JP2023006659A - multicore optical fiber - Google Patents

Abstract

A multi-core optical fiber of the present disclosure aims to improve the effect of suppressing crosstalk between cores. A multi-core optical fiber according to the present disclosure has at least one core of two or more types with different core refractive indices and different core radii in the clad, and the core center-clad edge distance differs for each of the types. and [Selection drawing] Fig. 2

Description

The present disclosure relates to a multi-core optical fiber having multiple cores arranged within a cladding.

In recent years, space division multiplexing technology has been studied to expand the optical transmission capacity. Among them, a multi-core optical fiber, in which a plurality of cores are arranged in the clad of one optical fiber, is expected to dramatically increase the capacity. Conventionally, in a multi-core optical fiber, multiple cores are arranged on a square lattice or a hexagonal close-packed lattice.

On the other hand, in multi-core optical fibers, inter-core crosstalk, which is signal interference between adjacent cores, is a limiting factor of transmission capacity. Various methods for reducing this crosstalk between cores have been studied. These studies have confirmed that a heterogeneous multi-core optical fiber in which cores with different structures are adjacent to each other is highly effective in reducing crosstalk between cores (see, for example, Non-Patent Document 1).

Y. Amma et al. , “High-density Multicore Fiber with Heterogeneous Core Arrangement”, In proceedings of OFC 2015, Th4C. 4 (2015)

However, even if the conventional multi-core optical fiber includes core A with strong light confinement and core B with weak light confinement, the core center-cladding edge distance is optimized for core B with weak light confinement. , the effect of suppressing crosstalk between cores was limited.

Description will be made with reference to FIG. FIG. 1 shows the structure of a related multi-core optical fiber. In FIG. 1, 20 is a multi-core optical fiber and 21 is a clad. In the cladding 21 of the multi-core optical fiber 20, a plurality of cores A (white circles) with strong optical confinement and a plurality of cores B (gray circles) with weak optical confinement are alternately arranged in a hexagonal close-packed lattice. It is As the core center-cladding edge distance Topt, the optimal core center-cladding edge distance Tc(B) for the core B with weak light confinement is set. Therefore, the core center-to-cladding edge distance Tc(A)<Topt, which is optimal for the core A with strong light confinement, is established, and there is a problem that the effect of suppressing crosstalk between cores is limited.

The present disclosure has been made in view of the above circumstances, and aims to improve the effect of suppressing inter-core crosstalk in a multi-core optical fiber.

Two or more types of cores of the multi-core optical fiber are arranged at a core center-cladding end distance suitable for each type of core.

Specifically, the multi-core optical fiber of the present disclosure includes:
One or more cores of two or more types with different core refractive indices or different core radii in the clad,
The core center-cladding edge distance is different for each type of the core.

Specifically, in the multi-core optical fiber of the present disclosure, the core with strong light confinement has a core center-cladding edge distance shorter than the core with weak light confinement. Characterized by

Specifically, the multi-core optical fiber of the present disclosure is characterized by being arranged on a hexagonal close-packed lattice with different lattice intervals for each type of core.

Specifically, the multi-core optical fiber of the present disclosure is characterized in that each core type is arranged on a square lattice with a different lattice interval.

Specifically, the multi-core optical fiber of the present disclosure is characterized in that the cores are arranged at equal intervals on a circular ring having a different radius for each core type.

Specifically, the multi-core optical fiber of the present disclosure includes:
The cladding has a diameter of 125 μm,
Three cores of two types are arranged,
The effective cross-sectional area of light in the LP01 mode of each core at a wavelength of 1550 nm is 80 μm ² or more,
Inter-core crosstalk at a wavelength of 1550 nm in the LP01 mode of each core is −40 dB/km or less,
The excess loss at a wavelength of 1565 nm of the LP01 mode of each core is 0.01 dB/km or less,
The cutoff wavelength of the LP11 mode of each core is 1530 nm or less.

