Multi-core fiber, multi-core fiber ribbon, manufacturing method of multi-core fiber, and processing method of multi-core fiber

Abstract

The purpose of the present invention is to provide multicore fiber in which crosstalk between cores is suppressed and a reduction in manufacturability is also suppressed. This multicore fiber comprises: a plurality of core parts (1) that have a center core part (1a), an intermediate layer (1b) formed on the outer circumference of the center core part, and a trench layer (1c) formed on the outer circumference of the intermediate layer; and a cladding part (2) that is formed on the outer circumference of the plurality of core parts, wherein for each of the plurality of core parts, when the maximum relative refractive index difference in the center core part with respect to the cladding part is Δ1, the average relative refractive index difference in the intermediate layer is Δ2, and the average relative refractive index difference in the trench layer is Δ3, Δ1>Δ2>Δ3 and -0.3%>Δ3 are true.

Description

[Technical field]

[0001] The present invention relates to a multicore fiber, a multicore fiber ribbon, a method for manufacturing a multicore fiber, and a method for treating a multicore fiber. [Background technology]

[0002] In the fields of datacom and telecom, multi-core fibers are known as optical fibers that realize high-density optical fiber cables. The multi-core fibers described in Patent Documents 1 and 2 have a core portion that employs a trench structure to suppress crosstalk between cores. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2012-118495 A [Patent Document 2] JP 2016-075938 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the multi-core fibers described in Patent Documents 1 and 2, the relative refractive index difference Δ3 of the trench layer with respect to the cladding is smaller than −0.3%. When the cladding is made of pure silica glass, in order to make the relative refractive index difference Δ3 smaller than −0.3%, it is necessary to increase the dopant that reduces the refractive index of the silica-based glass, such as fluorine, which reduces the manufacturability of the trench layer or the optical fiber including the same. In addition, since a multi-core fiber includes multiple cores, when each core includes a trench layer, the influence of the low manufacturability of the trench layer accumulates, resulting in a lower manufacturability compared to a single-core fiber.

[0005] The present invention has been made in consideration of the above, and an object of the present invention is to provide a multi-core fiber, a multi-core fiber ribbon, a manufacturing method of a multi-core fiber, and a processing method of a multi-core fiber in which inter-core crosstalk is suppressed and a decrease in manufacturability is suppressed. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems and achieve the object, one aspect of the present invention is a multi-core fiber comprising: a plurality of core portions, each having a central core portion, an intermediate layer formed on an outer periphery of the central core portion, and a trench layer formed on the outer periphery of the intermediate layer; and a cladding portion formed on the outer periphery of the plurality of core portions, wherein, in each of the plurality of core portions, when an average maximum relative refractive index difference of the central core portion with respect to the cladding portion is Δ1, an average relative refractive index difference of the intermediate layer is Δ2, and an average relative refractive index difference of the trench layer is Δ3, the relationships Δ1>Δ2>Δ3 and 0%>Δ3>−0.3% hold true.

[0007] When the center distance between the most adjacent core portions among the plurality of core portions is Λ and the shortest distance between the trench layers of the most adjacent core portions is w, w / Λ may be 0.179 or less.

[0008] In each of the multiple core portions, when the central core diameter of the central core portion is 2a, and the inner diameter and outer diameter of the trench layer are 2b and 2c, respectively, b / a may be 1.9 or more and 3.0 or less, and c / a may be 3.6 or more and 4.4 or less.

[0009] The Δ1 may be 0.35% or more and 0.39% or less.

[0010] The Δ2 may be −0.05% or more and 0.04% or less.

[0011] The central core diameter of each of the plurality of core portions may be set so that the effective cutoff wavelength is not less than 1000 nm and not more than 1260 nm.

[0012] Each of the plurality of core portions may have a mode field diameter of 8.6 μm or more and 9.2 μm or less at a wavelength of 1310 nm.

[0013] In each of the plurality of core portions, a bending loss at a wavelength of 1550 nm when bent with a diameter of 20 mm may be 1.57 dB / m or less.

[0014] In a length of 100 km, crosstalk between the most adjacent core portions among the plurality of core portions may be −25 dB or less.

[0015] The center distance between the most adjacent core portions among the plurality of core portions may be 37 μm or more and 41 μm or less.

[0016] The cladding thickness of the cladding portion on the outer circumferential side relative to the outermost core portion among the plurality of core portions may be 25 μm or less.

[0017] In each of the plurality of cores, the zero dispersion wavelength is 1300 nm or more and 1324 nm or less, and the dispersion slope at the zero dispersion wavelength is 0.092 ps / nm 2 / km or less is also acceptable.

