阅读说明：本技术 一种多波段模式弱耦合的双层纤芯光纤 (Double-layer fiber core optical fiber with multiband mode weak coupling ) 是由 刘洁 祝荷 莫舒淇 张景行 余思远 于 2021-09-09 设计创作，主要内容包括：本发明涉及光通信技术领域,公开了一种多波段模式弱耦合的双层纤芯光纤,包括由内至外依次设置的中心纤芯、环形纤芯和包层,所述环形纤芯的折射率均大于所述中心纤芯、所述包层的折射率,所述中心纤芯的折射率大于所述包层的折射率,所述环形纤芯的宽度大于所述中心纤芯的直径,可增加轨道角动量角相零阶(径向一阶)和角相一阶(径向一阶)模式的有效折射率差,有效抑制低阶模式间的串扰,增加光纤的传输数据容量。并且,在光通信C波段、L波段以及O波段支持的所有非简并传导模组之间的有效折射率差均大于1×10～(-3),且在三个通信波段均具有超低模式串扰特性,均可以独立采用强度调制直接检测的方式进行光信号传输,无需相干检测加MIMO-DSP辅助。(The invention relates to the technical field of optical communication, and discloses a multiband-mode weakly-coupled double-layer fiber core optical fiber which comprises a central fiber core, an annular fiber core and a cladding which are sequentially arranged from inside to outside, wherein the refractive indexes of the annular fiber core are respectively greater than those of the central fiber core and the cladding, the refractive index of the central fiber core is greater than that of the cladding, the width of the annular fiber core is greater than the diameter of the central fiber core, so that the effective refractive index difference of orbital angular momentum angular phase zeroth order (radial first order) and angular phase first order (radial first order) modes can be increased, the crosstalk among low-order modes can be effectively inhibited, and the transmission data capacity of the optical fiber can be increased. And the effective refractive index difference among all nondegenerate conduction modules supported by the optical communication C-band, L-band and O-band is larger than 1 multiplied by 10 ‑3 And all three communication bands are ultra-lowThe mode crosstalk characteristic can independently adopt an intensity modulation direct detection mode to carry out optical signal transmission without the assistance of coherent detection and MIMO-DSP.)

1. The multiband-mode weakly-coupled double-layer fiber core optical fiber is characterized by comprising a central fiber core (1), an annular fiber core (2) and a cladding (3) which are sequentially arranged from inside to outside, wherein the refractive index of the annular fiber core (2) is larger than that of the central fiber core (1) and that of the cladding (3), the refractive index of the central fiber core (1) is larger than that of the cladding (3), and the width of the annular fiber core (2) is larger than the diameter of the central fiber core (1).

2. The multiband mode weakly-coupled dual-core optical fiber according to claim 1, wherein the relative refractive index difference between the central core (1) and the cladding (3) is not less than 0.4%, and the relative refractive index difference between the annular core (2) and the cladding (3) is not less than 0.8%.

3. The multiband mode weakly-coupled dual-core optical fiber according to claim 2, wherein the relative refractive index difference between the central core (1) and the cladding (3) is 0.415%, and the relative refractive index difference between the ring-shaped core (2) and the cladding (3) is 0.824%.

4. The multiband mode weakly-coupled dual-core optical fiber according to claim 1, wherein the radius of the central core (1) is 0.5 μm to 1.5 μm, and the ring width of the ring-shaped core (2) is 5.5 μm to 8.5 μm.

5. The multiband mode weakly coupled dual core fiber according to claim 4, wherein the radius of the central core (1) is 1.4 μm and the ring width of the ring core (2) is 6.4 μm.

6. The multiband weakly-coupled dual-core optical fiber according to claim 1, wherein the refractive indices of the central core (1) and the annular core (2) are a step index profile or a graded index profile.

7. The multiband mode weakly coupled dual core fiber according to claim 1, wherein the central core (1) and the annular core (2) are both prepared with silica material doped with germanium dioxide or titanium dioxide or phosphorus pentoxide.

