Multi-core optical fiber and multi-core optical cable

Abstract

Provided is an MCF or the like having a configuration that is excellent in mass productivity, and that can suppress an increase in connection cost and connection loss. The MCF has a core group including 12 or 16 cores, a common cladding layer, and a resin covering portion. The cores are arranged in a line-symmetrical position in a state in which cores in an adjacent relationship with respect to any core do not have an adjacent relationship with each other. The covering outer diameter is 235 μm or more and 265 μm or less, and the nominal value of the diameter CD with respect to the common cladding layer is 195 μm or less, converging to a value range of CD nominal ±1 μm, the MFD at a wavelength of 1310 nm converges to a value range of the prescribed MDF reference value ±0.4 μm with respect to a prescribed MDF reference value of 8.2 μm or more and 9.2 μm or less, and the cable cutoff wavelength λ cc is 1260 nm or less or 1360 nm or less. The zero-dispersion wavelength of each core converges to a value range of a wavelength reference value ±12 nm with respect to a wavelength reference value of 1312 nm or more and 1340 nm or less, and the dispersion slope at the zero-dispersion wavelength is 0.092 ps / (nm 2 ·km) or less. The shortest distance from the covering-cladding layer interface to the center of each core, the configuration, and the optical characteristics satisfy prescribed conditions.

Description

TECHNICAL FIELD

[0001] The present application relates to a multi-core optical fiber (hereinafter referred to as "MCF") and a multi-core optical cable (hereinafter referred to as "MCF cable"). BACKGROUND

[0002] Currently, as a large-capacity optical transmission path, MCF is being actively researched.

[0003] For example, in Non-Patent Literature 1, a trench-assisted 4-core optical fiber having a cladding outer diameter of 125 μm is disclosed. The depth of the trench is about -0.7% or less, the mode field diameter (hereinafter referred to as "MFD") is 8.4 μm or more and 8.6 μm or less at a wavelength of 1310 nm, the cable cutoff wavelength is 1171 nm or more and 1195 nm or less, the zero-dispersion wavelength is 1317 nm or more and 1319 nm or less, and the wavelength dispersion slope at the zero-dispersion wavelength is 0.090 ps / (nm 2 ·km) or more and 0.091 ps / (nm 2 ·km) or less. In addition, the transmission loss is 0.33 dB / km or more and 0.35 dB / km or less at a wavelength of 1310 nm, and 0.19 dB / km or more and 0.21 dB / km or less at a wavelength of 1550 nm. The inter-core crosstalk (hereinafter, the crosstalk will be referred to as "XT") is -43 dB / km at a wavelength of 1625 nm.

[0004] In Non-Patent Literature 2, a trenchless 2-core optical fiber having a cladding outer diameter of 125 μm is disclosed. The MFD is 8.1 μm at a wavelength of 1310 nm, and 9.14 μm at a wavelength of 1550 nm. The inter-core XT at 5.8 km transmission is -79.3 dB at a wavelength of 1310 nm, -48.3 dB at a wavelength of 1490 nm, and -42.5 dB at a wavelength of 1550 nm. The cutoff wavelength is 1160 nm.

[0005] In Non-Patent Literature 3, a trenchless 4-core optical fiber having a cladding outer diameter of 125 μm is also disclosed. The MFD is 8.6 μm or more and 8.8 μm or less at a wavelength of 1310 nm, and 9.6 μm or more and 9.8 μm or less at a wavelength of 1550 nm. The cable cutoff wavelength is 1234 nm or more and 1244 nm or less. The zero-dispersion wavelength is 1318 nm or more and 1322 nm or less, and the wavelength dispersion slope at the zero-dispersion wavelength is 0.088 ps / (nm 2 ·km) or more and 0.089 ps / (nm 2·km) or less. The transmission loss is 0.328 dB / km or more and 0.330 dB / km or less at a wavelength of 1310 nm, 0.188 dB / km or more and 0.193 dB / km or less at a wavelength of 1550 nm, and 0.233 dB / km or more and 0.245 dB / km or less at a wavelength of 1625 nm. The inter-core XT is -56 dB / km or less at a wavelength band of 1360 nm (O band) and -30 dB / km or less at a wavelength band of 1565 nm (C band).

[0006] In Non-Patent Literature 4, a 12-core optical fiber having a cladding outer diameter of 147 μm and a core configuration in a square lattice shape, and a 12-core optical fiber having a cladding of 145 μm and a core configuration in a hexagonal lattice shape are disclosed. Each of the optical fibers has a configuration without a trench. The MFD 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 is 1.41 μm, the leakage loss to the cladding at a wavelength of 1565 nm is 0.01 dB / 2km, and the inter-core XT at a wavelength of 1565 nm is -30 dB / 2km.

[0007] Also, in Non-Patent Literature 5, as an ultra-high density optical cable of a spacer adhesive tape type, an example of a 12-fiber ribbon is disclosed.

[0008] Non-Patent Literature 1: Takashi Matsui, et al., “Design of 125 μm cladding multi-core fiber with full-band compatibility to conventional single-mode fiber,” Eur. Conf. Opt. Commun. (ECOC) 2015, Internet

[0009] <URL: https: / / doi.org / 10.1109 / ECOC.2015.<7341966>.

[0010] Non-Patent Literature 2: Ying Geng, et al., “High-speed, bi-directional, dual-core fiber transmission system for high-density, short-reach optical interconnects,” Proc. SPIE, Vol. 9390 939009-1 (March 9, 2015).

[0011] Non-Patent Literature 3: T. Matsui et al., “Step-index profile multi-core fibre with standard 125-μm cladding to full-band application,” in Eur. Conf. Opt. Commun. (ECOC) (2019), Internet

[0012] <URL: https: / / doi.org / 10.1049 / cp.2019.0751>.

[0013] Non-Patent Literature 4: Yusuke Sasaki, et al., “High Density Multicore Fibers Employing Small MFD Cores for Datacenters,” OECC2018 P2-07, Technical Digest July 02-06, 2018.

[0014] Non-Patent Literature 5: Fumiaki Sato, et al., “Characteristics of Ultra-High-Fiber-Count and High-Density Optical Cables with Pliable Ribbons,” Proceedings of the 66th IWCS Conference (2017), p. 304-311.

[0015] Non-Patent Literature 6: R. J. Black and C. Pask, J. Opt. Soc. Am. A, JOSAA 1(11), p. 1129-1131, 1984.

[0016] Non-Patent Literature 7: T. Matsui et al., in Eur. Conf. Opt. Commun. (ECOC 2017), p. W.1.B.2.

[0017] Non-Patent Literature 8: T. Hayashi et al., in Int. Wire Cable Symp. (IWCS) (2018), p. P-6. SUMMARY

[0018] [Problems to be Solved by the Invention]

[0019] As a result of the inventors' research on the above-described related art, the following problem was discovered. That is, the existing MCF is significantly inferior in mass productivity to a general single-mode optical fiber (hereinafter, the single-mode optical fiber will be referred to as "SMF"), and is high in manufacturing cost. The reason for this is that, in order to simultaneously achieve XT reduction, core number increase, cladding outer diameter reduction, and MFD expansion of each core, it is necessary to provide a trench layer of a low refractive index having a large relative refractive index difference from the cladding around each core as in the above-described Non-Patent Literature 1.

[0020] In addition, the existing MCF takes time (increases the operation cost) when fusion splicing is performed. In the existing optical fiber ribbon cable, as in the above-described Non-Patent Literature 1, 12 or more and 16 or fewer optical fibers are built in one piece of optical fiber ribbon, and it is possible to connect them all at once. On the other hand, the MCF requires core rotation, and thus fusion splicing needs to be performed for each optical fiber. However, even if the increase in time due to core rotation is ignored, it takes 3 to 8 times as much time as compared with fusion splicing of an optical fiber ribbon in which the number of cores of each MCF is 2 or more and 4 or less, and 12 or more and 16 or fewer optical fibers are built in as in the above-described Non-Patent Literature 1 to the above-described Non-Patent Literature 3.

[0021] Furthermore, in the existing MCF, the connection loss is significantly deteriorated. In order to build a large number of cores in a "not thick" cladding, it is necessary to significantly reduce the MFD as compared with a general SMF as in the above-described Non-Patent Literature 4. The MFD of the optical fiber described in the above-described Non-Patent Literature 4 is 5.4 μm at a wavelength of 1310 nm, and the connection loss caused by axial misalignment is deteriorated by 2.54 times (for example, the connection deterioration from a connection loss of 0.5 dB or less to a connection loss of 1.27 dB or less, and the connection deterioration from a connection loss of 0.35 dB or less to a connection loss of 0.89 dB or less) as compared with the connection loss caused by axial misalignment of a general SMF having a nominal value of 8.6 μm.

[0022] Regarding mass productivity, the existing MCF is also extremely low. The reason for this is that the tolerance of the refractive index distribution of each core is not sufficiently considered in the above-described Non-Patent Literature 1, the above-described Non-Patent Literature 3, and the above-described Non-Patent Literature 4, and thus the manufacturing yield is deteriorated.

[0023] The present application has been made in order to solve the above-described problems, and has an object to provide a multi-core optical fiber and a multi-core optical cable having a configuration in which mass productivity is excellent, and an increase in connection cost and transmission loss can be suppressed.

[0024] To address the aforementioned issues, the MCF of the present invention comprises multiple cores, a common cladding, and a resin coating. The multiple cores are composed of 12 or 16 cores extending along a central axis. The common cladding covers each of the multiple cores. The resin coating is disposed on the outer periphery of the common cladding. Furthermore, in a cross-section of the MCF orthogonal to the central axis, the multiple cores are arranged such that adjacent cores relative to any other core are not adjacent to each other. Additionally, in the cross-section, an axis passing through the center of the common cladding intersecting the central axis and not intersecting any of the multiple cores is used as the axis of symmetry, and the multiple cores are arranged in a linearly symmetrical position. The outer diameter of the resin coating, defined in this cross-section, is 235 μm to 265 μm, and the diameter CD [μm] of the common cladding, defined in this cross-section, converges to a nominal value CD of 195 μm or less. nominal CD based on [μm] nominal Values ​​above -1μm and CD nominal The range of values ​​below +1μm. The MFD at a wavelength of 1310nm converges to the range of values ​​above -0.4μm and below the MDF reference value, with a reference value between 8.2μm and 9.2μm. The cable cutoff wavelength λ was measured over a 22m fiber length. cc [nm] refers to wavelengths below 1260nm or 1360nm. The zero-dispersion wavelengths of multiple fiber cores converge to a range of values ​​above 12nm and below 0.12nm, with a wavelength reference value between 1312nm and 1340nm as the reference value. The dispersion slope of the zero-dispersion wavelength is 0.092 ps / (nm). 2 Below ·km). Furthermore, in this MCF, the shortest distance d from the interface between the resin coating and the common cladding to the center of each of the multiple fiber cores. coat [μm], structure and optical properties meet the specified conditions. Attached Figure Description

[0025] Figure 1 This is a diagram illustrating various constructions of the MCF cable (containing the MCF of the present invention).

[0026] Figure 2 This is a diagram illustrating various core configurations of the MCF of the present invention.

[0027] Figure 3 This is a diagram used to illustrate the main terms used in this specification.

[0028] Figure 4 This is a diagram showing the refractive index distribution around each fiber core of the MCF that can be applied to this invention.

