Weak coupling 19-core 32-mode groove auxiliary type ring core optical fiber

Abstract

The invention belongs to the field of optical fiber communication, and particularly discloses a weak coupling 19-core 32-mode groove auxiliary type ring core optical fiber, and the number of available radial first-order and angular l-order space channels can reach 380 (l is larger than or equal to 1). Each ring core fiber core is composed of a central layer fiber core, a ring core layer fiber core, an inner cladding and a low-refractive-index annular groove layer, and the 19 fiber cores are distributed in the outer cladding around the double-layer ring according to the center, so that the uniformity and consistency of the multi-core optical fiber are ensured, the preparation complexity of the optical fiber is reduced, the tolerance of a preparation process error is increased, and the production efficiency is improved. Under a limited cladding diameter, appropriate core spacing and low refractive index trench layer parameters are set to suppress inter-core crosstalk so as to ensure that all radial first-order modules can perform weak coupling communication.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber communication, and more specifically, to a weakly coupled 19-core 32-mode groove-assisted ring-core optical fiber. Background Art

[0002] With the development of 5G services and the Internet of Things, the information transmission capacity required by the world is growing at an exponential rate. In the future, Peta-b / s-level large-capacity systems will be needed to meet the growing capacity demand. However, the transmission capacity of traditional single-mode fiber communication systems has approached its theoretical limit - the nonlinear Shannon limit (~100TB / s), and it is difficult to continue to meet the rapidly developing interconnection needs. At present, the spatial mode of light waves is the only dimension that has not been widely used. Therefore, in order to surpass the nonlinear Shannon limit of single-mode fiber communication systems and solve the bottleneck problem of optical communication technology, it is urgent to study new principles and technologies of space-division multiplexing (SDM) systems.

[0003] Few-mode Multi-core fiber (FM-MCF) is one of the transmission media in the SDM system. It can utilize both spatial and mode dimensions at the same time. It has unparalleled advantages in capacity improvement space compared to other optical fiber technologies, while reducing energy consumption and cost per unit capacity. However, the core challenge faced by large-capacity SDM systems is the increase in signal processing costs caused by multi-dimensional channel crosstalk. That is, with the increase in the number of cores and the number of mode channels per core in FM-MCF, the degree of coupling crosstalk between many channels intensifies, resulting in an exponential increase in the complexity of the multiple-input multiple-output (MIMO) compensation algorithm at the receiving end, which restricts the expansion of the transmission capacity of SDM technology based on FM-MCF. In addition, existing FM-MCFs that support high spatial channel counts usually increase the number of cores at the cost of a cladding diameter greater than 200μm or even up to 440μm, while the cores only support a few low differential module delay modes. However, under this scheme, the MIMO scale at the receiving end still requires 2N×2N MIMO (N is the mode) to compensate for all received modes. And a large cladding diameter (especially more than 250μm) will make the optical fiber lose its toughness, reducing the mechanical stability and life of the optical fiber. Therefore, it is urgent to study revolutionary new principles and technologies for the transmission media of space division multiplexing systems.

[0004] In order to achieve weak coupling transmission of the inter-mode channel, the effective refractive index difference (Δn eff ) in 1×10 -3Above. In the multiplexing technology based on the orbital angular momentum mode (OAM) mode, the radial first-order angular |l|-order OAM mode field intensity distribution is a one-dimensional radial distribution, which is easy to match the circularly symmetric structure of the ring-core OAM fiber, so it is easy to suppress the crosstalk between modes by adjusting the radial refractive index of the fiber. The degenerate mode in its radial first-order angular |l|-order OAM module is always 4. As long as the weak coupling between the modules is controlled, a small-scale 4*4 MIMO can be used at the receiving end to recover the signal. Most optical fibers that support OAM modes have a ring-core step refractive index distribution structure. In addition, in order to achieve weak coupling transmission of spatial channels, a larger core spacing, a reasonable core arrangement method and a low refractive index structure are required to suppress the crosstalk between adjacent cores. Due to the limitation of the cladding size and the need for a large core spacing, it is difficult to further expand the number of cores in the FM-MCF. However, in the FM-MCF technology solution that supports OAM multiplexing, if the inter-mode / inter-core crosstalk can be kept at a very low level, additional MIMO compensation of inter-module and inter-core channels can be avoided, and only 4*4 MIMO is needed to restore the 4 degenerate modes within the module. Summary of the invention

[0005] In order to overcome at least one of the defects of the prior art, the present invention provides a weakly coupled 19-core 32-mode groove-assisted ring-core optical fiber.

