Fiber optic cable

Abstract

The purpose of the present invention is to ensure low crosstalk between all of the multicore optical fibers in an optical fiber cable having a plurality of identical non-coupled-type multicore optical fibers in different spiral shapes.　This optical fiber cable formed by twisting together a plurality of units formed by bundling a plurality of identical non-coupled-type multicore optical fibers is characterized in that: all of the units have the same diameter; in a cross section of the optical fiber cable, the units are arranged in a plurality of layers from the center; the units are arranged in a spiral shape for each layer in the longitudinal direction; the twist pitch of the spiral shape is the same in all of the units included in a single layer; and the twist pitch is different for each layer, and is set on the basis of the curvature Rpk of the multicore optical fiber in which crosstalk is greatest.

Description

[Technical field]

[0001] The present invention relates to an optical fiber cable having a small diameter and high density, in which optical fibers are bundled together. [Background technology]

[0002] An optical fiber cable with a small diameter and high density has been proposed by bundling optical fiber cores (for example, Patent Document 1). This optical fiber cable has a structure in which a plurality of units are formed by bundling single-core optical fiber cores, and these units are twisted together. By using such a structure, a multi-core optical fiber cable can be realized with a small diameter and light weight, which improves handling and enables installation in various locations.

[0003] In addition, in recent years, with the increase in transmission capacity, there is a demand to increase the spatial multiplexing of the optical fiber itself. As one technology for increasing the spatial multiplexing, a multi-core optical fiber having multiple cores that can propagate multiple light beams in a single optical fiber has been proposed (for example, see Non-Patent Document 1).

[0004] By forming a plurality of units each consisting of a bundle of multi-core optical fiber cores and twisting these units together, an optical fiber cable can be realized that can handle an increase in transmission capacity and has a small diameter and high density. In addition, by twisting a unit around another twisted unit to create an optical fiber cable structure consisting of multiple layers, the transmission capacity of the optical fiber cable can be further increased. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2007-41568 [Non-patent literature]

[0006] [Non-Patent Document 1] “Crosstalk suppressed hole-assisted 6-core fiber with cladding diameter of 125 μm” 39th European Conference and Exhibition on Optical Communication (ECOC 2013) [Non-Patent Document 2] “Analytical Expression of Average Power-Coupling Coefficients for Estimating Intercore Crosstalk in Multicore Fibers” IEEE Photonics Journal Year: 2012 | Volume: 4, Issue: 5 [Non-Patent Document 3] “Design of High-Density Cable Parameters for Controlling Spatial-Mode Dispersion of Randomly Coupled Multi-Core Fibers” Journal of Lightwave Technology Year: 2021 | Volume: 39, Issue: 4 Summary of the Invention [Problem to be solved by the invention]

[0007] On the other hand, in a multi-core optical fiber, it is important to suppress crosstalk between the lights propagating through each core. It is known that this crosstalk is affected by the bending, i.e., curvature, of the multi-core optical fiber (see, for example, Non-Patent Document 2). Therefore, a multi-core optical fiber can suppress crosstalk by its curvature.

[0008] In the optical fiber cable having multiple layers described above, the curvature of each layer in the optical fiber cable is different. In this case, even if a multi-core optical fiber capable of suppressing crosstalk in the curvature of any layer in the optical fiber cable is used in the optical fiber cable, the suppression of crosstalk cannot be guaranteed in other layers having different curvatures. Therefore, there is a problem that it is difficult to suppress crosstalk for all multi-core optical fibers in the optical fiber cable having multiple layers.

[0009] Therefore, in order to solve the above problem, an object of the present invention is to suppress crosstalk in all multi-core optical fibers in an optical fiber cable having a plurality of identical uncoupled multi-core optical fibers with different spiral shapes. [Means for solving the problem]

[0010] In order to achieve the above object, the optical fiber cable of the present disclosure is an optical fiber cable consisting of multiple layers formed by twisting together units each of which is a bundle of multi-core optical fibers, and in order to suppress crosstalk between the cores of the multi-core optical fibers, the twist pitch of the units in each layer of the optical fiber cable is appropriately set.

