Multi-core optical fiber and multi-core optical cable

Abstract

The present application is an MCF capable of O-band transmission for a short distance and having a standard cladding diameter with an MFD equivalent to a general SMF, and a 12-core MCF optical fiber capable of inter-fiber connection even without both of marking and polarity and capable of counter-propagation transmission. The MCF of the present application has 12 cores and a common cladding, the common cladding has a circular outer periphery in a cross section, the 12 cores are arranged such that cores in an adjacent relationship with respect to any core do not have an adjacent relationship with each other, and are respectively arranged such that an axis crossing a center axis and not passing through the center of any of the 12 cores is taken as a symmetry axis, the centers of the 12 cores are linearly symmetrical, and the arrangement of the centers of the 12 cores has a rotational symmetry of 1 order.

Description

Technical Field

[0001] This invention relates to multi-core optical fiber (hereinafter referred to as "MCF") and multi-core optical cable (hereinafter referred to as "MCF cable").

[0002] This application claims priority based on Japanese Patent Application No. 2020-171407, filed on October 9, 2020, the contents of which are incorporated herein by reference in their entirety. Background Technology

[0003] Patent document 1 discloses an MCF that can be applied to bidirectional communication.

[0004] Non-Patent Document 1 discloses an 8-core optical fiber having a central core and seven other cores arranged in a ring around the central core. Furthermore, in this 8-core optical fiber, the seven cores arranged in a ring around the central core have slightly different inter-core spacings (core spacing) between adjacent cores.

[0005] Non-Patent Document 2 discloses the following 12-core optical fibers: a 12-core optical fiber having a cladding with an outer diameter of 147 μm and 12 cores arranged in a square lattice configuration defined in the fiber cross-section; and a 12-core optical fiber having a cladding with an outer diameter of 145 μm and 12 cores arranged in a hexagonal lattice configuration defined in the fiber cross-section. Neither of the above 12-core optical fibers has a trench structure. The mode field diameter (hereinafter referred to as "MFD") of each core is 5.4 μm at a wavelength of 1310 nm and 6.1 μm at a wavelength of 1550 nm. The cutoff wavelength is 1.26 μm. The zero-dispersion wavelength of each core is 1.41 μm. The leakage loss from the cladding to the cladding portion at a wavelength of 1565 nm is 0.01 dB / 2 km. The crosstalk between fiber cores at a wavelength of 1565nm (hereinafter referred to as "XT") is -30dB / 2km.

[0006] Patent Document 1: Japanese Patent Application Publication No. 2013-106135 (Japanese Patent No. 5842556)

[0007] Non-patent document 1: Y. Sasaki, et al., "Asymmetrically Arranged 8-core Fiberswith Center Core Suitable for Side-view Alignment in Datacenter Networks", OFC2020, T4J.1.

[0008] Non-patent literature 2: Yusuke Sasaki, et al., “High Density Multicore Fibers Employing Small MFD Cores for Datacenters”, OECC2018, Technical Digest, P2-07, July 02-06, 2018, Jeju, Korea.

[0009] Non-patent literature 3: RJ Black and C. Pask, J. Opt. Soc. Am. A, JOSAA 1(11), 1129-1131 (1984).

[0010] Non-patent literature 4: T. Matsui et al., in Eur. Conf. Opt. Commun. (ECOC) (2017), pW1. B. 2. Summary of the Invention

[0011] The MCF of the present invention comprises: 12 cores extending along a central axis; and a common cladding covering each of the 12 cores. Specifically, in a cross-section of the MCF orthogonal to the central axis, the common cladding has a circular outer periphery. In the cross-section, the 12 cores are configured such that the adjacent relationship between any two cores is not valid. Furthermore, each of the 12 cores is configured such that the centers of the 12 cores are linearly symmetrical about an axis intersecting the central axis but not passing through the center of any of the 12 cores. Moreover, in the cross-section, the arrangement of the centers of the 12 cores does not exhibit more than one order of rotational symmetry, even when any point is taken as the center of rotation. Attached Figure Description

[0012] Figure 1 This is a diagram illustrating various constructions of the MCF cable (containing the MCF of the present invention).

[0013] Figure 2 This is a diagram illustrating the conditions used to determine the core configuration of the MCF of the present invention.

[0014] Figure 3 This is a diagram illustrating an example of the core configuration of the MCF of the present invention.

[0015] Figure 4 This is a diagram showing the core configuration of the first and second modifications of the MCF of the present invention.

[0016] Figure 5 This is a diagram showing the core configuration of the third and fourth modifications of the MCF of the present invention.

[0017] Figure 6 It is a diagram showing the various core configurations of the MCF involved in the comparative model.

[0018] Figure 7 This is a diagram used to illustrate the main terms used in this instruction manual.

[0019] Figure 8 This is a diagram showing the refractive index distribution around each fiber core of the MCF that can be applied to this invention.

[0020] Figure 9 This refers to the center-to-center spacing Λ and MFD / λ between adjacent fiber cores when the phase-to-phase transmission XT at a wavelength of 1360nm becomes -20dB (=-20dB / 10km) after 10km transmission in a 12-core MCF (12-core MCF) with a 12-core square lattice configuration and a wavelength of 10km (equivalent to a fiber length of 10km). cc A graph showing the relationship between the two.

[0021] Figure 10 This represents the center-to-center spacing Λ and MFD / λ between adjacent fiber cores when the phase-to-phase transmission XT becomes -40dB (=-40dB / 10km) at a wavelength of 1360nm in a 12-core MCF transmission over 10km (equivalent to a fiber length of 10km). cc A graph showing the relationship between the two.

[0022] Figure 11 This indicates that when the leakage loss to the cladding is 0.01 dB / km in a 12-core MCF at a wavelength of 1360 nm, d coat and MFD / λ cc A graph showing the relationship between the two.

[0023] Figure 12 This indicates that when the leakage loss to the cladding is 0.01 dB / km in a 12-core MCF at a wavelength of 1360 nm, d coat Adding a 1μm margin, and furthermore, after 10km transmission (equivalent to a 10km fiber length), the phase-to-phase transmission XT at a wavelength of 1360nm becomes -20dB (=-20dB / 10km) Λ with a 1μm margin, the CD (minimum permissible cladding diameter) and MFD / λ are calculated. cc A graph showing the relationship between the two.

[0024] Figure 13This refers to a 12-core MCF where, after 10km of transmission (equivalent to 10km of fiber length), the phase-to-phase transmission XT at a wavelength of 1360nm becomes -20dB (=-20dB / 10km), or the parallel transmission XT (the XT in typical co-directional transmission) becomes -20dB (=-20dB / 10km) after 10km of transmission (equivalent to 10km of fiber length), and the leakage loss to the cladding at a wavelength of 1360nm is 0.01dB / km. coat Adding a 1μm margin, and with an additional 1μm margin in Λ, the CD (minimum permissible cladding diameter) and MFD / λ cc A graph showing the relationship between the two.

[0025] Figure 14 This indicates that when the leakage loss to the cladding is 0.01 dB / km in a 12-core MCF at a wavelength of 1360 nm, d coat With a 1μm margin, the phase-to-phase transmission XT at a wavelength of 1360nm becomes -40dB (=-40dB / 10km) Λ with a 1μm margin, along with the CD (minimum permissible cladding diameter) and MFD / λ. cc A graph showing the relationship between the two.

[0026] Figure 15 This refers to a 12-core MCF where, under conditional conditions, the phase-to-phase transmission XT at a wavelength of 1360 nm becomes -40 dB (=-40 dB / 10 km) after 10 km of transmission (equivalent to a 10 km fiber length), or the parallel transmission XT becomes -40 dB (=-40 dB / 10 km) after 10 km of transmission (equivalent to a 10 km fiber length), the leakage loss to the cladding at a wavelength of 1360 nm is 0.01 dB / km. coat Adding a 1μm margin, and with an additional 1μm margin in Λ, the CD (minimum permissible cladding diameter) and MFD / λ cc A graph showing the relationship between the two. Detailed Implementation

[0027] [The problem to be solved by this invention]

[0028] The inventors studied the aforementioned prior art and, as a result, discovered the following problems. Specifically, the core configurations of the MCFs disclosed in Patent Document 1 to Non-Patent Document 2 all exhibit rotational symmetry of two or more orders, thus requiring marking to identify the cores. Furthermore, the core configurations lack linear symmetry, or while linearly symmetric, cores exist on the axis of symmetry; therefore, the connection between MCFs requires consideration of polarity in the transmission link (the state in which each core should be connected is specified). For example, taking a multi-core connector with an even number of fiber ribbons as an example, if the left half of the fiber is used for transmitting and the right half for receiving, no structural changes are needed at either end, and no polarity issue arises. However, in the case of an MCF with a core at the cladding center, if the core at the cladding center is used for transmitting at one end, it needs to be used for receiving at the other end, requiring a connection / link structure that considers polarity (requiring the use of fan-in / fan-out structures at both ends, or transceivers with different structures). Furthermore, the MFD is very small at a wavelength of 1310 nm, thus increasing the bending loss.

[0029] The present invention is proposed to solve the above-mentioned problems. Its purpose is to provide an MCF optical fiber that can be used for short-distance O-band transmission and has a standard cladding diameter with an MFD equivalent to that of general SMF. It has 12 cores that can be used for fiber-to-fiber connection even without markings and polarity, and can be used for opposite transmission.

[0030] [Description of embodiments of the present invention]

[0031] First, the contents of each embodiment of the present invention will be described separately.

[0032] (1) The MCF of the present invention, as one embodiment, comprises: 12 cores extending along a central axis; and a common cladding covering each of the 12 cores. Specifically, in a cross-section of the MCF orthogonal to the central axis, the common cladding has a circular outer periphery. In the cross-section, the 12 cores are configured such that the adjacent relationship between any two cores is not established. Furthermore, each of the 12 cores is configured such that the centers of the 12 cores are linearly symmetrical about an axis intersecting the central axis but not passing through the center of any of the 12 cores. Moreover, in the cross-section, the arrangement of the centers of the 12 cores does not possess more than one rotational symmetry, even when any point is taken as the center of rotation. In other words, in the cross-section, the arrangement of the centers of the 12 cores is such that even when rotating around any point, it only becomes the same configuration as itself when rotating 360 degrees.

[0033] As described above, this MCF has 12 fiber cores enclosed in a common cladding, allowing for the connection of more than 12 fiber cores per fusion splice. Furthermore, the outer periphery of the common cladding (defined by the cross-section of the MCF) is circular, enabling a fiber core configuration suitable for opposite transmission. The 12 fiber cores are configured such that adjacent cores are not adjacent to each other, thus allowing connection of the same type of MCF at any end face without polarity (the combination of optical signal transmission directions set for each fiber core). Moreover, each of the 12 fiber cores is configured such that the axis intersecting the central axis but not passing through the center of any of the 12 cores is used as the axis of symmetry, resulting in linear symmetry between the centers of the 12 fiber cores. Therefore, fiber core identification and comparison can be performed without markings.

[0034] (2) As one aspect of the present invention, the 12 fiber cores are each classified as either inner peripheral fiber cores or outer peripheral fiber cores, as shown below. Specifically, a square lattice is defined, wherein the square lattice has a lattice point spacing Λ. nominal The fiber has four inner circumferential grid points forming a minimum square and eight outer circumferential grid points surrounding these four inner circumferential grid points and having an adjacency relationship with any of the four inner circumferential grid points. A square grid is set in the cross-section such that the distance from each of the four inner circumferential grid points is equal. Relative to this square grid, the 12 fiber cores consist of four inner circumferential fiber cores distributed among the four inner circumferential grid points and eight outer circumferential fiber cores distributed among the eight outer circumferential grid points. In other words, each of the four inner circumferential fiber cores has an adjacency relationship with two of the eight outer circumferential fiber cores. Furthermore, the distance between the center position of each of the four inner circumferential fiber cores and the corresponding inner circumferential grid point is 0.5 μm or less. On the other hand, each of the eight outer circumferential fiber cores belongs to either a grid-point configured fiber core or a grid-point unconfigured fiber core. The lattice-point configured core is a core positioned at a distance of 0.5 μm or less from a corresponding outer lattice point among the eight outer lattice points. Conversely, the lattice-point unconfigured core is a core positioned at a distance of 2 μm from its corresponding outer lattice point. The preferred ratio of the number of lattice-point configured cores to the number of lattice-point unconfigured cores is 2 to 6, 4 to 4, or 6 to 2. Each lattice-point unconfigured core is positioned at a distance Λ from a specific inner lattice point among the four inner lattice points that is adjacent to its corresponding outer lattice point. nominal Values ​​above -0.5μm and Λ nominal The center of each lattice point is located at a value below +0.5 μm. The center of each non-configured core is configured such that it is farther from a specific outer lattice point adjacent to its corresponding outer lattice point than from the corresponding inner lattice point, and is separated from the center of any of the remaining outer cores by Λ.nominal +3μm or more.

[0035] The four inner periphery cores are each positioned such that their centers are located at a distance of less than 0.5 μm from their corresponding inner periphery lattice points. This square arrangement of the four inner periphery cores maintains a constant center spacing Λ between adjacent cores and prevents the outer periphery cores from excessively separating from the center of the common cladding (closer to the cladding portion). Furthermore, the centers of the lattice-point-unconfigured cores are separated from their corresponding outer periphery lattice points by more than 2 μm, thus achieving sufficient asymmetry relative to the core configuration of the MCF (defined in the cross-section of the MCF). The centers of each lattice-point-unconfigured core are positioned such that they are further from a specific outer periphery lattice point (other outer periphery lattice points where the adjacent relationship between corresponding outer periphery lattice points holds) than from their corresponding outer periphery lattice points. In this case, a core configuration in which the eight outer periphery cores do not approach each other can be achieved. Furthermore, the centers of each lattice-point-unconfigured core are separated by Λ from any center of the remaining lattice-point-unconfigured cores. nominal +3μm or more. In this case, the outer peripheral cores that are adjacent to any inner peripheral core and other outer peripheral cores that are adjacent to that arbitrary inner peripheral core are too close, thereby ensuring sufficient distance so that the adjacency relationship between these two outer peripheral cores does not hold.