[0018] The number of the core portions may be three or four.

[0019] The cladding may include a coating layer formed on the outer periphery of the cladding.

[0020] The coating layer may have a non-circular coating portion where at least a portion of the outer surface is deviated from a cylindrical shape along the extension direction of the cladding portion.

[0021] The cladding portion may have a non-circular cladding portion on at least a portion of an outer surface thereof, the non-circular cladding portion being deviated from a cylindrical shape along the non-circular coating portion of the coating layer.

[0022] The cladding diameter of the cladding portion may be 137 μm or less.

[0023] One aspect of the present invention is a method for processing a multi-core fiber, which processes the multi-core fiber using a jig or device for processing a standard optical fiber having a cladding diameter of 125 μm.

[0024] One aspect of the present invention is a multi-core fiber ribbon including a plurality of the multi-core fibers arranged in parallel.

[0025] Each of the multiple multi-core fibers may include a coating layer formed on an outer periphery of the cladding portion, and the coating layer may have a non-circular coating portion in which at least a portion of an outer surface deviates from a cylindrical shape along the extension direction of the cladding portion, and each of the multiple multi-core fibers may abut an adjacent multi-core fiber at the non-circular coating portion.

[0026] One aspect of the present invention is a method for manufacturing the multicore fiber, comprising: a first step of preparing a plurality of core members that will become at least a portion of the plurality of core portions; a second step of preparing a clad member that will become at least a portion of the clad portion; a third step of forming a preform using the plurality of core members and the clad member; and a fourth step of drawing the multicore fiber from the preform.

[0027] In the first step, the plurality of core members may be formed by a vapor-phase axial deposition (VAD) method or an outside vapor deposition (OVD) method.

[0028] In the third step, the base material may be formed by a drilling method or a stacking method.

[0029] In the third step, the preform may be formed so that the volume of the preform is equivalent to a length of 100 km or more of the multicore fiber. Effect of the Invention

[0030] The multi-core fiber according to the present invention has the effect of suppressing inter-core crosstalk and suppressing a decrease in manufacturability. [Brief description of the drawings]

[0031] [Figure 1] FIG. 1 is a schematic cross-sectional view of a multi-core fiber according to a first embodiment. [Diagram 2] FIG. 2 is a schematic diagram of the refractive index profile of the core portion and its periphery of the multi-core fiber of FIG. [Diagram 3] FIG. 3 is a schematic cross-sectional view of a multi-core according to the second embodiment. [Figure 4] FIG. 4 is a radar chart showing the cladding diameters of Samples Nos. 1 to 35. [Diagram 5] FIG. 5 is a schematic cross-sectional view of a multi-core fiber ribbon according to the third embodiment. [Figure 6A] FIG. 6A is a schematic cross-sectional view of a multi-core fiber according to embodiment 4 that is suitable for forming a multi-core fiber ribbon. [Figure 6B] FIG. 6B is a schematic cross-sectional view of a multi-core fiber according to embodiment 5, which is suitable for forming a multi-core fiber ribbon. [Figure 6C] FIG. 6C is a schematic cross-sectional view of a multi-core fiber according to embodiment 6 that is suitable for forming a multi-core fiber ribbon. [Figure 6D] FIG. 6D is a schematic cross-sectional view of a multi-core fiber according to embodiment 7, which is suitable for forming a multi-core fiber ribbon. [Figure 6E] FIG. 6E is a schematic cross-sectional view of a multi-core fiber according to embodiment 8, which is suitable for forming a multi-core fiber ribbon. [Figure 7]FIG. 7 is an explanatory diagram of a method for manufacturing a multi-core fiber. [Figure 8] FIG. 8 is a diagram illustrating a first example of a refractive index profile that can be regarded as a trench type. [Figure 9] FIG. 9 is a diagram illustrating a second example of a refractive index profile that can be regarded as a trench type. [Figure 10] FIG. 10 is a diagram illustrating a third example of a refractive index profile that can be regarded as a trench type. [Figure 11] FIG. 11 is a diagram illustrating a fourth example of a refractive index profile that can be regarded as a trench type. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiment described below. In addition, in each drawing, the same or corresponding components are appropriately assigned the same reference numerals. In addition, in this specification, the cutoff wavelength or effective cutoff wavelength refers to the cable cutoff wavelength defined in ITU (International Telecommunication Union)-T G.650.1. In addition, other terms not specifically defined in this specification shall follow the definitions and measurement methods in G.650.1 and G.650.2.

