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

Abstract

The object of the present invention is to provide a multi-core optical fiber that suppresses inter-core crosstalk and reduces the reduction in manufacturability. The multi-core optical fiber comprises: a plurality of cores (1), which have a central core (1a), an intermediate layer (1b) formed on the periphery of the central core, and a groove layer (1c) formed on the periphery of the intermediate layer; and a cladding portion (2) formed on the periphery of the plurality of cores. For each of the plurality of cores, if the maximum relative refractive index difference of the central core with respect to the cladding portion is set to Δ1, the average relative refractive index difference of the intermediate layer with respect to the cladding portion is set to Δ2, and the average relative refractive index difference of the groove layer with respect to the cladding portion is set to Δ3, then Δ1>Δ2>Δ3(0.3%-0.3%)>Δ3 holds.

Description

Technical Field

[0001] The present invention relates to a multi-core optical fiber, a multi-core optical fiber ribbon, a method for manufacturing the multi-core optical fiber and a method for processing the multi-core optical fiber. Background Art

[0002] In the field of data communication and telecommunication, multi-core optical fibers are known as optical fibers for realizing high-density optical fiber cables. The multi-core optical fibers described in Patent Documents 1 and 2 include a core portion having a groove structure in order to suppress crosstalk between cores.

[0003] Prior Art Literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2012-118495

[0006] Patent Document 2: Japanese Patent Application Publication No. 2016-075938 Summary of the invention

[0007] Problems to be solved by the invention

[0008] However, in the multi-core optical fibers described in Patent Documents 1 and 2, the relative refractive index difference Δ3 of the groove layer relative to the cladding portion is less than -0.3%. In the case where the cladding portion is composed of pure silica glass, if the relative refractive index difference Δ3 is to be less than -0.3%, it is necessary to add a dopant such as fluorine that lowers the refractive index of the silica glass, so the manufacturability of the groove layer or the optical fiber including the groove layer is reduced. In addition, in the case of a multi-core optical fiber, since it includes a plurality of cores, when each core includes a groove layer, the influence of the low manufacturability of the groove layer is accumulated, and the manufacturability is further reduced compared to a single-core optical fiber.

[0009] The present invention has been made in view of the above circumstances, and an object thereof is to provide a multi-core optical fiber, a multi-core optical fiber ribbon, a method for manufacturing a multi-core optical fiber, and a method for handling a multi-core optical fiber that suppress inter-core crosstalk and suppress reduction in manufacturability.

[0010] Solutions to Solve Problems

[0011] In order to solve the above-mentioned problems and achieve the purpose, one scheme of the present invention is a multi-core optical fiber, which comprises: a plurality of core portions, which have a central core portion, an intermediate layer formed on the periphery of the central core portion, and a groove layer formed on the periphery of the intermediate layer; and a cladding portion, which is formed on the periphery of the plurality of core portions. For each of the plurality of core portions, if the average maximum relative refractive index difference of the central core portion relative to the cladding portion is set to Δ1, the average relative refractive index difference of the intermediate layer relative to the cladding portion is set to Δ2, and the average relative refractive index difference of the groove layer relative to the cladding portion is set to Δ3, then Δ1>Δ2>Δ3 and 0%>Δ3>-0.3% holds.

[0012] It is also possible that, 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 / A is equal to or less than 0.179.

[0013] It can also be that for each of the multiple core portions, when the center core diameter of the central core portion is set to 2a, and the inner diameter and outer diameter of the groove layer are set to 2b and 2c respectively, b / a is greater than 1.9 and less than 3.0, and c / a is greater than 3.6 and less than 4.4.

[0014] The Δ1 may be greater than or equal to 0.35% and less than or equal to 0.39%.

[0015] The Δ2 may be greater than or equal to -0.05% and less than or equal to 0.04%.

[0016] 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.

[0017] For each of the plurality of cores, a mode field diameter at a wavelength of 1310 nm may be greater than or equal to 8.6 μm and less than or equal to 9.2 μm.

[0018] When each of the plurality of core portions is bent with a diameter of 20 mm, a bending loss at a wavelength of 1550 nm may be 1.57 dB / m or less.

[0019] It may be that at a length of 100 km, the crosstalk between the most adjacent cores among the plurality of cores is -25 dB or less.

[0020] The center distance between the most adjacent core portions among the plurality of core portions may be greater than or equal to 37 μm and less than or equal to 41 μm.

[0021] The cladding thickness of the cladding portion on the outer peripheral side relative to the core portion located on the outermost peripheral side among the plurality of core portions may be 25 μm or less.

[0022] For each of the plurality of cores, a zero dispersion wavelength may be greater than or equal to 1300 nm and less than or equal to 1324 nm, and a dispersion slope at the zero dispersion wavelength may be less than or equal to 0.092 ps / nm 2 / km.