[0036] (3) As one aspect of the present invention, each non-configured fiber core is configured such that the angle θ formed by the line segment connecting the corresponding outer peripheral grid point and the aforementioned specific inner peripheral grid point, and the line segment connecting the center of the non-configured fiber core and the specific inner peripheral grid point, is 3 degrees or more and 30 degrees or less, 3 degrees or more and 25 degrees or less, or 3 degrees or more and 20 degrees or less. In this case, it has asymmetry relative to the fiber core configuration of the MCF, and prevents the outer peripheral fiber core adjacent to any inner peripheral fiber core from being too close to other outer peripheral fiber cores adjacent to that arbitrary inner peripheral fiber core (ensuring sufficient distance so that the adjacency relationship between these two outer peripheral fiber cores is not established).

[0037] (4) As one aspect of the present invention, the number of non-configured lattice cores is two, and the adjacency relationship of the two peripheral lattice cores assigned to these two non-configured lattice cores is established. Furthermore, in this case, each of the two adjacent peripheral cores is adjacent to a different inner peripheral core. The non-configured lattice cores, as described above, are further from the center (central axis) of the common cladding (the greater the θ, the further away) from the OCT (Outer Cladding Thickness) than the configured lattice cores, or the outer diameter of the common cladding needs to be increased to suppress the deterioration of the OCT. In contrast, in the structure of this aspect, compared to the case where one of the two peripheral cores assigned to the two adjacent peripheral lattices is a non-configured lattice core, even if θ is small, the center spacing of the two peripheral cores, each a non-configured lattice core, can be further increased. As a result, even if θ is small, the visual recognizability of the asymmetry of the core configuration of the MCF can be improved.

[0038] (5) As one aspect of the present invention, it may also include a resin-coated portion that covers the outer periphery of the common coating layer and has an outer diameter that converges to a range of 235 μm to 265 μm based on 250 μm. The nominal coating diameter CD is relative to a specified coating diameter of 195 μm or less. nominal [μm], the diameter of the common cladding CD is expressed as CD nominal Converging to CD based on the baseline nominal Values ​​above -1μm and CD nominal The cutoff wavelength λ of each of the 12 fiber cores was determined within the range of +1μm and measured over a 22m fiber length. cc For wavelengths above 1260 nm or below 1360 nm, the zero-dispersion wavelength of each of the 12 fiber cores is defined by a wavelength reference value ranging from 1312 nm to 1340 nm. The wavelength converges to a value above the reference value minus 12 nm and below the reference value plus 12 nm. For each of the 12 fiber cores at a wavelength of 1310 nm, the dispersion slope is 0.092 ps / (nm). 2 Below ·km). Furthermore, for each of the 12 fiber cores, the mode field diameter MFD [μm] and cable cutoff wavelength λ relative to a wavelength of 1310nm. cc The ratio of [μm], the shortest distance dcoat[μm] from the center of the 12 cores to the interface between the resin coating and the common cladding (hereinafter referred to as "coating-cladding interface") satisfies the following equation (1):

[0039] d coat ≥2.88MFD / λ cc +5.36…(1)

[0040] The relationship is as follows. Additionally, the MCF satisfies either condition 1 or condition 2 below.

[0041] Furthermore, the first condition mentioned above applies to each of the 12 fiber cores, where the total crosstalk from the fiber core adjacent to the target fiber core to the target fiber core at a wavelength of 1360 nm is less than -6.7 dB / 10 km, and the center spacing Λ [μm] between the adjacent fiber cores among the 12 fiber cores satisfies the following equation (2):

[0042] Λ≥2.34MFD / λ cc +12.1…(2)

[0043] And the nominal value of the cladding diameter CD nominal [μm] satisfies the following equation (3):

[0044] CD nominal ≥13.15MFD / λ cc +54.25…(3)

[0045] Therefore, it is defined.

[0046] The second condition mentioned above is that for each of the 12 fiber cores, the total crosstalk from the fiber core adjacent to the target fiber core to the target fiber core at a wavelength of 1360nm is less than -16.7dB / 10km, and the center spacing Λ [μm] between the adjacent fiber cores satisfies the following equation (4):

[0047] Λ≥2.73MFD / λ cc +12.7…(4)

[0048] The relationship, and the nominal value of the cladding diameter CD nominal [μm] satisfies the following equation (5):

[0049] CD nominal ≥14.07MFD / λ cc +55.59…(5)

[0050] The relationship is defined accordingly. Based on this structure, an MCF with excellent mass production performance and the ability to effectively suppress the increase in connection cost and transmission loss is obtained.

[0051] (6) As one embodiment of the present invention, preferably, the 12 fiber cores include 4 fiber cores that surround the central axis with the shortest distance, the MFD [μm] converges to a range of 8.2μm to 9.0μm with a reference of 8.6μm, and the cable cutoff wavelength λ cc Below 1260nm. Additionally, MFD [μm] and cable cutoff wavelength λ. cc[μm] satisfies any of the following equations (6) to (10):

[0052] 6.5≤MFD / λ cc ≤7.5≤0.07606CD nominal -4.126…(6)

[0053] 6.5≤MFD / λ cc ≤8.0≤0.07606CD nominal -4.126…(7)

[0054] 6.5≤MFD / λ cc ≤8.4≤0.07606CD nominal -4.126…(8)

[0055] 6.5≤MFD / λ cc ≤9.0≤0.07606CD nominal -4.126…(9)

[0056] 6.5≤MFD / λ cc ≤9.5≤0.07606CD nominal -4.126…(10)

[0057] The relationship is as follows. In this case, an MCF with excellent mass production performance is obtained, which can effectively suppress the increase in connection cost and transmission loss.

[0058] (7) As one aspect of the present invention, the 12 fiber cores include 4 fiber cores that surround the central axis with the shortest distance, the total crosstalk to any of the 4 fiber cores (the substantially defined inner circumferential fiber cores) at a wavelength of 1360nm is -16.7dB / 10km or less, the MFD converges to a range of 7.8μm to 8.6μm with a reference of 8.2μm, and the cable cutoff wavelength λ cc The wavelength should be below 1260 nm. Additionally, a suitable MFD [μm] and cable cutoff wavelength λ are preferred. cc [μm] satisfies any of the following equations (11) to (15):

[0059] 6.2≤MFD / λ cc ≤7.2≤0.07105CD nominal -3.950…(11)

[0060] 6.2≤MFD / λ cc ≤7.7≤0.07105CD nominal -3.950…(12)

[0061] 6.2≤MFD / λ cc ≤8.1≤0.07105CDnominal -3.950…(13)

[0062] 6.2≤MFD / λ cc ≤8.7≤0.07105CD nominal -3.950…(14)

[0063] 6.2≤MFD / λ cc ≤9.2≤0.07105CD nominal -3.950…(15)

[0064] The relationship is as follows. In this case, an MCF with excellent mass production performance is obtained, which can effectively suppress the increase in connection cost and transmission loss.

[0065] (8) As one aspect of the present invention, the 12 fiber cores include 4 fiber cores that surround the central axis with the shortest distance, and the total crosstalk to any of the 4 fiber cores (the substantially defined inner circumferential fiber cores) at a wavelength of 1360nm is -16.7dB / 10km or less, the MFD converges to a range of 8.2μm to 9.0μm with a reference of 8.6μm, and the cable cutoff wavelength λ cc The wavelength should be below 1360 nm. Additionally, a suitable MFD [μm] and cable cutoff wavelength λ are preferred. cc [μm] satisfies any of the following equations (16) to (20):

[0066] 6.0≤MFD / λ cc ≤7.0≤0.07105CD nominal -3.950…(16)

[0067] 6.0≤MFD / λ cc ≤7.5≤0.07105CD nominal -3.950…(17)

[0068] 6.0≤MFD / λ cc ≤7.9≤0.07105CD nominal -3.950…(18)

[0069] 6.0≤MFD / λ cc ≤8.5≤0.07105CD nominal -3.950…(19)

[0070] 6.0≤MFD / λ cc ≤9.0≤0.07105CD nominal -3.950…(20)

[0071] The relationship is as follows. In this case, an MCF with excellent mass production performance is obtained, which can effectively suppress the increase in connection cost and transmission loss.

[0072] (9) As one embodiment of the MCF cable of the present invention, it comprises multiple MCFs including an MCF having the above-described structure. Furthermore, the MCF cable of the present invention can incorporate a multi-core optical fiber ribbon in which these multiple MCFs are spaced apart. As another embodiment of the MCF cable of the present invention, the multi-core optical fiber ribbon can be incorporated in a twisted spiral shape. As another embodiment of the MCF cable of the present invention, it can include MCFs with an average bending radius along the fiber length direction of 0.03m to 0.14m or 0.14m to 0.3m. The transmission capacity can be significantly increased through any structure.

[0073] The methods listed above in the "[Description of Embodiments of the Invention]" section can be applied to each of the remaining methods, or to all combinations of the remaining methods.

[0074] [Detailed Description of Embodiments of the Invention]

[0075] Hereinafter, specific examples of MCF (Multi-core Optical Fiber) and MCF cables (Multi-core Optical Cables) according to the present invention will be described in detail with reference to the accompanying drawings. Furthermore, the present invention is not limited to these examples, but is shown by the claims, and includes all modifications within the same meaning and scope as the claims. Additionally, in the description of the drawings, the same reference numerals are used to denote the same elements, and repeated descriptions are omitted.

[0076] Figure 1 This is a diagram illustrating various constructions of the MCF cable (containing the MCF of the present invention).

[0077] The MCF cable 1A having structure (A) includes: an outer sheath 300 containing an MCF housing space extending along the length direction of the MCF cable 1A; and a plurality of MCFs 100 (MCFs of the present invention). Two tension members 400A and 400B extending along the MCF housing space are embedded in the outer sheath 300. Each MCF 100 includes glass fiber 200 whose outer peripheral surface is covered by a resin coating. Furthermore, the MCFs 100 can form spaced-bonded MCF strips, in which case the MCF strips are incorporated into the MCF 1A in a twisted spiral shape.

[0078] On the other hand, the MCF cable 1B having structure (B) includes: an outer sheath 500 containing an MCF housing space extending along the length direction of the MCF cable 1B; a slotted core 600 dividing the MCF housing space into multiple portions; and a plurality of MCFs 100 (MCFs of the present invention). The slotted core 600, which divides the MCF housing space into multiple portions, is housed within the outer sheath 500. Tensile wires 700 extending along the length direction of the MCF cable 1B are embedded in the slotted core 600. The plurality of MCFs 100 are housed within arbitrary spaces divided by the slotted core 600.

[0079] Figure 2 This is a diagram illustrating the conditions used to determine the core configuration of the MCF in this invention. Figure 2 The upper part shows a square lattice 800 defined on the cross section of the MCF 100, and the lower part shows a diagram illustrating the configuration of two outer circumferential cores that maintain an adjacent relationship with respect to one inner circumferential core.

[0080] The MCF of the present invention preferably has 12 fiber cores. Thus, even when the MCFs are spliced ​​by rotating and adjusting them one by one, the number of connected fiber cores can be set to be the same for each splice, compared to the band splicing (splicing 12 fibers together) of cables with multiple 12 fiber bands built in when connecting cables with a large number of fiber cores.

[0081] Furthermore, the MCF of the present invention preferably has a fiber configuration in which the adjacency of multiple fibers adjacent to a specified fiber core is not established among themselves. Therefore, in bidirectional communication where signals are transmitted in different transmission directions between adjacent fibers (hereinafter referred to as "adjacent fibers"), the XT (reciprocal transmission XT) from other fibers that are also adjacent to the specified fiber core to that specified fiber core can be reduced. Here, the adjacent fibers of the specified fiber core will be described later (see reference). Figure 7 ), refers to the fiber core that has a large impact on the parallel transmission XT (the usual XT when light is transmitted in the same direction) of the specified fiber core. Specifically, the fiber core whose center spacing is closest to the specified fiber core and the fiber core with a center spacing equal to it (with a difference of less than 2 μm) are adjacent fiber cores.

[0082] As an example, such as Figure 2As in the example, it is preferable to have 12 fiber cores configured such that a portion of the 12 fiber cores are offset from the grid points, similar to a square grid configuration (adjacent fiber cores that are adjacent to each other do not have an adjacent relationship relative to any other fiber core). In this case, in the cross-section of the MCF, it is preferable to use a predetermined axis that passes through the center of the common cladding (fiber axis) but does not pass through the center of each fiber core as the axis of symmetry, and the centers of each fiber core are arranged in a linearly symmetrical position. Thus, when connecting MCFs, it is not necessary to consider "polarity" to connect a predetermined end of one MCF to any end of another MCF. Preferably, the fiber core configuration of the MCF of the present invention has one rotational symmetry (not more than two rotational symmetries). Thus, even without adding "markers" other than the fiber cores, it is possible to identify which fiber core is which.