[0033] (Embodiment 1) Fig. 1 is a schematic cross-sectional view of a multi-core fiber according to a first embodiment. The multi-core fiber 10 includes four core portions 1 as a plurality of core portions. The multi-core fiber 10 also includes a cladding portion 2 formed on the outer periphery of the four core portions 1. The four core portions 1 are arranged in a square shape with the central axis of the cladding portion 2 as the center. The multi-core fiber 10 may also include a coating layer formed on the outer periphery of the cladding portion 2. Such a coating layer is made of a resin or the like that can be used as a coating layer for optical fibers.

[0034] The core 1 and the cladding 2 are both made of silica glass. The cladding 2 has a substantially circular cross section and a refractive index lower than the maximum refractive index of the core 1.

[0035] The core portion 1 has a substantially circular cross section and has a substantially concentric structure including a central core portion 1a, an intermediate layer 1b formed on the outer periphery of the central core portion 1a, and a trench layer 1c formed on the outer periphery of the intermediate layer 1b.

[0036] Fig. 2 is a schematic diagram of the refractive index profile of an arbitrary core portion 1 and the surrounding cladding portion 2 of a multicore fiber 10. In Fig. 2, profile P11 shows the refractive index profile of the central core portion 1a, profile P12 shows the refractive index profile of the intermediate layer 1b, profile P13 shows the refractive index profile of the trench layer 1c, and profile P14 shows the refractive index profile of the cladding portion 2.

[0037] The central core portion 1a has a central core diameter 2a, and the average maximum relative refractive index difference of the central core portion 1a with respect to the cladding portion 2 is Δ1. Here, the refractive index profile of the central core portion 1a may not only be a step type having a geometrically ideal shape, but may also have a shape where the top is not flat but has irregularities formed due to manufacturing characteristics, or has a shape that trails from the top. In this case, the refractive index of a region that is approximately flat at the top of the refractive index profile within the range of the core diameter 2a in the manufacturing design is an index for determining Δ1.

[0038] The intermediate layer 1b has an outer diameter 2b, and an average relative refractive index difference of the intermediate layer 1b with respect to the cladding portion 2 is Δ2. The trench layer 1c has an inner diameter 2b, an outer diameter 2c, and an average relative refractive index difference of the trench layer 1c with respect to the cladding portion 2 is Δ3.

[0039] Here, in the multi-core fiber 10, Δ1>Δ2>Δ3 and 0%>Δ3>−0.3% are satisfied in each core portion 1. That is, in the multi-core fiber 10, each core portion 1 has a trench-type refractive index profile. For example, the above inequality is satisfied when the central core portion 1a is made of silica glass doped with a dopant such as germanium (Ge) that increases the refractive index, the intermediate layer 1b contains almost no dopant that changes the refractive index, the central core portion 1a is made of silica glass doped with a dopant that decreases the refractive index such as fluorine (F), and the cladding portion 2 is made of pure silica glass. Note that pure silica glass is extremely high-purity silica glass that does not substantially contain a dopant that changes the refractive index and has a refractive index of about 1.444 at a wavelength of 1550 nm.

[0040] Furthermore, in the multi-core fiber 10, Δ3>−0.3% holds in each core portion 1, so that it is possible to relatively reduce the amount of a dopant that reduces the refractive index, such as fluorine, that should be added to the trench layer 3. This prevents the multi-core fiber 10 from decreasing in manufacturability, and provides excellent mass productivity, for example.

[0041] Furthermore, in the multi-core fiber 10, as shown in FIG. 1, if the center distance between the most adjacent core parts 1 among the core parts 1 is Λ and the shortest distance between the trench layers 1c of the most adjacent core parts 1 is w, for example, w / Λ is 0.179 or less. If w / Λ is 0.179 or less, the trench width (c-b) / 2 of the trench layer 1c is relatively large, so that even if the absolute value of Δ3 of the trench layer 1c is small, the crosstalk between the core parts 1 (inter-core crosstalk) can be relatively high and the bending loss characteristics can be relatively good. In addition, w / Λ being 0.179 or less and the trench width (c-b) / 2 being relatively large means that the distance between the center of the field intensity of the light propagating through the core part 1 and the interface between the trench layer 1c and the cladding part 2 is relatively far. As a result, the increase in the propagation loss of the core part 1 caused by the presence of the interface is suppressed.

[0042] Incidentally, from the viewpoint of versatility, it is preferable that the optical characteristics of the multi-core fiber 10 conform to a standard that is widely accepted as an optical fiber standard, such as the standard defined by ITU-T G.652 (G.652 standard) or further the G.657 standard.