Specifically, the multi-core optical fiber of the present disclosure includes:
The cladding has a diameter of 125 μm,
Four cores of two types are arranged,
The effective cross-sectional area of light in the LP01 mode of each core at a wavelength of 1550 nm is 80 μm ² or more,
Inter-core crosstalk at a wavelength of 1550 nm in the LP01 mode of each core is −19 dB/km or less,
The excess loss at a wavelength of 1565 nm of the LP01 mode of each core is 0.01 dB/km or less,
The cutoff wavelength of the LP11 mode of each core is 1530 nm or less.

The multi-core optical fiber of the present disclosure can improve the effect of suppressing crosstalk between cores.

Fig. 3 shows the structure of a related multi-core optical fiber; 1 is a diagram showing an example of the structure of a multi-core optical fiber of the present disclosure; FIG. 1 is a diagram showing an example of the structure of a multi-core optical fiber of the present disclosure; FIG. 1 is a diagram showing an example of the structure of a multi-core optical fiber of the present disclosure; FIG. 1 is a diagram showing an example of the structure of a multi-core optical fiber of the present disclosure; FIG. FIG. 2 is a diagram showing an example of characteristics of a multi-core optical fiber of the present disclosure; FIG. FIG. 2 is a diagram showing an example of characteristics of a multi-core optical fiber of the present disclosure; FIG.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited to the embodiments shown below. These implementation examples are merely illustrative, and the present disclosure can be implemented in various modified and improved forms based on the knowledge of those skilled in the art. In addition, in this specification and the drawings, constituent elements having the same reference numerals are the same as each other.

(Embodiment 1)
An example of the structure of the multi-core optical fiber of the present disclosure is shown in FIG. In FIG. 2, 10 is a multi-core optical fiber and 11 is a clad. Here, as an example, a configuration in which two types of cores having different core refractive indices and different core radii are arranged is shown. The larger the core radius, the stronger the light confinement, and the larger the core refractive index, the stronger the light confinement. Either or both of the core refractive index and core radius are adjusted to achieve the desired optical confinement. The core center-cladding edge distance Tc of core A ensures sufficiently low loss in core A and core B when core B (gray circle) has weaker optical confinement than core A (white circle). For (A) and the core center-to-cladding edge distance Tc(B) of core B, Tc(A)<Tc(B).

In the multi-core optical fiber of the present disclosure, core A and core B are arranged such that the core center-cladding edge distances are Tc(A) and Tc(B), respectively. Here, core A and core B are arranged so that the core center-to-clad edge distances are Tc(A) and Tc(B), respectively, but they may be arranged at longer distances.

In the multi-core optical fiber of the present disclosure, by arranging the cores at the optimum core center-to-clad edge distance for each type of core, there is a margin in the distance between the cores, so the effect of suppressing crosstalk between cores can be improved. .

(Embodiment 2)
An example of the structure of the multi-core optical fiber of the present disclosure is shown in FIG. In FIG. 3, 10 is a multi-core optical fiber and 11 is a clad. Here, as an example, two types of cores having different core refractive indices and different core radii are arranged. The core center-cladding edge distance Tc of core A ensures sufficiently low loss in core A and core B when core B (gray circle) has weaker optical confinement than core A (white circle). For (A) and the core center-cladding edge distance Tc(B) of core B, Tc(A)<Tc(B).

Three cores A with strong light confinement are arranged on a hexagonal close-packed lattice with a wide lattice spacing, and three cores B with weak light confinement are arranged on a hexagonal close-packed lattice with a narrow lattice spacing. A hexagonal close-packed lattice with a wide lattice spacing and a hexagonal close-packed lattice with a narrow lattice spacing have the same inclination, and cores A and cores B are alternately arranged in the angular direction. Here, core A and core B are arranged so that the core center-to-clad edge distances are Tc(A) and Tc(B), respectively, but they may be arranged at longer distances. Also, although the arrangement of two types of cores has been shown, three or more types of cores may be arranged.

When six cores A with strong light confinement are arranged on a hexagonal close-packed lattice with a wide lattice spacing, and six cores B with weak light confinement are arranged on a hexagonal close-packed lattice with a narrow lattice spacing, the lattice spacing is A hexagonal close-packed lattice with a wide lattice spacing and a hexagonal close-packed lattice with a narrow lattice spacing have an inclination of 30 degrees, and cores A and cores B are arranged on each hexagonal close-packed lattice. Also, three or more hexagonal close-packed lattices with different lattice intervals may be used.