[0083] In addition, Figure 2 While the variation in core position is not considered, the core position (center of the core) can vary within 0.5 μm from a specified grid point. This increases manufacturing tolerance. In actual MCFs, the positions of the grid points (inner and outer grid points) for the inner and outer cores can be determined by optimizing the grid point spacing, orientation, and position of the square grid in a way that minimizes the sum of the squared errors of the positional deviations of the grid points corresponding to the core center. Alternatively, the grid point spacing of the square grid can also be optimized using nominal values ​​(design values) for the orientation and position of the square grid.

[0084] Specifically, Figure 2 The MCF 100 shown includes: a glass fiber 200 extending along a central axis (fiber axis AX); and a resin covering portion 130 covering the glass fiber 200. The glass fiber 200 includes: 12 cores 110 extending along the fiber axis AX; and a common cladding 120 covering each of the 12 cores.

[0085] Figure 2 The square lattice 800, which serves as the reference for the fiber core configuration, shown at the top, is defined in a cross-section of the MCF 100 orthogonal to the fiber axis AX. Furthermore, the shape of the outer periphery 210 of the common cladding 120 (defined in the cross-section of the MCF 100) is circular. That is, the square lattice 800 has a lattice point spacing Λ nominalThe square lattice is composed of a plurality of lattice points arranged symmetrically with respect to the central axis, with four inner lattice points surrounding it at the shortest distance. More specifically, the square lattice 800 includes: four inner lattice points 80; and eight outer lattice points 820, which surround the four inner lattice points 810, and are adjacent to any of the four inner lattice points 810. Furthermore, no fiber core is disposed at lattice points 830 that are not adjacent to any of the four inner lattice points 810.

[0086] Each of the 12 fiber cores belongs to either an inner peripheral fiber core 110A (hereinafter referred to as fiber core 110 in the case of "12 fiber cores") distributed among 4 inner peripheral grid points 810, or an outer peripheral fiber core distributed among 8 outer peripheral grid points 820. The distance between the center position of each of the 4 inner peripheral fiber cores 110A and the corresponding inner peripheral grid point among the 4 inner peripheral grid points 810 is 0.5 μm or less. On the other hand, each of the 8 outer peripheral fiber cores belongs to either a grid-point configured fiber core 110Ba or a grid-point unconfigured fiber core 110Bb. The grid-point configured fiber core 110Ba is a fiber core whose center is disposed at a position where the distance between it and the corresponding outer peripheral grid point among the 8 outer peripheral grid points 820 is 0.5 μm or less. In addition, the grid-point unconfigured fiber core 110Bb is a fiber core whose center is disposed at a position at a distance D1 (D1 > 2 μm) from the corresponding outer peripheral grid point. Furthermore, each of the non-configured grid point cores 110Bb is configured such that the angle θ (hereinafter referred to as the "offset angle") between the line segment connecting the corresponding outer circumferential grid point and a specific inner circumferential grid point (one of the four inner circumferential grid points that is adjacent to the corresponding outer circumferential grid point) and the line segment connecting the center of the non-configured grid point core and the specific inner circumferential grid point is 3 degrees or more and 30 degrees or less, 3 degrees or more and 25 degrees or less, or 3 degrees or more and 20 degrees or less. Additionally, the ratio of the number of configured grid point cores 110Ba to the number of non-configured grid point cores 110Bb is as follows: Figures 3 to 5 As shown in the example, it is preferred to have 2 to 6, 4 to 4, or 6 to 2. Each of the non-configured grid point cores 110Bb is a specific inner circumferential grid point from among the four inner circumferential grid points 810 that is adjacent to the corresponding outer circumferential grid point, with a distance D3 (Λ) between them. nominal -0.5μm≤D3≤Λ nominal The center of each of the non-grid core 110Bb is configured at a position of +0.5μm (on a circle centered on a specific inner circumferential grid point). The center of each grid point is configured such that, compared to the distance D1 from the corresponding outer circumferential grid point, it is located at a distance from a specific outer circumferential grid point adjacent to that corresponding outer circumferential grid point (referring to...). Figure 2The upper part shows the distance between adjacent peripheral grid points (pairs), and the distance from any center of the remaining grid points (non-configured core 110Bb) is longer, with a separation distance D2 (≥Λ). nominal +3μm). In this specification, under the conditions described above, the non-configured core 110Bb of the lattice point is also defined, in the same way as the adjacency relationship between lattice points, as maintaining an adjacency relationship with other cores (inner peripheral core 110A, other outer peripheral cores).

[0087] Figure 3 This is a diagram illustrating an example of the core configuration of the MCF (12-core MCF 100A) of the present invention. Figure 4 and Figure 5 This diagram illustrates the core configuration of the first to fourth modifications of the 12-core MCF of the present invention. Additionally, Figure 6 This is a diagram showing various core configurations of the 12-core MCF involved in the comparative model. Furthermore, Figures 3 to 6 This is a schematic diagram showing the fiber core location and dimensions, not based on an actual scale, for ease of visual identification. Additionally, in Figures 3 to 6 The axis of symmetry LA is shown in all cases so that it can be confirmed that the line is symmetrically configured with 12 fiber cores 110.

[0088] Figure 3 The 12-core MCF 100A shown includes: glass fiber 200A; and a resin coating 130 covering the glass fiber 200A. The glass fiber 200A has: 12 cores 110 extending along a central axis (fiber axis AX1); and a common cladding 120 covering each of the 12 cores 110. The 12 cores 110 are classified into 4 inner peripheral cores 110A and 8 outer peripheral cores according to the type of grid points assigned. Additionally, the 8 outer peripheral cores are classified into grid-point configured cores 110Ba and grid-point unconfigured cores 110Bb.

[0089] In the 12-core MCF 100A, the eight peripheral cores are classified into six grid-point configured cores 110Ba and two grid-point unconfigured cores 110Bb. The two grid-point unconfigured cores 110Bb are assigned to peripheral grid points 820 that are adjacent to each other, as shown in the figure, with their centers offset from the corresponding peripheral grid point 820 by an angle θ.

[0090] The first variation involves a 12-core MCF 100B ( Figure 4 The upper part), the 12-core MCF100C involved in the second modification example ( Figure 4 The lower part), the 12-core MCF 100D involved in the third modification example ( Figure 5 The upper part), the 12-core MCF100E involved in the fourth variation ( Figure 5(lower part), the 12-core MCF 900A involved in the first pair ratio ( Figure 6 The upper part) and the second pair of proportions involve 12-core MCF 900B ( Figure 6 In addition to the fiber core configuration, the lower part of the fiber core has the same characteristics as the fiber core. Figure 3 The 12-core MCF 100A shown has the same structure. That is, the 12-core MCF 100B to 100E have glass fibers 200B to 200E corresponding to the glass fiber 200A described above and a resin-coated portion 130. Similarly, the 12-core MCF 900A and 900B also have glass fibers 950A and 950B corresponding to the glass fiber 200A described above and a resin-coated portion 130.

[0091] Each of the glass fibers 200B to 200E has: 12 cores 110 extending along a central axis (fiber axis AX2 to AX5); and a common cladding 120 covering each of the 12 cores 110. In a cross-section orthogonal to the central axis of each of the glass fibers 200B to 200E, the common cladding 120 has a circular outer periphery. The 12 cores 110 are classified into 4 inner periphery cores 110A and 8 outer periphery cores according to the type of lattice points assigned. Furthermore, the 8 outer periphery cores are classified into lattice-point configured cores 110Ba and lattice-point unconfigured cores 110Bb.

[0092] On the other hand, glass fibers 950A and 950B each have: 12 cores extending along the central axis (fiber axes AX6 and AX7); and a common cladding 120 covering each of these 12 cores. Furthermore, in Figure 6 The comparative example shown illustrates a fiber core configuration of 12 cores, consisting of a first core 110a and a second core 110b with different light transmission directions. On the cross-sections of glass fibers 950A and 950B, which are orthogonal to the central axis, the common cladding 120 has a circular outer periphery. The 12 cores (first core 110a and second core 110b) are classified into four inner periphery cores 110A and eight outer periphery cores according to the type of lattice points assigned. Furthermore, as in the second comparative example, the eight outer periphery cores are classified into lattice-point configured cores 110Ba and lattice-point unconfigured cores 110Bb.

[0093] The 12-core MCF 100B involved in the first variation ( Figure 4In the upper part of the fiber, four inner periphery fiber cores 110A are respectively arranged on the inner periphery grid points 810 of a square grid set on a cross-section orthogonal to the fiber axis AX2 (the distance between the inner periphery grid point 810 and the center of the fiber core is less than 0.5 μm). Eight outer periphery fiber cores are arranged around these four inner periphery fiber cores 110A. Six of the eight outer periphery fiber cores are configured as grid point fiber cores 110Ba, with each assigned outer periphery grid point 820 and the center of the fiber core arranged at a distance of less than 0.5 μm. The remaining two outer periphery fiber cores are configured as grid point non-configured fiber cores 110Bb, maintaining... Figure 2 In the adjacent state shown in the lower part, the fiber cores are configured with their centers offset relative to their respective assigned peripheral grid points 820. Therefore, in this 12-core MCF 100B, the ratio of the number of grid-point configured fiber cores to the number of grid-point unconfigured fiber cores is 6 to 2. Furthermore, the respective offsets θ are consistent between the two pairs of grid-point unconfigured fiber cores 110Bb, which are arranged in a position that is linearly symmetrical with respect to the axis of symmetry LA (one pair in the first variant). However, the fiber core configuration of this 12-core MCF 100B does not have more than two rotational symmetries centered on the fiber axis AX2.

[0094] Furthermore, if Figure 3 Comparing the core configurations of the 12-core MCF 100A and the 12-core MCF 100B involved in the first variation, the 12-core MCF 100A, in which the outer peripheral cores allocated to the two adjacent outer peripheral grid points 820 are respectively the grid point non-configuration cores 110Bb, shows increased asymmetry compared to the 12-core MCF 100B, in which only one of the two adjacent outer peripheral grid points 820 is the grid point non-configuration core 110Bb.

[0095] The second variation involves a 12-core MCF 100C ( Figure 4 Similarly, in the lower part, four inner peripheral fiber cores 110A are respectively arranged on the inner peripheral grid points 810 of the square grid set on the cross-section orthogonal to the fiber axis AX3, and eight outer peripheral fiber cores are arranged around them. Four of the eight outer peripheral fiber cores are arranged as grid point configuration fiber cores 110Ba and are arranged on their respective assigned outer peripheral grid points 820. The remaining four outer peripheral fiber cores are arranged as grid point non-configuration fiber cores 110Bb, while maintaining Figure 2In the adjacent state shown in the lower part, the fiber cores are configured with their centers offset relative to their respective assigned peripheral grid points 820. Therefore, in this 12-core MCF 100C, the ratio of the number of grid-point configured fiber cores to the number of grid-point unconfigured fiber cores is 4 to 4. Furthermore, the pairs of two grid-point unconfigured fiber cores 110Bb are configured in a position that is linearly symmetrical with respect to the axis of symmetry LA, but the fiber core configuration of this 12-core MCF 100C does not have more than two rotational symmetries centered on the fiber axis AX3. In addition, regarding the pairs of linearly symmetrically configured grid-point unconfigured fiber cores 110Bb (two pairs in the second variation), one pair has an offset angle of θ1, and the other pair has an offset angle of θ2 (which does not need to be consistent with θ1).

[0096] The third variation involves a 12-core MCF 100D ( Figure 5 Similarly, on the upper part (of the fiber), four inner peripheral fiber cores 110A are respectively arranged on the inner peripheral grid points 810 of the square grid set on the cross-section orthogonal to the fiber axis AX4, and eight outer peripheral fiber cores are arranged around them. Two of the eight outer peripheral fiber cores are arranged as grid point cores 110Ba, arranged on their respective assigned outer peripheral grid points 820. The remaining six outer peripheral fiber cores are arranged as grid point non-configured fiber cores 110Bb, maintaining... Figure 2 In the adjacent state shown in the lower part, the fiber cores are configured with their centers offset relative to their respective assigned peripheral grid points 820. Therefore, in this 12-core MCF 100D, the ratio of the number of grid-point configured fiber cores to the number of grid-point unconfigured fiber cores is 2 to 6. Furthermore, the pairs of two grid-point unconfigured fiber cores 110Bb are arranged in a position that is linearly symmetrical with respect to the axis of symmetry LA, but the fiber core configuration of this 12-core MCF 100D does not have more than two rotational symmetries centered on the fiber axis AX4. Additionally, regarding the pairs of linearly symmetrically configured grid-point unconfigured fiber cores 110Bb (3 pairs in the third variation), the offset angle of the first pair is θ1, the offset angle of the second pair is θ2, and the offset angle of the third pair is θ3. The offset angles θ1, θ2, and θ3 do not need to be consistent with each other.

[0097] The fourth variation involves a 12-core MCF 100E ( Figure 5 Similarly, in the lower part, four inner peripheral fiber cores 110A are respectively arranged on the inner peripheral grid points 810 of the square grid set on the cross-section orthogonal to the fiber axis AX5, and eight outer peripheral fiber cores are arranged around them. Similar to the third variation, two of the eight outer peripheral fiber cores are arranged as grid point cores 110Ba, located on their respective assigned outer peripheral grid points 820. The remaining six outer peripheral fiber cores are arranged as grid point non-configured fiber cores 110Bb, maintaining... Figure 2In the adjacent state shown in the lower part, the fiber cores are configured with their centers offset relative to their respective assigned peripheral grid points 820. Therefore, in this 12-core MCF 100E, the ratio of the number of grid-point configured fiber cores to the number of grid-point unconfigured fiber cores is 2 to 6. The pairs of two grid-point unconfigured fiber cores 110Bb are configured in a position that is linearly symmetrical with respect to the axis of symmetry LA, but the fiber core configuration of this 12-core MCF 100E does not have more than two rotational symmetries centered on the fiber axis AX5. In addition, regarding the pairs of linearly symmetrically configured grid-point unconfigured fiber cores 110Bb (3 pairs in the fourth variation), the offset angle of the first pair is θ1, the offset angle of the second pair is θ2, and the offset angle of the third pair is θ3. The offset angles θ1, θ2, and θ3 do not need to be consistent with each other.

