# US 12,007,601 B2 · Multi-core optical fiber and multi-core optical fiber cable > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,007,601 B2 - Document ID: US12007601B2 - Status: Granted - Kind: B2 - Application number: 17/499,981 - Filed: 2021-10-13 - Published: 2022-04-21 - Granted: 2024-06-11 - Earliest claimed: 2020-10-16 - Assignees: Sumitomo Electric Industries, Ltd. - Applicants: Sumitomo Electric Industries, Ltd. - Inventors: Tetsuya Hayashi - Web page: https://patentgrep.com/patent/US12007601B2 ## CPC - G02B 6/02042: {Multicore optical fibres} - G02B 6/02009: {Large effective area or mode field radius, e.g. to reduce nonlinear effects in single mode fibres} - G02B 6/0288: {Multimode fibre, e.g. graded index core for compensating modal dispersion} - G02B 6/4407: {with internal fluted support member (G02B6/4429, G02B6/4439, G02B6/4479 take precedence)} - G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS ## Abstract An MCF or the like according to the present disclosure ensures sufficient manufacturing tolerance, is excellent in mass productivity, and is also capable of suppressing degradation of splice loss. The MCF includes four cores that extend along a central axis, and a common cladding. On a cross-section, the common cladding has a circular outer periphery, the four cores are arranged at positions to be line symmetric with respect to a straight line that intersects with a central axis and that intersects with none of the four cores, and a core arrangement defined by the four cores has rotational symmetry once with central axis being a center of rotation. ## Claims ### Claim 1 A four-core multi-core optical fiber comprising: only four cores, each extending along a central axis; and a common cladding covering each of the four cores, wherein the common cladding has an outer periphery that is circular on a cross-section of the multi-core optical fiber, the cross-section being orthogonal to the central axis, on the cross-section, the four cores are respectively arranged at positions to be line symmetric with respect to a straight line that intersects with the central axis and that intersects with none of the four cores, and on the cross-section, a core arrangement defined by the four cores has rotational symmetry at most once with any point being a center of rotation, wherein a diameter CD of the common cladding is 126 μm or less, in each of the four cores, a mode field diameter MFD at a wavelength of 1310 nm and a cable cutoff wavelength λcc measured on a 22 m length of fiber satisfy a following Formula (1): dcoat≥2.88MFD/λcc+5.36 (1), in each of the four cores, the mode field diameter MFD is 8.2 μm or more and 9.6 μm or less, and a difference between a maximum value and a minimum value is 0.8 μm or less, in each of the four cores, a zero-dispersion wavelength is 1300 nm or more and 1352 nm or less, and a difference between a maximum value and a minimum value is 24 nm or less, in each of the four cores, a dispersion slope at the zero-dispersion wavelength is 0.092 ps/(nm2·km) or less, in each of the four cores, the cable cutoff wavelength λcc is 1260 nm or less, either a first condition or a second condition is satisfied, the first condition is defined that a crosstalk between cores having an adjacent relationship for a fiber length of 10 km at a wavelength of 1360 nm is −10 dB or less, in each of the four cores, a relationship of a following Formula (2): CDnominal≥13.31MFD/λcc+24.47 (2) is satisfied, and in each of the four cores, MFD/λcc and a center-to-center interval Λ between the cores having the adjacent relationship satisfy a following Formula (3): 6.5≤MFD/λcc≤9.5≤0.443Λ−5.33 (3), and the second condition is defined that the crosstalk between the cores having the adjacent relationship for the fiber length of 10 km at the wavelength of 1360 nm is −20 dB or less, in each of the four cores, a relationship of a following Formula (4): CDnominal≥9.37MFD/λcc+31.73 (4) is satisfied, and in each of the four cores, MFD/λcc and the center-to-center interval Λ between the cores having the adjacent relationship satisfy a following Formula (5): 6.5≤MFD/λcc≤9.5≤0.392Λ−4.88 (5), and wherein an optical cladding having a depressed type refractive index profile without a trench layer is provided in the periphery of each of the four cores. ### Claim 2 (depends on 1) The multi-core optical fiber according to claim 1, wherein the four cores are arranged such that on the cross-section, centers of the four cores are each located within a region having a radius of 1.0 μm with a center being each of four vertexes of a 3-sides equal trapezoid, in which three sides each have a length Λnominal and one side has a length 1.2 times or more of the length Λnominal. ### Claim 3 (depends on 1) The multi-core optical fiber according to claim 1, wherein a distance dcoat from a center of each of the four cores to the outer periphery of the common cladding falls within a range of a value of dcoat,nominal−1 μm or more and a value of dcoat,nominal+1 μm or less with a predetermined nominal value dcoat,nominal−1 μm used as a basis. ### Claim 4 (depends on 1) The multi-core optical fiber according to claim 1, further comprising a coating surrounding the common cladding, wherein a leakage loss from at least any of the four cores to the coating either at a wavelength of 1550 nm or at a wavelength of 1625 nm is 0.05 dB/km or more, a transmission loss of at least any of the four cores at the wavelength of 1550 nm is 0.25 dB/km or more, or a transmission loss at the wavelength of 1625 nm is 0.25 dB/km or more. ### Claim 5 (depends on 1) The multi-core optical fiber according to claim 1, wherein the first condition is satisfied, and the crosstalk between the cores having the adjacent relationship at a wavelength of 1550 nm for the fiber length of 10 km is −10 dB or more. ### Claim 6 (depends on 4) The multi-core optical fiber according to claim 4, wherein the first condition is satisfied, and the crosstalk between the cores having the adjacent relationship at a wavelength of 1550 nm for the fiber length of 10 km is −10 dB or more. ### Claim 7 (depends on 1) The multi-core optical fiber according to claim 1, wherein the second condition is satisfied, and the crosstalk between the cores having the adjacent relationship at a wavelength of 1550 nm for the fiber length of 10 km is −20 dB or more. ### Claim 8 (depends on 4) The multi-core optical fiber according to claim 4, wherein the second condition is satisfied, and the crosstalk between the cores having the adjacent relationship at a wavelength of 1550 nm for the fiber length of 10 km is −20 dB or more. ### Claim 9 (depends on 1) A multi-core optical fiber cable comprising a plurality of multi-core optical fibers including the multi-core optical fiber defined in claim 1. ### Claim 10 (depends on 9) The multi-core optical fiber cable according to claim 9, wherein the multi-core optical fiber has an average bending radius of 0.03 m or more and 0.14 m or less, or 0.14 m or more and 0.3 m or less in a fiber longitudinal direction. ### Claim 11 (depends on 1) A multi-core optical fiber cable incorporating a multi-core optical fiber ribbon in which a plurality of multi-core optical fibers including the multi-core optical fiber defined in claim 1 are intermittently bonded. ### Claim 12 (depends on 11) The multi-core optical fiber cable according to claim 11, wherein the multi-core optical fiber ribbon is incorporated with spirally twisted. ### Claim 13 (depends on 11) The multi-core optical fiber cable according to claim 11, wherein the multi-core optical fiber has an average bending radius of 0.03 m or more and 0.14 m or less, or 0.14 m or more and 0.3 m or less in a fiber longitudinal direction.