers 10 are integrated with each other, the positions of the single-core fibers are not displaced when an external force acts on the multi-core fiber 1 during cutting, for example. Suppressed. Therefore, misalignment between cores can be suppressed.

Also, the width of the joint portion 21 in the clad 20 of the multi-core fiber 1 is smaller than the diameter of the clad portion 12 of the single-core fiber 10 . By the way, since the core 11 is arranged at the center of the clad portion 12, the distance from the center of the core 11 to the surface 12F2, which is a portion of the outer peripheral surface of the clad portion 12 other than the joint portion 21, is constant. tend to become Therefore, 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 an arc from the joint 21, as described above. Therefore, the clad 20 of this multicore fiber 1 has a constriction formed by a pair of surfaces 12F2 in the vicinity of the joint 21. As shown in FIG. Since the clad 20 of the multi-core fiber 1 has such a constriction, the shape of the outer peripheral surface in the cross section is, for example, the circumscribed circle Co shown in FIG. Compared to the cladding, the cross-sectional area can be small and the amount of glass in the cladding 20 can be small. It should be noted that the glass that forms the core 11 and the clad 20 is generally covered with a coating, and the resin that forms the coating is generally lighter than the glass. Therefore, according to the multi-core fiber 1 of this embodiment, the weight can be reduced. In addition, in the multi-core fiber 1 of the present embodiment, the outer peripheral surface of the clad 20 includes other parts of the outer peripheral surfaces of at least two clad portions 12, so that the outer peripheral surface of the clad 20 includes at least two clad portions. Compared to the case where the other part of the outer peripheral surface of 12 is not included, the thickness of the clad 20 can be reduced to the minimum necessary thickness in the other part, and the weight can be reduced more effectively. It is possible to realize a multi-core fiber 1 that can contribute to

In addition, according to this multi-core fiber 1, since the cladding portions 12 are integrated with each other, when the multi-core fiber 1 is cut, the cleaving force originates from the portion where the cutting blade is inserted and passes through the joint portion 21. of the single-core fiber 10, and the cut surface can be made flatter.

In addition, in the multi-core fiber 1 of the present embodiment, the outer peripheral surface of the clad 20 at the joint 21 is recessed in an arc shape toward the center of the joint 21 . In this way, when the inner coating layer 30 is provided on the outer periphery of the clad 20, the outer peripheral surface of the clad 20 at the joint portion 21 is recessed in an arc, so that when the inner coating layer 30 is provided on the outer periphery of the clad 20, the separation starting point between the clad 20 and the inner coating layer 30 is It is possible to suppress peeling of the inner coating layer 30 from the clad 20 . Therefore, nonuniformity of stress caused by peeling of the inner coating layer 30 can be suppressed, microbending can be suppressed, and transmission loss of light propagating through the core 11 can be suppressed.

Further, according to the multi-core fiber 1 of the present embodiment, the clad 20 has polygonal gaps G surrounded by the outer peripheral surface of the clad portion 12 of each single-core fiber 10 . According to such a configuration, the weight of the multi-core fiber can be reduced compared to the case where the gap G does not exist and the part of the gap G is filled with glass or the like. In addition, the presence of such gaps G can suppress crosstalk between cores.

Moreover, the multi-core fiber 1 of this 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 the multi-core fibers 1 are fusion-spliced, two non-parallel surfaces, for example, a surface in contact with both the pair of single-core fibers 10 and a surface in contact with both of the other pair of single-core fibers 10 If the ends of a pair of multi-core fibers 1 are placed facing each other in a V-shaped groove having 11 can be roughly matched. Therefore, according to this multi-core fiber 1, when the multi-core fibers 1 are fusion-spliced, the step of aligning the multi-core fiber 1 on one side with the multi-core fiber 1 on the other side can be simplified.

Next, a method for manufacturing the multicore fiber 1 will be described.