[0098] The first comparison involves the 12-core MCF 900A ( Figure 6 The upper part) is an example of 8 peripheral cores without grid point non-configured cores, the second comparison example involves 12 cores of MCF 900B ( Figure 6 The lower part of the fiber contains four non-configured lattice cores among the eight outer cores. Furthermore, any core configuration of the 12-core MCF 900A and 900B, regardless of polarity, consists of 12 linearly symmetrically arranged cores. Each core configuration of the 12-core MCF 900A and 900B exhibits rotational symmetry at least twice around fiber axes AX6 and AX7.

[0099] Figure 7 This is a diagram used to illustrate the main terms used in this specification (adjacent relationships of inner cores, cross-sectional structure of the core periphery, parallel transmission and parallel transmission XT (crosstalk), and opposite transmission and opposite transmission XT (crosstalk)).

[0100] (Adjacent relationships of the inner circumferential fiber core)

[0101] In this specification, when considering a specific core among the 12 cores arranged in the cross-section of the MCF, the adjacency relationship between cores is defined as a core that is adjacent to that specific core, provided that the minimum center-to-center spacing is relative to that specific core and the difference between that minimum center-to-center spacing is 2 μm or less. Specifically, in Figure 7 The four inner peripheral fiber cores 110A (fiber cores 110) arranged on four inner peripheral grid points 810 surrounding the fiber axis at grid point intervals Λ will be described. Among these four inner peripheral fiber cores 110A, the pairs of inner peripheral fiber cores 110A forming each side of the square grid are adjacent (the center-to-center distance between adjacent inner peripheral fiber cores 110A is substantially Λ). On the other hand, the pair of inner peripheral fiber cores 110A located on the diagonal of the square grid are not adjacent.

[0102] (Cross-sectional structure around the fiber core)

[0103] In each of the 12-core MCF 100A to 100E, the cross-sectional structure around each core 110 (including the inner peripheral core 110A, the lattice-dot configured core 110Ba, and the lattice-dot unconfigured core 110Bb) is such that a common cladding 120 surrounds the outer periphery of the core 110. The common cladding 120 may be configured to directly contact the core 110, but an optical cladding 121 may also be provided between the common cladding 120 and the core 110. Alternatively, a trench layer 122 having a small relative refractive index difference Δ3 may be provided between the optical cladding 121 and the common cladding 120. Furthermore, the optical cladding 121 is preferably prepared for each core 110, having a relative refractive index difference Δ2 of -0.1% to 0.1% relative to the refractive index of the common cladding 120. Furthermore, when the trench layer 122 is provided, the trench layer 122 preferably has a relative refractive index difference Δ3 relative to the refractive index of the common cladding that is -2.0% or more but less than -1.0%, -1.0% or more but less than -0.7%, -0.7% or more but less than -0.4%, or -0.4% or more but less than 0%.

[0104] (Parallel transmission and parallel transmission XT)

[0105] exist Figure 7 In the example shown, three fiber cores with adjacent relationships are illustrated (all are the first fiber core 110a transmitting light in the same direction). That is, an adjacent relationship is established between the left fiber core and the central fiber core, and an adjacent relationship is established between the central fiber core and the right fiber core. In other words, the state in which each fiber core with an adjacent relationship transmits light in the same direction is recorded as "parallel transmission". In this case, a normal inter-fiber XT (parallel transmission XT) is generated between adjacent fiber cores transmitting light in the same direction.

[0106] (Reciprocal transmission and reciprocal transmission XT)

[0107] On the other hand, opposite-direction transmission refers to two adjacent fiber cores transmitting light in different directions. That is, in Figure 7In the example, the left fiber core and the central fiber core are adjacent, but the left fiber core functions as the first fiber core 110a, while the central fiber core functions as the second fiber core 110b that transmits light in a direction different from the first fiber core 110a. The normal XT generated between these left and central fiber cores does not significantly affect communication quality. Similarly, the right fiber core, which is adjacent to the central fiber core, functions as the first fiber core 110a, and the normal XT generated between these right and central fiber cores does not significantly affect communication quality. As described above, the state where adjacent fiber cores transmit light in different directions is described as "opposite transmission". However, between the left and right fiber cores (both functioning as the first fiber core 110a), the XT, separated by the central fiber core (functioning as the second fiber core 110b), affects communication quality. As described above, the XT between fiber cores that are adjacent and transmit light in opposite directions but transmit light in the same direction is described as "opposite transmission XT".

[0108] In addition, please refer to the following instructions. Figure 7 The examples of "parallel transmission" and "opposite transmission" shown will be explained one by one, but if we consider the XT (parallel transmission XT: XT) between fiber cores (hereinafter referred to as "adjacent fiber cores") within the fiber length L1 range that have an adjacent relationship, co Set as XT co (L1), then when XT is expressed in decibels, it is expressed as the following equation (21):

[0109] XT co (L2)=XT co (L1)+10log 10 (L2 / L1)…(21)

[0110] At a distance of 10 times, XT increases by 10dB.

[0111] When XT is expressed in decibels, for example, in Figure 7 In the example of counter-current transmission shown, XT (counter-current transmission XT: XT) is transmitted from the right fiber core to the left fiber core across the central fiber core. counter Parallel transmission XT is used between the left and central fiber cores and between the central and right fiber cores. co It can be expressed as the following formula (22):

[0112] XT counter =2XT co -10log 10 2…(22)

[0113] If we define the phased transmission XT within the fiber length L1 as XTcounter (L1), then when XT is expressed in decibels, the phase-to-phase transmission XT within the fiber length L2 is expressed as the following equation (23):

[0114] XT counter (L2)=XT counter (L1)+20log 10 (L2 / L1)…(23)

[0115] At a distance of 10x XT counter Increased by 20dB.

[0116] XT from adjacent fiber cores to the specified fiber core co Total XT co，tot If the number of adjacent fiber cores of a given fiber core is set to N, then it becomes the following equation (24):

[0117] XT co,tot =XT co +10log 10 N…(24)

[0118] Equation (24) above is based on the XT between adjacent fiber cores. co Uniformity is the premise. XT between adjacent fiber cores co When the differences cannot be ignored, if XT from fiber core n is transferred from N adjacent fiber cores to a specified fiber core... co Set as XT co，n The total is XT co，tot It becomes the following formula (25):

[0119]

[0120] The total XT of the opposite transmission to the specified fiber core counter，tot If the specified fiber core also includes "adjacent fiber cores (in adjacent fiber cores)", Figure 7 In the example of the opposite transmission shown, if the specified fiber core is set as the left fiber core, then the number of the equivalent right fiber core is set to M, then it seems to become the following equation (26):

[0121] XT counter,tot =XT counter +10log 10 M = 2XT co -10log 10 2+10log 10 M…(26)

[0122] However, the inventors discovered that this was not the case. If the number of adjacent cores (including the specified core) corresponding to core n among the N adjacent cores (central core) of the specified core (left core) is set as K... n XT counter，tot It becomes the following formula (27):

[0123]

[0124] Therefore, in a 12-core MCF, XT is sent to any of the four cores belonging to the inner peripheral core group. counter,tot It can be expressed as the following formula (28):

[0125]

[0126] Therefore, in order to set the phase-to-phase transmission XT after 10km transmission through a 12-core MCF (equivalent to a fiber length of 10km) to below -20dB (=-20dB / 10km), the parallel transmission XT (XT) between adjacent fiber cores, converted to fiber length L (km), is... co The preferred form is (29):

[0127]

[0128] Furthermore, the sum of parallel transmissions XT from four adjacent fiber cores to any of the four fiber cores belonging to the inner peripheral fiber core group is preferably expressed by the following formula (30):

[0129]

[0130] To ensure that the phase-to-phase transmission XT after 10km transmission via a 12-core MCF (equivalent to 10km of fiber length) is below -40dB (=-40dB / 10km), it is preferable to set the parallel transmission XT (XT) between adjacent fiber cores, converted to fiber length L (km). co ) is the following formula (31):

[0131]

[0132] Furthermore, the sum of parallel transmissions XT from four adjacent fiber cores to any of the four fiber cores belonging to the inner periphery fiber core group is preferably expressed by the following formula (32):

[0133]

[0134] Next, the profile construction of the MCF that can be applied to the present invention will be described. Figure 8This is a diagram showing the refractive index distribution around each fiber core of the MCF applicable to this invention. Furthermore, unless otherwise stated, "relative refractive index difference Δ" refers to the relative refractive index difference relative to the refractive index of the common cladding (and therefore not the relative refractive index difference relative to the refractive index of pure silicon glass).

[0135] Regarding the core structure of the MCF of the present invention, the refractive index distribution of the core and its associated optical properties can be selected according to the application, for example, the following can be applied: Figure 8 The refractive index distributions of samples (A) to (K) are shown. Furthermore, in Figure 8 In this context, Δ is the relative refractive index difference based on the refractive index of the common cladding, and r is the radius from the center of each fiber core. This is represented by a local coordinate system with the center of each fiber core (Δ = 0%) as the origin O. The construction can be consistent or different between fiber cores.

[0136] Figure 8 The patterns shown (A) are stepped refractive index distributions, (B) are toroidal refractive index distributions, (C) are double-step refractive index distributions, (D) are gradient refractive index distributions, and (E) are drooping refractive index distributions. These patterns can be applied to the core structure of the MCF of the present invention. Furthermore, patterns (F) and (H) with a depressed refractive index distribution around the core, patterns (G), (I), and (J) with a raised refractive index distribution around the core, and pattern (E) with a matched refractive index distribution around the core can also be applied to the core structure.

[0137] The refractive index distribution other than that of the stepped refractive index distribution in pattern (A) can be approximated using ESI (Equivalent-step-index) to obtain the core radius a and the core Δ(Δ1) after the step approximation (see Non-Patent Document 3 above).

[0138] The aforementioned Non-Patent Document 3 can be easily applied when the boundaries between the core and cladding are clear, but it is difficult to apply to cases where the boundaries between the core and cladding (common cladding 120 or optical cladding 121) are unclear, such as the drooping refractive index distribution of Pattern (E). For example, if the method of the aforementioned Non-Patent Document 3 is directly applied by taking b of Pattern (E) as the radius of the core, the ESI approximation is poor. In the case described above, it is preferable to take the r corresponding to 2 / 5 of Δ at a specific r as the core radius a and apply the aforementioned Non-Patent Document 3, where the specific r is the slope of the refractive index distribution. The refractive index of the cladding (common cladding 120 or optical cladding 121) is the simple average of Δ over the range of a to b, as shown by the following equation (33):

[0139]

[0140] Alternatively, a weighted average of r can be shown by the following equation (34):

[0141]

[0142] The obtained values ​​can be used to determine a and Δ1 (the maximum relative refractive index difference between the first and second fiber cores 110a and 110b) based on the calculations in Non-Patent Document 3 mentioned above. Δ2 (the relative refractive index difference of the optical cladding 121) is preferably between -0.10% and 0.10%. Therefore, manufacturability is greatly improved.

[0143] A trench layer 122 with a lower refractive index than the optical cladding 121 and the common cladding 120 can be provided around the optical cladding 121. Figure 8 The pattern (K)). However, when the relative refractive index difference Δ3 of the trench layer 122 based on the refractive index of the common cladding 120 is less than -0.5%, manufacturability deteriorates significantly. Therefore, Δ3 ≥ -0.4% is preferred, Δ3 ≥ -0.3% is more preferred, and Δ3 ≥ -0.2% is most preferred. Furthermore, from the viewpoint of manufacturability, it is more preferable to have no trench layer.

[0144] Regarding the materials of the core and cladding (optical cladding 121 or common cladding 120), glass with silicon glass as the main component is preferred as it can achieve low transmission loss and high mechanical reliability. It is preferable to add Ge to the core, thereby creating a refractive index difference between the core and the cladding. Alternatively, it is preferable to add F to the cladding, thereby creating a refractive index difference between the core and the cladding. Adding trace amounts of F to the core and optical cladding results in good manufacturability and enables a depressed distribution, which is therefore preferred. Cl can be added to the core and cladding. This suppresses OH groups and absorption losses caused by OH groups. Trace amounts of P can be contained in the core and cladding. This improves manufacturability in some glass synthesis processes.

[0145] In addition, it has Figures 2 to 5 The cross-sectional structure of the MCF of the present invention shown has a resin-coated portion 130, the diameter of which preferably converges to a range of 235 μm to 265 μm with a reference diameter of 250 μm. Therefore, the cable-compatible MCF of the present invention can be realized without making significant changes to existing cable-connecting devices.

[0146] Furthermore, in a typical general-purpose SMF, the nominal value of the cladding diameter (diameter of glass fiber 200) is CD. nominal The nominal diameter of the resin-coated portion 130 is 245μm to approximately 250μm, but for small-diameter SMFs, the nominal diameter can be 180μm, 190μm, or 200μm. In these cases, the nominal thickness of the resin-coated portion 130 is 27.5μm, 32.5μm, and 37.5μm, respectively. If the resin-coated portion 130 becomes too thin, damage to the glass cladding can occur if sand, dust, or other contaminants damage the surface of the cladding, weakening the fiber's strength. Therefore, a sufficiently thick nominal cladding is desirable.