[0023] Alternatively, the number of the plurality of cores is three or four.

[0024] The multi-core optical fiber may include a coating layer formed on an outer periphery of the cladding portion.

[0025] At least a portion of the outer surface of the coating layer may include a non-circular coating portion that deviates from a cylindrical shape along an extending direction of the cladding portion.

[0026] At least a portion of the outer surface of the cladding portion may include a non-circular cladding portion along a shape in which the non-circular coating portion of the coating layer deviates from a cylindrical shape.

[0027] The cladding portion may have a cladding diameter of 137 μm or less.

[0028] One embodiment of the present invention is a method for processing a multi-core optical fiber, wherein the multi-core optical fiber is processed using a fixture or a device for processing a standard optical fiber with a cladding diameter of 125 μm.

[0029] One aspect of the present invention is a multi-core optical fiber ribbon including a plurality of the multi-core optical fibers arranged in parallel.

[0030] It is also possible that each of the multiple multi-core optical fibers has a coating formed on the outer periphery of the cladding portion, and at least a portion of the outer surface of the coating has a non-circular coating portion that deviates from the cylindrical shape along the extension direction of the cladding portion, and each of the multiple multi-core optical fibers abuts against adjacent multi-core optical fibers at the non-circular coating portion.

[0031] One embodiment of the present invention is a method for manufacturing the multi-core optical fiber, comprising: a first step, in which a plurality of core components that become at least a part of the plurality of core portions are prepared; a second step, in which a cladding component that becomes at least a part of the cladding portion is prepared; a third step, in which the plurality of core components and the cladding component are used to form a mother material; and a fourth step, in which the multi-core optical fiber is drawn from the mother material.

[0032] In the first step, the plurality of core members may be formed by a vapor axial deposition method or an outside vapor deposition method.

[0033] In the third step, the base material may be formed by a punching method or a stacking method.

[0034] In the third step, the base material may be formed so that the volume of the base material converted into the length of the multi-core optical fiber is 100 km or more.

[0035] Effects of the Invention

[0036] The multi-core optical fiber of the present invention has the effect of suppressing inter-core crosstalk and suppressing a decrease in manufacturability. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a schematic cross-sectional view of the multi-core optical fiber according to the first embodiment.

[0038] Figure 2 yes Figure 1 Schematic diagram of the refractive index profile of the core and its periphery of a multi-core optical fiber.

[0039] Figure 3 This is a schematic cross-sectional view of a multi-core according to the second embodiment.

[0040] Figure 4 It is a radar chart showing the cladding diameters of Samples No. 1 to 35.

[0041] Figure 5 This is a schematic cross-sectional view of a multi-core optical fiber ribbon according to the third embodiment.

[0042] Fig. 6A This is a schematic cross-sectional view of a multi-core optical fiber according to a fourth embodiment of the structure of a multi-core optical fiber ribbon.

[0043] Figure 6B This is a schematic cross-sectional view of a multi-core optical fiber according to a fifth embodiment of the structure applicable to a multi-core optical fiber ribbon.

[0044] Figure 6C This is a schematic cross-sectional view of a multi-core optical fiber according to a sixth embodiment of the structure of a multi-core optical fiber ribbon.

[0045] Fig.6D This is a schematic cross-sectional view of a multi-core optical fiber according to a seventh embodiment of the structure applicable to a multi-core optical fiber ribbon.

[0046] Fig. 6E This is a schematic cross-sectional view of a multi-core optical fiber according to an eighth embodiment of the structure of a multi-core optical fiber ribbon.

[0047] Figure 7 It is an explanatory diagram of a method for producing a multi-core optical fiber.

[0048] Figure 8 This is an explanatory diagram of a first example of a refractive index profile that can be regarded as a groove type.

[0049] Fig. 9 This is an explanatory diagram of a second example of a refractive index profile that can be regarded as a groove type.

[0050] Fig.10 This is an explanatory diagram of a third example of a refractive index profile that can be regarded as a groove type.

[0051] Fig.11 This is an explanatory diagram of a fourth example of a refractive index profile that can be regarded as a groove type. DETAILED DESCRIPTION

[0052] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that the present invention is not limited to the embodiments described below. In addition, in each of the accompanying drawings, the same or corresponding components are appropriately marked with the same reference numerals. In addition, in this specification, the cut-off wavelength or effective cut-off wavelength refers to the cable cut-off wavelength defined in ITU (International Telecommunication Union)-T G.650.1. In addition, for terms not particularly defined in this specification, the definitions and measurement methods in G.650.1 and G.650.2 are followed.