[0029] Figure 5is a graph showing the relationship between the center interval Λ and MFD / λ when the counter-propagating transmission XT becomes -20 dB (= -20 dB / 10 km) at a wavelength of 1360 nm after 10 km transmission (equivalent to a fiber length of 10 km) in a 12-core MCF (hereinafter referred to as "12-core MCF"). cc

[0030] Figure 6 is a graph showing the relationship between the center interval Λ and MFD / λ when the counter-propagating transmission XT becomes -40 dB (= -40 dB / 10 km) at a wavelength of 1360 nm after 10 km transmission (equivalent to a fiber length of 10 km) in a 12-core MCF. cc

[0031] Figure 7 is a graph showing the relationship between the center interval Λ and MFD / λ when the leakage loss to the cladding becomes 0.01 dB / km at a wavelength of 1360 nm in a 12-core MCF. coat cc

[0032] Figure 8 is a graph showing the relationship between the center interval Λ and MFD / λ when the leakage loss to the cladding becomes 0.01 dB / km at a wavelength of 1360 nm in a 12-core MCF, plus a margin of 1 μm, and the CD and MFD / λ when XT becomes -20 dB (= -20 dB / 10 km) at a wavelength of 1360 nm after 10 km transmission (equivalent to a fiber length of 10 km) in a 12-core MCF, plus a margin of 1 μm. coat cc

[0033] Figure 9 is a graph showing the relationship between the center interval Λ and MFD / λ when the leakage loss to the cladding becomes 0.01 dB / km at a wavelength of 1360 nm in a 12-core MCF, plus a margin of 1 μm, and the CD and MFD / λ when XT becomes -20 dB (= -20 dB / 10 km) at a wavelength of 1360 nm after 10 km transmission (equivalent to a fiber length of 10 km) in a 12-core MCF, plus a margin of 1 μm, or when the parallel transmission XT (XT at the time of normal co-propagating transmission) becomes -20 dB (= -20 dB / 10 km) at a wavelength of 1360 nm after 10 km transmission (equivalent to a fiber length of 10 km). coat cc

[0034] Figure 10 ​​​​​​​​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, and considering the phase-to-phase transmission XT at a wavelength of 1360nm after 10km transmission (equivalent to a 10km fiber length), the CD and MFD / λ become -40dB (=-40dB / 10km) with a 1μm margin. cc A graph showing the relationship between the two.

[0035] Figure 11 This refers to the condition that, after 10km of transmission (equivalent to 10km of fiber length), the phase-to-phase transmission XT at a wavelength of 1360nm becomes -40dB (=-40dB / 10km), or the parallel transmission XT becomes -40dB (=-40dB / 10km) after 10km of transmission (equivalent to 10km of fiber length). Specifically, for both 12-core and 16-core MCF cases, the leakage loss to the cladding at a wavelength of 1360nm is 0.01dB / km. coat With a 1μm margin added, and with a 1μm margin added to Λ, CD and MFD / λ cc A graph showing the relationship between the two. Detailed Implementation

[0036] [Effects of the Invention]

[0037] The MCF and MCF cable according to the present invention can improve mass production and effectively suppress the increase in connection cost and transmission loss.

[0038] [Description of embodiments of the present invention]

[0039] First, the contents of each embodiment of the present invention will be described separately.

[0040] (1) The MCF of the present application has, as one mode thereof, a plurality of cores, a common cladding, and a resin coating portion. The plurality of cores is composed of 12 cores or 16 cores each extending along a central axis. Further, in the case of referring to both a 12-core MCF in which 12 cores are arranged in a square lattice manner and a 16-core MCF in which 16 cores are arranged in a square lattice manner, it is simply noted as "the MCF of the present application". The common cladding covers each core of the plurality of cores. The resin coating portion is provided on the outer periphery of the common cladding. In addition, in a cross section of the MCF orthogonal to the central axis, the plurality of cores is arranged such that cores in an adjacent relationship with respect to an arbitrary core do not have an adjacent relationship with each other. In addition, in the cross section, the plurality of cores is arranged at positions of line symmetry with respect to an axis that passes through the center of the common cladding intersecting the central axis and does not intersect any of the plurality of cores. An outer diameter of the resin coating portion defined in the cross section is 235 μm or more and 265 μm or less, and a diameter CD [μm] of the common cladding defined in the cross section converges in a range of a nominal value CD nominal [μm] as a reference to a value of CD nominal -1 μm or more and a value of CD nominal +1 μm or less. An MFD [μm] at a wavelength of 1310 nm converges in a range of a reference value of MFD of 8.2 μm or more and 9.2 μm or less as a reference to a value of MFD reference value -0.4 μm or more and a value of MFD reference value +0.4 μm or less. A cable cutoff wavelength λ cc [nm] measured by a 22-m optical fiber length is 1260 nm or less or 1360 nm or less. A zero-dispersion wavelength of each of the plurality of cores converges in a range of a wavelength reference value of 1312 nm or more and 1340 nm or less as a reference to a value of wavelength reference value -12 nm or more and a value of wavelength reference value +0.12 nm or less. A dispersion slope of the zero-dispersion wavelength is 0.092 ps / (nm 2 ·km) or less.

[0041] Further, in the MCF, a shortest distance d coat [μm] among distances from an interface between the resin coating portion and the common cladding to the center of each of the plurality of cores satisfies the following formula (1):

[0042] d coat ≥ 2.88 MFD / λ cc + 5.36... (1)

[0043] In addition, the MCF has a configuration satisfying the first condition or the second condition below, and has optical properties satisfying any of the third to sixth conditions below.

[0044] In particular, the above-mentioned first condition is defined by the plurality of cores each being in direct contact with the common cladding. The above-mentioned second condition is defined by the optical cladding corresponding to each of the plurality of cores being disposed between the plurality of cores and the common cladding, and each of the optical claddings having a relative refractive index difference Δ2 of 0.1% or less with respect to the common cladding.

[0045] On the other hand, the above-mentioned third condition is defined by the plurality of cores including 12 cores, for each of the 12 cores, a total XT (total crosstalk) from cores in an adjacent relationship being -6.8 dB / 10 km or less at a wavelength of 1360 nm, and a center interval Λ between the cores in the adjacent relationship satisfying the following equation (2):

[0046] Λ ≥ 2.34 MFD / λ cc + 12.1... (2)

[0047] and the MCF satisfying the following equation (3):

[0048] CD nominal ≥ 13.15 MFD / λ cc + 54.25... (3).

[0049] The above-mentioned fourth condition is defined by the plurality of cores including 12 cores, for each of the 12 cores, a total XT from cores in an adjacent relationship being -16.8 dB / 10 km or less at a wavelength of 1360 nm, and a center interval Λ between the cores in the adjacent relationship satisfying the following equation (4):

[0050] Λ ≥ 2.73 MFD / λ cc + 12.7... (4)

[0051] and the MCF satisfying the following equation (5):

[0052] CD nominal ≥ 14.07 MFD / λ cc + 55.59... (5).

[0053] The above-mentioned fifth condition is defined by the plurality of cores including 16 cores, for each of the 16 cores, a total XT from cores in an adjacent relationship being -6.8 dB / 10 km or less at a wavelength of 1360 nm, and a center interval Λ between the cores in the adjacent relationship satisfying the following equation (6):

[0054] Λ ≥ 2.34 MFD / λ cc + 12.1... (6)

[0055] and the MCF satisfies the following formula (7):

[0056] CD nominal ≥ 15.77 MFD / λ cc + 68.58... (7).

[0057] The above 6th condition is defined by the following, that is, the plurality of cores include the 16 cores, for each core of the 16 cores, the total XT from the cores in the adjacent relationship at the wavelength of 1360 nm is -16.8 dB / 10 km or less, and the center interval A between the cores in the adjacent relationship satisfies the following formula (8):

[0058] A ≥ 2.73 MFD / λ cc + 12.7... (8)

[0059] and the MCF satisfies the following formula (9):

[0060] CD nominal ≥ 17.01 MFD / λ cc + 70.37... (9).

[0061] As described above, the MCF includes a plurality of cores composed of 12 cores or 16 cores. This configuration enables connection of the number of cores equal to or more than 12 optical fiber ribbons per 1 fusion. In addition, the outer diameter of the resin coating portion defined on the cross section of the MCF is 235 μm or more and 265 μm or less. In this case, a coating diameter equal to a general SMF can be achieved. In addition, the diameter CD [μm] of the common cladding defined on the cross section of the MCF converges to the range of the value of CD nominal - 1 μm or more and the value of CD nominal + 1 μm or less based on the reference value of CD nominal of 195 μm or less. Thereby, a practical coating thickness in a state where the possibility of damage to the common cladding, that is, the glass cladding is suppressed can be achieved.

[0062] The MFD at the wavelength of 1310 nm converges to the range of the value of the reference value of MDF - 0.4 μm or more and the value of the reference value of MDF + 0.4 μm or less based on the reference value of MDF of 8.2 μm or more and 9.2 μm or less. In this case, an increase in connection loss can be effectively suppressed. The cable cutoff wavelength λ cc[nm] is 1260 nm or less or 1360 nm or less. The zero-dispersion wavelengths of the plurality of cores converge in a range of a value of -12 nm or more to a value of +0.12 nm or less from a wavelength reference value of 1312 nm or more to 1340 nm or less. The dispersion slope of the zero-dispersion wavelength is 0.092 ps / (nm 2 km) or less.

[0063] The MCF has a configuration satisfying the above-described first condition or the above-described second condition (may have a trench layer with a small relative refractive index difference with respect to the common cladding layer, but does not substantially include a trench layer), whereby an optical fiber configuration excellent in mass productivity is obtained. Further, in a case where the plurality of cores of the MCF includes 12 cores, the above-described third condition is satisfied, and in a case where the plurality of cores of the MCF includes 16 cores, the above-described fifth condition is satisfied, whereby the total amount of the opposite transmission XT to the prescribed core after 10 km of transmission (corresponding to an optical fiber length of 10 km) is suppressed to -20 dB (-20 dB / 10 km). On the other hand, in a case where the plurality of cores of the MCF includes 12 cores, the above-described fourth condition is satisfied, and in a case where the plurality of cores of the MCF includes 16 cores, the above-described sixth condition is satisfied, whereby the total amount of the opposite transmission XT to the prescribed core after 10 km of transmission (corresponding to an optical fiber length of 10 km) is suppressed to -40 dB (-40 dB / 10 km). Furthermore, in a case of a wavelength of 1550 nm, the total crosstalk from the cores in the adjacent relationship corresponding to an optical fiber length of 10 km can be -15 dB or more.

[0064] (2) As one embodiment of the present application, in a structure in which the plurality of cores of the MCF includes 12 cores, the 12 cores each belong to either of an outer peripheral core group and an inner peripheral core group, and preferably the total XT to the arbitrary core belonging to the inner peripheral core group is -6.8 dB / 10 km or less at a wavelength of 1360 nm, wherein the outer peripheral core group is constituted by the outermost peripheral core that is designed to be arranged in such a manner that the distance from the interface of the resin coating portion and the common cladding to the center thereof becomes the shortest, and the inner peripheral core group is constituted by the cores surrounded by the outermost peripheral core. The MFD [μm] is preferably 8.2 μm or more and 9.0 μm or less at a wavelength of 1310 nm. The cable cutoff wavelength λ cc [nm] is preferably 1260 nm or less. Further, the MCF satisfies any of the following formulas (10) to (14):

[0065] 6.5 ≤ MFD / λ cc ≤ 7.5 ≤ 0.07606 CD nominal -4.126... (10)

[0066] 6.5 ≤ MFD / λcc ≤ 8.0 ≤ 0.07606 CD nominal - 4.126... (11)

[0067] 6.5 ≤ MFD / λ cc ≤ 8.4 ≤ 0.07606 CD nominal - 4.126... (12)

[0068] 6.5 ≤ MFD / λ cc ≤ 9.0 ≤ 0.07606 CD nominal - 4.126... (13)

[0069] 6.5 ≤ MFD / λ cc ≤ 9.5 ≤ 0.07606 CD nominal - 4.126... (14)

[0070] According to this structure, an MCF that is excellent in mass productivity and can effectively suppress an increase in connection cost and transmission loss is obtained.

[0071] (3) As one embodiment of the present application, in a structure in which a plurality of cores of the MCF include 12 cores, each of the 12 cores belongs to either of a peripheral core group and an inner peripheral core group, and preferably the total XT to any core belonging to the inner peripheral core group is -16.8 dB / 10 km or less at a wavelength of 1360 nm, wherein the peripheral core group is composed of an outermost peripheral core that is designed to be arranged in such a manner that the distance from the interface between the resin cladding portion and the common cladding layer to the center thereof becomes the shortest, and the inner peripheral core group is composed of cores surrounded by the outermost peripheral core. The MFD [μm] is preferably 7.8 μm or more and 8.6 μm or less at a wavelength of 1310 nm. The cable cutoff wavelength λ cc [nm] is preferably 1260 nm or less. Furthermore, the MCF satisfies any of the following formulas (15) to (19):

[0072] 6.2 ≤ MFD / λ cc ≤ 7.2 ≤ 0.07105 CD nominal - 3.950... (15)

[0073] 6.2 ≤ MFD / λ cc ≤ 7.7 ≤ 0.07105 CD nominal - 3.950... (16)

[0074] 6.2 ≤ MFD / λ cc ≤ 8.1 ≤ 0.07105 CD nominal - 3.950... (17)

[0075] 6.2 ≤ MFD / λ cc≤ 8.7 ≤ 0.07 1 05 CD nominal - 3.950... (18)

[0076] 6.2 ≤ MFD / λ cc ≤ 9.2 ≤ 0.07 1 05 CD nominal - 3.950... (19)

[0077] According to this structure, a MCF that is excellent in mass productivity and can effectively suppress an increase in connection cost and transmission loss is obtained.