[0043] The present inventors have comprehensively examined design parameters such as 2a, 2b, 2c, Δ1, Δ2, and Δ3 shown in FIG. 2, and as a result of thorough investigation, have confirmed that it is preferable for the design parameters in each of the core portions 1 to satisfy the following characteristics. That is, when Δ3>-0.3%, it is preferable that (1) b / a is 1.9 to 3.0, and c / a is 3.6 to 4.4. It is also preferable that (2) Δ1 is 0.35% to 0.39%. It is also preferable that (3) Δ2 is -0.05% to 0.04%. It is also preferable that (4) 2a is set so that the effective cutoff wavelength is 1000 nm to 1260 nm.

[0044] The present inventors have confirmed that by satisfying one or more of the above conditions (1) to (4), it is easy to realize a multi-core fiber 10 that satisfies the following optical characteristics (5) to (7) of the G.657 A2 standard. That is, (5) an effective cutoff wavelength of 1000 nm or more and 1260 nm or less, (6) a mode field diameter at a wavelength of 1310 nm of 8.6 μm or more and 9.2 μm or less, and (7) a bending loss at a wavelength of 1550 nm when bent at a diameter of 20 mm is 1.57 dB / m or less. Regarding the chromatic dispersion characteristics, when the multi-core fiber 10 is applied to communication using a digital coherent communication technology, dispersion compensation is possible to a certain extent, but it is preferable to satisfy the following optical characteristics (8) and (9) of the G.657 A2 standard. That is, (8) a zero-dispersion wavelength of 1300 nm or more and 1324 nm or less, and (9) a dispersion slope at the zero-dispersion wavelength of 0.092 ps / nm. 2 / km or less.

[0045] The present inventors have also confirmed that if Λ is 37 μm or more and 41 μm or less, in a multi-core fiber 10 having a length of 100 km, the inter-core crosstalk between the two most adjacent core portions 1 can be easily reduced to −25 dB or less, and further to −30 dB or less.

[0046] Furthermore, from the viewpoint of high density in the optical fiber cable, it is preferable that the outer diameter (cladding diameter) of the cladding portion 2 of the multi-core fiber 10 is small. It has been confirmed that when the multi-core fiber 10 satisfies one or more of the above conditions (1) to (4), if the cladding thickness t of the cladding portion 2 on the outer periphery side with respect to the core portion 1 located on the outermost side is 25 μm or less, the excess loss due to the thinning is negligible. Here, the cladding thickness t of the cladding portion 2 on the outer periphery side with respect to the core portion 1 located on the outermost side is the distance from the center of the core portion 1 closest to the outer periphery of the cladding portion 2 to the outer periphery of the cladding portion 2, as shown in FIG. 1. Note that, in the arrangement of the core portions 1 shown in FIG. 1, the distance from the center to the outer periphery of the cladding portion 2 is the same for all the core portions 1. Hereinafter, such a cladding thickness t may be referred to as a minimum cladding thickness.

[0047] As described above, in the multi-core fiber 10 according to the first embodiment, the inter-core crosstalk is suppressed by adopting a trench-type refractive index profile, and the deterioration of manufacturability is suppressed by satisfying Δ3>−0.3%.

[0048] (Embodiment 2) 3 is a schematic cross-sectional view of a multi-core fiber according to embodiment 2. The multi-core fiber 10A includes three core portions 1 as a plurality of core portions. The multi-core fiber 10 also includes a cladding portion 2 formed on the outer periphery of the three core portions 1. The three core portions 1 are arranged in an equilateral triangle shape with the central axis of the cladding portion 2 as the center.

[0049] The multi-core fiber 10A differs from the multi-core fiber 10A according to the embodiment 1 in the number and arrangement of core portions 1, but other configurations, such as the constituent materials and design parameter values, are the same. Therefore, the multi-core fiber 10A also suppresses inter-core crosstalk and suppresses deterioration in manufacturability.

[0050] (Example) As examples, multicore fiber samples were manufactured using the manufacturing method described below. All of Samples No. 1 to 35 were designed and manufactured to satisfy the above-mentioned conditions (1) to (4) for both the four-core structure having four cores shown in Fig. 1 and the three-core structure shown in Fig. 3.

[0051] The design parameters and optical characteristics of Samples No. 1 to 35 are shown in Tables 1A and 1B. In the tables, Λ was set so that the inter-core crosstalk was -30 dB at 100 km. The fiber diameter means the cladding diameter. "λ0" means the zero-dispersion wavelength. "Dispersion Slope@λ0" means the dispersion slope at the zero-dispersion wavelength. "MFD" means the mode field diameter. "λcc" means the cable cutoff wavelength (effective cutoff wavelength). As shown in Tables 1A and 1B, all of Samples No. 1 to 35 satisfied the optical characteristics (5) to (9) of the G.657 A2 standard, and the inter-core crosstalk at a length of 100 km was -25 dB or less.