8. The multiband weakly coupled dual core fiber of claim 1, wherein the cladding (3) is made of pure silica material.

9. The multiband mode weakly coupled dual-core optical fiber according to claim 1, wherein the cladding (3) is prepared with silica material doped with diboron pentoxide or fluorine.

10. The multiband weakly-coupled dual-mode core fiber of claim 1, wherein the fiber supports a fiber eigenmode, a linear polarization mode, or an orbital angular momentum mode.

Technical Field

The invention relates to the technical field of optical communication, in particular to a multiband mode weakly-coupled double-layer fiber core optical fiber.

Background

With the development of the internet, the demand of people for communication capacity is continuously increasing. At present, due to the influence of the nonlinear effect of optical fibers and the spontaneous radiation noise of optical amplifiers, the capacity increase of commercial single-mode optical fiber communication systems has already met the bottleneck and cannot meet the rapid increase of the future communication capacity requirement. The mode division multiplexing technique uses a plurality of modes as independent transmission channels, and is considered as an effective method for improving the degree of freedom of a spatial domain and enlarging the capacity of a signal. However, for the mode division multiplexing scheme based on few-mode optical fiber, as the system capacity is expanded and the transmission distance is increased, the complexity of the mimo algorithm is also increased to counter the mutual crosstalk between the modes and the inter-mode delay. The mode division multiplexing system of the weak coupling few-mode optical fiber is beneficial to reducing the complexity of a multi-input multi-output algorithm. However, the refractive index profile of the optical fiber supporting the weakly coupled mode division multiplexing system is relatively complex, and is usually designed to have three, six or more core layers to achieve weak coupling between high-order modules, resulting in an increase in the complexity of the manufacturing process. Currently, a ring core optical fiber supporting linear polarization or orbital angular momentum modes has been widely used for a mode division multiplexing system with low multiple input multiple output complexity. Due to the radial limitation of the ring-core fiber, the supported mode radial order is always one. Although ring-core fiber has good scalability to high-order azimuthal modes, there is still strong mode crosstalk between adjacent low-order modes, which greatly limits the number of weakly coupled mode channels available in ring-core fiber-based mode division multiplexing systems.

The conventional ring-core optical fiber is generally provided with a low-refractive-index region in the central region of the optical fiber, and the effective refractive index of the central region is generally equal to that of the cladding, so that the radial order of the supported mode is always one, and the crosstalk between high-order azimuth modes is reduced. However, since the electric field distribution of the orbital angular momentum angular phase zeroth order (first radial order) mode is mainly concentrated in the center of the optical fiber, the effective refractive index of the orbital angular momentum angular phase zeroth order (first radial order) mode is reduced in a low refractive index region at the center of the optical fiber, and crosstalk coupling between the orbital angular momentum angular phase zeroth order (first radial order) mode and an adjacent angular phase first order (first radial order) mode is increased, so that the mode utilization efficiency is low.

Chinese invention patent CN106950644A (published as 2017, 07, 14) discloses a weak guiding ring-shaped optical fiber, which is characterized by comprising: an annular core, a central region and a cladding; a relative refractive index difference between a refractive index of the annular core and a refractive index of the cladding is not more than 1%, and a relative refractive index difference between a refractive index of the annular core and a refractive index of the central region is not more than 1%; the scanning range of the inner ring radius of the annular fiber core is 12-24 mu m, and the scanning range of the ring width is 1-6 mu m; the weak guide ring-shaped structure optical fiber only supports a multi-channel radial first-order mode and is divided into different mode groups; the effective refractive index difference between the first mode group and the other mode groups except the first two mode groups is 2 modes, and the effective refractive index difference between the other mode groups is 4 modes>10^-4. The optical fiber of the patent adopts an annular fiber core design, the inner ring is large, the ring width is small, the effective refractive index of each mode is small, the mode coupling in the transmission process is large, and the crosstalk between modules is large.