[0078] (4) As one embodiment of the present application, it is preferable that the MFD be 8.2 μm or more and 9.0 μm or less at a wavelength of 1310 nm. The plurality of cores of the MCF each belong to either of an outer peripheral core group and an inner peripheral core group, and it is preferable that the total XT to any core belonging to the inner peripheral core group be -16.8 dB / 10 km or less at a wavelength of 1360 nm, wherein the outer peripheral core group is composed of an outermost peripheral core that is designed to be arranged in such a manner that the distance from the interface between the resin coating portion and the common cladding to the center thereof becomes the shortest, and a core that is located on a straight line connecting the centers of the outermost peripheral cores in an adjacent relationship to each other, and the inner peripheral core group is composed of a core surrounded by the cores belonging to the outer peripheral core group. The cable cutoff wavelength λ cc [nm] is preferably 1360 nm or less. Furthermore, the MCF satisfies any of the following formulas (20) to (24):

[0079] 6.0 ≤ MFD / λ cc ≤ 7.0 ≤ 0.07 1 05 CD nominal - 3.950... (20)

[0080] 6.0 ≤ MFD / λ cc ≤ 7.5 ≤ 0.07 1 05 CD nominal - 3.950... (21)

[0081] 6.0 ≤ MFD / λ cc ≤ 7.9 ≤ 0.07 1 05 CD nominal - 3.950... (22)

[0082] 6.0 ≤ MFD / λ cc ≤ 8.5 ≤ 0.07 1 05 CD nominal - 3.950... (23)

[0083] 6.0 ≤ MFD / λ cc ≤ 9.0 ≤ 0.07 1 05 CD nominal - 3.950... (24)

[0084] In the structure described above, a MCF that is excellent in mass productivity and can effectively suppress an increase in connection cost and transmission loss is also obtained.

[0085] (5) The MCF cable of the present application preferably includes a plurality of MCFs including the MCF having the above-described configuration (MCF of the present application). According to this structure, a MCF cable that is excellent in mass productivity and can effectively suppress an increase in connection cost and transmission loss is obtained. Further, the MCF cable can be built-in with a multi-core optical fiber ribbon that adheres a plurality of MCFs at intervals. In addition, the MCF cable can include a multi-core optical fiber having an average value of the bending radius in the length direction of the optical fiber of 0.03 m or more and 0.14 m or less or 0.14 m or more and 0.3 m or less.

[0086] In the above, each of the modes listed in the column of [Explanation of Embodiments of the Present Invention] can be applied to each of the remaining modes or all combinations of these remaining modes.

[0087] [Details of Embodiments of the Present Invention]

[0088] Hereinafter, specific examples of a multi-core optical fiber (MCF) and a multi-core optical cable (MCF cable) to which the present application is applied will be described in detail with reference to the drawings. Further, the present application is not limited by these examples, but is shown by the claims, and in addition, all modifications within the same meaning and range as the claims are included. In addition, the same reference numerals are attached to the same elements in the description of the drawings, and repeated description is omitted.

[0089] Figure 1 is a diagram showing various configurations of the MCF cable of the present application (including the MCF of the present application).

[0090] The MCF cable 1A having the configuration (A) has an outer skin 300 including a MCF housing space extending in the length direction of the MCF cable 1A, and a plurality of MCFs 100 (MCF of the present application). The outer skin 300 is embedded with two tension members 400A, 400B extending along the MCF housing space. Each of the MCFs 100 includes a glass fiber 200 whose outer peripheral surface is covered with a resin covering portion.

[0091] On the other hand, the MCF cable IB having the configuration (B) has: an outer skin 500 including an MCF housing space extending in a length direction of the MCF cable IB; a slotted core 600 dividing the MCF housing space into a plurality of spaces; and a plurality of MCFs 100 (MCFs of the present application). The slotted core 600 dividing the MCF housing space into a plurality of spaces is housed in the outer skin 500. The slotted core 600 is embedded with a tensile wire 700 extending in the length direction of the MCF cable IB. The plurality of MCFs 100 are housed in any of the spaces divided by the slotted core 600.

[0092] Figure 2 are diagrams showing various core configurations of the MCF of the present application. In particular, the upper part shows a cross-sectional view of a 12-core MCF 100A (MCF 100 of the present application) configured in a manner of a square lattice of 12 cores, and the lower part shows a cross-sectional view of a 16-core MCF 100B (MCF 100 of the present application) configured in a manner of a square lattice of 16 cores. Figure 2

[0093] The cross section of the cross-sectional view of the 12-core MCF 100A (100) shown in the upper part is a cross section orthogonal to a central axis extending in a length direction of the 12-core MCF 100A. The 12-core MCF 100A has: a glass fiber 200A; and a resin coating portion 130 provided to an outer periphery of the glass fiber 200A. The glass fiber 200A has: 12 cores; and a common cladding layer 120 covering each core, an outer peripheral surface of the glass fiber 200A and an outer peripheral surface of the common cladding layer 120 being coincident. Each of the 12 cores is any one of a first core 110a for transmitting light in a prescribed direction and a second core 110b for transmitting light in a direction opposite to that of the first core 110a.

[0094] In the core configuration shown in the upper part, each of the 12 cores (including the first core 110a and the second core 110b) belongs to any one of an outer peripheral core group and an inner peripheral core group, the outer peripheral core group being composed of outermost peripheral cores (8 cores in the example of the upper part of Figure 2 ), which should be configured so that a distance from an interface of the resin coating portion 130 and the common cladding layer 120 to a center thereof becomes the shortest (in the example of the upper part of Figure 2 , a distance represented by OCT (= d coat )), and the inner peripheral core group being composed of cores surrounded by the outermost peripheral cores. That is, in the example shown in the upper part of Figure 2 , the inner peripheral core group includes 4 cores (2 first cores 110a and 2 second cores 110b) constituting the smallest square lattice surrounding the center AX1 of the common cladding layer 120. ​

[0095] On the other hand, the cross-sectional view of the 16-core MCF 100B (100) shown below is a cross-section orthogonal to the central axis extending along the length direction of the 16-core MCF 100B. The 16-core MCF 100B includes: glass fiber 200B; and a resin-coated portion 130 disposed on the outer periphery of the glass fiber 200B. The glass fiber 200B has: 16 cores; and a common cladding 120 covering each core, the outer peripheral surface of the glass fiber 200B and the outer peripheral surface of the common cladding 120 being aligned. Each of the 16 cores is either a first core 110a for transmitting light in a predetermined direction or a second core 110b for transmitting light in the opposite direction to the first core 110a.

[0096] In the fiber core configuration shown below, the 16 fiber cores (including the first fiber core 110a and the second fiber core 110b) each belong to any fiber core group within the outer peripheral fiber core group and the inner peripheral fiber core group. The outer peripheral fiber core group consists of the outermost fiber core (in... Figure 2 In the lower example, there are 4 fiber cores) and the fiber core located on the straight line connecting the centers of the outermost adjacent fiber cores (in Figure 2 In the lower example, it consists of 8 fiber cores. The outermost fiber core should be configured such that the distance from the interface between the resin-coated portion 130 and the common cladding 120 to its center is minimized (in the design). Figure 2 The lower part, by OCT(=d coat (represented by the distance), the inner circumferential core group is composed of cores surrounded by cores belonging to the outer circumferential core group. In Figure 2 In the example shown below, the inner circumferential core group comprises four cores (two first cores 110a and two second cores 110b) forming a minimal square lattice that surrounds the center AX2 of the common cladding 120. Furthermore, in this… Figure 2 The definition of the outer core group illustrated in the lower example (a core arrangement consisting of 16 cores) applies to... Figure 2 In the example shown at the top (a core arrangement consisting of 12 cores), there are 8 outermost cores, and there are no cores located on the straight line connecting the centers of the outermost cores to each other.

[0097] Furthermore, in either the upper 12-core MCF 100A or the lower 16-core MCF 100B, the diagram shows that the center spacing Λ between all adjacent cores is equal. However, this can also be determined from the nominal value of Λ. nominal There are fluctuations within a specified range. This allows for an increase in manufacturing tolerance.

[0098] Figure 3This is a diagram used to illustrate the main terms used in this specification (adjacent relationship, cross-sectional structure around the fiber core, parallel transmission and parallel transmission XT (crosstalk), and opposite transmission and opposite transmission XT (crosstalk)).

[0099] (Adjacent relationship)

[0100] In this specification, when considering a specific core among 12 or 16 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. That is, as follows: Figure 3 As shown, when fiber core 111 (110a) is designated as a specific fiber core, the fiber cores adjacent to it are fiber cores 112 (110b) and 113 (110b). Furthermore, both the 12-core MCF 100A and 16-core MCF 100B described above are configured with fiber cores forming a square grid, therefore... Figure 3 As shown, the adjacency relationship does not hold between fiber core 112 (110b) and fiber core 113 (110b). However, fiber core 114 (110a) is adjacent to both fiber core 112 (110b) and fiber core 113 (110b).

[0101] (Cross-sectional structure around the fiber core)

[0102] In both the 12-core MCF 100A and 16-core MCF 100B, the cross-sectional structure around each fiber core (first fiber core 110a or second fiber core 110b) is such that a common cladding 120 surrounds the outer periphery of either the first fiber core 110a or the second fiber core 110b. The common cladding 120 can be configured to directly contact the first fiber core 110a or the second fiber core 110b, but an optical cladding 121 can also be provided between the common cladding 120 and the first fiber core 110a or the second fiber core 110b. Alternatively, a trench layer 122 with a small relative refractive index difference Δ3 can be provided between the optical cladding 121 and the common cladding 120. Furthermore, for each fiber core, the optical cladding 121 has 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 of -0.4% or more and less than 0% relative to the refractive index of the common cladding.

[0103] (Parallel transmission and parallel transmission XT)

[0104] exist Figure 3In 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.

[0105] (Reciprocal transmission and reciprocal transmission XT)

[0106] On the other hand, opposite-direction transmission refers to two adjacent fiber cores transmitting light in different directions. That is, in Figure 3 In 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".

[0107] In addition, please refer to the following instructions. Figure 3 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 (25):

[0108] XT co (L2)=XT co (L1)+10log 10 (L2 / L1)…(25)

[0109] At a distance of 10 times, XT increases by 10dB.

[0110] When XT is expressed in decibels, for example, in Figure 3 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 (26):

[0111] XT counter =2XT co -10log 10 2…(26).

[0112] If we define the phased transmission XT within the fiber length L1 as XT counter (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 (27):

[0113] XT counter (L2)=XT counter (L1)+20log 10 (L2 / L1)…(27)

[0114] At a distance of 10 times XT counter Increased by 20dB.