[0052] [Table 1A]

[0053] [Table 1B]

[0054] (cladding diameter) Next, a description will be given of the cladding diameter of the multi-core fibers 10 and 10A. It is preferable that the cladding diameter of the multi-core fibers 10 and 10A is close to 125 μm that complies with the G.652 standard and the G.657 standard.

[0055] Fig. 4 is a radar chart showing the cladding diameters of the multi-core fibers of Samples No. 1 to 35 in Tables 1A and 1B. In the figure, line L1 shows the cladding diameters of the multi-core fibers of Samples No. 1 to 35 in the case of a 3-core structure, and line L2 shows the cladding diameters of the multi-core fibers of Samples No. 1 to 35 in the case of a 4-core structure. As shown in the figure, the cladding diameters of all the manufactured samples are 120 µm or more and 137 µm or less.

[0056] Thus, a multi-core fiber with a cladding diameter of 137 μm or less is more suitable for ensuring long-term reliability of mechanical properties such as fracture properties through screening tests. Also, a multi-core fiber with a cladding diameter of 120 μm or more and 137 μm or less is within ±10% of 125 μm, so it can be processed using a tool or device for processing an optical fiber with a cladding diameter of 125 μm. An optical fiber with a cladding diameter of 125 μm is sometimes called a standard optical fiber, and is suitable because a tool or device for processing it is widely used. Such a processing tool or device is, for example, a coating removal tool, a cutting tool, or a fusion splicing device for a multi-core fiber.

[0057] (Embodiment 3) Fig. 5 is a schematic cross-sectional view of a multi-core fiber ribbon according to embodiment 3. The multi-core fiber ribbon 30 shown in Fig. 5 has a configuration in which four multi-core fibers 10B are arranged in parallel, and the outer peripheries of the multi-core fibers 10B are collectively coated with a coating layer 110 made of a resin or the like. The coating layer 110 is made of a resin or the like that can be used as a collective coating layer for an optical fiber ribbon. The four multi-core fibers 10B are an example of a plurality of multi-core fibers.

[0058] The multi-core fiber 10B includes four core portions 1, a cladding portion 2B formed on the outer periphery of the four core portions 1, and a coating layer 3B formed on the outer periphery of the cladding portion 2B. The core portions 1 have the same structure and are made of the same constituent materials as the core portion 1 of the first embodiment. The design and arrangement of the core portions 1 preferably satisfy the conditions that w / Λ is 0.179 or less, inter-core crosstalk is −25 dB, or the minimum cladding thickness t is 25 μm or less. Furthermore, it is preferable to satisfy one or more of the conditions (1) to (4).

[0059] The coating layer 3B is made of a resin or the like that can be used as a coating layer for an optical fiber. The coating layer 3B has a non-circular coating portion where at least a part of the outer surface is deviated from a cylindrical shape along the extension direction of the cladding portion 2B. In this embodiment, the coating layer 3B has planar outer surfaces parallel to two opposing sides of the quadrangle formed by the core portion 1 formed to face each other, constituting a non-circular coating portion 3Ba.

[0060] The cladding portion 2B is made of the same material as the cladding portion 2 of the first embodiment, but is different in that at least a part of the outer surface has a noncircular cladding portion. In this embodiment, the planar outer surfaces of the cladding portion 2B, which are parallel to two opposing sides of the rectangle formed by the core portion 1, are formed to face each other, thereby forming a noncircular cladding portion. The noncircular cladding portion has a shape that conforms to the noncircular coating portion 3Ba of the coating layer 3B.

[0061] In the multi-core fiber ribbon 30, each of the multi-core fibers 10B abuts on an adjacent multi-core fiber 10B at a non-circular coating portion 3Ba. This makes it easier to align the arrangement directions of the core portions 1 in each of the multi-core fibers 10B when ribbonizing the four multi-core fibers 10B. For example, in the case of Fig. 5, the arrangement direction of the core portions 1 in each of the multi-core fibers 10B is aligned along the parallel direction of the multi-core fibers 10B.

[0062] (Multicore fiber suitable for constructing multicore fiber ribbons) 6A, 6B, 6C, 6D, and 6E are schematic cross-sectional views of multi-core fibers according to embodiments 4, 5, 6, 7, and 8, respectively, which are suitable for forming a multi-core fiber ribbon.