[0006] The present invention aims to solve the above technical problems at least to a certain extent.

[0007] In order to solve the above technical problems, the technical solution of the present invention is as follows:

[0008] A weakly coupled 19-core 32-mode groove-assisted ring core optical fiber comprises: an outer cladding and 19 groove-assisted ring cores, wherein the groove-assisted ring core is placed at the center of the outer cladding, an inner groove-assisted ring core is arranged at the periphery of the center of the outer cladding, an outer groove-assisted ring core is arranged at the periphery of the inner groove-assisted ring core, and a preset distance is provided between the two layers of groove-assisted ring cores.

[0009] Furthermore, an outer groove-assisted ring core is provided on the periphery of the inner groove-assisted ring core, comprising:

[0010] The outer groove-assisted ring core is arranged on a circle with a radius of Λ / (2*sin15°) and a center of the outer cladding. The distance between the outer groove-assisted ring core and the inner groove-assisted ring core is Λ.

[0011] Furthermore, 6 groove-assisted ring cores are arranged at the periphery of the center position of the outer cladding, and the remaining 12 groove-assisted ring cores are arranged at the periphery of the inner groove-assisted ring cores.

[0012] Furthermore, the groove-assisted ring core includes, from the inside to the outside, a central layer, a ring core layer, an inner cladding layer and an annular groove layer.

[0013] Furthermore, the materials of the inner cladding and the outer cladding are both fused silica, and the refractive index of the inner cladding and the outer cladding is the same.

[0014] Furthermore, the groove-assisted ring core supports multiple orbital angular momentum modes, including: OAM with a degenerate state of 2 0,1 、OAM 0,2 and the OAM of the degenerate state is 4 1,1 、OAM 2,1 、OAM 3,1 、OAM 1,2 、OAM 4,1 、OAM 2,2 、OAM 5,1 model.

[0015] Further, the multiple orbital angular momentum modes operate in the C+L band.

[0016] Furthermore, the refractive index of the groove-assisted ring core is distributed in a step-type manner.

[0017] Furthermore, the refractive index difference Δ1 between the central layer and the outer cladding is 0.83%±0.01%, the radius r1 of the central layer is 1.8±0.1 μm, the refractive index difference Δ2 between the annular core layer and the outer cladding is 1.3%±0.01%, and the outer radius r2 of the annular core layer is 8.9±0.1 μm.

[0018] Furthermore, the refractive index difference between the annular groove layer and the outer cladding layer is Δ tr It is -0.6%±0.01%, the inner radius r3 of the annular groove layer is 11.9±0.1μm, and the outer radius r4 of the annular groove layer is 16.9±0.1μm.

[0019] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0020] In a weakly coupled 19-core 32-mode groove-assisted ring-core optical fiber provided by the present invention, 19 fiber cores are distributedly deployed in the outer cladding in a double-layer ring around the center to ensure the uniformity and consistency of the optical fiber, reduce the complexity of optical fiber preparation, and increase the tolerance of preparation process errors. Under a limited cladding diameter, appropriate core spacing and low-refractive index groove layer parameters are set to suppress inter-core crosstalk to ensure that all radial first-order modes can perform weakly coupled communication. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a core annular cross-sectional view of the weakly coupled 19-core 32-mode ring-core optical fiber of the present invention;

[0022] Figure 2 A cross-sectional view of a hexagonal deployment of the cores of a weakly coupled 19-core 32-mode ring-core optical fiber for comparison with the present embodiment;

[0023] Figure 3 is a diagram showing the relationship between core crosstalk and core spacing under different deployment modes described in this embodiment;

[0024] Figure 4 A cross-sectional diagram of the refractive index distribution of one of the cores in the 19-core 32-mode ring-core optical fiber of the present invention;

[0025] Figure 5 This is a schematic diagram of the working range of the weakly coupled 19-core 32-mode ring-core optical fiber described in this embodiment. DETAILED DESCRIPTION

[0026] The drawings are for illustrative purposes only and should not be construed as limiting the present patent;

[0027] In order to better illustrate the present embodiment, some parts in the drawings may be omitted, enlarged or reduced, and do not represent the size of the actual product;

[0028] It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0029] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0030] Example 1

[0031] A weakly coupled 19-core 32-mode groove-assisted ring-core optical fiber, such as Figure 1 As shown, it includes: an outer cladding 5 and 19 groove-assisted ring cores, wherein the groove-assisted ring core is placed at the center of the outer cladding 5, an inner layer of groove-assisted ring cores is arranged at the periphery of the center of the outer cladding 5, an outer layer of groove-assisted ring cores is arranged at the periphery of the inner layer of groove-assisted ring cores, and a preset distance is set between the two layers of groove-assisted ring cores.