[0053] (Implementation Method 1)

[0054] Figure 1 1 is a schematic cross-sectional view of a multi-core optical fiber according to Embodiment 1. The multi-core optical fiber 10 includes four core portions 1 as a plurality of core portions. In addition, the multi-core optical fiber 10 includes a cladding portion 2 formed on the 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. It should be noted that the multi-core optical fiber 10 may also include a coating formed on the periphery of the cladding portion 2. Such a coating is composed of a resin or the like that can be used as a coating for an optical fiber.

[0055] The core 1 and the cladding 2 are both made of quartz glass. The cladding 2 has a substantially circular cross section and has a refractive index lower than the maximum refractive index of the core 1 .

[0056] The core 1 has a substantially circular cross section and has a substantially concentric structure of a central core 1 a , an intermediate layer 1 b formed on the periphery of the central core 1 a , and a groove layer 1 c formed on the periphery of the intermediate layer 1 b .

[0057] Figure 2 Schematic diagram of the refractive index profile of an arbitrary core portion 1 and its surrounding cladding portion 2 in a multi-core optical fiber 10. Figure 2, the profile P11 represents the refractive index profile of the central core portion 1 a , the profile P12 represents the refractive index profile of the intermediate layer 1 b , the profile P13 represents the refractive index profile of the trench layer 1 c , and the profile P14 represents the refractive index profile of the cladding portion 2 .

[0058] The center core diameter of the center core 1a is 2a, and the average maximum relative refractive index difference of the center core 1a relative to the cladding portion 2 is Δ1. Here, the refractive index profile of the center core 1a is not only a geometrically ideal shape, i.e., a step-shaped case, but also has a top shape that is not flat and is formed with concave and convex according to manufacturing characteristics, or a shape that is drawn from the top. In this case, the refractive index of the region that is roughly flat at the top of the refractive index profile within the range of the core diameter 2a in the manufacturing design becomes an index for determining Δ1.

[0059] The outer diameter of the intermediate layer 1b is 2b, and the average relative refractive index difference of the intermediate layer 1b with respect to the cladding portion 2 is Δ2. The inner diameter of the trench layer 1c is 2b, the outer diameter is 2c, and the average relative refractive index difference of the trench layer 1c with respect to the cladding portion 2 is Δ3.

[0060] Here, in the multi-core optical fiber 10, for each core 1, Δ1>Δ2>Δ3 and 0%>Δ3>-0.3% hold. That is, in the multi-core optical fiber 10, each core 1 has a groove-type refractive index profile. For example, the above inequality holds true in the following case: the central core 1a is composed of silica glass to which a dopant such as germanium (Ge) is added to increase the refractive index, the intermediate layer 1b contains almost no dopant that changes the refractive index, the central core 1a is composed of silica glass to which a dopant such as fluorine (F) is added to decrease the refractive index, and the cladding 2 is composed of pure silica glass. It should be noted that pure silica glass refers to extremely high purity silica glass that does not substantially contain a dopant that changes the refractive index and has a refractive index of approximately 1.444 at a wavelength of 1550nm.

[0061] Furthermore, in the multi-core optical fiber 10, since Δ3>-0.3% holds in each core 1, the amount of dopant such as fluorine to be added to the trench layer 3 to reduce the refractive index can be relatively small. This suppresses the reduction in manufacturability of the multi-core optical fiber 10, and, for example, improves mass productivity.

[0062] Furthermore, in the multi-core optical fiber 10, as Figure 1As shown, if the center distance between the most adjacent cores 1 in the core 1 is set to Λ and the shortest distance between the groove layers 1c of the most adjacent cores 1 is set to w, then, for example, w / A is less than 0.179. If w / A is less than 0.179, the groove width (cb) / 2 of the groove layer 1c is relatively large, so even if the absolute value of Δ3 of the groove layer 1c is small, the crosstalk between the cores 1 (core-to-core crosstalk) can be made relatively low, and the bending loss characteristics can also be made relatively good. In addition, w / A is less than 0.179 and the groove width (cb) / 2 is relatively large, which means that the center of the intensity of the field of light propagating in the core 1 is relatively far from the interface between the groove layer 1c and the cladding portion 2. As a result, the increase in the propagation loss of the core 1 caused by the presence of the interface can be suppressed.

[0063] Furthermore, from the viewpoint of versatility, the optical characteristics of the multi-core optical fiber 10 preferably conform to a standard defined in, for example, ITU-T G.652 (G.652 standard) or a standard widely accepted as an optical fiber standard such as the G.657 standard.

[0064] The inventors have comprehensively studied Figure 2 The design parameters 2a, 2b, 2c, Δ1, Δ2, Δ3, etc. shown in the figure were studied in depth, and it was confirmed that in each core 1, the design parameters are preferably set to satisfy the following characteristics. That is, when Δ3>-0.3% holds, (1) b / a is preferably greater than 1.9 and less than 3.0, and c / a is preferably greater than 3.6 and less than 4.4. In addition, (2) Δ1 is preferably greater than 0.35% and less than 0.39%. In addition, (3) Δ2 is preferably greater than -0.05% and less than 0.04%. Furthermore, (4) 2a is preferably set so that the effective cutoff wavelength is greater than 1000nm and less than 1260nm.