[0147] In the MCF of the present invention, in order to achieve a nominal diameter of 250 μm and a nominal coating thickness of 27.5 μm or more for the resin coating portion 130, a nominal coating diameter of CD is preferred. nominal It is below 195μm.

[0148] Furthermore, in order to achieve a nominal diameter of 245 μm and a nominal coating thickness of 27.5 μm or more for the resin-coated portion 130, CD is preferred. nominal The diameter is 190 μm or less. To achieve a nominal diameter of 250 μm and a nominal coating thickness of 32.5 μm or more for the resin-coated portion 130, CD is preferred. nominal The diameter is 185 μm or less. To achieve a nominal diameter of 245 μm and a nominal coating thickness of 32.5 μm or more for the resin-coated portion 130, CD is preferred. nominal The diameter is 180 μm or less. To achieve a nominal diameter of 250 μm and a nominal coating thickness of 37.5 μm or more for the resin-coated portion 130, CD is preferred. nominal The diameter is 175 μm or less. Furthermore, to achieve a nominal diameter of 245 μm and a nominal coating thickness of 37.5 μm or more for the resin-coated portion 130, CD is preferred. nominal The thickness is 170 μm or less. In each case, it is preferable that the tolerance of the coating thickness converges to a value of more than 15 μm from the nominal value and less than 15 μm from the nominal value, and more preferably to a value of more than 10 μm from the nominal value and less than 10 μm from the nominal value.

[0149] Each core of the MCF of the present invention preferably has an MFD that converges to an MFD reference value within a range of 8.6 μm to 9.2 μm at a wavelength of 1310 nm, and an MFD reference value of -0.4 μm to +0.4 μm. In this case, the MFD value is consistent with the nominal MFD value in the general SMF specified in ITU-T G.652. nominalSmall (MFD) nominal Compared to the connection loss of general SMFs of the type with ≥8.6μm and suppressed bending loss, the connection loss caused by the axial offset of the MCFs of the present invention (in the case of given axial offset) can be suppressed to the same level or below.

[0150] Each core of the MCF of the present invention preferably has an MFD that converges to a range of 8.2 μm to 9.0 μm based on 8.6 μm at a wavelength of 1310 nm. Therefore, when connecting a general SMF (such as the type of general SMF specified in ITU-T G.652, which has a small nominal MFD value and suppresses bending loss) with the MCF of the present invention, the connection loss caused by core center axis offset (axis offset) can be set to be equal (in the case of a specified axis offset).

[0151] Each core of the MCF of the present invention preferably has an MFD that, at a wavelength of 1310 nm, has an MFD reference value of 8.2 μm to 8.6 μm and converges to a value of -0.4 μm to 0.4 μm from the MFD reference value and below the MFD reference value. Thus, compared to the MFD in the general SMFs specified in ITU-T G.652, this is particularly advantageous. nominal Small (MFD) nominal A general-purpose SMF of the type with a diameter of ≥8.6 μm and suppressing bending loss can suppress the increase in connection loss (in the case of a specified axial offset) caused by the axial offset of the MCF of the present invention to less than 10%. This means that when the connection loss of a general-purpose SMF of the type with suppressed bending loss is 0.15 dB with an axial offset, the connection loss of the MCF of the present invention is 0.15 dB to 0.165 dB; when the connection loss of a general-purpose SMF of the type with suppressed bending loss is 0.25 dB with an axial offset, the connection loss of the MCF of the present invention is 0.25 dB to 0.275 dB; when the connection loss of a general-purpose SMF of the type with suppressed bending loss is 0.50 dB with an axial offset, the connection loss of the MCF of the present invention is 0.50 dB to 0.55 dB; and when the connection loss of a general-purpose SMF of the type with suppressed bending loss is 0.75 dB with an axial offset, the connection loss of the MCF of the present invention is 0.75 dB to 0.825 dB. At this time, MFD nominal Small size can enhance the sealing of the optical fiber core and suppress leakage loss between the optical fiber cores and the resin coating, therefore it is preferred.

[0152] The MCF of the present invention preferably has a zero-dispersion wavelength of 1300 nm to 1324 nm. Therefore, the distortion of the signal waveform transmitted in the O-band can be suppressed to the same level as that of a general-purpose SMF.

[0153] The MCF of the present invention preferably has a zero-dispersion wavelength that converges to a value between -12 nm and +12 nm, with a wavelength reference value of 1312 nm to 1340 nm. Therefore, compared with a general SMF, it can suppress the distortion of the signal waveform after transmission in the O-band (see Non-Patent Document 4 above).

[0154] In the operating band, the sum of XT from adjacent fiber cores to any fiber core is preferably below -20dB (=-20dB / 10km) after 10km of transmission (equivalent to a fiber length of 10km). The XT from outside adjacent fiber cores is sufficiently low to be negligible, thus achieving a sufficient signal-to-noise ratio even when coherent detection is performed.

[0155] In the operating band, the sum of XT from adjacent fiber cores to any fiber core is preferably below -40dB (=-40dB / 10km) after 10km of transmission (equivalent to a fiber length of 10km). The XT from outside adjacent fiber cores is sufficiently low to be negligible, thus achieving a sufficient signal-to-noise ratio even with intensity-modulated direct detection.

[0156] In the MCF of the present invention, the sum of XT from adjacent fiber cores (parallel transmission XT) in the operating band is preferably below -6.8dB (=-6.8dB / 10km) after 10km of transmission (equivalent to a fiber length of 10km). Thus, in a 12-core MCF having 12 fiber cores arranged in a square grid (in this embodiment, a fiber core configuration in which 4 inner perimeter fiber cores are arranged on a square grid, and its center is offset from a grid point allocated to a portion of the 8 outer perimeter fiber cores is denoted as a "square fiber core configuration"), when performing bidirectional communication by pairing all adjacent fiber cores and setting the signal transmission directions between adjacent fiber cores to opposite directions, the problem of the opposite transmission XT to the aforementioned arbitrary fiber cores (e.g., ...) can be solved. Figure 7 As in the example, the sum of XT reaching the light from adjacent fiber cores that are propagating in the opposite direction is still suppressed to below -20dB (= -20dB / 10km) after 10km of transmission (equivalent to a fiber length of 10km).

[0157] In the operating band of the present invention, the parallel transmission XT is preferably below -16.8dB (= -16.8dB / 10km) after 10km of transmission (equivalent to 10km of optical fiber). Thus, the opposing transmission XT can be suppressed to below -40dB (= -40dB / 10km) after 10km of transmission (equivalent to 10km of optical fiber).

[0158] The following description shows the relationship with... Figure 8 The results of the study are related to the refractive index distribution of the core of the samples (E), (H) and (J), where a is 3 μm or more and 5 μm or less, Δ1-Δ2 is 0.3% or more and 0.6% or less, Δ2 is -0.1% or more and 0.1% or less, and b / a is 2 or more and 5.

[0159] By calculating the electric field distribution of the fundamental mode and the wavelength dependence of the effective refractive index using methods such as the finite element method, those skilled in the art can design the structure of a fiber core with a specified zero-dispersion wavelength and MFD. For example, the relationship between a and (Δ1-Δ2) for the zero-dispersion wavelength λ0 [μm] is in the range of 3μm≤a≤5μm and 0.3%≤(Δ1-Δ2)≤0.6%, which is expressed as the following equation (35):

[0160] a≈0.0667(λ0-1343.1)(Δ1-Δ2) 2 +0.0900(λ0-1354.6)(Δ1-Δ2)-0.0517(λ0-1411.2)…(35)

[0161] Therefore, in order for the zero-dispersion wavelength λ0[μm] to converge to λ 0nominal Values ​​above -12nm and λ 0nominal For values ​​below +12nm, the relationship between a and (Δ1-Δ2) preferably satisfies the following equations (36) and (37):

[0162] a≤0.0667(λ 0nominal -12-1343.1)(Δ1-Δ2) 2 +0.0900(λ 0nominal -12-1354.6)(Δ1-Δ2)-0.0517(λ 0nominal -12-1411.2)…(36)

[0163] a≥0.0667(λ 0nominal +12-1343.1)(Δ1-Δ2) 2 +0.0900(λ 0nominal +12-1354.6)(Δ1-Δ2)-0.0517(λ 0nominal +12-1411.2)…(37)

[0164] These two formulas.

[0165] Furthermore, the relationship between a and (Δ1-Δ2) corresponding to MFD[μm] at wavelength 1310nm is in the range of 3μm≤a≤5μm and 0.3%≤(Δ1-Δ2)≤0.6%, which becomes the following equation (38):

[0166] (Δ1-Δ2)=(-0.0148MFD+0.213)[a-0.619MFD+2.01] 2 -0.0771MFD+1.033…(38)

[0167] Therefore, in order for MFD[μm] to converge to MFD nominal Values ​​above -0.4 μm and MFD nominal For values ​​below +0.4 μm, the relationship between a and (Δ1-Δ2) preferably satisfies the following equations (39) and (40):

[0168] (Δ1-Δ2)≤[-0.0148(MFD nominal +0.4)+0.213][a-0.619(MFD nominal +0.4)+2.01] 2 -0.0771(MFD nominal +0.4)+1.033…(39)

[0169] (Δ1-Δ2)≥[-0.0148(MFD nominal -0.4)+0.213][a-0.619(MFD nominal -0.4)+2.01] 2 -0.0771(MFD nominal -0.4)+1.033…(40)

[0170] These two formulas.

[0171] b / a and Δ2 only need to be set to λ cc It becomes below 1260nm or 1360nm, and the zero-dispersion slope becomes 0.092ps / (nm). 2 ·km) is sufficient. Therefore, it is preferable that Δ2 is between -0.1% and 0.0%, and b / a is between 2 and 4.

[0172] Next, the preferred center spacing Λ between adjacent fiber cores will be explained. Figure 9 This refers to the center-to-center spacing Λ and MFD / λ between adjacent fiber cores when the phase-to-phase transmission XT becomes -20dB (=-20dB / 10km) at a wavelength of 1360nm after 10km transmission of a 12-core MCF configured in a square lattice of 12 fiber cores at a wavelength of 1260nm. cc A graph showing the relationship between MFD and λ. Furthermore, MFD / λ cc For dimensionless quantities, MFD and λ ccThe units are consistent to determine the value. Here, the average value R of the fiber bending radius is 0.14 m. If R is below 0.14 m, a lower XT can be achieved. Furthermore, λ... cc The cable cutoff wavelength was determined using the structure (without cabled optical fiber) in Figure 12 of ITU-T G.650.1 (03 / 2018).

[0173] To ensure that the phase-to-phase transmission XT is below -20dB after 10km transmission at a wavelength of 1360nm (equivalent to a fiber length of 10km), the center spacing Λ between adjacent fiber cores and MFD / λ are... cc It must satisfy at least the following equation (41) or equation (42):

[0174] Λ≥2.34MFD / λ cc +12.1…(41)

[0175] MFD / λ cc ≤0.428Λ-5.19…(42)

[0176] (from Figure 9 The area above the dotted line on the lower side), and preferably satisfies the following equation (43) or equation (44):

[0177] Λ≥2.34MFD / λ cc +14.6…(43)

[0178] MFD / λ cc ≤0.428Λ-6.25…(44)

[0179] (from Figure 9 The area above the dotted line on the upper side).

[0180] To allow for fluctuations in the position of each fiber core from the design center, Λ preferably has a margin of 1 μm in the range shown in equations (41) to (44) above. Therefore, if the nominal value of this Λ ​​is set to Λ nominal Then Λ must satisfy at least the following equation (45):

[0181] Λ nominal ≥2.34MFD / λ cc +12.1+1.0…(45)

[0182] Furthermore, relative to the following equation (46):

[0183] Λ nominal ≥2.34MFD / λ cc +14.6+1.0…(46)

[0184] Λ nominalΛ preferably satisfies the following equation (47):

[0185] Λ nominal -0.9≤Λ≤Λ nominal +0.9…(47)

[0186] At this point, the position of the fiber core can be independently considered as an approximation of the case where the probability distribution fluctuates from the design center by a Gaussian distribution of 3σ = 0.9 μm. The probability that Λ does not satisfy equation (41) or equation (43) is suppressed to less than 1%. Furthermore, Λ preferably satisfies the following equation (48):

[0187] Λ nominal -0.7≤Λ≤Λ nominal +0.7…(48)

[0188] This means that the position of each fiber core can be independently considered as an approximation of the case where the probability distribution fluctuates from the design center by a Gaussian distribution of 3σ = 0.7 μm. The probability that Λ does not satisfy equation (41) or equation (43) is suppressed to less than 0.1%. Furthermore, Λ preferably satisfies the following equation (49):

[0189] Λ nominal -0.5≤Λ≤Λ nominal +0.5…(49)

[0190] This means that the position of each fiber core can be independently considered as an approximation of the case where the probability distribution fluctuates from the design center by a Gaussian distribution of 3σ = 0.5μm. The probability that Λ does not satisfy equation (41) or equation (43) is suppressed to less than 0.001%.