In the multi-core optical fiber of the present disclosure, by arranging the cores at the optimum core center-to-clad edge distance for each type of core, there is a margin in the distance between the cores, so the effect of suppressing crosstalk between cores can be improved. .

(Embodiment 3)
An example of the structure of the multi-core optical fiber of the present disclosure is shown in FIG. In FIG. 4, 10 is a multi-core optical fiber and 11 is a clad. Here, as an example, two types of cores having different core refractive indices and different core radii are arranged. The core center-cladding edge distance Tc of core A ensures sufficiently low loss in core A and core B when core B (gray circle) has weaker optical confinement than core A (white circle). For (A) and the core center-cladding edge distance Tc(B) of core B, Tc(A)<Tc(B).

Five cores A with strong light confinement are arranged on a square lattice with a wide lattice interval and in the center, and four cores B with weak light confinement are arranged on a square lattice with a narrow lattice interval. A square lattice with a wide lattice interval and a square lattice with a narrow lattice interval have an inclination of 45 degrees, and cores A and cores B are alternately arranged in the angular direction. Here, core A and core B are arranged so that the core center-to-clad edge distances are Tc(A) and Tc(B), respectively, but they may be arranged at longer distances. Also, although the arrangement of two types of cores has been shown, three or more types of cores may be arranged.

Although the core A is arranged at the center of the multi-core optical fiber 10 in FIG. 4, the core may not be arranged at the center. Also, three or more square lattices with different lattice intervals may be used.

In the multi-core optical fiber of the present disclosure, by arranging the cores at the optimum core center-to-clad edge distance for each type of core, there is a margin in the distance between the cores, so the effect of suppressing crosstalk between cores can be improved. .

(Embodiment 4)
An example of the structure of the multi-core optical fiber of the present disclosure is shown in FIG. In FIG. 5, 10 is a multi-core optical fiber and 11 is a clad. Here, as an example, two types of cores having different core refractive indices and different core radii are arranged. The core center-cladding edge distance Tc of core A ensures sufficiently low loss in core A and core B when core B (gray circle) has weaker optical confinement than core A (white circle). For (A) and the core center-cladding edge distance Tc(B) of core B, Tc(A)<Tc(B).

Four cores A with strong light confinement are arranged on a ring with a large radius at equal intervals, and four cores B with weak light confinement are arranged on a ring with a small radius at equal intervals. The cores A and B are arranged alternately in the angular direction. Here, core A and core B are arranged so that the core center-to-clad edge distances are Tc(A) and Tc(B), respectively, but they may be arranged at longer distances. Also, although the arrangement of two types of cores has been shown, three or more types of cores may be arranged.

Although four cores A and four cores B are arranged in FIG. 5, five or more of each may be arranged. Alternatively, it may be arranged at the center of the multi-core optical fiber 10 . In the case of FIG. 5, core A is arranged at the center of multi-core optical fiber 10 .

In the multi-core optical fiber of the present disclosure, by arranging the cores at the optimum core center-to-clad edge distance for each type of core, there is a margin in the distance between the cores, so the effect of suppressing crosstalk between cores can be improved. .

(Embodiment 5)
FIG. 6 shows an example of the characteristics of the multicore optical fiber of the present disclosure. 3 shows an example of crosstalk characteristics between cores with respect to Tc(B) at a wavelength of 1550 nm for a six-core configuration in which three cores of two types with different core radii and core refractive indices are arranged in the multi-core optical fiber according to FIG. . Here, Tc(A)=30 μm. The clad diameter is 125 μm.

The core radius and core refractive index of each core are such that the effective cross-sectional area of light at a wavelength of 1550 nm in the LP01 mode of each core is 80 μm ² or more, and the excess loss at a wavelength of 1565 nm in the LP01 mode of each core is 0.01 dB/km or less. , and the cutoff wavelength of the LP11 mode of each core is set to 1530 nm or less. Core B has a smaller normalized frequency than core A. Tc(B)=30 μm is a conventional heterogeneous multi-core optical fiber, and by setting 37 μm≧Tc(B)≧32 μm, the crosstalk becomes −40 dB/km or less.