[0011] Specifically, the optical fiber cable according to the present disclosure comprises: An optical fiber cable formed by twisting together a plurality of units each formed by bundling a plurality of identical uncoupled multi-core optical fibers, all said units have the same diameter; The units are arranged in a plurality of layers from the center in a cross section; the units are arranged in a spiral shape for each layer in the longitudinal direction; all of the units in one of the layers have the same twist pitch in the helical configuration; and The twist pitch is different for each layer and is set based on the curvature Rpk of the multi-core optical fiber at which crosstalk is maximized. It is characterized by:

[0012] For example, the optical fiber cable according to the present disclosure may include: the twist radius r1 of the spiral shape of the unit arranged in the innermost layer is set to the number C1, the curvature ρ1 of the spiral shape of the unit arranged in the innermost layer is set to the number C2, the curvature ρm of the spiral shape of the unit arranged in a specific layer different from the innermost layer is set to the number C3, and the twist pitch Pm of the spiral shape of the unit arranged in the specific layer is set to the number C4, The curvature Rpk does not match the curvature ρ1 It is characterized by:

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[0013] For example, the optical fiber cable according to the present disclosure may include: the twist radius r1 of the spiral shape of the unit arranged in the innermost layer is set to the number C5, the curvature ρ1 of the spiral shape of the unit arranged in the innermost layer is set to the number C6, the curvature ρm of the spiral shape of the unit arranged in a specific layer different from the innermost layer is set to the number C7, and the twist pitch Pm of the spiral shape of the unit arranged in the specific layer is set to the number C8, The curvature Rpk is smaller than the curvature ρ1 It is characterized by:

number

number

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[0014] For example, the optical fiber cable according to the present disclosure may include: the twist radius r1 of the spiral shape of the unit arranged in the innermost layer is set to the number C9, the curvature ρ1 of the spiral shape of the unit arranged in the innermost layer is set to the number C10, the curvature ρm of the spiral shape of the unit arranged in a specific layer different from the innermost layer is set to the number C11, and the twist pitch Pm of the spiral shape of the unit arranged in the specific layer is set to the number C12, The curvature Rpk is greater than the curvature ρ1 It is characterized by:

number

number

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[0015] In the optical fiber cable of the present disclosure, the curvature of the multi-core optical fibers forming the unit is shifted from the curvature Rpk at which the crosstalk of the multi-core optical fiber is maximized by adjusting the twist pitch of the unit for each layer, thereby suppressing the crosstalk of all the multi-core optical fibers in the optical fiber cable.

[0016] In addition, the optical fiber cable according to the present disclosure includes: The twist directions of the spiral shapes of the units arranged in adjacent layers may be different from each other.

[0017] This makes it possible to prevent the positions of adjacent units between adjacent layers from being swapped, and to stably manufacture the fibers with the desired twist pitch.

[0018] The above-mentioned inventions can be combined as much as possible. Effect of the Invention

[0019] According to the present disclosure, low crosstalk can be ensured for all multi-core optical fibers in an optical fiber cable having a plurality of identical uncoupled multi-core optical fibers with different spiral shapes. [Brief description of the drawings]

[0020] [Figure 1] 1 shows an example of a schematic configuration of an optical fiber cable according to an embodiment. [Diagram 2] 1 shows an example of a procedure for a method for designing an optical fiber cable according to an embodiment. [Diagram 3] FIG. 4 is a diagram illustrating a twist direction of a unit according to the embodiment. [Figure 4] FIG. 4 is a diagram illustrating a twist direction of a unit according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Hereinafter, the embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments shown below. These implementation examples are merely illustrative, and the present disclosure can be implemented in various forms with various modifications and improvements based on the knowledge of those skilled in the art. Note that components with the same reference numerals in this specification and drawings are assumed to indicate the same components.