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

(Bundling process SP1)
FIG. 4 is a diagram showing the process in the first half of this process. In this step, first, as shown in FIG. 4, a single-core fiber rod 10R including a core glass body 11R arranged at the center and serving as a core, and a clad glass body 12R surrounding the core glass body 11R and serving as a clad portion 12. Prepare multiple In this 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, the single-core fiber rods 10R have the same size and the same configuration. In this embodiment, since each single-core fiber 10 has the inner clad layer 13 and the trench layer 14, each single-core fiber rod 10R surrounds the core glass body 11R and serves as the inner clad layer 13. It has a cladding glass body 13R and a trench glass body 14R that surrounds the inner cladding glass body 13R and serves as the trench layer 14 .

Next, as shown in FIG. 4, a plurality of single-core fiber rods 10R are arranged at a bundling position. In this embodiment, the centers of the three single-core fiber rods 10R are positioned on the vertices of an equilateral triangle. Next, the arranged single-core fiber rods 10R are bound with a binding band 51, for example. In this way, the single-core fiber rods 10R are bundled with each other in a state in which the plurality of single-core fiber rods 10R are bundled. In this embodiment, three single-core fiber rods 10R are bundled so that adjacent single-core fiber rods 10R are in contact with each other. Note that, unlike the example of FIG. 4, the single-core fiber rods 10R do not necessarily have to be in contact with each other when the single-core fiber rods 10R are bundled together.

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 preform 1P. By fixing the dummy glass rods 52 in this way, even if the fixing jig such as the binding band 51 is removed, the bundled state of the single-core fiber rods 10R is maintained, and the positional deviation between the single-core fiber rods 10R is prevented. is suppressed. Note that it is preferable to fix the dummy glass rod 52 by welding. Fixing by welding can effectively prevent impurities from adhering to the single-core fiber rod 10R. Also, the dummy glass rod 52 may be fixed to only one end of the bundled single-core fiber rods 10R. Alternatively, a plurality of single-core fiber rods 10</b>R may be bundled without using the binding band 51 . In this case, for example, by fixing the single-core fiber rods 10R one by one to the dummy glass rod 52 and fixing the plurality of single-core fiber rods 10R to the dummy glass rod 52, as a result, a plurality of single-core The fiber rods 10R may be bundled.

(Pretreatment step SP2)
Next, this process is performed. FIG. 6 is a side view of the multi-core fiber preform after this step. In this step, after removing the binding band 51, as shown in FIG. 5, while part of the side surface of the bundled single-core fiber rods 10R is heated, one dummy glass rod 52 is attached to the other dummy glass rod. Pull to the side opposite to the 52 side. As a result, as shown in FIG. 6, one dummy glass rod 52 and the portion of the single-core fiber rod 10R on the side of the dummy glass rod 52 are fused and removed, and the multi-core fiber preform 1P is fused. The vicinity of the part has a tapered shape. FIG. 7 is a view of the multi-core fiber preform 1P shown in FIG. 6 as viewed from the fused tip side. As shown in FIG. 7, by being fused as described above, the outer peripheral surfaces of the clad glass bodies 12R of the adjacent single-core fiber rods 10R are welded together at the front end portion 1PF of the multi-core fiber preform 1P. and three joints 21R are formed. The preform 1P for multi-core fiber is drawn from this tapered side. Therefore, in the present embodiment, the outer peripheral surfaces of the clad glass body 12R are welded together including the end portion where drawing of the single-core fiber rod 10R is started.

In the above description, an example in which the joint portion 21R is formed only at the tip portion 1PF of the multi-core fiber preform 1P is explained. The joint portion 21R may be formed along the entire longitudinal length of the base material 1P.

Also, in the present embodiment, an example in which one dummy glass rod 52 is removed as described above has been described, but only the one dummy glass rod 52 may be heated to make it conical. In this way, a multi-core fiber preform 1P having a conical dummy glass rod 52 fixed to one side and a columnar dummy glass rod 52 fixed to the other side may be formed.