Disclosure of Invention

The invention aims to provide a multiband mode weakly-coupled double-layer core optical fiber with low crosstalk between modules.

In order to achieve the above object, the present invention provides a multiband mode weakly-coupled dual-core optical fiber, including a central core, an annular core and a cladding, which are sequentially arranged from inside to outside, wherein the refractive index of the annular core is greater than that of the central core and that of the cladding, the refractive index of the central core is greater than that of the cladding, and the width of the annular core is greater than the diameter of the central core.

Preferably, the relative refractive index difference between the central core and the cladding is not less than 0.4%, and the relative refractive index difference between the annular core and the cladding is not less than 0.8%.

Preferably, the relative refractive index difference between the central core and the cladding is 0.415%; the relative refractive index difference between the annular core and the cladding is 0.824%.

Preferably, the radius of the central core is 0.5 to 1.5 μm, and the ring width of the ring core is 5.5 to 8.5 μm.

Preferably, the radius of the central core is 1.4 μm, and the ring width of the ring core is 6.4 μm.

Preferably, the refractive indices of the central core (1) and the ring core are a step index profile or a graded index profile.

Preferably, the central core and the annular core are both made of silica material doped with germanium dioxide, titanium dioxide or phosphorus pentoxide.

Preferably, the cladding is made of pure silica material.

Preferably, the cladding is made of silica material doped with diboron pentoxide or fluorine.

Preferably, the optical fiber supports a fiber eigenmode, a linear polarization mode or an orbital angular momentum mode.

Compared with the prior art, the invention has the beneficial effects that:

(1) the width of the annular fiber core is larger than the diameter of the central fiber core, and the effective refractive index of orbital angular momentum angular phase zeroth order (radial first order) is adjusted by reducing the size of the central fiber core through increasing the width of the annular fiber core and reducing the diameter of the central fiber core so as to reduce the low refractive index area of the optical fiber center, thereby reducing the crosstalk among low-order modes.

(2) The double-layer fiber core structure optical fiber effectively increases the effective refractive index difference between orbital angular momentum angular phase zeroth order (radial first order) and angular phase first order (radial first order), reduces the inter-mode crosstalk and the multi-input multi-output calculation complexity, and increases the number of available independent modes.

(3) The central fiber core is prepared by the positively doped material, so that the refractive index of the central fiber core can be improved, the effective refractive index of the orbital angular momentum angular phase zeroth order (radial second order) mode can be adjusted in an auxiliary mode, and the crosstalk between the orbital angular momentum angular phase zeroth order (radial second order) mode and an adjacent mode is further reduced.

(4) The effective refractive index difference of the optical fiber of the invention among all nondegenerate conduction modules supported by C wave band, L wave band and O wave band of optical communication is larger than 1 x 10^-3And the transmission of three wave bands can be realized.

Drawings

FIG. 1 is a cross-sectional view and refractive index profile of an optical fiber according to an embodiment of the present invention.

FIG. 2 is a graph showing the variation of the effective refractive index with wavelength for 5 orbital angular momentum modules supported by the optical fiber in the C-band according to the embodiment of the present invention.

FIG. 3 is a graph showing the variation of the effective refractive index with wavelength for 5 orbital angular momentum modules supported by an optical fiber according to an embodiment of the present invention in the L-band.

FIG. 4 is a graph of effective refractive index versus wavelength for 7 orbital angular momentum modules supported in the O-band for an optical fiber in accordance with an embodiment of the present invention.

In the figure, 1-the central core; 2-a ring-shaped fiber core; and 3-cladding.

Detailed Description

The following detailed description of embodiments of the present invention is provided in connection with the accompanying drawings and examples. The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.

In the description of the present invention, it should be noted that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and thus, should not be construed as limiting the present invention.