[0063] The multi-core fiber 10C shown in Fig. 6A is different from the multi-core fiber 10B in the following two points. The first point is that the outer surface of the coating layer 3C has a non-circular coating portion having a regular hexagonal shape. In this embodiment, the coating layer 3C has planar outer surfaces parallel to two opposing sides of the rectangle formed by the core portion 1 so as to face each other. The other point is that the non-circular cladding portion of the cladding portion 2C has a regular hexagonal shape along the non-circular coating portion of the coating layer 3C.

[0064] The multi-core fiber 10D shown in Fig. 6B is different from the multi-core fiber 10B in the following two points. The first point is that the outer surface of the coating layer 3D has a non-circular coating portion in a square shape. In this embodiment, the coating layer 3D is concentric with the rectangle formed by the core portion 1. The other point is that the non-circular cladding portion of the cladding portion 2D has a square shape along the non-circular coating portion of the coating layer 3D.

[0065] The multi-core fiber 10E shown in Fig. 6C is different from the multi-core fiber 10C in the following respect: the outer surface of the coating layer 3E has a non-circular coating portion similar to that of the multi-core fiber 10C, but the cladding portion 2E has a circular shape rather than a shape that follows the non-circular coating portion of the coating layer 3D.

[0066] The multi-core fiber 10F shown in Fig. 6D is different from the multi-core fiber 10B in the following respect: the outer surface of the coating layer 3F has a non-circular coating portion similar to that of the multi-core fiber 10B, but the cladding portion 2E is circular.

[0067] The multi-core fiber 10G shown in Fig. 6E is different from the multi-core fiber 10D in the following respects: One of the differences is that the outer surface of the coating layer 3G has a non-circular coating portion similar to that of the multi-core fiber 10D, but the cladding portion 2E is circular.

[0068] In any of the multi-core fibers 10C to 10G shown in FIGS. 6A to 6E, the arrangement direction of the core portions 1 can be easily aligned when ribbonized, similar to the multi-core fiber 10B.

[0069] (Manufacturing method) A method for manufacturing a multi-core fiber according to the embodiment will be described by taking as an example a case where a multi-core fiber 10B is manufactured. First, a first step is performed in which a plurality of core members that will become at least a portion of the plurality of core portions 1 is prepared. Then, a second step is performed in which a cladding member that will become at least a portion of the cladding portion 2B is prepared. Then, a third step is performed in which a preform is formed using the plurality of core members and the cladding member. Then, a fourth step is performed in which a multi-core fiber is drawn from the preform.

[0070] Each step will be described below. In the first step, for example, a core member having the same refractive index profile as the refractive index profile formed by the central core portion 1a, the intermediate layer 1b, and the trench layer 3 in the core portion 1 is formed. Such a core member is also called a core rod. Note that in the core member, a glass layer that will become part of the cladding portion 2 may be formed on the outermost layer of the glass layer that will become the trench layer 3. Such a core rod can be formed by, for example, the VAD (Vapor-phase Axial Deposition) method or the OVD (Outside Vapor Deposition) method.

[0071] In the second step, for example, a cylindrical glass rod that will become at least a part of the cladding portion 2 is prepared, and a plurality of holes into which a core preform can be inserted are drilled along the cylindrical axis of the glass rod to form a cladding member. Alternatively, in the second step, a glass capillary that has an inner diameter into which a plurality of core members can be inserted and that will become a part of the core portion 1 may be prepared as one of the core members.

[0072] In the third step, a glass rod is inserted into each of the holes in the cladding member to form a base material. This type of base material forming method is also called a drilling method. Alternatively, in the third step, multiple core rods are inserted into a glass capillary, and glass rods that will become part of the core portion 1 are inserted between the core rods and the glass capillary, and between the core rods to form a base material. This type of base material forming method is also called a stack method.

[0073] In the case of the stack method, the outermost layer of the core preform is generally a glass layer that will become a part of the cladding portion 2. In the case of the drilling method, the outermost layer of the core preform may be a glass layer that will become a part of the cladding portion 2, or may be a glass layer that will become the trench layer 3. When the outermost layer of the core preform is a glass layer that will become the trench layer 3, the propagation loss is likely to increase when light passes through the interface between the trench layer 3 and the cladding portion 2B in the manufactured multi-core fiber. In this case, by setting w / Λ to 0.179 or less, the effect of suppressing the increase in the propagation loss of the core portion 1 caused by the presence of the interface is more effectively exhibited.

[0074] In addition, in the third step, the outer periphery of the base material is processed so as to have the shape of the cladding portion 2B of the multi-core fiber 10B. The processing can be performed by mechanical polishing, chemical polishing, or the like.

