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US-20260126580-A1 - MULTICORE OPTICAL FIBER AND OPTICAL CABLE

US20260126580A1US 20260126580 A1US20260126580 A1US 20260126580A1US-20260126580-A1

Abstract

A multicore optical fiber includes a glass fiber. The glass fiber includes a plurality of cores extending along a central axis of the glass fiber and a first cladding surrounding the plurality of cores. The plurality of cores includes a first core and a second core that are closest to each other. An inequality of 250×10 −6 ≤n1−n2≤950×10 −6 is satisfied, where, at a wavelength that is at least one of wavelengths in a range of 1260 nm to 1625 nm, inclusive, n1 is an effective refractive index of the first core, and n2 is an effective refractive index of the second core. An inequality of d1−d2≤−0.1 μm is satisfied, where d1 is a mode field diameter of the first core at the wavelength and d2 is a mode field diameter of the second core at the wavelength.

Inventors

  • Yuto Kobayashi
  • Takemi Hasegawa

Assignees

  • SUMITOMO ELECTRIC INDUSTRIES, LTD.

Dates

Publication Date
20260507
Application Date
20250221
Priority Date
20240306

Claims (13)

  1. 1 . A multicore optical fiber comprising: a glass fiber, wherein the glass fiber includes a plurality of cores extending along a central axis of the glass fiber and a first cladding surrounding the plurality of cores, wherein the plurality of cores includes a first core and a second core that are closest to each other, wherein an inequality of 250×10 −6 ≤n1−n2≤950×10 −6 is satisfied, where, at a wavelength that is at least one of wavelengths in a range of 1260 nm to 1625 nm, inclusive, n1 is an effective refractive index of the first core, and n2 is an effective refractive index of the second core, and wherein an inequality of d1−d2≤−0.17 [μm] is satisfied, where d1 [μm] is a mode field diameter of the first core at the wavelength and d2 [μm] is a mode field diameter of the second core at the wavelength.
  2. 2 . (canceled)
  3. 3 . The multicore optical fiber according to claim 1 , wherein an inequality of d1−d2≤−0.45 [μm] is satisfied.
  4. 4 . The multicore optical fiber according to claim 1 , wherein an inequality of d1−d2≥−1.4 [μm] is satisfied.
  5. 5 . The multicore optical fiber according to claim 1 , wherein the plurality of cores is arranged in a square lattice pattern in a cross section orthogonal to the central axis.
  6. 6 . The multicore optical fiber according to claim 1 , wherein the number of the plurality of cores is two.
  7. 7 . The multicore optical fiber according to claim 5 , wherein the plurality of cores is arranged such that a centroid of the plurality of cores as a whole is shifted from the central axis in the cross section orthogonal to the central axis.
  8. 8 . The multicore optical fiber according to claim 5 , wherein the glass fiber further includes a marker surrounded by the first cladding, and wherein the marker has a refractive index different from a refractive index of the first cladding.
  9. 9 . The multicore optical fiber according to claim 1 , wherein the glass fiber further includes a second cladding surrounding the first cladding, and wherein the second cladding has a refractive index higher than the refractive index of the first cladding and lower than any of refractive indices of the plurality of cores.
  10. 10 . The multicore optical fiber according to claim 9 , wherein the first cladding is a common cladding that collectively surrounds the plurality of cores.
  11. 11 . The multicore optical fiber according to claim 9 , wherein the first cladding includes a plurality of individual claddings surrounding a respective one of the plurality of cores.
  12. 12 . The multicore optical fiber according to claim 1 , wherein the glass fiber further includes a low-refractive-index portion having a refractive index lower than the refractive index of the first cladding, and wherein the low-refractive-index portion is provided on a line segment connecting a central axis of the first core to a central axis of the second core in the cross section orthogonal to the central axis.
  13. 13 . An optical cable comprising: a plurality of multicore optical fibers according to claim 1 ; and an outer sheath that accommodates the plurality of multi-core optical fibers.