(Drawing process SP3)
Next, this process is performed. FIG. 8 is a diagram showing the state of this step. As shown in FIG. 8, first, as a preparatory stage for performing this step, the multi-core fiber preform 1P is placed so that the front end portion 1PF of the multi-core fiber preform 1P that has undergone the pretreatment step SP2 faces vertically downward. is installed in the spinning furnace 110. Then, the heating portion 111 of the spinning furnace 110 is heated, and the multi-core fiber preform 1P is inserted into the heating portion 111 from the front end portion 1PF side to be heated. At this time, the portion of the preform 1P for multi-core fiber located in the heating section 111 is heated to, for example, 1900° C. to 2300° C. to be in a molten state. In this step, the preform 1P for multi-core fiber is drawn so that parts of the outer peripheral surfaces of the clad glass body 12R are in contact with each other over a width smaller than the diameter of the clad glass body 12R in this molten state. By drawing the wire at such a temperature, the clad glass bodies 12R adjacent to each other are melted and integrated through mutual surface tension even in the portions other than the tip portion 1PF. Thus, three joints 21R are formed along the longitudinal direction of the multi-core fiber preform 1P.

The part of the preform 1P for multi-core fiber coming out of the spinning furnace 110 is immediately solidified. Thus, in each single-core fiber rod 10R, the core glass body 11R serves as the above-described core element, and the clad glass body 12R serves as the clad portion 12 . As a result, each single-core fiber rod 10R becomes three single-core fibers 10 having outer peripheral surfaces that tend to have a constant distance from the center of the core 11. FIG. Also, the joint portion 21</b>R in the molten state is immediately solidified to form three joint portions 21 . Thus, the multi-core fiber bare wire shown in FIG. 1 is formed. Thereafter, as shown in FIG. 8, this multi-core fiber bare wire 1N passes through a cooling device 120 and is cooled to an appropriate temperature. For example, it is cooled to 40°C to 50°C.

Next, the multi-core fiber bare wire 1N passes through a first coating device 131 containing a first thermosetting resin to be the inner coating layer 30, and the clad 20 is coated with the first thermosetting resin. The bare multi-core fiber 1N coated with the first thermosetting resin passes through the first heating furnace 132 and is heated within the first heating furnace 132 . By this heating, the material forming the first thermosetting resin is crosslinked, the first thermosetting resin is cured, and the inner coating layer 30 is formed.

When forming the inner coating layer 30 from an ultraviolet curable resin, the resin is cured after the clad 20 is coated with the first coating device 131 containing the first ultraviolet curable resin.

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 subjected to the second thermosetting. Covered with resin. The multi-core fiber bare wire 1N coated with the second thermosetting resin passes through the second heating furnace 134 and is heated within the second heating furnace 134 . By this heating, the material forming the second thermosetting resin is cross-linked, the second thermosetting resin is cured, and the outer coating layer 40 is formed.

When forming the inner coating layer 30 from an ultraviolet curable resin, the clad 20 is coated with the second coating device 133 containing the second ultraviolet curable resin, and then the resin is cured.

Thus, the multicore fiber 1 shown in FIG. 1 is formed.

After that, the direction of the multi-core fiber 1 is changed by the turn pulley 141 and wound up by the reel 142 .

According to the method for manufacturing the multi-core fiber 1 of the present embodiment, portions of the outer peripheral surfaces of the clad glass bodies 12R that are in contact with each other in the molten state are part of the outer peripheral surfaces of the clad portions 12 of the respective single-core fibers 10. They can be joined together over a width smaller than the diameter of the cladding 12 . Another portion of the outer peripheral surface of each clad glass body 12R is a portion of the outer peripheral surface of each clad portion 12 in the single-core fiber 10 where the distance from the center of the core 11 tends to be constant. . Therefore, according to this method for manufacturing a multicore fiber, the multicore fiber 1 described above can be manufactured.

In addition, according to this method of manufacturing a multi-core fiber, a multi-core fiber can be manufactured simply by drawing a plurality of single-core fiber rods 10R in a bundled state. It is possible to omit the step of inserting a glass member to be the core into the hole. Therefore, it is possible to reduce the number of steps and the manufacturing cost.

In addition, in this method of manufacturing a 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 in the bundling step SP1, the single-core fiber rods are close to each other but are not in contact with each other. The clad glass bodies are easily welded to each other as compared with the case. Therefore, joints can be formed more effectively.