[0065] The inventors of the present invention have confirmed that by satisfying one or more of the above conditions (1) to (4), it is easy to realize a multi-core optical fiber 10 that satisfies the optical characteristics of the G.657A2 standard of the following (5) to (7). That is, (5) the effective cutoff wavelength is greater than 1000nm and less than 1260nm, (6) the mode field diameter at a wavelength of 1310nm is greater than 8.6μm and less than 9.2μm, and (7) the bending loss at a wavelength of 1550nm when bent with a diameter of 20mm is less than 1.57dB / m. It should be noted that with respect to the wavelength dispersion characteristics, when the multi-core optical fiber 10 is applied to communications using digital coherent communication technology, a certain degree of dispersion compensation can be achieved, but it is preferred to satisfy the optical characteristics of the G657A2 standard of the following (8) and (9). That is, (8) the zero dispersion wavelength is greater than 1300nm and less than 1324nm, and (9) the dispersion slope at the zero dispersion wavelength is 0.092ps / nm 2 / km or less.

[0066] The present inventors have confirmed that if Λ is 37 μm or more and 41 μm or less, the inter-core crosstalk between the two most adjacent cores 1 in the multi-core optical fiber 10 with a length of 100 km can be easily reduced to -25 dB or less, and further to -30 dB or less.

[0067] Furthermore, from the viewpoint of high density of optical fiber cable, the outer diameter (cladding diameter) of the cladding portion 2 of the multi-core optical fiber 10 is preferably small. With respect to the multi-core optical fiber 10, it has been confirmed that when one or more of the above conditions (1) to (4) are satisfied, if the cladding thickness t of the cladding portion 2 on the outer peripheral side is 25 μm or less relative to the core portion 1 located on the outermost peripheral side, the excess loss associated with the thinning is negligible. Figure 1 As shown, relative to the core 1 located at the outermost peripheral side, the cladding thickness t of the cladding 2 on the outer peripheral side is the distance from the center of the core 1 closest to the outer periphery of the cladding 2 to the outer periphery of the cladding 2. It should be noted that Figure 1 In the arrangement of the cores 1 shown, the distance from the center to the outer periphery of the cladding 2 is equal for any core 1. Such a cladding thickness t may be hereinafter referred to as a minimum cladding thickness.

[0068] As described above, the multi-core optical fiber 10 according to the first embodiment suppresses the inter-core crosstalk by adopting the trench-type refractive index profile and suppresses the reduction in manufacturability by establishing Δ3>−0.3%.

[0069] (Implementation Method 2)

[0070] Figure 3 Schematic cross-sectional view of a multi-core optical fiber according to Embodiment 2. The multi-core optical fiber 10A includes three cores 1 as a plurality of cores. In addition, the multi-core optical fiber 10 includes a cladding 2 formed on the outer periphery of the three cores 1. The three cores 1 are arranged in an equilateral triangle shape with the central axis of the cladding 2 as the center.

[0071] The multi-core optical fiber 10A is different from the multi-core optical fiber 10A of Embodiment 1 in the number and arrangement of the cores 1, but the other structures, such as the structural materials and the values ​​of the design parameters, are the same. Therefore, the multi-core optical fiber 10A also suppresses the crosstalk between the cores and suppresses the reduction of the manufacturability.

[0072] (Example)

[0073] As an example, samples of multi-core optical fibers were manufactured using the manufacturing method described below. Samples No. 1 to 35 were all for Figure 1 The four-core structure shown has four cores and Figure 3 Both of the three-core structures shown are designed and manufactured to satisfy the above-mentioned conditions (1) to (4).

[0074] The design parameters and optical characteristics of samples No. 1 to 35 are shown in Table 1A and Table 1B. It should be noted that in the table, Λ is set to -30 dB for the core-to-core crosstalk at 100 km. In addition, the fiber diameter refers to the cladding diameter. In addition, "λ0" represents the zero dispersion wavelength. In addition, "Dispersion Slope@λ0" refers to the dispersion slope at the zero dispersion wavelength. In addition, "MFD" refers to the mode field diameter. In addition, "λcc" refers to the cable cutoff wavelength (effective cutoff wavelength). As shown in Table 1A and Table 1B, samples No. 1 to 35 all meet the optical characteristics of (5) to (9) of the G.657A2 standard, and the core-to-core crosstalk at a length of 100 km is less than -25 dB.