[0191] With a 12-core MCF configured in a square fiber core, after 10km of transmission at a wavelength of 1360nm (equivalent to a fiber length of 10km), the parallel transmission XT becomes -20dB when the center spacing Λ between adjacent cores and MFD / λ are... cc Regarding the relationship, if the same study is conducted, in order to set the parallel transmission XT below -20dB after 10km transmission at a wavelength of 1360nm (equivalent to a fiber length of 10km), the center spacing Λ between adjacent fiber cores and MFD / λ... cc At least the following equation (50) or equation (51) must be satisfied:

[0192] Λ≥2.73MFD / λ cc +12.7…(50)

[0193] MFD / λ cc ≤0.367Λ-4.66…(51)

[0194] Furthermore, it is preferable to satisfy either equation (52) or equation (53) below:

[0195] Λ≥2.73MFD / λ cc +15.1…(52)

[0196] MFD / λ cc ≤0.367Λ-5.54…(53)

[0197] To allow for fluctuations in the position of each fiber core from the design center, Λ preferably has a margin of 1 μm in the range from equation (50) to equation (53) above. Therefore, if the nominal value of Λ is set to Λ... nominal Then Λ must satisfy at least the following equation (54):

[0198] Λ nominal ≥2.73MFD / λ cc +12.7+1.0…(54)

[0199] Furthermore, relative to the following equation (55):

[0200] Λ nominal ≥2.73MFD / λ cc +15.1+1.0…(55)

[0201] The Λnominal, Λ preferably satisfies the following equation (56):

[0202] Λ nominal -0.9≤Λ≤Λ nominal +0.9…(56)

[0203] This means that the position of each fiber core can be independently considered as an approximation of the case where the probability distribution fluctuates from the design center by a Gaussian distribution of 3σ = 0.9 μm. The probability that Λ does not satisfy equation (50) or equation (52) is suppressed to less than 1%. Furthermore, Λ preferably satisfies the following equation (57):

[0204] Λ nominal -0.7≤Λ≤Λ nominal +0.7…(57)

[0205] This means that the position of each fiber core can be independently considered as an approximation of the case where the probability distribution fluctuates from the design center by a Gaussian distribution of 3σ = 0.7 μm. The probability that Λ does not satisfy equation (50) or equation (52) is suppressed to less than 0.1%. Furthermore, Λ preferably satisfies the following equation (58):

[0206] Λ nominal -0.5≤Λ≤Λ nominal +0.5…(58)

[0207] This means that the position of each fiber core can be independently considered as an approximation of the case where the probability distribution fluctuates from the design center by a Gaussian distribution of 3σ = 0.5μm. The probability that Λ does not satisfy equation (50) or equation (52) is suppressed to less than 0.001%.

[0208] Figure 10 This refers to the center-to-center spacing Λ and MFD / λ between adjacent fiber cores when the phase-to-phase transmission XT becomes -40dB (=-40dB / 10km) at a wavelength of 1360nm after 10km transmission with a 12-core MCF configuration in a square fiber core. cc A graph showing the relationship between the two.

[0209] To ensure that the phase transmission XT after 10km transmission at a wavelength of 1360nm is below -40dB, the center-to-center spacing Λ between adjacent fiber cores and the MFD / λ are... cc The following equations (59) or (60) must be satisfied:

[0210] Λ≥2.63MFD / λ cc +12.5…(59)

[0211] MFD / λ cc ≤0.380Λ-4.77…(60)

[0212] ( Figure 10 The region above the dotted line on the lower side), and preferably satisfies the following equation (61) or equation (62):

[0213] Λ≥2.63MFD / λ cc +15.0…(61)

[0214] MFD / λ cc ≤0.380Λ-5.69…(62)

[0215] ( Figure 10 (The area above the dotted line on the top side).

[0216] To allow for fluctuations in the position of each fiber core from the design center, it is preferable to have a margin of at least 1 μm Λ in the range from equation (59) to equation (62). Therefore, Λ is relative to the nominal value Λ of this Λ. nominal It must at least satisfy the following equation (63):

[0217] Λ nominal ≥2.63MFD / λ cc +12.5+1.0…(63)

[0218] Furthermore, relative to the following equation (64):

[0219] Λnominal ≥2.63MFD / λ cc +15.0 +1.0…(64)

[0220] Λ nominal Λ preferably satisfies the following equation (65):

[0221] Λ nominal -0.9≤Λ≤Λ nominal +0.9…(65)

[0222] In this case, the position of each fiber core can be independently considered as an approximation of a Gaussian distribution fluctuating from the design center with a probability distribution of 3σ = 0.9 μm. At this point, the probability that Λ does not satisfy the above equation (59) or equation (61) is suppressed to less than 1%. Furthermore, it satisfies the following equation (66):

[0223] Λ nominal -0.7≤Λ≤Λ nominal +0.7…(66)

[0224] In this case, the position of each fiber core can be independently considered as an approximation of the fluctuation of a Gaussian distribution with a probability distribution of 3σ = 0.7 μm from the design center. In this case, the probability that Λ does not satisfy the above equation (59) or the above equation (61) is suppressed to less than 0.1%. Furthermore, when the following equation (67) is satisfied:

[0225] Λ nominal -0.5≤Λ≤Λ nominal +0.5…(67)

[0226] In this case, the position of each fiber core can be independently considered as an approximation of the case where the probability distribution fluctuates from the design center by a Gaussian distribution of 3σ = 0.5μm. In this case, the probability that Λ does not satisfy the above equation (59) or the above equation (61) is suppressed to less than 0.001%.

[0227] In a 12-core MCF configuration with a square fiber core, if the parallel transmission XT after 10km transmission at a wavelength of 1360nm becomes -40dB when the center-to-center spacing Λ between adjacent fiber cores and MFD / λ are... cc To conduct the same study on the relationship, in order to set the parallel transmission XT after 10km transmission at a wavelength of 1360nm to below -40dB, the center spacing Λ between adjacent fiber cores and MFD / λ are... cc Preferably, at least the following equation (68) or equation (69) is satisfied:

[0228] Λ≥3.31MFD / λ cc +12.6…(68)

[0229] MFD / λ cc ≤0.377Λ-4.75…(69)

[0230] ( Figure 10 The region above the dotted line on the lower side of the map, and satisfies either equation (70) or equation (71):

[0231] Λ≥3.31MFD / λ cc +15.0…(70)

[0232] MFD / λ cc ≤0.377Λ-5.66…(71)

[0233] ( Figure 10 (The area above the dotted line on the top side).

[0234] To allow for fluctuations in the position of each fiber core from the design center, it is preferable to have a margin of at least 1 μm Λ in the range from equation (68) to equation (71) above. Therefore, relative to the nominal value Λ nominal Λ must satisfy at least the following equation (72):

[0235] Λ nominal ≥3.31MFD / λ cc +12.6+1.0…(72)

[0236] Furthermore, relative to the following equation (73):

[0237] Λ nominal ≥3.31MFD / λ cc +15.0 +1.0…(73)

[0238] Λ nominal Λ is preferably in the following formula (74):

[0239] Λ nominal -0.9≤Λ≤Λ nominal +0.9…(74)

[0240] The range. This is an approximation of the case where the position of each fiber core can be independently considered as a probability distribution fluctuating from the design center by a Gaussian distribution of 3σ = 0.9 μm. In this case, the probability that Λ does not satisfy the above equation (68) or the above equation (70) is suppressed to less than 1%. Furthermore, it is preferable to satisfy the following equation (75):

[0241] Λ nominal -0.7≤Λ≤Λ nominal +0.7…(75)

[0242] In this case, the position of each fiber core can be independently considered as an approximation of a Gaussian distribution with a probability distribution of 3σ = 0.7 μm from the design center. In this case, the probability that Λ does not satisfy the above equation (68) or equation (70) is suppressed to less than 0.1%. Furthermore, when the following equation (76) is satisfied:

[0243] Λ nominal -0.5≤Λ≤Λ nominal +0.5…(76)

[0244] In this case, the position of each fiber core can be independently considered as an approximation of the case where the probability distribution fluctuates from the design center by a Gaussian distribution of 3σ = 0.5μm. In this case, the probability that Λ does not satisfy the above equation (68) or the above equation (70) is suppressed to less than 0.001%.

[0245] Figure 11 This indicates that when the leakage loss to the cladding is 0.01 dB / km in a 12-core MCF with a wavelength of 1360 nm, d coat and MFD / λ cc A graph showing the relationship between the two.

[0246] To set the leakage loss to the cladding at a wavelength of 1360 nm to 0.01 dB / km, d coat and MFD / λ cc Preferably, the following equation (77) or equation (78) is satisfied:

[0247] d coat ≥2.88MFD / λ cc +5.36…(77)

[0248] MFD / λ cc ≤0.347d coat -1.86…(78)

[0249] ( Figure 11 The region above the dotted line on the lower side of the map, and satisfies either equation (79) or equation (80):

[0250] d coat ≥2.88MFD / λ cc +6.95…(79)

[0251] MFD / λ cc ≤0.347d coat -2.41…(80)

[0252] ( Figure 11 (The area above the dotted line on the top side).

[0253] The outermost core dcoat (i.e. d) coat The minimum value of d is usually referred to as the outer cladding thickness (OCT), but the d in this specification coat Set to a value that can be defined for each fiber core.

[0254] To allow for fluctuations in the position of each fiber core from the design center, and for fluctuations in the cladding diameter from the design center, it is preferable to have a d value of at least 1 μm in the range from equation (77) to equation (80) above. coat The margin. Therefore, d coat Preferred is relative to d coat The nominal value d coat,nominal The nominal value of the cladding diameter CD nominal At least the following equation (81) must be satisfied:

[0255] d coat,nominal ≥2.88MFD / λ cc +5.36+1.0…(81)

[0256] Furthermore, it satisfies the following equation (82):

[0257] d coat,nominal ≥2.88MFD / λ cc +6.95+1.0…(82)

[0258] The range. At this time, the following equations (83) and (84) are satisfied:

[0259] Λ nominal -0.9≤Λ≤Λ nominal +0.9…(83)

[0260] CD nominal -0.9≤CD≤CD nominal +0.9…(84)

[0261] In these two cases, d coat The probability of not satisfying equation (77) or equation (79) above is suppressed to less than 1%. Furthermore, equations (85) and (86) below are satisfied:

[0262] Λ nominal -0.7≤Λ≤Λ nominal +0.7…(85)

[0263] CD nominal -0.7≤CD≤CD nominal +0.7…(86)

[0264] In these two cases, d coatThe probability of not satisfying equation (77) or equation (79) above is suppressed to less than 0.1%. Furthermore, equations (87) and (88) below are satisfied:

[0265] Λ nominal -0.5≤Λ≤Λ nominal +0.5…(87)

[0266] CD nominal -0.5≤CD≤CD nominal +0.5…(88)

[0267] In these two cases, d coat The probability of not satisfying the above equation (77) or above equation (79) is suppressed to less than 0.001%.

[0268] Figure 12 This indicates that when the leakage loss to the cladding is 0.01 dB / km in a 12-core MCF (square core configuration) at a wavelength of 1360 nm, d coat With a 1μm margin, the phase-to-phase transmission XT at a wavelength of 1360nm becomes -20dB (=-20dB / 10km) Λ with a 1μm margin, along with the CD (minimum permissible cladding diameter) and MFD / λ. cc A diagram illustrating the relationship. Furthermore, in Figure 12 In representing MFD / λ cc When the axis representing CD is set as the x-axis and the axis representing CD is set as the y-axis, the upper dashed line passes through y = 13.15x + 64.88 (x = 7.606 × 10⁻⁶). －2 Assigned by y - 4.935), the lower dashed line passes through y = 13.15x + 54.25 (x = 7.606 × 10⁻⁶). －2 y-4.126) is given.

[0269] When considering the tolerances of the dimensions of each fiber core position and the outer diameter of the cladding, in order to set the leakage loss to the cladding at a wavelength of 1360nm to below 0.01dB / km, and the back-to-back transmission XT after 10km transmission to below -20dB, CD nominal and MFD / λ cc The relationship preferably satisfies the following equation (89) or equation (90):

[0270] CD nominal ≥13.15MFD / λ cc +54.25…(89)

[0271] MFD / λ cc ≤0.07606CD nominal-4.126…(90)

[0272] ( Figure 12 The region above the dotted line at the bottom (in the middle) and satisfies either equation (91) or equation (92):

[0273] CD nominal ≥13.15MFD / λ cc +64.88…(91)

[0274] MFD / λ cc ≤0.07606CD nominal -4.935…(92)

[0275] ( Figure 12 (The area above the dotted line on the top side).

[0276] Figure 13 This refers to a 12-core MCF (square fiber configuration) where, after 10km of transmission (equivalent to 10km of fiber length), the phase-to-phase transmission XT at a wavelength of 1360nm becomes -20dB (=-20dB / 10km), or the parallel transmission XT (XT in typical co-directional transmission) becomes -20dB (=-20dB / 10km) after 10km of transmission (equivalent to 10km of fiber length), the leakage loss to the cladding is 0.01dB / km at a wavelength of 1360nm. coat Adding a 1μm margin, and with an additional 1μm margin in Λ, the CD (minimum permissible cladding diameter) and MFD / λ cc A diagram illustrating the relationship. Furthermore, in Figure 13 The symbol "●" is used to mark the area. Figure 13 The symbol “■” (displayed as a slash) shows the relationship of 12 MCF cores transmitting in parallel between adjacent fiber cores. Figure 13 (Displayed as diagonal lines) shows the relationship of 12 MCF cores transmitting in opposite directions between adjacent fiber cores.

[0277] According to Figure 13 As is known, it is preferable to use opposite transmission instead of parallel transmission to reduce the CD size by 10μm, therefore it is preferred.