Description

TECHNICAL FIELD The present disclosure relates to a multicore optical fiber and an optical cable. This application claims priority based on Japanese Patent Application No. 2024-034104 filed on Mar. 6, 2024, the entire contents of which are incorporated herein by reference. BACKGROUND ART In an uncoupled multicore optical fiber (hereinafter also referred to as “MCF”), it is an important matter to reduce inter-core crosstalk (hereinafter also referred to as “XT”). Patent literature 1 describes that heterogeneity is provided between cores in order to reduce XT. Patent literature 2 also describes that heterogeneity is provided between cores. Non-patent literature 1 describes that XT has the dependence on the bending radius in an MCF in which heterogeneity is provided between cores. Non-patent literature 2 describes an equation for calculating the peak position of the dependence of XT on the bending radius. Non-Patent Literature 3 describes that an MCF with heterogeneity between cores is manufactured and the dependence of XT on the bending radius is actually measured in the MCF. CITATION LIST Patent Literature Patent literature 1: WO 2023/189621 Patent literature 2: U.S. Patent Application Publication No. 2024/0053530 Non Patent Literature Non-patent literature 1: Koshiba et al., “Analytical Expression of Average Power-Coupling Coefficients for Estimating Intercore Crosstalk in Multicore Fibers” October 2012, IEEE Photonics Journal Vol. 4, No. 5, pp. 1987-1995 Non-Patent Literature 2: Hayashi et al., “Physical interpretation of intercore crosstalk in multicore fiber: effects of macrobend, structure fluctuation, and microbend” 11 Mar. 2013, OPTICS EXPRESS Vol. 21, No. 5, pp. 5401-5412 Non-Patent Literature 3: Kobayashi et al., “Characterization of Inter-core Crosstalk of Multi-core Fiber as a Function of Bending Radius with Multi-channel OTDR” OECC/PSC 2022 TuC2-2 SUMMARY OF INVENTION An MCF according to one aspect of the present disclosure is an MCF including a glass fiber. The glass fiber includes a plurality of cores extending along a central axis of the glass fiber and a first cladding surrounding the plurality of cores. The plurality of cores includes a first core and a second core that are closest to each other. An inequality of 250×10−6≤n1−n2≤950×10−6 is satisfied, where, at a wavelength that is at least one of wavelengths in a range of 1260 nm to 1625 nm, inclusive, n1 is an effective refractive index of the first core, and n2 is an effective refractive index of the second core. An inequality of d1−d2≤−0.1 μm is satisfied, where d1 is a mode field diameter of the first core at the wavelength and d2 is a mode field diameter of the second core at the wavelength. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing dependence of XT of an MCF on the bending radius. FIG. 2 is a graph showing effective refractive index difference dependence of XT at a bending radius of 300 mm. FIG. 3 is a graph showing effective refractive index difference dependence of XT at a bending radius of 150 mm. FIG. 4 is a graph showing MFD dependence of cutoff wavelength. FIG. 5 is a graph showing a relationship between effective refractive index and cutoff wavelength. FIG. 6 is a graph showing a relationship between difference in MFDs and difference in cutoff wavelengths. FIG. 7 is a graph showing a relationship between difference in effective refractive indices and difference in MFDs when a difference in cutoff wavelengths is 100 nm. FIG. 8 is a diagram showing a cross section and a refractive index distribution orthogonal to a central axis of an MCF according to an embodiment. FIG. 9 is a diagram showing an optical cable according to an embodiment. FIG. 10 is a diagram showing a cross section and a refractive index distribution orthogonal to a central axis of an MCF according to a first modification. FIG. 11 is a diagram showing a cross section and a refractive index distribution orthogonal to a central axis of an MCF according to a second modification. FIG. 12 is a diagram showing a cross section and a refractive index distribution orthogonal to a central axis of an MCF according to a third modification. FIG. 13 is a diagram showing a cross section and a refractive index distribution orthogonal to a central axis of an MCF according to a fourth modification. FIG. 14 is a diagram showing a cross section and a refractive index distribution orthogonal to a central axis of an MCF according to a fifth modification. FIG. 15 is a diagram showing a cross section orthogonal to a central axis of an MCF according to a sixth modification. FIG. 16 is a diagram showing a cross section orthogonal to a central axis of an MCF according to a seventh modification. FIG. 17 is a diagram showing a cross section orthogonal to a central axis of an MCF according to an eighth modification. FIG. 18 is a diagram showing a cross section orthogonal to a central axis of an MCF according to a ninth modification. FIG. 19 is a diagram showing a cross section