[0032] The present invention proposes a weakly coupled 19-core 32-mode groove-assisted ring-core optical fiber, in which the 18 cores in the optical fiber are distributed in a double-layer ring around the center in the outer cladding to ensure the uniformity and consistency of the multi-core optical fiber, reduce the complexity of optical fiber preparation, and increase the tolerance of preparation process errors.

[0033] Example 2

[0034] This embodiment further discloses the following contents based on the embodiment 1:

[0035] The outer circumference of the inner groove auxiliary type ring core is provided with an outer groove auxiliary type ring core, comprising:

[0036] The outer groove-assisted ring core is arranged on a circle with a radius of Λ / (2*sin15°) and a center at the center of the outer cladding 5. The distance between the outer groove-assisted ring core and the inner groove-assisted ring core is Λ, where Λ refers to the core spacing between adjacent fiber cores, and the Λ value is 44μm.

[0037] A groove-assisted annular fiber core is placed at the cross-sectional geometric center of the outer cladding 5, and the remaining 18 fiber cores are deployed in a double-layer annular arrangement. The number of the first layer of fiber cores is 6, and the fiber cores of this layer are evenly arranged on a circle with the cross-sectional geometric center of the outer cladding 5 as the center and the radius as the core spacing Λ, and the number of the second layer of fiber cores is 12.

[0038] In the specific implementation process, in order to ensure the mechanical reliability of the optical fiber, the cladding size of the optical fiber should be controlled within 250μm as much as possible, but the bending loss of the core and the crosstalk between cores need to be kept at a low level to avoid the impact of compensating for the crosstalk between cores at the receiving end. Considerations of the cladding size and the core spacing have largely limited the number of cores in the cladding. When the annular groove layer is introduced, the optical fiber accommodates 19 cores, the cladding diameter is 250μm, and the core spacing Λ is 44μm.

[0039] Six groove-assisted ring cores are arranged at the periphery of the center position of the outer cladding 5 , and the remaining 12 groove-assisted ring cores are arranged at the periphery of the inner groove-assisted ring cores.

[0040] In the specific implementation process, the present invention adopts the above-mentioned optical fiber arrangement method in order to reduce the difficulty of optical fiber preparation and increase the tolerance of preparation process errors. Figure 2 The hexagonal arrangement shown is a typical arrangement of multi-core optical fibers. However, the distances from the outer core to the outermost layer of the cladding under the hexagonal arrangement structure are different, resulting in uneven stress and ineffective use of the cladding area. Figure 3 The graphs show the variation of crosstalk between the outer cores caused by adjacent cores in the two-core model, hexagonal arrangement and annular arrangement as the core spacing changes. The comparison shows that the annular arrangement method is superior, which can ensure the uniformity and consistency of the multi-core optical fiber, reduce the complexity of optical fiber preparation, and increase the tolerance of preparation process errors.

[0041] The groove-assisted toroidal core comprises, from inside to outside, a central layer 1, a toroidal core layer 2, an inner cladding layer 3 and an annular groove layer 4 in sequence.

[0042] The materials of the inner cladding 3 and the outer cladding 5 in each ring core have the same refractive index.

[0043] like Figure 4As shown, the radii of the central layer 1, the annular core layer 2, the inner cladding layer 3 and the annular groove layer 4 are r1, r2, r3 and r4 respectively, the refractive index difference between the central layer 1 and the outer cladding layer 5 is Δ1; the refractive index difference between the annular core layer 2 and the outer cladding layer 5 is Δ2, and the refractive index difference between the annular groove layer 4 and the outer cladding layer 5 is Δ tr , the material of the outer cladding 5 is fused silica.

[0044] The refractive index of the groove-assisted ring core is distributed in a step-type manner.

[0045] The groove-assisted ring core supports multiple orbital angular momentum modes, including: OAM with a degenerate state of 2 0,1 、OAM 0,2 and the OAM of the degenerate state is 4 1,1 、OAM 2,1 、OAM 3,1 、OAM 1,2 、OAM 4,1 、OAM 2,2 and OAM 5,1 model.