[0278] exist Figure 13 The dotted line is not recorded, but it is consistent with... Figure 12 Similarly, in a 12-core MCF configuration with a square fiber core, in order to set the parallel transmission XT below -20dB after 10km transmission, CD nominal and MFD / λ cc The relationship preferably satisfies the following equation (93) or equation (94):

[0279] CDnominal ≥14.38MFD / λ cc +56.03…(93)

[0280] MFD / λ cc ≤0.06954CD nominal -3.896…(94)

[0281] And it satisfies either equation (95) or equation (96):

[0282] CD nominal ≥14.38MFD / λ cc +66.47…(95)

[0283] MFD / λ cc ≤0.06954CD nominal -4.622…(96)

[0284] On CD nominal For wavelengths of 195μm, 190μm, 185μm, 180μm, 175μm, and 170μm, in a 12-core MCF, considering the tolerances for core position and cladding diameter, to ensure leakage loss to the resin-coated portion at 1360nm is below 0.01dB / km, the phase-to-phase transmission XT after 10km transmission (equivalent to a 10km fiber length) is set to below -20dB, MFD / λ cc According to the above CD nominal The numerical values ​​are listed in the following order, preferably 9.66 or less, 9.32 or less, 8.97 or less, 8.62 or less, 8.27 or less, and 7.93 or less, and according to the above CD ominal The order of the listed values ​​is preferably 8.94 or less, 8.59 or less, 8.24 or less, 7.89 or less, 7.55 or less, and 7.20 or less.

[0285] On CD nominal For wavelengths of 195μm, 190μm, 185μm, 180μm, 175μm, and 170μm, in a 12-core MCF, considering the tolerances for core position and cladding diameter, to ensure leakage loss to the resin-coated portion at 1360nm is below 0.01dB / km and back-to-back transmission XT after 10km transmission (equivalent to 10km fiber length) is below -20dB, MFD / λ cc According to the above CD nominal The numerical values ​​are preferably listed in the following order: 10.71 or less, 10.33 or less, 9.94 or less, 9.56 or less, 9.18 or less, and 8.80 or less, and according to the above CD. nominalThe order of the values ​​listed is more preferably 9.90 or less, 9.52 or less, 9.14 or less, 8.76 or less, 8.38 or less, and 8.00 or less.

[0286] Figure 14 This indicates that when the leakage loss to the cladding is 0.01 dB / km in a 12-core MCF (square core configuration) at a wavelength of 1360 nm, d coat With a 1μm margin, the phase-to-phase transmission XT at a wavelength of 1360nm becomes -40dB (=-40dB / 10km) Λ with a 1μm margin, along with the CD (minimum permissible cladding diameter) and MFD / λ. cc A diagram illustrating the relationship. Furthermore, in Figure 14 In representing MFD / λ cc When the axis representing CD is set as the x-axis and the axis representing CD is set as the y-axis, the upper dashed line passes through y = 14.07x + 66.07 (x = 7.105 × 10⁻⁶). －2 Assigned by y - 4.694), the lower dashed line passes through y = 14.07x + 55.59 (x = 7.105 × 10⁻⁴). －2 (y-3.950) is given.

[0287] When considering the tolerances of the dimensions of each fiber core position and the outer diameter of the cladding, in order to set the leakage loss to the cladding at a wavelength of 1360nm to below 0.01dB / km and the back-to-back transmission XT after 10km transmission to below -40dB, CD nominal and MFD / λ cc The relationship preferably satisfies the following equation (97) or equation (98):

[0288] CD nominal ≥14.07MFD / λ cc +55.59…(97)

[0289] MFD / λ cc ≤0.07105CD nominal -3.950…(98)

[0290] (from Figure 14 The area above the dotted line on the lower side of the boundary), and satisfies the following equation (99) or equation (100):

[0291] CD nominal ≥14.07MFD / λ cc +66.07…(99)

[0292] MFD / λ cc ≤0.07105CD nominal-4.694…(100)

[0293] ( Figure 14 (The area above the dotted line on the top side).

[0294] Figure 15 This refers to a conditional 12-core MCF (square core configuration) at a wavelength of 1360nm where the phase-to-phase transmission XT becomes -40dB (=-40dB / 10km) or the parallel transmission XT becomes -40dB (=-40dB / 10km) after 10km transmission (equivalent to a fiber length of 10km), and the leakage loss to the cladding is 0.01dB / km at a wavelength of 1360nm. coat Adding a 1μm margin, and with an additional 1μm margin in Λ, the CD (minimum permissible cladding diameter) and MFD / λ cc A graph showing the relationship between the two.

[0295] In addition, Figure 15 In the middle, the symbol "●" (in) Figure 15 The symbol “■” (displayed as a slash) shows the relationship of 12 MCF cores transmitting in parallel between adjacent fiber cores. Figure 15 (Displayed as diagonal lines) shows the relationship of 12 MCF cores transmitting in opposite directions between adjacent fiber cores.

[0296] In Figure 15 The dotted line is not recorded, but it is consistent with... Figure 12 Similarly, in the case of a 12-core MCF configured on a square fiber core, in order to set the parallel transmission XT below -40dB after 10km transmission, CD nominal and MFD / λ cc The relationship preferably satisfies either equation (101) or equation (102):

[0297] CD nominal ≥16.24MFD / λ cc +58.71…(101)

[0298] MFD / λ cc ≤0.06159CD nominal -3.616…(102)

[0299] And it satisfies either equation (103) or equation (104):

[0300] CD nominal ≥16.24MFD / λ cc +68.86…(103)

[0301] MFD / λ cc≤0.06159CD nominal -4.241…(104)

[0302] On CD nominal For wavelengths of 195μm, 190μm, 185μm, 180μm, 175μm, and 170μm, in a 12-core MCF, considering the tolerances for core position and cladding diameter, to ensure leakage loss to the resin-coated portion at 1360nm is below 0.01dB / km and back-to-back transmission XT after 10km transmission (equivalent to 10km fiber length) is below -40dB, MFD / λ cc According to the above CD nominal The numerical values ​​are preferably listed in the following order: 8.39 or less, 8.09 or less, 7.78 or less, 7.47 or less, 7.16 or less, and 6.85 or less, and according to the above CD... ominal The order of the listed values ​​is preferably 7.77 or less, 7.46 or less, 7.15 or less, 6.85 or less, 6.54 or less, and 6.23 or less.

[0303] On CD nominal For wavelengths of 195μm, 190μm, 185μm, 180μm, 175μm, and 170μm, in a 12-core MCF, considering the tolerances for core position and cladding diameter, to ensure leakage loss to the resin-coated portion at 1360nm is below 0.01dB / km and back-to-back transmission XT after 10km transmission (equivalent to 10km fiber length) is below -40dB, MFD / λ cc According to the order listed above for CDnominal values, the preferred values ​​are 9.91 or less, 9.55 or less, 9.19 or less, 8.84 or less, 8.48 or less, and 8.13 or less, and according to the above CDnominal values... nominal The order of the listed values ​​is preferably 9.16 or less, 8.80 or less, 8.45 or less, 8.09 or less, 7.74 or less, and 7.38 or less.

[0304] λ cc The wavelength is below 1260nm, which ensures single-mode operation in the O-band, making it the preferred choice. In this case, by adjusting the MFD / λ... cc Setting it to 6.2 or higher allows for consideration of λ wavelengths below 1260nm. cc And an MFD that converges to a range of 7.8μm to 8.6μm with a reference of 8.2μm is preferred. This is achieved by adjusting the MFD / λ. cc Setting it to 6.5 or higher allows for consideration of λ wavelengths below 1260nm. ccAnd an MFD that converges to a range of 8.2μm to 9.0μm with a reference of 8.6μm is therefore preferred.

[0305] In addition, λ is preferred. cc The wavelength is below 1360nm. At this point, the high-mode transmission in the O-band occurs at a distance of 22m or more. However, if short-distance local bending and connection are not repeated, de facto single-mode operation can be guaranteed, and the fundamental mode is more strongly enclosed within the fiber core, making this preferable. Furthermore, by using MFD / λ... cc Set to 6.0 or higher to accommodate λ wavelengths below 1360nm. cc And an MFD that converges to a range of 8.2μm to 9.0μm with a reference of 8.6μm is therefore preferred.

[0306] In these cases, MFD / λ cc Preferred choice is from the CD mentioned above. nominal The upper limit is specified and from MFD and λ cc The range is between the specified lower limit and the specified value.

[0307] When setting the nominal value of MFD to MFD nominal And set the tolerance to MFD nominal Values ​​above -0.4μm and MFD nominal For values ​​below +0.4 μm, the nominal value of the zero-dispersion wavelength λ0 is set as λ. 0nominal And the tolerance is set to λ 0nominal Values ​​above -12nm and λ 0nominal When the value is below +12nm, MFD / λ cc The value is when MFD is MFD nominal -0.4μm and λ0 is λ 0nominal It becomes the minimum at -12nm, and the MFD is MFD. nominal +0.4μm and λ0 is λ 0nominal It reaches its maximum at +12nm. At this point, "MFD / λ" cc The preferred tolerance is MFD / λ cc The difference between the upper and lower limits is set to at least 1.9 for the MCF construction, more preferably 2.5 or more, and most preferably 3.0 or more.

[0308] In fact, the parameters of the refractive index distribution of each fiber core (a, b, Δ1, Δ2, Δ3, or a) ESI Δ1 ESI Δ2 ESI (etc.) does not fluctuate independently and randomly from the nominal value, but rather can be adjusted by measuring the refractive index distribution of each fiber core. ESI Therefore, it is possible to reduce MFD / λ. ccThe tolerance is acceptable, but MFD / λ is preferred. cc The MCF structure has an upper and lower limit difference of 1.0 or more, and more preferably 1.5 or more. This allows the yield of the MCF to be improved to a level with sufficient manufacturability.

[0309] While taking into account λ below 1260nm cc In the case of MFD with a reference of 8.2 μm and convergence in the range of 7.8 μm to 8.6 μm, MFD / λ cc To achieve a value above 6.2, therefore, in order to make MFD / λ... cc The tolerances are ≥1.0, ≥1.5, ≥1.9, ≥2.5, and ≥3.0, MFD / λ cc The upper limit is based on the above MFD / λ cc The order of the listed tolerance values ​​is preferably 7.2 or higher, 7.7 or higher, 8.1 or higher, 8.7 or higher, and 9.2 or higher for MCF constructions. Therefore, CD nominal In a 12-core MCF, to reduce the leakage loss to the resin-coated portion to below 0.01 dB / km at a wavelength of 1360 nm, the phase-to-phase transmission XT at 1360 nm becomes below -20 dB after 10 km of transmission (equivalent to a 10 km fiber length). This is achieved at Λ and d. coat Permissible CDs with margin nominal According to equation (89), based on the above MFD / λ cc The tolerance values ​​are listed in the following order, preferably 149 μm or more, 156 μm or more, 161 μm or more, 169 μm or more, and 175 μm or more, and according to equation (91), based on the above MFD / λ cc The preferred order of the listed tolerance values ​​is 160μm or higher, 166μm or higher, 171μm or higher, 179μm or higher, and 186μm or higher. At this time, CD... nominal In a 12-core MCF, to achieve a leakage loss to the resin-coated portion below 0.01 dB / km at a wavelength of 1360 nm, the phase-to-phase transmission XT at 1360 nm becomes below -40 dB after 10 km of transmission (equivalent to a 10 km fiber length). This is achieved at Λ and d. coat Permissible CDs with margin nominal According to equation (97), based on the above MFD / λ cc The tolerance values ​​are listed in the following order, preferably 157 μm or more, 164 μm or more, 170 μm or more, 178 μm or more, and 185 μm or more, and according to equation (99), based on the above MFD / λ ccThe tolerance values ​​are listed in the following order, preferably 167μm or more, 174μm or more, 173μm or more, 182μm or more, and 189μm or more.

[0310] While taking into account λ below 1260nm cc In the case of MFD with a reference of 8.6 μm that converges to a range between 8.2 μm and 9.0 μm, MFD / λ cc To achieve a value above 6.5, therefore, in order to make MFD / λ... cc The tolerances are ≥1.0, ≥1.5, ≥1.9, ≥2.5, and ≥3.0, with MFD / λ. cc The upper limit is based on the above MFD / λ cc The order of the listed tolerance values ​​is preferably MCF structures that allow for tolerances of 7.5 or higher, 8.0 or higher, 8.4 or higher, 9.0 or higher, and 9.5 or higher. Therefore, CD nominal In a 12-core MCF, to achieve a leakage loss to the resin-coated portion below 0.01 dB / km at a wavelength of 1360 nm, the phase-to-phase transmission XT at 1360 nm becomes below -20 dB after 10 km of transmission (equivalent to a 10 km fiber length). This is achieved at Λ and d. coat Permissible CDs with margin nominal According to equation (89), based on the above MFD / λ cc The tolerance values ​​are listed in the following order, preferably 153 μm or more, 159 μm or more, 165 μm or more, 173 μm or more, and 179 μm or more, and according to equation (91), based on the above MFD / λ cc The preferred order of the listed tolerance values ​​is 163μm or higher, 170μm or higher, 175μm or higher, 183μm or higher, and 190μm or higher. At this time, CD... nominal In a 12-core MCF, to achieve a leakage loss to the resin-coated portion below 0.01 dB / km at a wavelength of 1360 nm, the phase-to-phase transmission XT at 1360 nm becomes below -40 dB after 10 km of transmission (equivalent to a 10 km fiber length). This is achieved at Λ and d. coat Permissible CDs with margin nominal According to equation (97), based on the above MFD / λ cc The tolerance values ​​are listed in the following order, preferably 161 μm or more, 168 μm or more, 174 μm or more, 182 μm or more, and 189 μm or more, and according to equation (99), based on the above MFD / λ cc The tolerance values ​​are listed in the following order, preferably 172μm or more, 179μm or more, 184μm or more, 193μm or more, and 199μm or more.