Referring to FIG. 1, a dual-core optical fiber with weak coupling in multiband mode according to a preferred embodiment of the present invention includes an inside-out claddingThe fiber comprises a central fiber core 1, an annular fiber core 2 and a cladding 3 which are arranged in a secondary mode, wherein the refractive index of the annular fiber core 2 is larger than that of the central fiber core 1 and that of the cladding 3, the refractive index of the central fiber core 1 is larger than that of the cladding 3, and the width of the annular fiber core 2 is larger than the diameter of the central fiber core 1. The width of the annular fiber core 2 is larger than the diameter of the central fiber core 1, and the effective refractive index of orbital angular momentum angular phase zeroth order (first radial order) is adjusted by reducing the size of the diameter of the central fiber core 1 by increasing the width of the annular fiber core 2 so as to reduce the low refractive index area of the optical fiber center, thereby reducing the crosstalk between low-order modes. In addition, the double-layer fiber core structure optical fiber effectively increases the effective refractive index difference between orbital angular momentum angular phase zeroth order (first radial order) and angular phase first order (first radial order), reduces the inter-mode crosstalk and the multi-input multi-output calculation complexity, and increases the number of available independent modes. The fiber structure of this embodiment introduces higher order modes, namely angular phase zeroth order and radial first order. In addition, the effective refractive index difference of the optical fiber of the embodiment among all the nondegenerate guided modules supported by the optical communication C-band, L-band and O-band is larger than 1 × 10^-3And the transmission of three wave bands can be realized. The cross-sectional structure of the optical fiber of this embodiment enables the effective refractive index of each mode supported by the optical fiber in O-band, C-band and L-band to be uniformly distributed, and the effective refractive index difference is greater than 1 × 10^-3And three-band transmission is realized.

Further, the relative refractive index difference between the central core 1 and the cladding 3 is not less than 0.4%, and the relative refractive index difference between the annular core 2 and the cladding 3 is not less than 0.8%. In the present embodiment, the relative refractive index difference between the central core 1 and the cladding 3 is 0.415%, and the relative refractive index difference between the annular core 2 and the cladding 3 is 0.824%.

Further, the radius of the central core 1 is 0.5 μm to 1.5 μm, and the ring width of the ring core 2 is 5.5 μm to 8.5 μm. The radius of the central core 1 of this embodiment is 1.4 μm and the ring width of the ring core 2 is 6.4 μm.

Alternatively, the refractive indices of the central core 1 and the annular core 2 are a step index profile or a graded index profile. The present embodiment employs a step index profile, as shown in fig. 1. In addition, the central core 1 and the annular core 2 are both prepared by using a silica material doped with germanium dioxide or titanium dioxide or phosphorus pentoxide. Because the mode field distribution of the orbital angular momentum angular phase zero order (radial second order) mode is mainly concentrated on the central fiber core 1, the central fiber core 1 is prepared by adopting the positively doped material, the refractive index of the central fiber core 1 can be improved, and the effective refractive index of the orbital angular momentum angular phase zero order (radial second order) mode can be adjusted in an auxiliary manner. Further, the clad 3 is made of a pure silica material, or the clad 3 is made of a silica material doped with diboron pentoxide or fluorine.

The optical fiber of this embodiment supports the eigenmode, the linearly polarized mode, or the orbital angular momentum mode of the optical fiber.

The structural design parameters of the optical fiber of the present embodiment include the radius r1 of the central core 1 and the ring width d of the ring core 2. The radius of the cladding 3 was taken to be 62.5 μm. In the full vector finite element analysis method, the preliminary ranges of all parameters of the optical fiber are determined according to the requirements on the number of modes, the ranges of all parameters of the optical fiber are further determined according to the requirements on the difference of the effective refractive index of the modes, and the basic structural parameters of the double-layer ring core optical fiber meeting the requirements are provided. The method specifically comprises the steps of carrying out point-by-point scanning on four variables of radius r1 of a central fiber core 1, ring width d of an annular fiber core 2, refractive index n1 of the central fiber core 1 and refractive index n2 of the annular fiber core 2 in a certain range through COMSOL Multiphysics 5.4with MATLAB software, simulating to obtain the number of modes supported in the optical fiber and the mode effective refractive index distribution under the condition of one optical fiber parameter combination, and finding out the double-layer annular core optical fiber structure meeting the requirements. Wherein the scanning range of the radius r1 of the central fiber core 1 is 0.5-1.5 μm, and the scanning range of the ring width d of the outer annular fiber core is 5.5-8.5 μm.