[0046] In the specific implementation process, OAM can be reduced by adjusting the structural parameters of the core layer. 01 and OAM 11 The overlap integral between them is controlled and the isolation of each order is controlled within a suitable range to ensure that all radial first-order modules can perform weakly coupled communication.

[0047] Example 3

[0048] This embodiment further discloses the following contents based on Embodiments 1 and 2:

[0049] The refractive index difference Δ1 between the central layer 1 and the outer cladding 5 is 0.83%±0.01%, the radius r1 of the central layer 1 is 1.8±0.1μm, the refractive index difference Δ2 between the annular core layer 2 and the outer cladding 5 is 1.3%±0.01%, and the outer radius r2 of the annular core layer 2 is 8.9±0.1μm.

[0050] The doping concentrations of the central layer 1 and the ring core layer 2 are different. The ring core layer 2 mainly regulates the number of modes supported by the optical fiber under weak guidance conditions and ensures that each module can operate in the C+L band. Figure 3 Schematic diagram of the working range of 32-mode ring core optical fiber. The horizontal axis is the outer radius r3 of the ring core layer 2, and the vertical axis is the refractive index difference Δ2 between the ring core layer 2 and the outer cladding.

[0051] The working range of ring core fiber is as follows Figure 5 As shown, the solid circle line represents the OAM at a wavelength of 1530nm 6,1 Mode cutoff line, the solid line with asterisks represents OAM at a wavelength of 1625 nm5,1 In order to ensure that the ring core fiber can stably support 32 modes in the C+L band, it is necessary to select the outer radius r3 of the ring core and the refractive index difference Δ in the area sandwiched by these two lines. tr . Figure 3 The solid black line in the middle represents the OAM at a wavelength of 1550 nm. 5,1 Modules and OAM 4,1 Differential mode group delay (DMGD) between modules. The black and white background represents the low-order module OAM at a wavelength of 1550nm. 0,1 With OAM 1,1 Δn between eff When the ring core size is a fixed value, the higher the doping concentration, the lower the OAM of the low-cost module. 0,1 With OAM 1,1 Δn eff The larger the value, the more effective it is in reducing the inter-mode crosstalk of low-order modules. 4,1 and OAM 5,1 The DMGD between the two will also increase, resulting in an increase in the MIMO complexity at the receiving end. In the working range, it is necessary to consider Δn eff and DMGD to find an optimal solution.

[0052] The refractive index of the center area of ​​the traditional ring-core fiber is compressed into the cladding refractive index, which will inevitably lead to more serious mode field overlap between low-order modes (especially OAM 0,1 With OAM 1,1 Therefore, it is necessary to raise the refractive index of the center layer to alleviate this phenomenon, and at the same time increase the Δn between modules. eff The central layer 1 is mainly used to adjust the Δn between modules. eff , control the crosstalk between modules of each order to a low level and alleviate the crosstalk between low-order modules (especially OAM 0,1 With OAM 1,1 The main parameters to be controlled are the radius r1 and doping concentration Δ1 of the center layer 1.

[0053] Table 1 Effective refractive index difference at wavelengths of 1550nm and 1625nm

[0054]

[0055] Table 1 shows the effective refractive index difference Δn between the OAM modules of the trench-assisted ring-core optical fiber of this embodiment at 1550nm and 1625nm respectively. eff . Minimum Δn between modules eff In OAM 0,2 and OAM 3,1 Between, Δn effAt 1550nm and 1625nm, they are 0.8×10 -3 and 1.045×10 -3 , due to radial high-order mode OAM 0,2 and radial first-order module OAM 3,1 The mode fields of the two modes are quite different, and the degree of overlap between the mode fields is very small. Therefore, their power coupling coefficient h is also very small, which does not affect the communication performance between the weakly coupled radial first-order modules.

[0056] The refractive index difference between the annular groove layer 4 and the outer cladding layer 5 is Δ tr It is -0.6%±0.01%, and the inner radius r3 of the annular groove layer 4 and the outer radius r4 of the annular groove layer 4 are 11.9±0.1 μm and 16.9±0.1 μm respectively.