In the present embodiment, in the bundling step SP1, the outer peripheral surfaces of the clad glass bodies 12R of the single-core fiber rods 10R that are adjacent to each other are welded together. Therefore, it is possible to suppress positional deviation between the single-core fiber rods 10R that are adjacent to each other. In particular, in the present embodiment, the outer peripheral surfaces of the clad glass bodies 12R are welded together on the side where the drawing of the single-core fiber rod 10R is started. It can be used as an opportunity for some to come into contact with each other.

(Second embodiment)
Next, a second embodiment will be described. Constituent elements that are the same as or equivalent to those of the first embodiment are denoted by the same reference numerals, and overlapping descriptions are omitted unless otherwise specified.

FIG. 9 is a view showing the multicore fiber 1 of this embodiment from the same viewpoint as in FIG. As shown in FIG. 9, the multi-core fiber 1 of this embodiment mainly differs from the multi-core fiber 1 of the first embodiment in that it has four single-core fibers 10 . In this embodiment, four single-core fibers 10 are arranged such that the center of each core 11 is positioned on the vertex of the square.

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

Also in this embodiment, the other portions of the pair of single-core fibers 10 adjacent to each other are separated from each other while drawing an arc from the joint 21, and the clad 20 is formed with a constriction. Moreover, the clad 20 has polygonal gaps G surrounded by the outer peripheral surfaces of the four single-core fibers 10, and square-shaped gaps G exist in this embodiment.

According to such a configuration, as in the first embodiment, the cladding portions 12 of the single-core fiber 10 are integrated with each other, so positional deviation between the cores 11 can be suppressed. Moreover, 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. Moreover, since the air gap G as described above exists, it is possible to further reduce the weight.

(Third embodiment)
Next, a third embodiment will be described. Constituent elements that are the same as or equivalent to those of the first embodiment are denoted by the same reference numerals, and overlapping descriptions are omitted unless otherwise specified.

FIG. 10 is a view showing the multicore fiber 1 of this embodiment from the same viewpoint as in FIG. As shown in FIG. 10, the multi-core fiber 1 of this embodiment mainly differs from the multi-core fiber 1 of the first embodiment in that it has six single-core fibers 10 . In this embodiment, six single-core fibers 10 are arranged such that the center of each core 11 is located on the vertex of a regular hexagon. Moreover, in the multi-core fiber 1 of this 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 trench layer, and is made of the same material as the clad section 12 . Also, the dummy fiber 90 may have a portion with a lower refractive index than the clad portion 12 . In this case, crosstalk to the cores present on the diagonal of the dummy fiber 90 can be suppressed. The multi-core fiber 1 of this embodiment differs from the multi-core fiber 1 of the first embodiment, which does not have dummy fibers, in that it has such dummy fibers 90 .

The multicore fiber 1 of this embodiment has six joints 21 and six joints 22 . At each joint 21 , portions of the outer peripheral surfaces of the clad portions 12 of the pair of single-core fibers 10 adjacent to each other are integrated over a width smaller than the diameter of the clad portions 12 . Moreover, at each joint 22, a portion of the outer peripheral surface of each single core fiber 10 and a portion of the outer peripheral surface of the dummy fiber 90 extend over a width smaller than the diameter of the cladding portion 12 and the diameter of the dummy fiber. are unified. Therefore, the clad 20 of the multi-core fiber 1 of this embodiment consists of the clad portion 12 of each single-core fiber 10 and the dummy fiber 90 .

The outer peripheral surface of the clad 20 of the multi-core fiber 1 includes portions other than the joints 21 and 22 on the outer peripheral surface of each clad portion 12, and the other portions are at a constant distance from the core 11. It is the surface. Also in this embodiment, the other portions of the pair of single-core fibers 10 adjacent to each other are separated from each other while drawing an arc from the joint 21, and the clad 20 is formed with a constriction. Moreover, six gaps G exist in the clad 20 of the present embodiment. Each gap G is surrounded by the outer peripheral surface of each of the pair of single-core fibers 10 adjacent to each other and the outer peripheral surface of the dummy fiber 90 .