[0115] 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 (28):

[0116] XT co,tot =XT co +10log 10 N…(28)

[0117] Equation (28) 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 equation (28a):

[0118]

[0119] 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 3 In the example of the opposite direction transmission shown, if the prescribed core is set to the left core, the number of cores equivalent to the right core) is set to M, then it appears to become the following equation (29):

[0120] XT counter,tot = XT counter + 10 log 10 M = 2XT co - 10 log 10 2 + 10 log 10 M... (29)

[0121] However, the inventors found that this is not the case, if the number of adjacent cores (including the prescribed core) corresponding to core n among the N adjacent cores (central cores) to the prescribed core (left core) is set to K n , then XT counter，tot becomes the following equation (30):

[0122] Therefore, in a 16-core MCF, XT counter,tot to any of the 4 cores (inner peripheral core group) located near the center can be expressed by the following equation (31):

[0123]

[0124] In a 12-core MCF, XT counter,tot to any of the 4 cores belonging to the inner peripheral core group can be expressed by the following equation (32):

[0125]

[0126] Therefore, in order to set the opposite direction transmission XT after 10 km transmission by a 12-core MCF (equivalent to an optical fiber length of 10 km) to -20 dB (= -20 dB / 10 km) or less, the parallel transmission XT between adjacent cores (XT co ) in terms of the optical fiber length L (km) is preferably the following equation (33):

[0127]

[0128] In addition, the sum of the parallel transmission XT from the 4 cores having an adjacent relationship to any of the 4 cores belonging to the inner peripheral core group is preferably the following equation (34):

[0129]

[0130] In order to set the counter-propagation XT after 10 km transmission by the 12-core MCF (equivalent to an optical fiber length of 10 km) to -40 dB (= -40 dB / 10 km) or less, the parallel propagation XT between adjacent cores (XT co ) converted into an optical fiber length L (km) is preferably the following formula (35):

[0131]

[0132] In addition, the sum of the parallel propagations XT from the four cores having an adjacent relationship to any of the four cores belonging to the inner peripheral core group is preferably the following formula (36):

[0133]

[0134] On the other hand, in order to set the counter-propagation XT after 10 km transmission by the 16-core MCF (equivalent to an optical fiber length of 10 km) to -20 dB (= -20 dB / 10 km) or less, the parallel propagation XT between adjacent cores (XT co ) converted into an optical fiber length L (km) is preferably the following formula (37):

[0135]

[0136] In addition, the sum of the parallel propagations XT from the four cores having an adjacent relationship to any of the four cores belonging to the inner peripheral core group is preferably the following formula (38):

[0137]

[0138] In order to set the counter-propagation XT after 10 km transmission by the 16-core MCF (equivalent to an optical fiber length of 10 km) to -40 dB (= -40 dB / 10 km) or less, the parallel propagation XT between adjacent cores (XT co ) converted into an optical fiber length L (km) is preferably the following formula (39):

[0139]

[0140] In addition, the sum of the parallel propagations XT from the four cores having an adjacent relationship to any of the four cores belonging to the inner peripheral core group is preferably the following formula (40):

[0141]

[0142] Next, the profile configuration of the MCF that can be applied to the present application will be described. Figure 4is a graph showing the refractive index distribution of each core periphery that can be applied to the MCF of the present application. Further, in the case where no specific declaration is made, the "relative refractive index difference Δ" refers to the relative refractive index difference with respect to the refractive index of the common cladding (thus, not the relative refractive index difference with respect to the refractive index of pure silica glass).

[0143] Regarding the core configuration of the MCF of the present application, for the refractive index distribution of the core, the optical characteristics accompanying the same, an appropriate configuration can be selected according to the use, for example, the refractive index distribution of the following patterns (A) to (K) can be applied. Figure 4 Further, in the case where no specific declaration is made, the "relative refractive index difference Δ" refers to the relative refractive index difference with respect to the refractive index of the common cladding (thus, not the relative refractive index difference with respect to the refractive index of pure silica glass). Figure 4 In the above, Δ is the relative refractive index difference with respect to the refractive index of the common cladding, r is the radius from the center of each core, and is expressed by a local coordinate system in which the center of each core, Δ = 0%, is set as the origin O. The configuration can be uniform among the cores, or can be different.

[0144] Figure 4 The pattern (A) shown above is a step-type refractive index distribution, the pattern (B) is a ring-type refractive index distribution, the pattern (C) is a double-step-type refractive index distribution, the pattern (D) is a graded-type refractive index distribution, and the pattern (E) is a drop-dead-type refractive index distribution, which can be applied to the core configuration of the MCF of the present application. Further, the pattern (F) and the pattern (H) in which the depressed-type refractive index distribution is provided around the core, the pattern (G), the pattern (I), and the pattern (J) in which the raised-type refractive index distribution is provided around the core, and the pattern (E) in which the matched-type refractive index distribution is provided around the core can also be applied to the core configuration.

[0145] The refractive index distribution other than the step-type refractive index distribution of the pattern (A) can be approximated using ESI (Equivalent-step-index) to obtain the core radius a and Δ (Δ1) of the core in the case where the step-type approximation is performed (Non-patent Literature 6).

[0146] Non-patent Literature 6 described above can be easily applied in the case where the boundary between the core and the cladding is clear, but it is difficult to apply to the case where the boundary between the core and the cladding (the common cladding 120 or the optical cladding 121) is not clear, such as the drop-dead-type refractive index distribution of the pattern (E). For example, if the b of the pattern (E) is regarded as the radius of the core and the method of Non-patent Literature 6 is directly applied, the ESI approximation is not good. In the case described above, it is preferable to regard the r corresponding to Δ of 2 / 5 of Δ at a specific r as the core radius a and to apply Non-patent Literature 6, in which the specific r is the radius at which the slope of the refractive index distribution is 2 / 5 of the slope at the center of the core. 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 (41):

[0147]

[0148] Alternatively, the weighted average of r can be expressed by the following equation (42):

[0149]

[0150] 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 calculations in Non-Patent Document 6. Δ2 (the relative refractive index difference of the optical cladding 121) is preferably -0.10% or more and 0.10% or less. Therefore, manufacturability is greatly improved.

[0151] 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 4 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.

[0152] 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.

[0153] have Figure 2 The cross-sectional structure of the MCF of the present invention shown has a resin-coated portion 130, the diameter of which is preferably 235 μm or more and 265 μm or less. Therefore, the cable-compatible MCF of the present invention can be realized without making significant changes to existing cable-connecting devices.

[0154] 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.

[0155] 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.

[0156] 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, the preferred tolerance for coating thickness is -15 μm or more and +15 μm or less, and more preferably -10 μm or more and +10 μm or less.

[0157] The MCF of the present invention preferably has at least 12 fiber cores. Thus, even if the MCF is spliced ​​after rotating and aligning the optical fibers one by one, the number of connected fiber cores in each splice can be set to be the same compared to the band splicing (splicing all 12 optical fibers together) when connecting a large number of fiber core cables with 12 fibers and most of the built-in cables.

[0158] The MCF of the present application can have 16 cores. In this case, even after the MCF is fusion spliced after the optical fiber is rotated one by one, the number of connected cores per fusion splice can be set to be the same as compared to the case where a cable having a plurality of 16-fiber ribbons built in is fusion spliced (16 fibers are fusion spliced at once) when a super multi-core cable is connected.

[0159] The MCF of the present application preferably has a core configuration in which adjacent cores corresponding to an arbitrary core do not satisfy the adjacent relationship with each other. Thereby, in bidirectional communication in which signals are transmitted in different transmission directions between adjacent cores with respect to a specific core, the counter transmission XT can be reduced. Here, the adjacent cores of the prescribed core (specific core) are, as described above, cores in which the parallel transmission XT (normal XT in the case of transmitting light in the same direction) to the specific core is greatly affected, and specifically, cores in which the position of the shortest center distance with respect to the specific core and the position of the center distance equivalent to the shortest center distance (difference of 2 μm or less) are present.

[0160] Each core of the MCF of the present application preferably has an MFD that converges to a value of MDF reference value + 0.4 μm or less from a value of MDF reference value - 0.4 μm or more with respect to the MDF reference value of 8.6 μm or more and 9.2 μm or less at a wavelength of 1310 nm. In this case, the connection loss between the MCF of the present application and the general SMF of the type in which the nominal value of the MFD is small (MFD nominal (MFD nominal ≒8.6 μm) and in which the bending loss is suppressed can be set to be the same as or less than the connection loss between the general SMFs of the type in which the nominal value of the MFD is small (MFD

[0161] Each core of the MCF of the present application preferably has an MFD of 8.2 μm or more and 9.0 μm or less at a wavelength of 1310 nm. Thereby, with respect to the connection between the general SMF of the type in which the nominal value of the MFD is small and in which the bending loss is suppressed and the MCF of the present application among the general SMFs prescribed in ITU-T G.652, the connection loss caused by the core center axis misalignment (axis misalignment) can be set to be the same as or less than the case where a prescribed axis misalignment is given.

[0162] Each core of the MCF of the present application preferably has an MFD that converges to a value of MDF reference value + 0.4 μm or less from a value of MDF reference value - 0.4 μm or more with respect to the MDF reference value of 8.2 μm or more and 8.6 μm or less at a wavelength of 1310 nm. Thereby, with respect to the connection between the general SMF of the type in which the nominal value of the MFD is small (MFD nominal (MFDnominal ≒8.6 μm), and the type of suppressing the bending loss, the connection loss caused by the axis offset of the MCF of the present application (in the case where the prescribed axis offset is imparted) is suppressed to an increase of 10% or less. This means that in the case where the connection loss of the general-purpose SMF of the type of suppressing the bending loss is 0.15 dB at the axis offset, the connection loss of the MCF of the present application is 0.15 dB or more and 0.165 dB or less, in the case where the connection loss of the general-purpose SMF of the type of suppressing the bending loss is 0.25 dB at the axis offset, the connection loss of the MCF of the present application is 0.25 dB or more and 0.275 dB or less, in the case where the connection loss of the general-purpose SMF of the type of suppressing the bending loss is 0.50 dB at the axis offset, the connection loss of the MCF of the present application is 0.50 dB or more and 0.55 dB or less, and in the case where the connection loss of the general-purpose SMF of the type of suppressing the bending loss is 0.75 dB at the axis offset, the connection loss of the MCF of the present application is 0.75 dB or more and 0.825 dB or less. At this time, the MFD nominal The smaller the MFD, the more the light can be confined to the core, and the leakage loss to the inter-core XT and the resin cladding portion can be suppressed, and thus it is preferable.

[0163] The MCF of the present application preferably has a zero-dispersion wavelength of 1300 nm or more and 1324 nm or less. Thereby, the distortion of the signal waveform after transmission in the O band can be suppressed to the same degree as the general-purpose SMF.

[0164] The MCF of the present application preferably has a zero-dispersion wavelength that converges to a value of 12 nm or more and a value of 0.12 nm or less with respect to a wavelength reference value of 1312 nm or more and 1340 nm or less. Thereby, the distortion of the signal waveform after transmission in the O band can be suppressed compared to the general-purpose SMF (see the above Non-Patent Literature 7).

[0165] The MCF of the present application preferably has a total sum of the XT from the adjacent cores to any of the cores of -20 dB (= -20 dB / 10 km) or less after 10 km of transmission (corresponding to a fiber length of 10 km) in the use band. The XT from the cores other than the adjacent cores is sufficiently low and can be ignored, and thus a sufficient signal-to-noise ratio can be achieved even in the case of coherent detection.

[0166] The MCF of the present application preferably has a total sum of the XT from the adjacent cores to any of the cores of -40 dB (= -40 dB / 10 km) or less after 10 km of transmission (corresponding to a fiber length of 10 km) in the use band. The XT from the cores other than the adjacent cores is sufficiently low and can be ignored, and thus a sufficient signal-to-noise ratio can be achieved even in the case of intensity modulation direct detection.

[0167] The MCF of the present application is such that the total of the XT to any of the cores, preferably the total of the XT from the adjacent cores (parallel transmission XT) is still -6.8 dB (= -6.8 dB / 10 km) or less after 10 km transmission (equivalent to an optical fiber length of 10 km) in the use wavelength band. Thus, in a core arrangement in which 12 or more and 16 or less cores are arranged in a manner constituting a square lattice, in the case where bidirectional communication is performed in which the signal transmission directions between the adjacent cores are set to be opposite to each other by pairing with respect to all the adjacent cores, the XT to the above-mentioned any of the cores (such as the total of the XT arriving through the adjacent cores transmitting light in the opposite direction, as in the example of Fig. 6) which becomes a problem can be suppressed to be -20 dB (= -20 dB / 10 km) or less after 10 km transmission (equivalent to an optical fiber length of 10 km). Figure 3

[0168] The MCF of the present application is such that the parallel transmission XT is still -16.8 dB (= -16.8 dB / 10 km) or less after 10 km transmission (equivalent to an optical fiber length of 10 km) in the use wavelength band. Thus, the XT in the opposite direction can be suppressed to be -40 dB (= -40 dB / 10 km) or less after 10 km transmission (equivalent to an optical fiber length of 10 km).

[0169] In the following description, the results of the study relating to the MCF having the refractive index profile of the pattern (E), the pattern (H), and the pattern (J) of Figure 4 , and 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 or less are shown.

[0170] By calculating the wavelength dependence of the electric field distribution and the effective refractive index of the fundamental mode using the finite element method or the like, the person skilled in the art can design the configuration of the core having a prescribed zero dispersion wavelength and MFD. For example, the relationship of a and (Δ1 - Δ2) which becomes the zero dispersion wavelength λ0 [μm] in the range of 3 μm ≤ a ≤ 5 μm, 0.3% ≤ (Δ1 - Δ2) ≤ 0.6% becomes the following equation (43):

[0171] a ≈ 0.0667 (λ0 - 1343.1) (Δ1 - Δ2) 2 + 0.0900 (λ0 - 1354.6) (Δ1 - Δ2) - 0.0517 (λ0 - 1411.2)... (43)

[0172] . Thus, in order for the zero dispersion wavelength λ0 [μm] to converge to the value of λ 0nominal - 12 nm and λ 0nominal ​the relationship between a and (Δ1- Δ2) preferably satisfies the following formula (44) and formula (45) :

[0173] 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)... (44)

[0174] 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)... (45)

[0175] These two formulas.