[0311] While taking into account λ below 1360nm cc In the case of MFD with a reference of 8.6 μm that converges to a range between 8.2 μm and 9.0 μm, MFD / λ cc To reach 6.0 or higher, therefore, in order to make MFD / λ cc The tolerances are 1.0, 1.5, 1.9, 2.5, or 3.0, MFD / λ cc The upper limit is based on the above MFD / λ cc The order of the listed tolerance values ​​is preferably one that allows for MCF constructions of at least 7.0, 7.5, 7.9, 8.5, or 9.0. Therefore, CD nominal In a 12-core MCF, to achieve a leakage loss to the resin-coated portion below 0.01 dB / km at a wavelength of 1360 nm, the phase-to-phase transmission XT at 1360 nm becomes below -20 dB after 10 km of transmission (equivalent to a 10 km fiber length). This is achieved at Λ and d. coat Permissible CDs with margin nominal According to equation (89), based on the above MFD / λ cc The tolerance values ​​are listed in the following order, preferably 146 μm or more, 153 μm or more, 158 μm or more, 166 μm or more, and 173 μm or more, and according to equation (91), based on the above MFD / λ cc The preferred order of the listed tolerance values ​​is 157 μm or higher, 164 μm or higher, 169 μm or higher, 177 μm or higher, and 183 μm or higher. At this time, CD... nominal In a 12-core MCF, to achieve a leakage loss to the resin-coated portion below 0.01 dB / km at a wavelength of 1360 nm, the phase-to-phase transmission XT at 1360 nm becomes below -40 dB after 10 km of transmission (equivalent to a 10 km fiber length). This is achieved at Λ and d. coat Permissible CDs with margin nominal According to equation (97), based on the above MFD / λ cc The tolerance values ​​are listed in the following order, preferably 154 μm or more, 161 μm or more, 167 μm or more, 175 μm or more, and 182 μm or more, and according to equation (99), based on the above MFD / λ cc The tolerance values ​​are listed in the following order, preferably 165μm or more, 170μm or more, 176μm or more, 184μm or more, and 191μm or more.

[0312] In λ ccFor wavelengths exceeding 1260 nm but below 1360 nm, using the structure in Figure 12 of ITU-T G.650.1 (03 / 2018) (non-cable-connected optical fiber), a bend with a radius of 140 mm or greater is added to 20 m of a 22 m sample optical fiber. Then, one bend with a radius of 40 mm is added before and after the aforementioned 20 m interval. With uniform excitation of all modes, the intensity of the higher mode is set to P. h Let the strength of the fundamental model be P. f At that time, it will become 10log10[P] h / (P f +P h The wavelength with a value of 0.1 dB is used as λ. cc Measurements were performed, but regarding the MCF of the present invention, it is preferable to replace the radius of the bend added in the 20m interval of the 22m sample fiber with the cutoff wavelength (λ) when the bend is added with a radius of 60mm to 100mm. ccR The wavelength is below 1260nm. This ensures single-mode operation in the O-band after cable installation. Additionally, the sample fiber length L... sample [m] The range exceeding 22m and below 1000m, in L sample -2 [m] plus a bend with a bending radius of 140 mm or more, in the L sample Add one bend with a radius of 40 mm before and after the -2 [m] interval, and the optimal cutoff wavelength (λ) is determined. ccL The wavelength is below 1260nm. Therefore, in a cable length of L... sample The [m] cable ensures single-mode operation in the O-band.

[0313] In the MCF of the present invention, the bending loss of each fiber core at wavelengths between 1310 nm and 1360 nm is preferably 0.15 dB / turn or less, more preferably 0.02 dB / turn or less, when the bending radius is 10 mm. Therefore, when the MCF of the present invention is installed in an ultra-high density cable of the spacer adhesive tape type, the increase in cable loss can be suppressed.

[0314] When the MCF cable incorporating the MCF of the present invention is stretched in a straight line (with a bending radius of at least 1m), the average bending radius of the MCF installed within the cable is preferably 0.14m or less, more preferably 0.10m or less. Furthermore, the average bending radius of the MCF installed within the cable is preferably 0.14m or more and 0.3m or less. This reduces the XT (thickness factor).

[0315] Furthermore, in the MCF cable in which the MCF of the present invention is incorporated, the average bending radius of the MCF installed within the cable is preferably 0.03 m or more, more preferably 0.06 m or more. This reduces losses caused by bending.

[0316] Furthermore, the MCF cable incorporating the MCF of the present invention is preferably a spacer tape type cable. This allows the flexible spacer tape to be twisted into a spiral shape while being installed inside the cable, enabling the cable to be made with a small bending radius of the MCF, thus reducing the XT (thickness factor).

[0317] The MCF cable incorporating the present invention is a grooved cable, preferably with a tensile strength member at the center of the groove component. This facilitates control of the MCF's bending radius and reduces the bending radius (XT). Furthermore, the presence of the tensile strength member at the center of the groove component allows for easy bending of the cable in any orientation, facilitating cable laying operations.

[0318] The MCF cable incorporating the MCF of the present invention preferably does not have slotted components inside the sheath, but has a tensile-resistant body inside the sheath. This allows for efficient use of the space inside the sheath and increases the number of fiber cores per unit cross-sectional area of ​​the MCF cable.

[0319] As described above, according to the present invention, a 12-core MCF that can be used for short-distance O-band transmission and has a standard cladding diameter equivalent to that of a general SMF can be realized. It is a 12-core MCF fiber that can be used for fiber-to-fiber connection even without markings and polarity and can be used for opposite transmission.

Claims

1. A multi-core optical fiber, which has the following characteristics: 12 fiber cores, each extending along the central axis; and A common cladding layer covers each of the 12 fiber cores. In this multi-core optical fiber, In a cross-section of the multi-core optical fiber orthogonal to the central axis, the common cladding has a circular outer perimeter. In the cross-section, the 12 fiber cores are configured such that adjacent fiber cores are not adjacent to each other, and each is configured with an axis that intersects the central axis but does not pass through the center of any of the 12 fiber cores as its axis of symmetry, and the centers of the 12 fiber cores are linearly symmetrical. In the cross-section, the arrangement of the centers of the 12 fiber cores ensures that even if any point is taken as the center of rotation, it does not possess more than one order of rotational symmetry. Its features are, Define the following square grid, which has a grid point spacing Λ. nominal It has four inner circumferential grid points forming a minimum square and eight outer circumferential grid points surrounding the four inner circumferential grid points and having an adjacent relationship with any one of the four inner circumferential grid points. A square grid is set on the cross-section such that the distances from the central axis to each of the four inner circumferential grid points are equal. Relative to this square grid, the 12 fiber cores are composed of four inner circumferential fiber cores distributed among the four inner circumferential grid points and eight outer circumferential fiber cores distributed among the eight outer circumferential grid points. The distance between the center of each of the four inner circumferential fiber cores and the corresponding inner circumferential grid point among the four inner circumferential grid points is less than 0.5 μm. Each of the eight peripheral cores belongs to either a core with its center arranged at a position less than 0.5 μm from the corresponding peripheral grid point, or a non-core with its center arranged at a position 2 μm away from the corresponding peripheral grid point. The ratio of the number of configured fiber cores to the number of unconfigured fiber cores at each grid point is 2 to 6, 4 to 4, or 6 to 2. Each of the non-configured lattice cores is separated from a specific inner circumferential lattice point among the four inner circumferential lattice points that is adjacent to the corresponding outer circumferential lattice point. nominal Values ​​above -0.5μm and Λ nominal The position below +0.5μm is centered. The centers of the non-configured cores of each grid point are arranged such that, compared to the distance to the corresponding specific inner grid point, the distance to the specific outer grid point that is adjacent to the corresponding outer grid point is longer, and the distance is separated from the center of any of the remaining outer grid points by Λ. nominal +3μm and above.

2. The multi-core optical fiber according to claim 1, wherein, Each of the non-configured fiber cores is configured such that the angle θ between the line segment connecting the corresponding outer perimeter fiber core and the specific inner perimeter fiber core and the line segment connecting the center of the non-configured fiber core and the specific inner perimeter fiber core is more than 3 degrees and less than 30 degrees.

3. The multi-core optical fiber according to claim 1, wherein, The number of non-configured fiber cores in the grid point is 2, and the adjacency relationship of the 2 peripheral grid points allocated with the 2 non-configured fiber cores is established.

4. The multi-core optical fiber according to claim 2, wherein, The number of non-configured fiber cores in the grid point is 2, and the adjacency relationship of the 2 peripheral grid points allocated with the 2 non-configured fiber cores is established.

5. A multi-core optical fiber, which has the following characteristics: 12 fiber cores, each extending along the central axis; and A common cladding layer covers each of the 12 fiber cores. In this multi-core optical fiber, In a cross-section of the multi-core optical fiber orthogonal to the central axis, the common cladding has a circular outer perimeter. In the cross-section, the 12 fiber cores are configured such that adjacent fiber cores are not adjacent to each other, and each is configured with an axis that intersects the central axis but does not pass through the center of any of the 12 fiber cores as its axis of symmetry, and the centers of the 12 fiber cores are linearly symmetrical. In the cross-section, the arrangement of the centers of the 12 fiber cores ensures that even if any point is taken as the center of rotation, it does not possess more than one order of rotational symmetry. Its features are, It also has a resin-coated portion that covers the outer periphery of the common coating layer, having an outer diameter that converges to a range of 235 μm to 265 μm based on 250 μm. The nominal value CD is defined as the cladding diameter of a specified diameter of less than 195 μm. nominal Based on [μm], the diameter CD of the common cladding converges to CD. nominal Values ​​above -1μm and CD nominal The range below +1μm, The cable cutoff wavelength λ of each of the 12 fiber cores was determined using a fiber length of 22m. cc For wavelengths below 1360nm The zero-dispersion wavelength of each of the 12 fiber cores is based on a wavelength range of 1312 nm to 1340 nm, converging within a range of -12 nm to the wavelength reference value and +12 nm. The dispersion slope of each of the 12 fiber cores at the zero-dispersion wavelength is 0.092 ps / (nm). 2 (km) or less, For each of the 12 fiber cores, the shortest distance d from the center of the fiber core to the interface between the resin coating and the common cladding is calculated as follows: (This is the ratio of the mode field diameter MFD [μm] at wavelength 1310nm to the cable cutoff wavelength λcc [μm]). coat [μm] satisfies the following equation (1): …（1） Relationship, For each of the 12 fiber cores, the total crosstalk from the fiber core adjacent to the target fiber core at a wavelength of 1360 nm is less than -6.7 dB / 10 km. The center spacing Λ[μm] between adjacent fiber cores among the 12 fiber cores satisfies the following equation (2): …（2） And the nominal value of the cladding diameter CD nominal [μm] satisfies the following equation (3): …（3） Therefore, it is defined.

6. The multi-core optical fiber according to claim 5, wherein, In each of the 12 fiber cores, the total crosstalk from the fiber core adjacent to the target fiber core at a wavelength of 1360 nm is less than -16.7 dB / 10 km. The center spacing Λ[μm] between the adjacent fiber cores satisfies the following equation (4): …（4） The relationship, and the nominal value of the cladding diameter CD nominal [μm] satisfies the following equation (5): …（5） The relationship is defined accordingly.

7. The multi-core optical fiber according to claim 5 or 6, wherein, The 12 fiber cores include 4 fiber cores that surround the central axis with the shortest distance. The mode field diameter MFD [μm] converges to a range between 8.2μm and 9.0μm, with 8.6μm as a reference. The cable cutoff wavelength λ cc Below 1260nm The mode field diameter MFD [μm] and the cable cutoff wavelength λcc [μm] satisfy the following equation (6): …（6） The relationship.

8. The multi-core optical fiber according to claim 5 or 6, wherein, The 12 fiber cores include 4 fiber cores that surround the central axis with the shortest distance. The total crosstalk to any of the 4 fiber cores at a wavelength of 1360nm is below -16.7dB / 10km. The mode field diameter (MFD) converges to a range of 7.8 μm to 8.6 μm with a reference diameter of 8.2 μm. The cable cutoff wavelength λ cc Below 1260nm The mode field diameter MFD [μm] and the cable cutoff wavelength λcc [μm] satisfy the following equation (7): …（7） The relationship.

9. The multi-core optical fiber according to claim 5 or 6, wherein, The 12 fiber cores include 4 fiber cores that surround the central axis with the shortest distance. The total crosstalk to any of the 4 fiber cores at a wavelength of 1360nm is below -16.7dB / 10km. The mode field diameter (MFD) is based on 8.6 μm and converges to a range between 8.2 μm and 9.0 μm. The cable cutoff wavelength λ cc For wavelengths below 1360nm The mode field diameter MFD [μm] and the cable cutoff wavelength λ cc [μm] satisfies the following equation (8): …（8） The relationship.

10. A multi-core optical cable having a plurality of multi-core optical fibers comprising any one of claims 1 to 9.

11. The multi-core optical cable according to claim 10, wherein, The multi-core optical cable comprises multi-core optical fibers with an average bending radius along the fiber length direction of 0.03m to 0.14m or 0.14m to 0.3m.

12. A multi-core optical cable having a built-in multi-core optical fiber ribbon, the multi-core optical fiber ribbon being formed by bonding together at intervals a plurality of multi-core optical fibers comprising the multi-core optical fiber of any one of claims 1 to 9.

13. The multi-core optical cable according to claim 12, wherein, The multi-core optical cable incorporates the multi-core optical fiber ribbon in a twisted spiral shape.

14. The multi-core optical cable according to claim 12, wherein, The multi-core optical cable comprises multi-core optical fibers with an average bending radius along the fiber length direction of 0.03m to 0.14m or 0.14m to 0.3m.

15. The multi-core optical cable according to claim 13, wherein, The multi-core optical cable comprises multi-core optical fibers with an average bending radius along the fiber length direction of 0.03m to 0.14m or 0.14m to 0.3m.

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