The multi-core fiber 1 of the present embodiment having such a dummy fiber 90 is obtained by arranging six single-core fiber rods 10R in a regular hexagonal shape around the dummy fiber rod that becomes the dummy fiber 90 in the bundling step SP1. , are bound in the same manner as in the first embodiment. Then, each bundled single-core fiber rod is drawn together with the dummy fiber rod in the same manner as in the drawing step SP3.

According to the configuration of the multi-core fiber 1 of the present embodiment, as in the first embodiment, the cladding portions 12 of the single-core fiber 10 are integrated with each other, so misalignment between the cores 11 can be suppressed. Moreover, 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. Moreover, since the air gap G as described above exists, it is possible to further reduce the weight.

In addition, in the multi-core fiber 1 of the present embodiment, the dummy fiber 90 is arranged in the space surrounded by the six single-core fibers 10, and the junction 22 with the dummy fiber 90 is present. The number of joints is large compared to . Therefore, when the multi-core fiber 1 is cut, the cleaving force is easily propagated to the multi-core fiber 1 starting from the portion where the cutting blade is inserted, and the cut surface can be made flatter. Moreover, this multi-core fiber 1 is stronger and can prevent breakage compared to the case without the dummy fiber.

(Fourth embodiment)
Next, a fourth embodiment will be described. Constituent elements that are the same as or equivalent to those of the first embodiment are denoted by the same reference numerals, and overlapping descriptions are omitted unless otherwise specified.

FIG. 11 is a view showing the multi-core fiber 1 of this embodiment from the same viewpoint as in FIG. The multicore fiber 1 of this embodiment has one dummy fiber 91 and three dummy fibers 92 . The dummy fibers 91 and 92 do not have cores or trench layers, are made of the same material as the clad portion 12 , and have diameters smaller than the diameters of the respective single-core fibers 10 .

A dummy fiber 91 is arranged in a space surrounded by three single-core fibers 10 . A portion of the outer peripheral surface of the dummy fiber 91 is smaller than a portion of the outer peripheral surface of the clad portion 12 of each single-core fiber 10, the diameter of the clad portion 12, and the diameter of the dummy fiber 91 at each joint portion 22. Integrated across the width. Thus, in the clad 20 of the multi-core fiber 1, three gaps G1 surrounded by a part of the outer peripheral surface of the clad part 12 of each single-core fiber 10 and a part of the outer peripheral surface of the dummy fiber 91 are formed. . The gap G1 is not filled with resin, glass, or the like.

Each dummy fiber 92 is arranged in a space surrounded by each outer peripheral surface of each single core fiber 10 and a circumscribing triangle LA indicated by a dashed line contacting each outer peripheral surface of each of the three single core fibers 10. . A part of the outer peripheral surface of the dummy fiber 92 , at each joint 23 , is a part of the outer peripheral surface of each clad part 12 of the pair of single-core fibers 10 adjacent to each other, the diameter of the clad part 12 and the diameter of the dummy fiber 92 . is integrated over a width smaller than the diameter of the Thus, in the clad 20 of the multi-core fiber 1, three gaps G2 surrounded by a part of the outer peripheral surface of each of the pair of adjacent single-core fibers 10 and a part of the outer peripheral surface of the dummy fiber 92 are formed. there is The gap G2 is not filled with resin, glass, or the like.

The clad 20 of the multi-core fiber 1 of this embodiment consists of the clad portion 12 of each single-core fiber 10 and dummy fibers 91 and 92 . The outer peripheral surface of the clad 20 includes portions other than the joint portions 21 , 22 , and 23 on the outer peripheral surface of each clad portion 12 . The other part is a surface with a constant distance from the core 11 . Further, the other portions of the pair of single-core fibers 10 adjacent to each other are separated from each other while drawing an arc from the joint 23 . Therefore, a constriction is formed in the clad 20 .

In the multi-core fiber 1 of the present embodiment having such dummy fibers 91 and 92, the dummy fiber rods to be the dummy fibers 91 and 92 are inserted between the single-core fiber rods 10R bundled into an equilateral triangle in the bundling step SP1. After arranging, each single-core fiber rod and each dummy fiber rod are bound, and each single-core fiber rod is drawn together with each dummy fiber rod as in the drawing step SP3. can be manufactured by

According to such a configuration, as in the first embodiment, since the cladding portions 12 of the single-core fiber are integrated with each other, positional deviation between the cores 11 can be suppressed. Moreover, 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.