[0057] In the specific implementation process, the annular groove layer is added to the outside of the core to suppress the overlap of the mode field between the cores, thereby achieving the effect of suppressing the crosstalk between the cores. Since the cladding diameter is limited to 250μm, it is necessary to adjust the structural parameters of the annular groove layer. In order to achieve high-capacity optical interconnection with ultra-low signal processing complexity, the present invention explores the limits of the number of cores and the number of modes within the limited optical fiber aperture resources based on the mechanism of optical fiber orbital angular momentum. Since the fiber cladding diameter is too large to reduce the toughness and life of the optical fiber, the cladding diameter of 250μm is often considered to be the critical value of the multi-core and few-mode optical fiber size design. Therefore, the 19-core 32-mode groove-assisted ring-core optical fiber disclosed in the present invention is already the limit number of cores and the number of modes under the above-mentioned physical limitations. In view of the fact that the low transmission loss of the optical fiber is an important indicator for the optical communication system, the doping concentration of the core is limited. Under the above-mentioned physical limitations, the present invention solves at least one defect of the existing large-capacity space-division multiplexing optical fiber communication technology by increasing the number of mode channels in the core, without relying too much on the number of cores to expand, so the present invention proposes the most physical limitation technical solution.

[0058] The same or similar reference numerals correspond to the same or similar components;

[0059] The terms used in the drawings to describe positional relationships are only used for illustrative purposes and should not be construed as limiting this patent;

[0060] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A weakly coupled 19-core 32-mode groove-assisted ring-core optical fiber, characterized in that: include: An outer cladding (5) and 19 groove-assisted ring cores, wherein the groove-assisted ring core is placed at the center of the outer cladding (5), an inner layer of groove-assisted ring cores is arranged at the periphery of the center of the outer cladding (5), an outer layer of groove-assisted ring cores is arranged at the periphery of the inner layer of groove-assisted ring cores, and a preset distance is provided between the two layers of groove-assisted ring cores.

2. The weakly coupled 19-core 32-mode groove-assisted ring-core optical fiber according to claim 1, characterized in that: The outer circumference of the inner groove auxiliary type ring core is provided with an outer groove auxiliary type ring core, comprising: The outer groove-assisted ring core is arranged on a circle with a radius of Λ / (2*sin15°) and a center of the outer cladding (5). The distance between the outer groove-assisted ring core and the inner groove-assisted ring core is Λ.

3. The weakly coupled 19-core 32-mode groove-assisted ring-core optical fiber according to claim 2, characterized in that: Six groove-assisted ring cores are arranged on the periphery of the center position of the outer cladding (5), and the remaining 12 groove-assisted ring cores are arranged on the periphery of the inner groove-assisted ring cores.

4. The weakly coupled 19-core 32-mode groove-assisted ring-core optical fiber according to any one of claims 1 to 3, characterized in that: The groove-assisted ring core comprises, from the inside to the outside, a central layer (1), a ring core layer (2), an inner cladding layer (3) and an annular groove layer (4).

5. The weakly coupled 19-core 32-mode groove-assisted ring-core optical fiber according to claim 4, characterized in that: The materials of the inner cladding (3) and the outer cladding (5) are both fused silica, and the refractive index of the inner cladding (3) and the outer cladding (5) is the same.

6. The weakly coupled 19-core 32-mode groove-assisted ring-core optical fiber according to claim 4, characterized in that: The groove-assisted ring core supports multiple orbital angular momentum modes, including: OAM with a degenerate state of 2 0,1 、OAM 0,2 and OAM with a degenerate state of 4 1,1 、OAM 2,1 、OAM 3,1 、OAM 1,2 、OAM 4,1 、OAM 2,2 、OAM 5,1 model.

7. The weakly coupled 19-core 32-mode groove-assisted ring-core optical fiber according to claim 6, characterized in that: The multiple orbital angular momentum modes operate in the C+L band.

8. The weakly coupled 19-core 32-mode groove-assisted ring-core optical fiber according to claim 4, characterized in that: The refractive index of the groove-assisted ring core is distributed in a step-type manner.

9. The weakly coupled 19-core 32-mode groove-assisted ring-core optical fiber according to claim 4, characterized in that: The refractive index difference Δ1 between the central layer (1) and the outer cladding (5) is 0.83%±0.01%, the radius r1 of the central layer (1) is 1.8±0.1μm, the refractive index difference Δ2 between the annular core layer (2) and the outer cladding (5) is 1.3%±0.01%, and the outer radius r2 of the annular core layer (2) is 8.9±0.1μm.

10. The weakly coupled 19-core 32-mode groove-assisted ring-core optical fiber according to claim 9, characterized in that: The refractive index difference Δ between the annular groove layer (4) and the outer cladding layer (5) tr The value is -0.6%±0.01%, the inner radius r3 of the annular groove layer (4) is 11.9±0.1 μm, and the outer radius r4 of the annular groove layer (4) is 16.9±0.1 μm.

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