[0075] [Table 1A]

[0076]

[0077] [Table 1B]

[0078]

[0079] (Cladding diameter)

[0080] Next, the cladding diameter of the multi-core optical fiber 10 or 10A will be described. The cladding diameter of the multi-core optical fiber 10 or 10A is preferably close to 125 μm in accordance with the G.652 standard or the G.657 standard. Figure 4 This is a radar chart showing the cladding diameter of the multi-core optical fiber of sample No. 1 to 35 in Tables 1A and 1B. In the figure, the cladding diameter of the multi-core optical fiber of sample No. 1 to 35 is shown when line L1 is a three-core structure and line L2 is a four-core structure. As shown in the figure, for any manufactured sample, the cladding diameter is 120 μm or more and 137 μm or less.

[0081] Thus, in order to ensure the long-term reliability of mechanical properties such as fracture characteristics through screening tests, a multi-core optical fiber with a cladding diameter of 137 μm or less is more preferred. In addition, if the multi-core optical fiber has a cladding diameter of 120 μm or more and 137 μm or less, the diameter is within ±10% relative to 125 μm, so it can be processed using a fixture or device for processing optical fibers with a cladding diameter of 125 μm. Optical fibers with a cladding diameter of 125 μm are sometimes referred to as standard optical fibers, and fixtures or devices for processing them are widely used, so they are preferred. Such processing fixtures or devices are, for example, fixtures for removing the coating of multi-core optical fibers, cutting fixtures, fusion splicing devices, and the like.

[0082] (Implementation method 3)

[0083] Figure 5 This is a schematic cross-sectional view of a multi-core optical fiber ribbon according to the third embodiment. Figure 5The multi-core optical fiber ribbon 30 shown has a structure in which four multi-core optical fibers 10B are arranged in parallel and their outer circumferences are collectively coated with a coating layer 110 composed of resin, etc. The coating layer 110 is composed of a resin, etc. that can be used as a collectively coated layer of the optical fiber ribbon. The four multi-core optical fibers 10B are an example of a plurality of multi-core optical fibers.

[0084] The multi-core optical fiber 10B includes four cores 1, claddings 2B formed on the peripheries of the four cores 1, and coatings 3B formed on the peripheries of the claddings 2B. The cores 1 are made of the same structure and structural materials as the cores 1 of Embodiment 1. The design and arrangement of the cores 1 preferably satisfy the conditions that w / A is less than 0.179, the crosstalk between the cores is -25 dB, or the minimum cladding thickness t is less than 25 μm. Furthermore, it is preferred that at least one of the conditions (1) to (4) is satisfied.

[0085] The coating 3B is made of a resin or the like that can be used as a coating for an optical fiber. In addition, at least a portion of the outer surface of the coating 3B has a non-circular coating portion that deviates from the cylindrical shape along the extending direction of the cladding portion 2B. In the present embodiment, the planar outer surfaces of the coating 3B that are parallel to the two opposing sides of the quadrilateral formed by the core 1 are formed in a mutually opposing manner, constituting a non-circular coating portion 3Ba.

[0086] The cladding portion 2B is made of the same structural material as the cladding portion 2 of the first embodiment, but is different in that at least a portion of the outer surface has a non-circular cladding portion. In the present embodiment, the planar outer surfaces of the cladding portion 2B that are parallel to the two opposite sides of the quadrilateral formed with respect to the core portion 1 are formed in a mutually opposing manner to constitute a non-circular cladding portion. In addition, the non-circular cladding portion has a shape along the non-circular coating portion 3Ba of the coating 3B.

[0087] In the multi-core optical fiber ribbon 30, the multi-core optical fibers 10B are in contact with adjacent multi-core optical fibers 10B at the non-circular coating portion 3Ba. Thus, when four multi-core optical fibers 10B constitute a ribbon, it is easy to make the arrangement direction of the cores 1 in each multi-core optical fiber 10B consistent. Figure 5 In this case, in each multi-core optical fiber 10B, the arrangement direction of the cores 1 is arranged along the parallel direction of the multi-core optical fibers 10B.

[0088] (Applicable to multi-core optical fiber with multi-core optical fiber ribbon structure)

[0089] Fig. 6A , Figure 6B , Figure 6C , Fig.6D ,and Fig. 6E Schematic cross-sectional views of multi-core optical fibers of Embodiments 4, 5, 6, 7, and 8 respectively applicable to the structure of a multi-core optical fiber ribbon.

[0090] Fig. 6A The multi-core optical fiber 10C shown is different from the multi-core optical fiber 10B in the following two points. First, the outer surface of the coating 3C has a non-circular coating portion that is a regular hexagon. In this embodiment, the planar outer surfaces of the coating 3C that are parallel to the two opposite sides of the quadrilateral formed by the core 1 are formed in a mutually opposed manner. In addition, another point is that the non-circular cladding portion of the cladding portion 2C is along the non-circular coating portion of the coating 3C, and the cladding portion 2C is a regular hexagon.