[0022] (Embodiment) FIG. 1 shows an example of an optical fiber cable 10 according to this embodiment. The optical fiber cable 10 according to the present embodiment is The optical fiber cable 10 is formed by twisting together a plurality of units 11 each formed by bundling a plurality of identical uncoupled multi-core optical fibers, All units 11 have the same diameter; In a cross section, the units 11 are arranged in a plurality of layers from a center O. The units 11 are arranged in a spiral shape for each layer in the longitudinal direction; All the units 11 in one layer have the same helical twist pitch; and The twist pitch is different for each layer and is set based on the curvature Rpk of the multi-core optical fiber at which crosstalk is the largest. It is characterized by:

[0023] The cross-sectional view of FIG. 1(a) shows a cross-sectional view perpendicular to the longitudinal direction of the optical fiber cable 10. In the optical fiber cable 10 according to the present embodiment, as shown in the cross-sectional view of FIG. 1(a), a first layer is formed by units 11 each having a center on a circumference having a radius of a distance r1 from the center O in the cross section of the optical fiber cable 10. A second layer is formed by units 11 each having a center on a circumference having a radius of a distance r2 from the center O in the cross section of the optical fiber cable 10. A third layer is formed by units 11 each having a center on a circumference having a radius of a distance r3 from the center O in the cross section of the optical fiber cable 10. In the present embodiment, a three-layer structure is used, but the number of layers is arbitrary. In addition, the optical fiber cable 10 according to the present embodiment has a structure in which the outer circumference of the twisted units 11 is covered with an outer jacket 12.

[0024] In the optical fiber cable 10 according to this embodiment, the unit 11 forming the first layer has a twist radius of distance r1 and a spiral shape along the longitudinal direction of the optical fiber cable 10. Similarly, the unit 11 forming the second layer has a twist radius of distance r2, and the unit 11 forming the third layer has a twist radius of distance r3 and a spiral shape along the longitudinal direction of the optical fiber cable 10.

[0025] The side view of these spiral shapes is shown in FIG. 1(b). The side view of FIG. 1(b) shows the side view of each unit 11 included in each layer. As shown in the side view of FIG. 1(b), the units in each layer have a sinusoidal wave shape when viewed from the side. The amplitude of this wave shape corresponds to the twist radius. The wavelength of this wave shape is called the twist pitch, and the first layer is P1, the second layer is P2, and the third layer is P3.

[0026] The multi-core optical fiber included in each unit 11 is similarly bent into a spiral shape according to the unit 11, and the curvature of the multi-core optical fiber is the same as the curvature of the unit 11 in which it is included.

[0027] Focusing on the unit 11 included in the first layer (hereinafter abbreviated as "first layer unit 11"), the curvature ρ1 of the spiral shape of the first layer unit 11 can be expressed by the following equation.

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[0028] The twist radius r1 can be expressed by the following formula using the number n of the first layer units 11 and the diameter d of the units 11.

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[0029] Next, we will focus on the unit 11 included in the second layer (hereinafter abbreviated as "second layer unit 11"). Since the second layer is twisted around the outer periphery of the first layer, the curvature ρ2 of the helical shape of the second layer unit 11 can be expressed by the following equation.

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[0030] The unit 11 included in the third layer (hereinafter abbreviated as "third layer unit 11") can be expressed by the following formula, similar to the above formula.

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[0031] That is, the curvature ρm of the spiral shape of the unit 11 included in the m-th layer (hereinafter abbreviated as “m-th layer unit 11”) can be expressed by the following formula, where m is an integer of 2 or more.

number

[0032] Here, in order to make the curvature of the helical shape of the optical fiber in the first layer unit 11 the same as that of the optical fiber in the mth layer unit 11, the units 11 are twisted together so as to satisfy the following equation, which equalizes the right side of equation (1) and the right side of equation (5).

number

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[0033] By adopting such a structure, the curvature of the optical fibers in the optical fiber cable 10 can be made uniform. Here, an example of a manufacturing method of the optical fiber cable 10 according to the present embodiment is shown in FIG. 2. A curvature capable of suppressing crosstalk is calculated according to the design of the multi-core optical fiber, i.e., the crosstalk characteristic of the multi-core optical fiber (for example, see Non-Patent Document 2), (step S01), and the number of units and twist pitch of the first layer unit 11 are set so as to obtain the curvature (step S02). Furthermore, the twist pitch of the units 11 arranged in each layer is set using Equation (7) so that the curvature of the units in each layer in the optical fiber cable is uniform (step S03). Here, in step S01, a curvature that avoids a curvature Rpk, which will be described later, is calculated. By these procedures, the optical fiber cable 10 according to the present embodiment can be manufactured, and crosstalk of all the multi-core optical fiber cores in the optical fiber cable 10 can be suppressed.