In addition, in the multi-core fiber 1 of the present embodiment, the dummy fibers 91 and 92 are arranged, and the joints 22 and 23 with the dummy fibers 91 and 92 are present. a large number of Therefore, when the multi-core fiber 1 is cut, the cleaving force is easily propagated to the multi-core fiber 1 starting from the portion where the cutting blade is inserted, and the cut surface can be made flatter. Moreover, this multi-core fiber 1 is stronger and can prevent breakage compared to the case without the dummy fiber.

As described above, the present invention has been described by taking the above embodiment as an example, but the present invention is not limited to this.

For example, in the above embodiments, the clad of the multi-core fiber has a gap surrounded by three or more single-core fiber clads or dummy fibers. However, the presence of such voids is not essential. FIG. 12 is a view showing a modification of the multi-core fiber from the same viewpoint as in FIG. In this modified example, constituent elements that are the same as or equivalent to those of the first embodiment are denoted by the same reference numerals, and overlapping explanations will be omitted unless otherwise specified.

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

According to such a configuration, as in the first embodiment, since the cladding portions of the single-core fibers are integrated with each other, it is possible to suppress misalignment between the cores. Moreover, 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. Moreover, according to this modification, since three single-core fibers 10 are arranged in parallel, it can be used as a so-called tape fiber. In this modified example, an example in which the multi-core fiber 1 is composed of three single-core fibers has been described. may be arranged in parallel to form a multi-core fiber.

Further, in the above embodiment, an example in which the core 11 is circular has been described, but the core 11 may be oval as shown in FIG. 13, for example. FIG. 13 is a diagram showing another modification of such a multicore fiber from the same viewpoint as in FIG. 13, 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.

Such an elliptical core 11 can be formed, for example, in the wire drawing step 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 drawing, the single-core fiber rod 10R receives surface tension from both of the other two welded single-core fiber rods 10R. This surface tension is a force that pulls the core glass body 11R in the direction of the joint portion 21R. In this example, surface tension is applied to one core glass body 11R in the direction of two joints 21R. At least one of may be deformed into an elliptical shape. Such deformation of the core 11 into an elliptical shape can be realized by adjusting the temperature of the spinning furnace 110 to adjust the magnitude of the surface tension in the drawing step SP3. Such an elliptical shape of the core 11 can maintain the polarization modes of light propagating through the core 11 .

Further, in the above-described embodiment, an example in which the outer peripheral surface of the clad 20 at the joint portion 21 is recessed in an arc shape has been described. However, the outer peripheral surface of the clad 20 at the joint portion 21 does not have to be recessed in an arc shape. FIG. 14 is a diagram showing still another modified example of such a multicore fiber 1 from the same viewpoint as in FIG. As shown in FIG. 14, in this example, there is a portion where the width W of the joint portion 21 is constant. That is, in this example, the width of the joint portion 21 is constant when the joint portion 21 is moved along the line connecting the adjacent cores 11 . Therefore, at least a portion of the outer peripheral surface of the clad 20 at the joint 21 becomes planar. Since the outer peripheral surface of the clad 20 at the joint portion 21 has such a shape, the inner coating layer 30 can be easily peeled off.

Moreover, in the above-described embodiment, an 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, it is possible to reduce the weight of the multi-core fiber 1 and suppress misalignment between the cores at the part of the location.

Moreover, in the above-described embodiment, the joint portion 21 has explained an example in which portions of the outer peripheral surfaces of at least two clad portions 12 are integrated over a width smaller than the diameter of the clad portions 12 . However, in the joint portion 21 , portions of the outer peripheral surfaces of at least two clad portions 12 may be integrated over a width larger than the diameter of the clad portions 12 . In this case, misalignment between cores in the multi-core fiber 1 can be suppressed at the location where the joint 21 is directed. Also, even if an external force is applied to the clad 20, the joint 21 integrated over a width larger than the diameter of the clad 12 can protect it, and damage to the clad 12 can be reduced. In addition, since the cross-sectional area of the joint 21 becomes large, when the multi-core fiber 1 is cut, the force of cleaving starts from the part where the cutting blade is inserted, and the force of cleaving passes through the joint 21 having a large cross-sectional area to each single core fiber. 10 may be easier to propagate and the cut surface may be more flattened.