[0091] Figure 6B The multi-core optical fiber 10D shown is different from the multi-core optical fiber 10B in the following two points. First, the outer surface of the coating 3D has a non-circular coating portion that is square. In the present embodiment, the coating 3D is concentric with the quadrilateral formed by the core 1. In addition, another point is that the non-circular cladding portion of the cladding portion 2D is along the non-circular coating portion of the coating 3D, and the cladding portion 2D is square.

[0092] Figure 6C The multi-core optical fiber 10E shown is different from the multi-core optical fiber 10C in that the outer surface of the coating 3E has the same non-circular coating portion as the multi-core optical fiber 10C, but the cladding 2E is not in the shape of the non-circular coating portion of the coating 3D, but is circular.

[0093] Fig.6D The multi-core optical fiber 10F shown is different from the multi-core optical fiber 10B in that the outer surface of the coating 3F has a non-circular coating portion similar to the multi-core optical fiber 10B, but the cladding portion 2E is circular.

[0094] Fig. 6E The multi-core optical fiber 10G shown is different from the multi-core optical fiber 10D in that the outer surface of the coating 3G has a non-circular coating portion similar to the multi-core optical fiber 10D, but the cladding portion 2E is circular.

[0095] Figure 6A to Figure 6E In all of the multi-core optical fibers 10C to 10G shown, similarly to the multi-core optical fiber 10B, it is easy to align the arrangement directions of the cores 1 when forming a ribbon.

[0096] (Manufacturing method)

[0097] The method for manufacturing a multi-core optical fiber of the embodiment is described by taking the case of manufacturing a multi-core optical fiber 10B as an example. First, a first step of preparing a plurality of core components that will become at least a part of the plurality of core portions 1 is performed. Next, a second step of preparing a cladding component that will become at least a part of the cladding portion 2B is performed. Next, a third step of forming a mother material using the plurality of core components and the cladding component is performed. Next, a fourth step of drawing a multi-core optical fiber from the mother material is performed.

[0098] Each process is described below. In the first process, for example, a core member having a refractive index profile identical to that formed by the central core 1a, the intermediate layer 1b, and the groove layer 3 is formed in the core 1. Such a core member is also called a core rod. It should be noted that, in the core member, a glass layer that becomes a part of the cladding part 2 may be formed on the outermost layer of the glass layer that becomes the groove layer 3. Such a core rod can be formed, for example, by a VAD (vapor axial deposition) method or an OVD (outside vapor deposition) method.

[0099] In the second step, for example, a cylindrical glass rod is prepared to become at least a part of the cladding part 2, and a plurality of holes capable of inserting the core matrix are bored in the glass rod along the cylindrical axis of the glass rod to form the cladding member. Alternatively, in the second step, a glass capillary tube having an inner diameter capable of inserting a plurality of core members and being a part of the core part 1 may be prepared as one of the core members.

[0100] In the third step, glass rods are inserted into the holes of the cladding member to form a matrix. Such a matrix forming method is also called a perforation method. Alternatively, in the third step, a plurality of core rods are inserted into the glass capillary, and a glass rod that will become a part of the core 1 is inserted between the core rod and the glass capillary, and between the core rods to form a matrix. Such a matrix forming method is also called a stacking method.

[0101] It should be noted that, in the case of the stacking method, the outermost layer of the core mother material is generally set to be a glass layer that becomes a part of the cladding part 2. In addition, in the case of the perforation method, there are cases where the outermost layer of the core mother material is set to be a glass layer that becomes a part of the cladding part 2, and cases where it is set to be a glass layer that becomes the groove layer 3. In the case where the outermost layer of the core mother material is set to be a glass layer that becomes the groove layer 3, in the multi-core optical fiber after manufacture, if light passes through the interface between the groove layer 3 and the cladding part 2B, the propagation loss is likely to increase. In this case, setting w / A to less than 0.179 can more effectively exert the effect of suppressing the increase in the propagation loss of the core 1 caused by the presence of the interface.

[0102] 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 optical fiber 10B. The processing can be performed by mechanical polishing, chemical polishing, or the like.

[0103] In addition, in the third process, the mother material is preferably formed in such a manner that the volume of the mother material is converted into a length of more than 100 km of the drawn multi-core optical fiber. Thus, a longer multi-core optical fiber can be manufactured from one mother material, thereby reducing the manufacturing cost of the multi-core optical fiber. In addition, if the mother material is of such a large volume, when the perforation method is used, the thickness of the glass formed between the holes of the glass rod is thick enough, so that, for example, cracks are not easily generated during the process. It should be noted that the volume of the qualified part of the mother material that can be used to manufacture a multi-core optical fiber that meets the desired standard directly becomes the volume of the multi-core optical fiber. Therefore, the volume required as the qualified part of the mother material can be calculated based on the length and cladding diameter of the multi-core optical fiber to be manufactured.