In the multi-core optical fiber of the present disclosure, different Tc(A) and Tc(B) can improve the effect of suppressing inter-core crosstalk compared to conventional heterogeneous multi-core optical fibers. Here, the core structure has an excess loss of 0.01 dB/km at a wavelength of 1565 nm, but it is also possible to optimize the core structure and have an excess loss of 0.01 dB/km at a wavelength of 1625 nm.

(Embodiment 6)
FIG. 7 shows an example of the characteristics of the multi-core optical fiber of the present disclosure. FIG. 5 shows an example of inter-core crosstalk characteristics with respect to Tc(B) at a wavelength of 1550 nm for an 8-core configuration in which four cores of two types with different core radii and core refractive indices are arranged in the multi-core optical fiber according to FIG. . Here, Tc(A)=30 μm. The clad diameter is 125 μm.

The core radius and core refractive index of each core are such that the effective cross-sectional area of light at a wavelength of 1550 nm in the LP01 mode of each core is 80 μm ² or more, and the excess loss at a wavelength of 1565 nm in the LP01 mode of each core is 0.01 dB/km or less. , and the cutoff wavelength of the LP11 mode of each core is set to 1530 nm or less. Core B has a smaller normalized frequency than core A. Tc(B)=30 μm is a conventional heterogeneous multi-core optical fiber, and by setting 37 μm≧Tc(B)≧32 μm, the crosstalk becomes −19 dB/km or less.

In the multi-core optical fiber of the present disclosure, different Tc(A) and Tc(B) can improve the effect of suppressing inter-core crosstalk compared to conventional heterogeneous multi-core optical fibers. Here, the core structure has an excess loss of 0.01 dB/km at a wavelength of 1565 nm, but it is also possible to optimize the core structure and have an excess loss of 0.01 dB/km at a wavelength of 1625 nm.

As described above, the multi-core optical fiber of the present disclosure can improve the effect of suppressing crosstalk between cores compared to conventional heterogeneous multi-core optical fibers.

The present disclosure can be applied to the information and communications industry.

10: multicore optical fiber 11: clad 20: multicore optical fiber 21: clad

Claims (7)

One or more cores of two or more types with different core refractive indices or different core radii in the clad,
A multi-core optical fiber, wherein the core center-cladding edge distance differs for each type of the core. 2. The multi-core optical fiber according to claim 1, wherein, among the cores, the core with strong light confinement has a core center-cladding edge distance shorter than the core center-cladding edge distance of the core with weak light confinement. 3. The multi-core optical fiber according to claim 1, wherein the cores are arranged on a hexagonal close-packed lattice having different lattice intervals for each type of core. 3. The multi-core optical fiber according to claim 1, wherein the cores are arranged on a square lattice with different lattice intervals for each core type. 3. The multi-core optical fiber according to claim 1, wherein the cores are arranged at equal intervals on a circular ring having a different radius for each core type. The cladding has a diameter of 125 μm,
Three cores of two types are arranged,
The effective cross-sectional area of light in the LP01 mode of each core at a wavelength of 1550 nm is 80 μm ² or more,
Inter-core crosstalk at a wavelength of 1550 nm in the LP01 mode of each core is −40 dB/km or less,
The excess loss at a wavelength of 1565 nm of the LP01 mode of each core is 0.01 dB/km or less,
6. The multi-core optical fiber according to claim 3, wherein the LP11 mode cutoff wavelength of each core is 1530 nm or less. The cladding has a diameter of 125 μm,
Four cores of two types are arranged,
The effective cross-sectional area of light in the LP01 mode of each core at a wavelength of 1550 nm is 80 μm ² or more,
Inter-core crosstalk at a wavelength of 1550 nm in the LP01 mode of each core is −19 dB/km or less,
The excess loss at a wavelength of 1565 nm of the LP01 mode of each core is 0.01 dB/km or less,
6. The multi-core optical fiber according to claim 4, wherein the LP11 mode cutoff wavelength of each core is 1530 nm or less.

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