[0034] Next, we will explain the possible range of the twist pitch considering the crosstalk characteristics of the multi-core optical fiber. As shown in Non-Patent Document 2, it is known that the crosstalk of the multi-core optical fiber reaches a maximum value at a certain curvature Rpk, and the cable should be constructed so as to avoid this Rpk.

[0035] For example, the curvature of Rpk is ρ = 20 m -1 (When expressed as bending radius, 1 / ρ[m -1 ] = 50 [mm]), unit diameter d = 1.5 mm (measured example of unit diameter when 20 fibers with diameter 0.25 mm are bundled), and the number of units n = 3, then from equation (2) the twist radius r1 = 0.86 mm, and substituting this into equation (1) gives P1 = 41 mm, so it is sufficient to avoid this pitch during manufacturing.

[0036] Here, if P1 is set so that ρ1 is sufficiently smaller than Rpk, for example by about one order of magnitude, the amount of change in crosstalk relative to the change in curvature of the optical fiber becomes small (for example, see Non-Patent Document 2). Therefore, it is not necessary for the curvatures of the first layer unit 11 and the m-th layer unit 11 to be exactly the same, and it is sufficient that the crosstalk does not deteriorate. In this case, the pitch Pm of the m-th layer unit 11 can be set so as to satisfy formula (8).

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[0037] Also, even if P1 is set so that ρ1 is sufficiently larger than Rpk, for example by about one order of magnitude, the amount of change in crosstalk with respect to the change in curvature of the optical fiber becomes small (for example, see Non-Patent Document 2). Therefore, it is not necessary for the curvatures of the first layer unit 11 and the m-th layer unit 11 to be exactly the same, and it is sufficient that the crosstalk does not deteriorate. In this case, the pitch Pm of the m-th layer unit 11 can be set so as to satisfy formula (9).

number

[0038] The above-mentioned manufacturing method of the optical fiber cable 10 can also be applied to the case where formula (8) or formula (9) is used. Specifically, steps S01 and S02 are performed as described above. After that, in step S03, the twist pitch of the units 11 of each layer is set based on formula (8) if the curvature (ρ1) calculated in step S01 is sufficiently smaller than Rpk, and based on formula (9) if the curvature (ρ1) calculated in step S01 is sufficiently larger than Rpk.

[0039] The twisting structure of the units shown so far is based on the premise that the units of each layer are not interchanged with the units of the adjacent layers. Here, the case where the units of each layer are twisted together in the same rotation direction as viewed from the cross-sectional direction of the optical fiber cable, that is, the case where they are wound in the same direction with respect to the longitudinal direction of the optical fiber cable 10, will be described with reference to FIG. 3. In FIG. 3, the first layer and the second layer are illustrated as examples of adjacent layers, and each layer is simply represented by a cylinder, and the twisting direction of each layer is shown. When the units of adjacent layers are wound in the same direction with respect to the longitudinal direction of the optical fiber cable 10 as shown in FIG. 3, the units are twisted together approximately in parallel when viewed from the side of the cable. For this reason, when there is a gap between the units of a certain layer, the units of the adjacent layer may enter the layer, and there is a concern that the position of the units may change between the adjacent layers, and the preset twisting pitch may not be maintained. Therefore, the units 11 arranged in adjacent layers may be twisted together so that the twisting directions of the spiral shapes are different from each other.

[0040] As an example, the twisting direction of the helical shape in the first layer and the second layer will be described with reference to FIG. 4. In FIG. 4, the first layer and the second layer are illustrated as adjacent layers, and each layer is simply represented by a cylinder, and the twisting direction of each layer is shown. In the optical fiber cable 10 according to the present embodiment, the twisting direction of the first layer may be right-handed and the twisting direction of the second layer may be left-handed with respect to the longitudinal direction of the optical fiber cable 10, as shown in FIG. 4. With this structure, the units are twisted to cross each other as shown in FIG. 4 when viewed from the side of the optical fiber cable, so that the positions of adjacent units between adjacent layers are prevented from being swapped, and stable manufacturing with a desired twisting pitch is possible.