[0104] The fourth step is, for example, Figure 7 The method shown is performed. That is, first, the base material 40 formed by the third step is set in the drawing furnace 100. Then, one end of the base material 40 is heated and melted by the heater 101, and the glass multi-core optical fiber 50 is drawn. The glass multi-core optical fiber 50 is composed of a core 1 and a cladding 2B. Next, a UV curing resin is applied to the periphery of the glass multi-core optical fiber 50 by a resin coating device 102. It should be noted that the mold in the resin coating device 102 is set to a shape that can form the outer shape of the coating 3B. Next, the resin coated on the periphery of the glass multi-core optical fiber 50 is irradiated with ultraviolet rays by an ultraviolet irradiation device 103 to cure it and form a coating 3B. Next, the multi-core optical fiber 10B is guided to the winding device 105 by a guide roller 104. The winding device 105 is a device having a bobbin for winding the multi-core optical fiber 10B. The drawing speed of the multi-core optical fiber 10B is changed by the rotation speed of the bobbin.

[0105] It should be noted that, when manufacturing the multi-core optical fibers 10 , 10A, 10E, 10F, and 10G, the outer periphery of the base material may not be processed in the third step.

[0106] (Refractive Index Profile)

[0107] exist Figure 2 In the diagram, the refractive index profile is composed of straight lines, but the refractive index profile of the actually manufactured multi-core optical fiber is mostly not composed of straight lines. In such a case, the design parameters such as a, b, c, Δ1, Δ2, Δ3 can be confirmed by the refractive index profile measured by a profile analyzer or the like.

[0108] Figure 8 to Figure 11 The following are diagrams for explaining the first to fourth examples of refractive index profiles that can be considered as groove-type. Figure 8 In FIG. 1 , the profile P22 shown by the dotted line can be determined relative to the profile P21 shown by the solid line actually measured. Fig. 9 In , the profile P32 can be determined relative to the measured profile P31. Fig.10 In , the profile P42 can be determined relative to the measured profile P41. Fig.11 In the embodiment, the profile P52 can be determined relative to the actually measured profile P51.

[0109] for Figure 8 to Figure 11 Such a measured refractive index profile is not composed of straight lines in part at least, but a person skilled in the art can recognize it as a groove-type refractive index profile and determine its design parameters and the extent of the refractive index profile that can be represented by the design parameters.

[0110] It should be noted that the present invention is not limited to the above-mentioned embodiments. The scheme formed by appropriately combining the above-mentioned constituent elements is also included in the present invention. In addition, those skilled in the art can easily derive further effects and variations. Therefore, the scheme of the wider range of the present invention is not limited to the above-mentioned embodiments, and various changes can be made.

[0111] Industrial Applicability

[0112] As described above, the multi-core optical fiber, the multi-core optical fiber ribbon, the method for manufacturing a multi-core optical fiber, and the method for processing a multi-core optical fiber of the present invention are useful for a multi-core optical fiber having a core portion adopting a trench structure.

[0113] Description of reference numerals:

[0114] 1 Core

[0115] 1a Center core

[0116] 1b Middle layer

[0117] 1c Groove layer

[0118] 2, 2B, 2C, 2D, 2E cladding

[0119] 3 Groove layer

[0120] 3B coating

[0121] 3Ba Non-circular coating part

[0122] 3C, 3D, 3E, 3F, 3G coating

[0123] 10, 10A, 10B, 10C, 10D, 10E, 10F, 10G multi-core fiber

[0124] 30 Multi-core Fiber Ribbon

[0125] 40 base material

[0126] 50 Glass multi-core optical fiber

[0127] 100 Wire drawing furnace

[0128] 101 Heater

[0129] 102 Resin coating device

[0130] 103 Ultraviolet irradiation device

[0131] 104 guide roller

[0132] 105 Winding device

[0133] 110 coating

[0134] P11, P12, P13, P14, P21, P22, P31, P32, P41, P42, P51, P52 profiles.

Claims

1. A multi-core optical fiber having: a plurality of cores having a central core, an intermediate layer formed on an outer periphery of the central core, and a groove layer formed on an outer periphery of the intermediate layer; and a cladding portion formed on the outer periphery of the plurality of core portions, For each of the plurality of cores, if the average maximum relative refractive index difference of the central core with respect to the cladding portion is set to Δ1, the average relative refractive index difference of the intermediate layer with respect to the cladding portion is set to Δ2, and the average relative refractive index difference of the trench layer with respect to the cladding portion is set to Δ3, then Δ1>Δ2>Δ3 and 0%>Δ3>-0.3% holds true, If the center distance between the most adjacent cores among the plurality of cores is Λ, and the shortest distance between the trench layers of the most adjacent cores is w, then w / Λ is less than or equal to 0.