[0075] Moreover, in the third step, it is preferable to form the preform so that the volume of the preform is equivalent to 100 km or more in terms of the length of the multicore fiber to be drawn. This allows a long multicore fiber to be manufactured from one preform, thereby reducing the manufacturing cost of the multicore fiber. Furthermore, with such a large volume of preform, the glass thickness between the holes formed in the glass rod becomes sufficiently thick when a drilling method is used, so that cracks are unlikely to occur during the process, for example. Note that the volume of a non-defective part of the preform that can be used to manufacture a multicore fiber that meets the desired specifications is the volume of the multicore fiber as it is. Therefore, the volume required for the non-defective part of the preform can be calculated from the length and cladding diameter of the multicore fiber to be manufactured.

[0076] The fourth step is performed, for example, by the method shown in FIG. 7. That is, first, the preform 40 formed in the third step is set in a drawing furnace 100. Then, one end of the preform 40 is heated and melted by a heater 101, and a glass multi-core fiber 50 is drawn. The glass multi-core fiber 50 is composed of a core portion 1 and a cladding portion 2B. Next, an ultraviolet curing resin is applied to the outer periphery of the glass multi-core fiber 50 by a resin application device 102. Note that the die in the resin application device 102 is shaped so as to be able to form the outer shape of the coating layer 3B. Next, an ultraviolet irradiation device 103 irradiates the resin applied to the outer periphery of the glass multi-core fiber 50 with ultraviolet light to cure it, thereby forming the coating layer 3B. Next, the multi-core fiber 10B is guided to a winding device 105 by a guide roll 104. The winding device 105 is a device equipped with a bobbin for winding the multi-core fiber 10B. The drawing speed of the multi-core fiber 10B is changed according to the rotation speed of the bobbin.

[0077] When manufacturing the multi-core fibers 10, 10A, 10E, 10F, and 10G, it is not necessary to process the outer periphery of the preform in the third step.

[0078] (Refractive index profile) In Figure 2, the refractive index profile consists of straight lines, but the refractive index profile of an actually manufactured multicore fiber often does not consist of straight lines. Even in such cases, the design parameters a, b, c, Δ1, Δ2, Δ3, etc. can be confirmed from the refractive index profile measured by a profile analyzer, etc.

[0079] 8 to 11 are explanatory diagrams of first to fourth examples of refractive index profiles that can be regarded as trench types. In FIG. 8, a profile P22 shown by a dashed line can be identified for a profile P21 shown by a measured solid line. In FIG. 9, a profile P32 can be identified for a measured profile P31. In FIG. 10, a profile P42 can be identified for a measured profile P41. In FIG. 11, a profile P52 can be identified for a measured profile P51.

[0080] Although the measured refractive index profiles such as those shown in Figures 8 to 11 are not composed of at least a portion of straight lines, those skilled in the art can recognize them as trench-type refractive index profiles, identify their design parameters, and identify a refractive index profile that can be expressed by those design parameters.

[0081] The present invention is not limited to the above-mentioned embodiment. The present invention also includes a configuration in which the above-mentioned components are appropriately combined. Further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspects of the present invention are not limited to the above-mentioned embodiment, and various modifications are possible. [Industrial Applicability]

[0082] INDUSTRIAL APPLICABILITY As described above, the multi-core fiber, the multi-core fiber ribbon, the manufacturing method of a multi-core fiber, and the processing method of a multi-core fiber according to the present invention are useful for a multi-core fiber including a core portion employing a trench structure. [Explanation of symbols]

[0083] 1 Core 1a Central core 1b Middle layer 1c Trench layer 2, 2B, 2C, 2D, 2E Clad section 3 Trench layer 3B Coating Layer 3Ba Non-circular coating part 3C, 3D, 3E, 3F, 3G coating layers 10, 10A, 10B, 10C, 10D, 10E, 10F, 10G Multi-core fiber 30 Multi-core fiber ribbon 40 Base material 50 Glass multicore fiber 100 Wire drawing furnace 101 Heater 102 Resin application device 103 Ultraviolet irradiation device 104 Guide Roll 105 Winding device 110 Coating layer P11, P12, P13, P14, P21, P22, P31, P32, P41, P42, P51, P52 Profiles

Claims

1. A plurality of core portions each having a central core portion, an intermediate layer formed on the outer periphery of the central core portion, and a trench layer formed on the outer periphery of the intermediate layer; A cladding portion formed on the outer periphery of the plurality of core portions; Equipped with In each of the plurality of core portions, when the average maximum relative refractive index difference of the central core portion with respect to the cladding portion is Δ1, the average relative refractive index difference of the intermediate layer is Δ2, and the average relative refractive index difference of the trench layer is Δ3, Δ1>Δ2>Δ3 and 0%>Δ3>−0.3% are satisfied, The center distance between the most adjacent core portions among the plurality of core portions is 37 μm or more and 41 μm or less, When the center distance between the most adjacent core portions is Λ and the shortest distance between the trench layers of the most adjacent core portions is w, w / Λ is 0.179 or less. Multicore fiber.