[0041] As described above, the optical fiber cable according to the present disclosure can ensure low crosstalk for all multi-core optical fibers in the optical fiber cable having a plurality of identical uncoupled multi-core optical fibers with different spiral shapes by shifting the curvatures of all multi-core optical fibers contained in the optical fiber cable from the curvature Rpk at which the crosstalk of the multi-core optical fiber is maximum.

[0042] The above-mentioned inventions can be combined as much as possible. [Industrial Applicability]

[0043] The optical fiber cable according to the present disclosure can be applied to the information and communication industry. [Explanation of symbols]

[0044] 10: Fiber optic cable 11: Unit 12:Outer cover

Claims

1. An optical fiber cable formed by twisting together a plurality of units each formed by bundling a plurality of identical uncoupled multi-core optical fibers, all said units have the same diameter; The units are arranged in a plurality of layers from the center in a cross section; the units are arranged in a spiral shape for each layer in the longitudinal direction; all of the units included in one of the layers have the same twist pitch of the helical shape; The relationship between the twist pitch P1 of the spiral shape of the unit arranged in the innermost layer and the twist pitch Pm of the spiral shape of the unit arranged in the m-th layer (m is an integer of 2 or more) counting from the innermost layer is C4; and The curvature ρ1 of the spiral shape of the unit arranged in the innermost layer calculated by the formula C2 is different from the curvature Rpk at which crosstalk is maximized in the multi-core optical fiber. A fiber optic cable comprising: [Number C1] [Number C2] [Number C4] Here, d is the diameter of the unit, n is the number of the units arranged in the innermost layer, and r1 is the twist radius of the spiral shape of the units arranged in the innermost layer calculated by number C1.

2. An optical fiber cable formed by twisting together a plurality of units each formed by bundling a plurality of identical uncoupled multi-core optical fibers, all said units have the same diameter; The units are arranged in a plurality of layers from the center in a cross section; the units are arranged in a spiral shape for each layer in the longitudinal direction; all of the units included in one of the layers have the same twist pitch of the helical shape; The relationship between the twist pitch P1 of the spiral shape of the unit arranged in the innermost layer and the twist pitch Pm of the spiral shape of the unit arranged in the m-th layer (m is an integer of 2 or more) counting from the innermost layer is C8; and The curvature ρ1 of the spiral shape of the unit arranged in the innermost layer calculated by the formula C2 is one order of magnitude smaller than the curvature Rpk at which crosstalk is maximized in the multi-core optical fiber. A fiber optic cable comprising: [Number C1] [Number C2] [Number C8] Here, d is the diameter of the unit, n is the number of the units arranged in the innermost layer, and r1 is the twist radius of the spiral shape of the units arranged in the innermost layer calculated by number C1.

3. An optical fiber cable formed by twisting together a plurality of units each formed by bundling a plurality of identical uncoupled multi-core optical fibers, all said units have the same diameter; The units are arranged in a plurality of layers from the center in a cross section; the units are arranged in a spiral shape for each layer in the longitudinal direction; all of the units included in one of the layers have the same twist pitch of the helical shape; The relationship between the twist pitch P1 of the spiral shape of the unit arranged in the innermost layer and the twist pitch Pm of the spiral shape of the unit arranged in the m-th layer (m is an integer of 2 or more) counting from the innermost layer is C12; and The curvature ρ1 of the spiral shape of the unit arranged in the innermost layer calculated by the formula C2 is one order of magnitude larger than the curvature Rpk at which crosstalk is maximized in the multi-core optical fiber. A fiber optic cable comprising: [Number C1] [Number C2] [Number C12] Here, d is the diameter of the unit, n is the number of the units arranged in the innermost layer, and r1 is the twist radius of the spiral shape of the units arranged in the innermost layer calculated by number C1.

4. The twist directions of the spiral shapes of the units arranged in adjacent layers are different from each other.

4. The optical fiber cable according to claim 1, wherein

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