[0176] Further, the relationship between a and (Δ1- Δ2) corresponding to MFD [μm] at a wavelength of 1310 nm in the range of 3 μm < a < 5 μm, 0.3% < (Δ1- Δ2) < 0.6% becomes the following formula (46) :

[0177] (Δ1- Δ2) = (-0.0148 MFD + 0.213) [a - 0.619 MFD + 2.01] 2 -0.0771 MFD + 1.033... (46)

[0178] Therefore, in order for MFD [μm] to converge to MFD nominal -0.4 μm, MFD nominal +0.4 μm, the relationship between a and (Δ1- Δ2) preferably satisfies the following formula (47) and formula (48) :

[0179]

[0180]

[0181] These two formulas.

[0182] b / a and Δ2 are set to λ cc become 1260 nm or less or 1360 nm or less, and the zero dispersion slope becomes 0.092 ps / (nm 2 ·km) or less. Therefore, Δ2 is preferably in the range of -0.1% or more and 0.0% or less, and b / a is preferably in the range of 2 or more and 4 or less.

[0183] Next, the preferred center spacing Λ between adjacent fiber cores will be explained. Figure 5 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 cc The units were consistent to obtain the result. The same result was obtained for a 16-core MCF configured with 16 cores forming a square lattice. Figure 5 The following discussion can also be applied to 16-core MCF. Here, the average fiber bending radius R is 0.14m; if R is below 0.14m, a lower XT can be achieved. Furthermore, λ cc The cable cutoff wavelength was measured using the structure (non-cable-based optical fiber) in Figure 12 of ITU-T G.650.1 (03 / 2018). Furthermore, while increasing the tolerance of the fiber core structure, the effective refractive index difference between adjacent cores fluctuates. As described in Non-Patent Document 8 above, even with a larger bending radius of the optical fiber (R = 0.14 m to 0.3 m), a low XT can be achieved.

[0184] 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 At least the following equation (49) or equation (50) must be satisfied:

[0185] Λ≥2.34MFD / λ cc +12.1…(49)

[0186] MFD / λ cc ≤0.428Λ-5.19…(50)

[0187] (from Figure 5 (The area above the dashed line on the lower side is shown). Furthermore, the center spacing Λ between adjacent fiber cores and MFD / λ... cc Preferably, the following equation (51) or equation (52) is satisfied:

[0188] Λ≥2.34MFD / λ cc +14.6…(51)

[0189] MFD / λ cc ≤0.428Λ-6.25…(52)

[0190] (from Figure 5 the upper side of the dotted line shown).

[0191] In order to allow the positions of the respective cores to fluctuate from the design center, Λ is preferably given a margin of 1 μm from the ranges shown in the above formulae (49) to (52). Thus, if the nominal value of this Λ is set to Λ nominal , then Λ satisfies at least the following formula (53) :

[0192] Λ nominal ≥ 2.34 MFD / λ cc + 12.1 + 1.0... (53)

[0193] And, with respect to Λ that satisfies the following formula (54) :

[0194] Λ nominal ≥ 2.34 MFD / λ cc + 14.6 + 1.0... (54)

[0195] Λ nominal , Λ preferably satisfies the following formula (55) :

[0196] Λ nominal - 0.9 ≤ Λ ≤ Λ nominal + 0.9... (55)

[0197] At this time, the positions of the cores can each independently be considered to be an approximation of a case where a Gaussian distribution of 3σ = 0.9 μm from the design center is fluctuated as a probability distribution, and the probability of Λ not satisfying formula (49) or formula (51) is suppressed to 1% or less. And, Λ preferably satisfies the following formula (56) :

[0198] Λ nominal - 0.7 ≤ Λ ≤ Λ nominal + 0.7... (56)

[0199] At this time, the positions of the cores can each independently be considered to be an approximation of a case where a Gaussian distribution of 3σ = 0.7 μm from the design center is fluctuated as a probability distribution, and the probability of Λ not satisfying formula (49) or formula (51) is suppressed to 0.1% or less. And, Λ preferably satisfies the following formula (57) :

[0200] Λ nominal - 0.5 ≤ Λ ≤ Λ nominal + 0.5... (57)

[0201] At this time, the positions of the cores can each independently be considered to be an approximation of a case where a Gaussian distribution of 3σ = 0.5 μm from the design center is fluctuated as a probability distribution, and the probability that Λ does not satisfy the formula (49) or the formula (51) is suppressed to 0.001% or less.

[0202] In both the 12-core MCF and the 16-core MCF, the relationship between the center interval Λ between adjacent cores and MFD / λ when the parallel transmission XT after 10 km transmission (equivalent to an optical fiber length of 10 km) at a wavelength of 1360 nm becomes -20 dB was investigated, and if the same investigation was performed, the same result was obtained in the case of the 12-core MCF and the case of the 16-core MCF. That is, in order to set the parallel transmission XT after 10 km transmission (equivalent to an optical fiber length of 10 km) at a wavelength of 1360 nm to be -20 dB or less, the center interval Λ between adjacent cores and MFD / λ cc cc at least satisfy the following formula (58) or formula (59):

[0203] Λ ≥ 2.73 MFD / λ cc + 12.7... (58)

[0204] MFD / λ cc ≤ 0.367 Λ - 4.66... (59)

[0205] . Furthermore, the center interval Λ between adjacent cores and MFD / λ cc It is preferable that the following formula (60) or formula (61) be satisfied:

[0206] Λ ≥ 2.73 MFD / λ cc + 15.1... (60)

[0207] MFD / λ cc ≤ 0.367 Λ - 5.54... (61).

[0208] In order to allow the positions of the cores to fluctuate from the design center, Λ is preferably within a range of 1 μm from the above formula (58) to formula (61). Thereby, if the nominal value of Λ is set to Λ nominal , Λ at least satisfies the following formula (62):

[0209] Λ nominal ≥ 2.73 MFD / λ cc + 12.7 + 1.0... (62)

[0210] . Furthermore, with respect to the following formula (63):

[0211] Λ nominal ≥ 2.73 MFD / λ cc + 15.1 + 1.0... (63)​

[0212] Λnominal, Λoptimum satisfy the following formula (64) :

[0213] Λ nominal -0.9 ≤ Λ ≤ Λ nominal +0.9... (64)

[0214] At this time, the positions of the cores can each independently be considered to be an approximation of a case where a Gaussian distribution of 3σ = 0.9 μm from the design center is fluctuated as a probability distribution, and the probability that Λ does not satisfy formula (58) or formula (60) is suppressed to 1% or less. Also, Λ preferably satisfies the following formula (65) :

[0215] Λ nominal -0.7 ≤ Λ ≤ Λ nominal +0.7... (65)

[0216] At this time, the positions of the cores can each independently be considered to be an approximation of a case where a Gaussian distribution of 3σ = 0.7 μm from the design center is fluctuated as a probability distribution, and the probability that Λ does not satisfy formula (58) or formula (60) is suppressed to 0.1% or less. Also, Λ preferably satisfies the following formula (66) :

[0217] Λ nominal -0.5 ≤ Λ ≤ Λ nominal +0.5... (66)

[0218] At this time, the positions of the cores can each independently be considered to be an approximation of a case where a Gaussian distribution of 3σ = 0.5 μm from the design center is fluctuated as a probability distribution, and the probability that Λ does not satisfy formula (58) or formula (60) is suppressed to 0.001% or less.

[0219] Figure 6 is a graph showing the relationship between the center interval Λ and MFD / λ cc of the 12-core MCF in which 12 cores are arranged in a square lattice manner, and XT which is the counter-propagating transmission XT at a wavelength of 1360 nm after a transmission of 10 km (equivalent to a fiber length of 10 km) becomes -40 dB (= -40 dB / 10 km). Also, substantially the same result is obtained in the 16-core MCF, and therefore Figure 6 the following discussion can also be applied to the 16-core MCF.

[0220] In order to set the counter-propagating transmission XT at a wavelength of 1360 nm after a transmission of 10 km (equivalent to a fiber length of 10 km) to be -40 dB or less, the center interval Λ and MFD / λ cc satisfy the following formula (67) or formula (68) :

[0221] Λ≥2.63MFD / λ cc +12.5…(67)

[0222] MFD / λ cc ≤0.380Λ-4.77…(68)

[0223] (from Figure 6 (The area above the dashed line on the lower side is shown). Furthermore, the center spacing Λ between adjacent fiber cores and MFD / λ... cc Preferably, the following equation (69) or equation (70) is satisfied:

[0224] Λ≥2.63MFD / λ cc +15.0…(69)

[0225] MFD / λ cc ≤0.380Λ-5.69…(70)

[0226] (from Figure 6 The area above the dotted line on the upper side is shown.

[0227] To allow for fluctuations in the position of each fiber core from the design center, Λ preferably has a margin of at least 1 μm in the range from equation (67) to equation (70) above. Therefore, if Λ is set as the nominal value of Λ... nominal Then Λ must satisfy at least the following equation (71):

[0228] Λ nominal ≥2.63MFD / λ cc +12.5+1.0…(71)

[0229] Furthermore, relative to the following equation (72):

[0230] Λ nominal ≥2.63MFD / λ cc +15.0 +1.0…(72)

[0231] Λ nominal Λ preferably satisfies the following equation (73):

[0232] Λ nominal -0.9≤Λ≤Λ nominal +0.9…(73)

[0233] 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 (67) or equation (69) is suppressed to less than 1%. Furthermore, Λ preferably satisfies the following equation (74):

[0234] Λ nominal -0.7≤Λ≤Λnominal +0.7…(74)

[0235] 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 = 0.7 μm. The probability that Λ does not satisfy equation (67) or equation (69) is suppressed to less than 0.1%. Furthermore, Λ preferably satisfies the following equation (75):

[0236] Λ nominal -0.5≤Λ≤Λ nominal +0.5…(75)

[0237] 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 = 0.5μm. The probability that Λ does not satisfy equation (67) or equation (69) is suppressed to less than 0.001%.

[0238] In 12-core and 16-core MCF, if the parallel transmission XT becomes -40dB when 10km of transmission is performed at a wavelength of 1360nm (equivalent to a fiber length of 10km), the center spacing Λ and MFD / λ between adjacent cores are... cc If the same research is conducted on the relationship, the results will be exactly the same for both 12-core and 16-core MCF cases. In order to set the parallel transmission XT below -40dB 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 satisfies at least the following equation (76) or equation (77):

[0239] Λ≥3.31MFD / λ cc +12.6…(76)

[0240] MFD / λ cc ≤0.377Λ-4.75…(77)

[0241] (from Figure 6 (The area above the dashed line on the lower side is shown). Furthermore, the center spacing Λ between adjacent fiber cores and MFD / λ... cc Preferably, the following equation (78) or equation (79) is satisfied:

[0242] Λ≥3.31MFD / λ cc +15.0…(78)

[0243] MFD / λ cc ≤0.377Λ-5.66…(79)

[0244] (from Figure 6The upper dotted line shown is the upper region.

[0245] In order to allow the positions of the respective cores to fluctuate from the design center, Λ is preferably given a margin of at least 1 μm from the ranges of the above formulae (76) to (79). Thus, if Λ is set to a nominal value Λ nominal , then Λ at least satisfies the following formula (80):

[0246] Λ nominal ≥ 3.31 MFD / λ cc + 12.6 + 1.0... (80)

[0247] And, with respect to Λ that satisfies the following formula (81):

[0248] Λ nominal ≥ 3.31 MFD / λ cc + 15.0 + 1.0... (81)

[0249] Λ nominal , Λ preferably satisfies the following formula (82):

[0250] Λ nominal - 0.9 ≤ Λ ≤ Λ nominal + 0.9... (82)

[0251] At this time, the positions of the cores can each independently be considered to be an approximation of a case where a Gaussian distribution of 3σ = 0.9 μm from the design center is fluctuated as a probability distribution, and the probability that Λ does not satisfy formula (76) or formula (78) is suppressed to 1% or less. Also, Λ preferably satisfies the following formula (83):

[0252] Λ nominal - 0.7 ≤ Λ ≤ Λ nominal + 0.7... (83)

[0253] At this time, the positions of the cores can each independently be considered to be an approximation of a case where a Gaussian distribution of 3σ = 0.7 μm from the design center is fluctuated as a probability distribution, and the probability that Λ does not satisfy formula (76) or formula (78) is suppressed to 0.1% or less. Also, Λ preferably satisfies the following formula (84):

[0254] Λ nominal - 0.5 ≤ Λ ≤ Λ nominal + 0.5... (84)

[0255] At this time, the positions of the cores can each independently be considered to be an approximation of a case where a Gaussian distribution of 3σ = 0.5 μm from the design center is fluctuated as a probability distribution, and the probability that Λ does not satisfy formula (76) or formula (78) is suppressed to 0.001% or less.