179. The Δ1 is greater than or equal to 0.35% and less than or equal to 0.39%.

2. The multi-core optical fiber according to claim 1, wherein: For each of the multiple core portions, when the center core diameter of the center core portion is set to 2a and the inner diameter and outer diameter of the groove layer are set to 2b and 2c respectively, b / a is greater than 1.9 and less than 3.0, and c / a is greater than 3.6 and less than 4.

4.

3. The multi-core optical fiber according to claim 1 or 2, wherein: The Δ2 is greater than or equal to -0.05% and less than or equal to 0.04%.

4. The multi-core optical fiber according to claim 1 or 2, wherein: The center core diameter of the center core portion of each of the plurality of core portions is set so that the effective cutoff wavelength is greater than or equal to 1000 nm and less than or equal to 1260 nm.

5. The multi-core optical fiber according to claim 1 or 2, wherein: For each of the plurality of cores, a mode field diameter at a wavelength of 1310 nm is not less than 8.6 μm and not more than 9.2 μm.

6. The multi-core optical fiber according to claim 1 or 2, wherein: When each of the plurality of cores is bent with a diameter of 20 mm, a bending loss at a wavelength of 1550 nm is 1.57 dB / m or less.

7. The multi-core optical fiber according to claim 1 or 2, wherein: At a length of 100 km, the crosstalk between the most adjacent cores among the plurality of cores is -25 dB or less.

8. The multi-core optical fiber according to claim 1 or 2, wherein: 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.

9. The multi-core optical fiber according to claim 1 or 2, wherein: The cladding thickness of the cladding portion on the outer peripheral side relative to the core portion located on the outermost peripheral side among the plurality of core portions is 25 μm or less.

10. The multi-core optical fiber according to claim 1 or 2, wherein: For each of the plurality of cores, a zero dispersion wavelength is greater than or equal to 1300 nm and less than or equal to 1324 nm, and a dispersion slope at the zero dispersion wavelength is 0.092 ps / nm 2 / km or less.

11. The multi-core optical fiber according to claim 1 or 2, wherein: The number of the plurality of cores is three or four.

12. The multi-core optical fiber according to claim 1 or 2, wherein: The multi-core optical fiber includes a coating layer formed on the outer periphery of the cladding portion.

13. The multi-core optical fiber according to claim 12, wherein: At least a portion of the outer surface of the coating layer has a non-circular coating portion that deviates from a cylindrical shape along an extending direction of the cladding portion.

14. The multi-core optical fiber according to claim 13, wherein: At least a portion of the outer surface of the cladding portion has a non-circular cladding portion along a shape in which the non-circular coating portion of the coating layer deviates from a cylindrical shape.

15. The multi-core optical fiber according to claim 1 or 2, wherein: The cladding portion has a cladding diameter of 137 μm or less.

16. A method for processing a multi-core optical fiber, wherein: The multi-core optical fiber of claim 15 was processed using an apparatus for processing a standard optical fiber having a cladding diameter of 125 μm.

17. A multi-core optical fiber ribbon, wherein: The multi-core optical fiber ribbon includes a plurality of multi-core optical fibers according to any one of claims 1 to 15 arranged in parallel.

18. The multi-core optical fiber ribbon according to claim 17, wherein: Each of the plurality of multi-core optical fibers includes a coating layer formed on the outer periphery of the cladding portion, wherein at least a portion of the outer surface of the coating layer has a non-circular coating portion that deviates from the cylindrical shape along the extending direction of the cladding portion. Each of the plurality of multi-core optical fibers abuts against an adjacent multi-core optical fiber at the non-circular coating portion.

19. A method for manufacturing a multi-core optical fiber, which is the method for manufacturing a multi-core optical fiber according to any one of claims 1 to 15, wherein: The method for manufacturing the multi-core optical fiber comprises: a first step of preparing a plurality of core members to be at least a part of the plurality of core portions; a second step of preparing a cladding member that will become at least a part of the cladding portion; a third step of forming a base material using the plurality of core members and the cladding member; and A fourth step, in which the multi-core optical fiber is drawn from the base material.

20. The method for manufacturing a multi-core optical fiber according to claim 19, wherein: In the first process, the plurality of core members are formed by a vapor axial deposition method or an outside vapor deposition method.

21. The method for manufacturing a multi-core optical fiber according to claim 19 or 20, wherein: In the third step, the base material is formed by a punching method or a stacking method.

22. The method for manufacturing a multi-core optical fiber according to claim 19 or 20, wherein: In the third step, the base material is formed so that the volume of the base material is 100 km or more when converted into the length of the multi-core optical fiber.

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