Further, in the above-described embodiment, when three or more single core fibers 10 are provided, the joint portion 21 is provided so that parts of the outer peripheral surfaces of the respective clad portions 12 are integrated with each other. It is not limited, and parts of the outer peripheral surfaces of at least two cladding portions 12 may be integrated with each other. In this case, the outer peripheral surface of the clad 20 includes another portion of the outer peripheral surfaces of the at least two clad portions 12 .

Further, in the above embodiment, the light propagating through at least two cores 11 of the multi-core fiber 1 may have a mode-uncoupled region, and the light propagating through the at least two cores 11 of the multi-core fiber 1 may It may have a region capable of mode coupling.

Further, in the above embodiments, an example in which the cladding portion of the single-core fiber includes the trench layer has been described, but such a trench layer is not an essential configuration.

INDUSTRIAL APPLICABILITY According to the present invention, a multi-core fiber and a method for manufacturing the multi-core fiber that can reduce the weight and suppress misalignment between cores are provided, and can be used in the field of communication, for example.

REFERENCE SIGNS LIST 1 multi-core fiber 10 single-core fiber 10R single-core fiber rod 11 core 12 clad portion 14 trench layer 20 clad 21 junction G... Gap

Claims (12)

multiple cores;
a clad surrounding each of the plurality of cores;
with
The clad has a width smaller than the diameter of the clad part at least two parts of the outer peripheral surface of the clad part in a plurality of single-core fibers in which each of the cores is arranged at the center and the clad part surrounds the core. having a joint united over the
A multi-core fiber, wherein the outer peripheral surface of the clad includes other parts of the outer peripheral surfaces of the at least two clad portions. 2. The multi-core fiber according to claim 1, wherein the outer peripheral surface of the clad in at least one of the joints is arcuately recessed toward the center of the joint. 3. The multi-core fiber according to claim 1, comprising three or more of the single-core fibers arranged in parallel. Having three or more of the single-core fibers,
3. The multi-core fiber according to claim 1, wherein the clad has polygonal voids surrounded by outer peripheral surfaces of the clad portions of the three or more single-core fibers. 5. The multi-core fiber according to claim 4, wherein at least one portion of the outer peripheral surface of each of the cladding portions forming the void is curved so as to surround the core closest to the portion. 6. The multi-core fiber according to claim 4, wherein the width of at least one portion of the outer peripheral surface of each of the cladding portions forming the void is greater than or equal to the diameter of the core closest to the portion. at least one of the single-core fibers has a trench layer surrounding the core of the single-core fiber and having a lower refractive index than the cladding of the single-core fiber;
7. The multi-core fiber according to any one of claims 1 to 6, wherein the width of the junction in the single-core fiber is smaller than the diameter of the trench layer. 8. The multi-core fiber according to any one of claims 1 to 7, wherein the width of the joint is smaller than the diameter of the core of the single-core fiber having the joint. 9. A multicore fiber according to any one of claims 1 to 8, wherein at least one of said cores is elliptical. a bundling step of bundling single-core fiber rods including a centrally arranged core glass body and a clad glass body surrounding the core glass body;
a drawing step of drawing the bundled single-core fiber rod so that parts 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 bodies in a molten state;
A method of manufacturing a multi-core fiber, comprising: 11. The method for producing a multi-core fiber according to claim 10, wherein in the bundling step, the plurality of single-core fiber rods are bundled so that the outer peripheral surfaces of the adjacent single-core fiber rods are in contact with each other. 12. The method of manufacturing a multi-core fiber according to claim 11, wherein in the bundling step, the outer peripheral surfaces of the adjacent single-core fiber rods are welded together.

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