[0256] Next, the preferred dcoat (The shortest distance from the resin-coated portion and the cladding interface to the center of the fiber core) will be explained. Figure 7 This indicates that when the leakage loss to the cladding is 0.01 dB / km in an MCF with 12 fiber cores arranged in a square lattice at a wavelength of 1360 nm. coat and MFD / λ cc A graph showing the relationship between the two.

[0257] To set the leakage loss to the resin-coated portion at a wavelength of 1360 nm to 0.01 dB / km, d coat and MFD / λ cc The following equation (85) or equation (86) must be satisfied:

[0258] d coat ≥2.88MFD / λ cc +5.36…(85)

[0259] MFD / λ cc ≤0.347d coat -1.86…(86)

[0260] (from Figure 7 (The area above the dashed line on the lower side is shown). And, d coat and MFD / λ cc Preferably, the following equation (87) or equation (88) is satisfied:

[0261] d coat ≥2.88MFD / λ cc +6.95…(87)

[0262] MFD / λ cc ≤0.347d coat -2.41…(88)

[0263] (from Figure 7 The area above the dotted line on the upper side is shown.

[0264] The outermost core d coat (i.e. d) coat The minimum value of the outer cladding thickness (OCT) is usually referred to as the outer cladding thickness (OCT), but the d of this invention coat It is defined as a value that can be specified for each fiber core.

[0265] To allow for fluctuations in the position of each fiber core from the design center, and for the cladding diameter to fluctuate from the design center, d coat Preferably, the range from equation (85) to equation (88) above has a margin of at least 1 μm. Therefore, d coat If set to d coat The nominal value dcoat,nominal then at least the following formula (89) is satisfied:

[0266] d coat,nominal ≥ 2.88 MFD / λ cc + 5.36 + 1.0... (89)

[0267] . Also, the nominal value CD of the cladding diameter nominal is preferably set to satisfy the following formula (90):

[0268] d coat,nominal ≥ 2.88 MFD / λ cc + 6.95 + 1.0... (90)

[0269] At this time, the following formula (91) and formula (92) are preferably satisfied:

[0270] Λ nominal - 0.9 ≤ Λ ≤ Λ nominal + 0.9... (91)

[0271] CD nominal - 0.9 ≤ CD ≤ CD nominal + 0.9... (92)

[0272] These two formulas, d coat the probability that formula (85) or formula (87) is not satisfied is suppressed to 1% or less. Also, the following formula (93) and formula (94) are preferably satisfied:

[0273] Λ nominal - 0.7 ≤ Λ ≤ Λ nominal + 0.7... (93)

[0274] CD nominal - 0.7 ≤ CD ≤ CD nominal + 0.7... (94)

[0275] These two formulas. At this time, d coat the probability that formula (85) or formula (87) is not satisfied is suppressed to 0.1% or less. Also, the following formula (95) and formula (96) are preferably satisfied:

[0276] Λ nominal - 0.5 ≤ Λ ≤ Λ nominal + 0.5... (95)

[0277] CD nominal - 0.5 ≤ CD ≤ CD nominal + 0.5... (96)

[0278] These two formulas. At this time, d coat the probability that formula (85) or formula (87) is not satisfied is suppressed to 0.001% or less.

[0279] Next, for the smallest allowable CD nominal Please provide an explanation. Figure 8 This indicates that when the leakage loss to the cladding is 0.01 dB / km in a 12-core MCF arranged in a square lattice of 12 cores at a wavelength of 1360 nm, d coat With a 1μm margin, and considering the phase-to-phase transmission XT at a wavelength of 1360nm after 10km transmission (equivalent to a 10km fiber length), the CD and MFD / λ become -20dB (=-20dB / 10km) with a 1μm margin. cc A graph showing the relationship between the two.

[0280] When considering the tolerances for core position and cladding diameter, in order to set the leakage loss to the resin-clad portion at a wavelength of 1360nm to below 0.01dB / km, the back-to-back transmission XT after 10km transmission (equivalent to a fiber length of 10km) is set to below -20dB. nominal and MFD / λ cc The relationship satisfies the following equation (97) or equation (98):

[0281] CD nominal ≥13.15MFD / λ cc +54.25…(97)

[0282] MFD / λ cc ≤0.07606CD nominal -4.126…(98)

[0283] (from Figure 8 The area above the dashed line on the lower side (as shown). And, CD nominal and MFD / λ cc The relationship preferably satisfies the following equation (99) or equation (100):

[0284] CD nominal ≥13.15MFD / λ cc +64.88…(99)

[0285] MFD / λ cc ≤0.07606CD nominal -4.935…(100)

[0286] (from Figure 8 (The area above the dotted line shown on the upper side). Furthermore, in Figure 8 In the equation, when the vertical axis is set to y and the horizontal axis to x, the upper dashed line changes from y = 13.15x + 64.88 (x = 7.606 × 10⁻⁶) to x = 7.606 × 10⁻⁶. －2given by y = 4.935x, the broken line on the lower side is given by y = 13.15x + 54.25 (x = 7.606 x 10 －2 given by y = 4.126x.

[0287] Figure 9 is the condition under which XT after 10 km transmission (corresponding to a fiber length of 10 km) becomes -20 dB (= -20 dB / 10 km) and XT after 10 km transmission (corresponding to a fiber length of 10 km) of the parallel transmission (XT at the time of the usual copropagating transmission) becomes -20 dB (= -20 dB / 10 km) in the case of the 12-core MCF in which 12 cores are arranged in a square lattice manner and the case of the 16-core MCF in which 16 cores are arranged in a square lattice manner, d coat with a margin of 1 μm, and the graph of the relationship between CD and MFD / λ cc in the case where Λ is added with a margin of 1 μm. Further, in Figure 9 , the mark "O" shows the relationship of the 16-core MCF in which the parallel transmission is performed between the adjacent cores, the mark "□" shows the relationship of the 16-core MCF in which the counter propagating transmission is performed between the adjacent cores, the mark "● (shown by a diagonal line in Figure 9 )" shows the relationship of the 12-core MCF in which the parallel transmission is performed between the adjacent cores, and the mark "■ (shown by a diagonal line in Figure 9 )" shows the relationship of the 12-core MCF in which the counter propagating transmission is performed between the adjacent cores.

[0288] As is known from Figure 9 , the MCF of the present application can reduce CD by 10 μm or more when used in the counter propagating transmission rather than the parallel transmission, and therefore it is preferable that the 12-core MCF can reduce CD by 35 μm or more as compared with the 16-core MCF, and therefore it is preferable.

[0289] Further, in Figure 9 , the broken line is not described, but as in the case of Figure 8 , in the 16-core MCF, in consideration of the tolerance of the size of the core position and the cladding diameter, in order to set the leakage loss to the resin cladding portion at 1360 nm to 0.01 dB / km or less, XT after 10 km transmission (corresponding to a fiber length of 10 km) of the parallel transmission is set to -20 dB or less, the relationship between CD nominal and MFD / λ cc satisfies the following formula (101) or formula (102):

[0290] CD nominal ≥ 17.33 MFD / λ cc+ 70.83... (101)

[0291] MFD / λ cc ≤ 0.05772 CD nominal - 4.088... (102)

[0292] CD nominal and MFD / λ cc preferably satisfy the following equation (103) or equation (104):

[0293] CD nominal ≥ 17.33 MFD / λ cc + 83.86... (103)

[0294] MFD / λ cc ≤ 0.05772 CD nominal - 4.840... (104)

[0295] In order to set the counter-propagating transmission XT to be -20 dB or less after 10 km transmission (equivalent to an optical fiber length of 10 km), CD nominal and MFD / λ cc satisfy the following equation (105) or equation (106):

[0296] CD nominal ≥ 15.77 MFD / λ cc + 68.58... (105)

[0297] MFD / λ cc ≤ 0.06342 CD nominal - 4.349... (106)

[0298] CD nominal and MFD / λ cc preferably satisfy the following equation (107) or equation (108):

[0299] CD nominal ≥ 15.77 MFD / λ cc + 81.85... (107)

[0300] MFD / λ cc ≤ 0.06342 CD nominal - 5.191... (108).

[0301] In a 12-core MCF, in order to set the parallel transmission XT to be -20 dB or less after 10 km transmission (equivalent to an optical fiber length of 10 km), CD nominal and MFD / λ cc satisfy the following equation (109) or equation (110):

[0302] CD nominal ≥ 14.38 MFD / λ cc + 56.03 (109)

[0303] MFD / λ cc ≤ 0.06954 CD nominal - 3.896 (110)

[0304] . Also, the relationship between CD nominal and MFD / λ cc is preferably satisfied by the following equation (111) or equation (112):

[0305] CD nominal ≥ 14.38 MFD / λ cc + 66.47 (111)

[0306] MFD / λ cc ≤ 0.06954 CD nominal - 4.622 (112).

[0307] When CD nominal is 195 μm, 190 μm, 185 μm, 180 μm, 175 μm, or 170 μm, in a 16-core MCF, in consideration of the tolerance of the size of the core position and the cladding diameter, in order to set the leakage loss to the resin coating portion at a wavelength of 1360 nm to be 0.01 dB / km or less, the parallel transmission XT after 10 km of transmission (equivalent to an optical fiber length of 10 km) is set to be -20 dB or less, MFD / λ cc In the order of the numerical values of CD nominal listed above, it is preferably 7.17 or less, 6.88 or less, 6.59 or less, 6.30 or less, 6.01 or less, or 5.72 or less, and in the order of the numerical values of CD ominal listed above, it is preferably 6.41 or less, 6.13 or less, 5.84 or less, 5.55 or less, 5.26 or less, or 4.97 or less.

[0308] When CD nominal is 195 μm, 190 μm, 185 μm, 180 μm, 175 μm, or 170 μm, in a 16-core MCF, in consideration of the tolerance of the size of the core position and the cladding diameter, in order to set the leakage loss to the resin coating portion at a wavelength of 1360 nm to be 0.01 dB / km or less, the opposite direction transmission XT after 10 km of transmission (equivalent to an optical fiber length of 10 km) is set to be -20 dB or less, MFD / λ ccIn the order of the values of CDnominal listed above, it is preferable to be 8.02 or less, 7.70 or less, 7.38 or less, 7.07 or less, 6.75 or less, 6.43 or less, and in the order of the values of CD nominal In the order of the values of CD

[0309] In the order of the values of CD nominal When CD is 195 μm, 190 μm, 185 μm, 180 μm, 175 μm, 170 μm, in a 12-core MCF, in consideration of the tolerance of the size of the core position and the cladding diameter, in order to set the leakage loss to the resin coating portion at a wavelength of 1360 nm to be 0.01 dB / km or less, the opposite direction transmission XT after 10 km of transmission (equivalent to the optical fiber length of 10 km) is set to be -20 dB or less, and MFD / λ cc In the order of the values of CD nominal In the order of the values of CD nominal In the order of the values of CD

[0310] In the order of the values of CD nominal When CD is 195 μm, 190 μm, 185 μm, 180 μm, 175 μm, 170 μm, in a 12-core MCF, in consideration of the tolerance of the size of the core position and the cladding diameter, in order to set the leakage loss to the resin coating portion at a wavelength of 1360 nm to be 0.01 dB / km or less, the opposite direction transmission XT after 10 km of transmission (equivalent to the optical fiber length of 10 km) is set to be -20 dB or less, and MFD / λ cc In the order of the values of CD nominal In the order of the values of CD nominal In the order of the values of CD

[0311] Figure 10 is a value of d when the leakage loss to the coating portion at a wavelength of 1360 nm becomes 0.01 dB / km in a 12-core MCF in which 12 cores are arranged in a square lattice form coatAdding a 1μm margin, and considering the phase-to-phase transmission XT at a wavelength of 1360nm after 10km transmission (equivalent to a 10km fiber length), the CD and MFD / λ become -40dB (=-40dB / 10km) with a 1μm margin. cc A graph showing the relationship between the two.