2. In each of the plurality of core portions, when the central core portion has a central core diameter of 2a, and the trench layer has an inner diameter of 2b and an outer diameter of 2c, respectively, b / a is 1.9 or more and 3.0 or less, and c / a is 3.6 or more and 4.4 or less. The multicore fiber according to claim 1 .

3. The Δ1 is 0.35% or more and 0.39% or less. The multicore fiber according to claim 1 or 2.

4. The Δ2 is −0.05% or more and 0.04% or less. The multicore fiber according to any one of claims 1 to 3.

5. The central core diameter of each of the central core portions is set so that the effective cutoff wavelength is 1000 nm or more and 1260 nm or less. The multicore fiber according to any one of claims 1 to 4.

6. In each of the plurality of core portions, a mode field diameter at a wavelength of 1310 nm is 8.6 μm or more and 9.2 μm or less. The multicore fiber according to any one of claims 1 to 5.

7. In each of the plurality of core portions, the bending loss at a wavelength of 1550 nm when bent with a diameter of 20 mm is 1.57 dB / m or less. The multicore fiber according to any one of claims 1 to 6.

8. In a length of 100 km, the crosstalk between the most adjacent core parts among the plurality of core parts is −25 dB or less. The multicore fiber according to any one of claims 1 to 6.

9. The clad thickness of the clad portion on the outer periphery side of the core portion located on the outermost side of the plurality of core portions is 25 μm or less. The multicore fiber according to any one of claims 1 to 8.

10. In each of the plurality of cores, the zero dispersion wavelength is 1300 nm or more and 1324 nm or less, and the dispersion slope at the zero dispersion wavelength is 0.092 ps / nm 2 / km or less The multicore fiber according to any one of claims 1 to 9.

11. The number of the cores is 3 or 4. The multicore fiber according to any one of claims 1 to 10.

12. A coating layer is formed on the outer periphery of the clad portion. The multicore fiber according to any one of claims 1 to 11.

13. The coating layer has a non-circular coating portion in which at least a portion of an outer surface is deviated from a cylindrical shape along the extension direction of the cladding portion. The multicore fiber according to claim 12.

14. The cladding portion has a non-circular cladding portion on at least a portion of an outer surface thereof, the non-circular cladding portion being deviated from a cylindrical shape along the non-circular coating portion of the coating layer. The multicore fiber according to claim 13.

15. The cladding diameter of the cladding portion is 137 μm or less. The multicore fiber according to any one of claims 1 to 14.

16. The multi-core fiber according to claim 15 is processed using a jig or device for processing a standard optical fiber having a cladding diameter of 125 μm. Methods for processing multicore fibers.

17. A multi-core fiber ribbon comprising the multi-core fibers according to any one of claims 1 to 15, the multi-core fibers being arranged in parallel.

18. Each of the plurality of multi-core fibers includes a coating layer formed on an outer periphery of the cladding portion, and the coating layer has a non-circular coating portion in which at least a part of an outer surface is deviated from a cylindrical shape along an extension direction of the cladding portion, Each of the plurality of multi-core fibers abuts on an adjacent multi-core fiber at the non-circular coating portion. The multi-core fiber ribbon according to claim 17.

19. A method for producing a multi-core fiber according to any one of claims 1 to 15, A first step of preparing a plurality of core members which will become at least a portion of the plurality of core portions; A second step of preparing a clad member that will become at least a part of the clad portion; a third step of forming a base material using the plurality of core members and the clad member; a fourth step of drawing the multi-core fiber from the preform; Includes A method for manufacturing a multicore fiber.

20. In the first step, the plurality of core members are formed by a vapor-phase axial deposition (VAD) method or an outside vapor deposition (OVD) method. The method for producing a multicore fiber according to claim 19.

21. In the third step, the base material is formed by a drilling method or a stacking method. The method for producing a multicore fiber according to claim 19 or 20.

22. In the third step, the preform is formed so that the volume of the preform is equivalent to a length of 100 km or more of the multicore fiber. The method for manufacturing a multicore fiber according to any one of claims 19 to 21.

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