[0312] When considering the tolerances for core position and cladding diameter, in order to set the leakage loss to the resin-coated portion at a wavelength of 1360nm to below 0.01dB / km, the back-to-back transmission XT after 10km transmission (equivalent to a fiber length of 10km) is set to below -40dB. nominal and MFD / λ cc The relationship satisfies the following equation (113) or equation (114):

[0313] CD nominal ≥14.07MFD / λ cc +55.59…(113)

[0314] MFD / λ cc ≤0.07105CD nominal -3.950…(114)

[0315] (from Figure 10 The area above the dashed line on the lower side (as shown). And, CD nominal and MFD / λ cc The relationship preferably satisfies the following equation (115) or equation (116):

[0316] CD nominal ≥14.07MFD / λ cc +66.07…(115)

[0317] MFD / λ cc ≤0.07105CD nominal -4.694…(116)

[0318] (from Figure 10 (The area above the dotted line shown on the upper side). Furthermore, in Figure 10 In the equation, when the vertical axis is set to y and the horizontal axis to x, the upper dashed line changes from y = 14.07x + 66.07 (x = 7.105 × 10⁻⁶) to x = 7.105 × 10⁻⁶. －2 The given value is y - 4.694, and the lower dashed line is given by y = 14.07x + 55.59 (x = 7.105 × 10⁻⁴). －2 The value is given as y-3.950).

[0319] Figure 11is a condition under which XT after 10 km transmission (equivalent to an optical fiber length of 10 km) (XT at 10 km transmission) becomes -40 dB (= -40 dB / 10 km) and XT after 10 km transmission (equivalent to an optical fiber length of 10 km) (XT at 10 km transmission) becomes -40 dB (= -40 dB / 10 km) in the case of a wavelength of 1360 nm, and d coat is added with a margin of 1 μm, and a graph of the relationship of CD and MFD / λ cc in the case of Λ added with a margin of 1 μm. Further, in Figure 11 , the mark "O" shows the relationship of a 16-core MCF in which parallel transmission is performed between adjacent cores, the mark "□" shows the relationship of a 16-core MCF in which opposite transmission is performed between adjacent cores, the mark "● (shown by a diagonal line in Figure 11 )" shows the relationship of a 12-core MCF in which parallel transmission is performed between adjacent cores, and the mark "■ (shown by a diagonal line in Figure 11 )" shows the relationship of a 12-core MCF in which opposite transmission is performed between adjacent cores.

[0320] As is known from Figure 11 , it is possible to reduce CD by 10 μm or more by using the MCF of the present application in opposite transmission rather than in parallel transmission, and therefore it is preferable that CD be reduced by 35 μm or more in a 12-core MCF compared to a 16-core MCF, and therefore it is preferable.

[0321] Further, in Figure 11 , the broken line is not shown, but as in the case of Figure 10 , in a 16-core MCF, in consideration of the tolerance of the size of the core position and the cladding diameter, in order to set the leakage loss to the resin cladding portion at 1360 nm to 0.01 dB / km or less, XT at 10 km transmission (equivalent to an optical fiber length of 10 km) is set to -40 dB or less, the relationship of CD nominal and MFD / λ cc satisfies the following formula (117) or formula (118):

[0322] CD nominal ≥ 19.81 MFD / λ cc + 74.42... (117)

[0323] MFD / λ cc ≤ 0.05047 CD nominal - 3.756... (118)

[0324] And, CD nominal and MFD / λ cc preferably satisfy the following equation (119) or equation (120) :

[0325] CD nominal ≥ 19.81 MFD / λ cc + 87.07... (119)

[0326] MFD / λ cc ≤ 0.05047 CD nominal - 4.394... (120)

[0327] In order to set the counter-propagating transmission XT to be -40 dB or less after 10 km transmission (equivalent to an optical fiber length of 10 km), CD nominal and MFD / λ cc satisfy the following equation (121) or equation (122) :

[0328] CD nominal ≥ 17.01 MFD / λ cc + 70.37... (121)

[0329] MFD / λ cc ≤ 0.05878 CD nominal - 4.137... (122)

[0330] And, CD nominal and MFD / λ cc preferably satisfy the following equation (123) or equation (124) :

[0331] CD nominal ≥ 17.01 MFD / λ cc + 83.45... (123)

[0332] MFD / λ cc ≤ 0.05878 CD nominal - 4.906... (124).

[0333] In a 12-core MCF, in order to set the parallel transmission XT to be -40 dB or less after 10 km transmission (equivalent to an optical fiber length of 10 km), CD nominal and MFD / λ cc satisfy the following equation (125) or equation (126) :

[0334] CD nominal ≥ 16.24 MFD / λ cc + 58.71... (125)

[0335] MFD / λcc ≤ 0.06159 CD nominal - 3.616... (126)

[0336] CD nominal and MFD / λ cc The relationship preferably satisfies the following equation (127) or equation (128):

[0337] CD nominal ≥ 16.24 MFD / λ cc + 68.86... (127)

[0338] MFD / λ cc ≤ 0.06159 CD nominal - 4.241... (128).

[0339] In the case where CD nominal is 195 μm, 190 μm, 185 μm, 180 μm, 175 μm, 170 μm, in a 16-core MCF, in consideration of the tolerance of the size of the core position and the cladding diameter, in order to set the leakage loss to the resin coating portion at a wavelength of 1360 nm to be 0.01 dB / km or less, the parallel transmission XT after 10 km of transmission (corresponding to an optical fiber length of 10 km) is set to be -40 dB or less, MFD / λ cc In the order of the values of CD nominal listed above, it is preferable to be 6.09 or less, 5.83 or less, 5.58 or less, 5.33 or less, 5.08 or less, 4.82 or less, and in the order of the values of CD ominal listed above, it is preferable to be 5.45 or less, 5.19 or less, 4.94 or less, 4.69 or less, 4.44 or less, 4.19 or less.

[0340] In the case where CD nominal is 195 μm, 190 μm, 185 μm, 180 μm, 175 μm, 170 μm, in a 16-core MCF, in consideration of the tolerance of the size of the core position and the cladding diameter, in order to set the leakage loss to the resin coating portion at a wavelength of 1360 nm to be 0.01 dB / km or less, the opposite direction transmission XT after 10 km of transmission (corresponding to an optical fiber length of 10 km) is set to be -40 dB or less, MFD / λ cc In the order of the values of CD nominal listed above, it is preferable to be 6.56 or less, 6.26 or less, 5.97 or less, 5.68 or less, 5.38 or less, 5.09 or less.

[0341] In the CD nominal For 195 μm, 190 μm, 185 μm, 180 μm, 175 μm, 170 μm, in a 12-core MCF, in consideration of the tolerance of the size of the core position and the cladding diameter, in order to set the leakage loss to the resin coating portion at a wavelength of 1360 nm to be 0.01 dB / km or less, the opposite direction transmission XT after 10 km of transmission (equivalent to the optical fiber length of 10 km) is set to be -40 dB or less, MFD / λ cc In the CD nominal In the order of the numerical values of the CD nominal In the order of the numerical values of the CD

[0342] In the CD nominal For 195 μm, 190 μm, 185 μm, 180 μm, 175 μm, 170 μm, in a 12-core MCF, in consideration of the tolerance of the size of the core position and the cladding diameter, in order to set the leakage loss to the resin coating portion at a wavelength of 1360 nm to be 0.01 dB / km or less, the opposite direction transmission XT after 10 km of transmission (equivalent to the optical fiber length of 10 km) is set to be -40 dB or less, MFD / λ cc In the CD nominal In the order of the numerical values of the CD nominal In the order of the numerical values of the CD

[0343] λ cc is 1260 nm or less, thereby being able to ensure single mode operation in the O-band, and thus is preferable. At this time, by setting MFD / λ cc to be 6.2 or more, it is possible to take into account λ cc of 1260 nm or less and MFD of 7.8 μm or more and 8.6 μm or less, and thus is preferable. By setting MFD / λ cc to be 6.5 or more, it is possible to take into account λ cc of 1260 nm or less and MFD of 8.2 μm or more and 9.0 μm or less, and thus is more preferable.

[0344] Further, λ ccThe 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 MFDs with a diameter of 8.2 μm or more and a diameter of 9.0 μm or less are preferred.

[0345] 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.

[0346] When setting the nominal value of MFD to MFD nominal The tolerance is set to an absolute value of less than 0.4 μm, and the nominal value of the zero-dispersion wavelength λ0 is set to λ. 0nominal When the absolute value of the tolerance 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.

[0347] 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. cc The 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.

[0348] While taking into account λ below 1260nm cc For MFDs of 7.8 μm to 8.6 μm, MFD / λ cc6.2 or more, and therefore in order to make the tolerance of MFD / λ cc 1.0 or more, 1.5 or more, 1.9 or more, 2.5 or more, 3.0 or more, the upper limit value of MFD / λ cc in the order of the numerical values of the tolerance of MFD / λ cc is preferably an MCF configuration that allows 7.2 or more, 7.7 or more, 8.1 or more, 8.7 or more, 9.2 or more. For this reason, CD nominal in a 12-core MCF, in order for the leakage loss to the resin coating portion to be 0.01 dB / km or less at a wavelength of 1360 nm, the opposite transmission XT at a wavelength of 1360 nm becomes -20 dB or less after 10 km of transmission (equivalent to an optical fiber length of 10 km), and the allowable CD coat in the case where Λ and d nominal According to Equation (97), in the order of the numerical values of the tolerance of MFD / λ cc is preferably 149 μm or more, 156 μm or more, 161 μm or more, 169 μm or more, 175 μm or more, and according to Equation (99), in the order of the numerical values of the tolerance of MFD / λ cc is preferably 160 μm or more, 166 μm or more, 171 μm or more, 179 μm or more, 186 μm or more. At this time, CD nominal in a 12-core MCF, in order for the leakage loss to the resin coating portion to be 0.01 dB / km or less at a wavelength of 1360 nm, the opposite transmission XT at a wavelength of 1360 nm becomes -40 dB or less after 10 km of transmission (equivalent to an optical fiber length of 10 km), and the allowable CD coat in the case where Λ and d nominal According to Equation (113), in the order of the numerical values of the tolerance of MFD / λ cc is preferably 157 μm or more, 164 μm or more, 170 μm or more, 178 μm or more, 185 μm or more, and according to Equation (115), in the order of the numerical values of the tolerance of MFD / λ cc is preferably 167 μm or more, 174 μm or more, 173 μm or more, 182 μm or more, 189 μm or more.

[0349] In the case where both λ cc of 1260 nm or less and MFD of 8.2 μm or less, 9.0 μm or less are taken into account, MFD / λ cc becomes 6.5 or more, and therefore in order to make the tolerance of MFD / λ cc 1.0 or more, 1.5 or more, 1.9 or more, 2.5 or more, 3.0 or more, the upper limit value of MFD / λcc the upper limit value of MFD / λ cc In the order of the numerical value of the tolerance of MFD / λ nominal In the 12-core MCF, in order for the leakage loss to the resin coating portion to be 0.01 dB / km or less at a wavelength of 1360 nm, the opposite transmission XT at a wavelength of 1360 nm becomes -20 dB or less after 10 km of transmission (equivalent to an optical fiber length of 10 km), and Λ and d coat The tolerable CD nominal According to formula (97), in the order of the numerical value of the tolerance of MFD / λ cc is preferably 153 μm or more, 159 μm or more, 165 μm or more, 173 μm or more, 179 μm or more, and according to formula (99), in the order of the numerical value of the tolerance of MFD / λ cc is preferably 163 μm or more, 170 μm or more, 175 μm or more, 183 μm or more, 190 μm or more. At this time, CD nominal In the 12-core MCF, in order for the leakage loss to the resin coating portion to be 0.01 dB / km or less at a wavelength of 1360 nm, the opposite transmission XT at a wavelength of 1360 nm becomes -40 dB or less after 10 km of transmission (equivalent to an optical fiber length of 10 km), and Λ and d coat The tolerable CD nominal According to formula (113), in the order of the numerical value of the tolerance of MFD / λ cc is preferably 161 μm or more, 168 μm or more, 174 μm or more, 182 μm or more, 189 μm or more, and according to formula (115), in the order of the numerical value of the tolerance of MFD / λ cc is preferably 172 μm or more, 179 μm or more, 184 μm or more, 193 μm or more, 199 μm or more.

[0350] In consideration of λ cc of 1360 nm or less and MFD of 8.2 μm or more and 9.0 μm or less, MFD / λ cc becomes 6.0 or more, and therefore in order for the tolerance of MFD / λ cc to be 1.0, 1.5, 1.9, 2.5, or 3.0, the upper limit value of MFD / λ cc the upper limit value of MFD / λ ccthe order of the numerical values of the tolerance of CD, preferably at least 7.0, 7.5, 7.9, 8.5, or 9.0 of the MCF configuration. To this end, CD nominal In the 12-core MCF, in order for the leakage loss to the resin coating portion to be 0.01 dB / km or less at a wavelength of 1360 nm, the opposite transmission XT at a wavelength of 1360 nm becomes -20 dB or less after 10 km of transmission (equivalent to an optical fiber length of 10 km), and Λ and d coat The tolerable CD with the margin added nominal According to the formula (97), in the order of the numerical values of the tolerance of MFD / λ cc According to the formula (99), in the order of the numerical values of the tolerance of MFD / λ cc According to the formula (99), in the order of the numerical values of the tolerance of MFD / λ nominal In the 12-core MCF, in order for the leakage loss to the resin coating portion to be 0.01 dB / km or less at a wavelength of 1360 nm, the opposite transmission XT at a wavelength of 1360 nm becomes -40 dB or less after 10 km of transmission (equivalent to an optical fiber length of 10 km), and Λ and d coat The tolerable CD with the margin added nominal According to the formula (113), in the order of the numerical values of the tolerance of MFD / λ cc According to the formula (115), in the order of the numerical values of the tolerance of MFD / λ cc According to the formula (115), in the order of the numerical values of the tolerance of MFD / λ

[0351] In the case where λ cc In the case where λ is more than 1260 nm and is 1360 nm or less, by the structure of Figure 12 of ITU-T G.650.1 (03 / 2018) (optical fiber without cabling) in a 20 m of the sample optical fiber 22 m, plus a bend of a bend radius of 140 mm or more, plus a bend of 1 turn of a radius of 40 mm at the front and back of the 20 m interval, in the case where the entire mode is uniformly excited, the intensity of the high mode is set to P h , and the intensity of the fundamental mode is set to P f , it becomes 10 log10 [P h / (P f + P h) = 0.1 dB as λ cc The measurement is performed, but with the MCF of the present application, the cutoff wavelength (λ ccR ) is preferably 1260 nm or less when the measurement is performed with a 20 m section of the sample fiber 22 m being added with a bend having a radius of 60 mm or more and 100 mm or less. Thus, the single mode operation in the O-band after the cable installation can be ensured. Also, in the range where the length L sample [m] of the sample fiber exceeds 22 m and is 1000 m or less, the cutoff wavelength (λ sample ) is preferably 1260 nm or less when the measurement is performed with the L sample -2 [m] being added with a bend having a radius of 140 mm or more, and a 1-turn bend having a radius of 40 mm is added before and after the L ccL -2 [m] section. Thus, in the cable where the length L sample [m] of the cable, the single mode operation in the O-band can be ensured.

[0352] The bend loss of each core of the MCF of the present application at a wavelength of 1310 nm or more and 1360 nm or less is preferably 0.15 dB / turn or less when the bend radius is 10 mm, and more preferably 0.02 dB / turn or less. Thus, in the case where the MCF of the present application is installed in the ultra-high density cable of the spacer tape type, the increase in the cable loss can be suppressed.

[0353] The average bend radius of the MCF installed in the cable of the MCF cable in which the MCF of the present application is built-in is preferably 0.14 m or less, and more preferably 0.10 m or less when the cable is stretched in a straight line (at least a bend radius of 1 m or more). Also, the average bend radius of the MCF installed in the cable of the MCF cable in which the MCF of the present application is built-in is preferably 0.14 m or more and 0.3 m or less. Thus, XT can be reduced.

[0354] Also, the average bend radius of the MCF installed in the cable of the MCF cable in which the MCF of the present application is built-in is preferably 0.03 m or more, and more preferably 0.06 m or more. Thus, the loss caused by the bend can be reduced.

[0355] Also, the MCF cable in which the MCF of the present application is built-in is preferably a spacer tape type cable. Thus, the soft spacer tape can be installed in the cable while being twisted into a spiral shape, the MCF can be cable-ized while being given a small bend radius, and thus XT can be reduced.

[0356] The MCF cable in which the MCF of the present application is built in is a grooved cable, and preferably has a tension resistance body at the center of the groove member. Thus, the bending radius of the MCF can be easily controlled, and the XT can be reduced. In addition, the presence of the tension resistance body at the center of the groove member makes it easy to bend the cable in any direction, and cable laying work can be easily performed.

[0357] The MCF cable in which the MCF of the present application is built in preferably has no groove member in the space inside the sheath, and has a tension resistance body inside the sheath. Thus, the space inside the sheath can be effectively used, and the number of cores per unit cross-sectional area of the MCF cable can be increased.

Claims

1. A multi-core optical fiber, having the following characteristics: The core assembly consists of multiple cores extending along the central axis. A common cladding covering each of the plurality of fiber cores, having a refractive index smaller than that of each of the plurality of fiber cores; and A resin-coated portion is disposed on the outer periphery of the common coating layer. In this multi-core optical fiber, In the cross-section of this multi-core optical fiber orthogonal to the central axis, the multiple cores are configured such that the adjacent relationship between any two cores is not valid. In the cross-section, an axis passing through the center of the common cladding that intersects the central axis and does not intersect any of the plurality of fiber cores is taken as the axis of symmetry, the plurality of fiber cores being arranged in a linearly symmetrical position. The outer diameter of the resin-coated portion defined on the cross-section is 235 μm or more and 265 μm or less. The diameter CD [μm] of the common cladding defined on the cross section converges to a nominal value CD less than 195 μm. nominal CD based on [μm] nominal Values ​​above -1μm and CD nominal The range of values ​​below +1μm The mode field diameter (MFD) [μm] of each of the multiple fiber cores acting as waveguides at a wavelength of 1310 nm converges to a range of values ​​greater than or equal to the MDF reference value (between 8.2 μm and 9.2 μm) and less than or equal to the MDF reference value (between +0.4 μm). The cable cutoff wavelength λ was measured using a 22m fiber optic cable. cc [nm] refers to nm and below. The zero-dispersion wavelengths of each of the plurality of fiber cores, relative to a wavelength reference value between 1312 nm and 1340 nm, converge to a range of values ​​above -12 nm and below +0.12 nm from the wavelength reference value. The dispersion slope of the zero-dispersion wavelength is 0.092 ps / (nm). 2 Below km), The shortest distance d among the distances from the interface between the resin-coated portion and the common cladding to the center of each of the plurality of fiber cores. coat [μm] satisfies the following equation (1): …（1）， The multi-core optical fiber has a structure that satisfies either condition 1 or condition 2 below, and optical properties that satisfy any of conditions 3 through 6 below. The first condition is that each fiber core is in direct contact with the common cladding. The second condition is that the optical cladding corresponding to each of the individual fiber cores is disposed between each fiber core and the common cladding, and each optical cladding has a relative refractive index difference Δ2 of more than -0.1% and less than 0.1% relative to the common cladding. The third condition is that the plurality of fiber cores comprises 12 fiber cores, and for each of the 12 fiber cores, the total crosstalk from adjacent fiber cores at a wavelength of 1360nm, equivalent to a fiber length of 10km, is below -6.8dB, and the center spacing Λ between adjacent fiber cores satisfies the following equation (2): …（2）， Furthermore, the multi-core optical fiber satisfies the following equation (3): …（3）， The fourth condition is that the plurality of fiber cores comprises 12 fiber cores, and for each of the 12 fiber cores, the total crosstalk from adjacent fiber cores at a wavelength of 1360nm, equivalent to a fiber length of 10km, is below -16.8dB, and the center spacing Λ between adjacent fiber cores satisfies the following equation (4): …（4）， Furthermore, the multi-core optical fiber satisfies the following equation (5): …（5）， The fifth condition is that the plurality of fiber cores comprises 16 fiber cores, and for each of the 16 fiber cores, the total crosstalk from adjacent fiber cores at a wavelength of 1360nm, equivalent to a fiber length of 10km, is below -6.8dB, and the center spacing Λ between adjacent fiber cores satisfies the following equation (6): …（6）， Furthermore, the multi-core optical fiber satisfies the following equation (7): …（7）， The sixth condition is that the plurality of fiber cores comprises 16 fiber cores, and for each of the 16 fiber cores, the total crosstalk from adjacent fiber cores at a wavelength of 1360nm, equivalent to a fiber length of 10km, is below -16.8dB, and the center spacing Λ between adjacent fiber cores satisfies the following equation (8): …（8）， Furthermore, the multi-core optical fiber satisfies the following equation (9): …（9）。 2. The multi-core optical fiber according to claim 1, wherein, The plurality of fiber cores comprises 12 fiber cores. The 12 fiber cores each belong to any fiber core group of the inner peripheral fiber core group and the outer peripheral fiber core group. The inner peripheral fiber core group consists of 4 fiber cores that should be arranged in a way that minimizes the distance from its center to the center of the common cladding in the cross-section. The outer peripheral fiber core group consists of 8 fiber cores that are adjacent to the 4 fiber cores and should be arranged in a way that does not minimize the distance from their center to the center of the common cladding in the cross-section. The mode field diameter MFD [μm] is between 8.2 μm and 9.0 μm at a wavelength of 1310 nm. The cable cutoff wavelength λ cc [nm] refers to nm and below. The multi-core optical fiber satisfies the following equation (10): …（10）。 3. The multi-core optical fiber according to claim 1, wherein, The plurality of fiber cores comprises 12 fiber cores. The 12 fiber cores each belong to either the inner or outer perimeter fiber core group. The total crosstalk from adjacent fiber cores to any fiber core belonging to the inner perimeter fiber core group, at a wavelength of 1360 nm and equivalent to a fiber length of 10 km, is below -16.8 dB. The inner perimeter fiber core group consists of four fiber cores configured in a way that minimizes the distance from its center to the center of the common cladding in the cross-section. The outer perimeter fiber core group consists of eight fiber cores adjacent to the four cores, configured in a way that does not minimize the distance from their center to the center of the common cladding in the cross-section. The mode field diameter MFD [μm] is between 7.8 μm and 8.6 μm at a wavelength of 1310 nm. The cable cutoff wavelength λ cc [nm] refers to nm and below. The multi-core optical fiber satisfies the following equation (11): …（11）。 4. The multi-core optical fiber according to claim 1, wherein, The plurality of fiber cores comprises 12 fiber cores. The 12 fiber cores each belong to either the inner or outer perimeter fiber core group. The total crosstalk from adjacent fiber cores to any fiber core belonging to the inner perimeter fiber core group, at a wavelength of 1360 nm and equivalent to a fiber length of 10 km, is below -16.8 dB. The inner perimeter fiber core group consists of four fiber cores configured in a way that minimizes the distance from its center to the center of the common cladding in the cross-section. The outer perimeter fiber core group consists of eight fiber cores adjacent to the four cores, configured in a way that does not minimize the distance from their center to the center of the common cladding in the cross-section. The mode field diameter (MFD) is between 8.2 μm and 9.0 μm at a wavelength of 1310 nm. The cable cutoff wavelength λ cc [nm] refers to nm and below. The multi-core optical fiber satisfies the following equation (12): …（12）。 5. The multi-core optical fiber according to any one of claims 1 to 4, wherein, The center interval Λ is relative to the nominal value Λ of the center interval Λ. nominal [μm] converges to the following equation (13): …（13） Scope The nominal value Λ nominal Under the condition that either the third condition or the fifth condition is met, the following equation (14) is satisfied: …（14）， Alternatively, under the condition that the fourth condition or the sixth condition is met, the following equation (15) can be satisfied: …（15）。 6. The multi-core optical fiber according to any one of claims 1 to 4, wherein, At a wavelength of 1550 nm, the total crosstalk from adjacent fiber cores, equivalent to a fiber length of 10 km, is greater than -15 dB.

7. The multi-core optical fiber according to claim 5, wherein, At a wavelength of 1550 nm, the total crosstalk from adjacent fiber cores, equivalent to a fiber length of 10 km, is greater than -15 dB.

8. A multi-core optical cable having a plurality of multi-core optical fibers comprising any one of claims 1 to 7.

9. 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 7.

10. The multi-core optical cable according to claim 9, wherein, The multi-core optical fiber ribbon is embedded in a spiral twisted state.

11. The multi-core optical cable according to any one of claims 8 to 10, wherein, The multi-core optical fiber includes those 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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