For the step-index dual-layer core structured fiber used in the present embodiment, the effective refractive index difference between all the nondegenerate guided modes providing support in the C-band, L-band and O-band of optical communication is greater than 1 × 10^-3. The radius of the central core 1 and the ring width of the ring core 2 are 1.4 μm and 6.4 μm, respectively. The radius of the cladding 3 is 62.5 μm. The relative refractive index difference between the central core 1 and the cladding 3 is 0.415%, and the relative refractive index difference between the annular core 2 and the cladding 3 is 0.824%.

As shown in the figureFIG. 2 shows the effective refractive index as a function of wavelength for all the nondegenerate conducting modes supported by the fiber of this embodiment in the entire C-band (1520nm to 1565 nm). The optical fiber structure supports 5 nondegenerate conduction modules in C waveband, and the effective refractive index difference between adjacent modules is larger than 1 multiplied by 10^-3。

As shown in FIG. 3, FIG. 3 shows the effective refractive index as a function of wavelength for all the nondegenerate conductive modes supported by the optical fiber of this embodiment in the entire L-band (1565nm to 1625 nm). The optical fiber structure supports 5 nondegenerate conducting modules in L waveband, and the effective refractive index difference between adjacent modules is larger than 1 multiplied by 10^-3。

As shown in FIG. 4, FIG. 4 shows the effective refractive index as a function of wavelength for all non-degenerate conductive modes supported by the fiber of this embodiment over the entire O-band (1260nm to 1360 nm). The optical fiber structure supports 7 nondegenerate conduction modules in O waveband, and the effective refractive index difference between adjacent modules is larger than 1 multiplied by 10^-3。

The optical fiber of the embodiment can support transmission in three bands (C band, L band and O band), ultra-low crosstalk between modes is realized, all modes independently support an optical signal transmission scheme of intensity modulation direct detection, and coherent detection and MIMO-DSP technology are not needed.

In summary, the embodiment of the present invention provides a multiband mode weakly-coupled dual-core optical fiber, in which the dual-core structural optical fiber is designed to increase the effective refractive index difference between orbital angular momentum angular phase zeroth order (first radial order) and angular phase first order (first radial order) modes, effectively suppress crosstalk between low-order modes, and increase the transmission data capacity of the optical fiber. The invention solves the problems of complex structure, high manufacturing process difficulty, single transmission waveband, small number of modes, large crosstalk among modes, short transmission distance and the like of the conventional optical fiber, and has important application value in long-distance (hundred kilometers), large capacity and three-waveband information transmission industrialization. Specifically, the double-layer fiber core structure optical fiber provided by the invention has the following advantages: (1) the effective refraction difference between the zero order (radial first order) and the first order (radial first order) of the orbital angular momentum angular phase is increased, the crosstalk between modes is reduced, and the available modes are increasedCounting; (2) the effective refractive index difference among all nondegenerate conducting modules supported by optical communication C-band, L-band and O-band is larger than 1 x 10^-3The optical fiber has the ultra-low mode crosstalk characteristic in three communication bands, can independently adopt a mode of intensity modulation direct detection to carry out optical signal transmission, does not need coherent detection and MIMO-DSP assistance, and can realize the transmission of three bands; (3) the drawing process is compatible with the existing mature commercial common single-mode fiber and multimode fiber drawing process, and has low fiber loss and low processing cost.

The above description is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and substitutions can be made without departing from the technical principle of the present invention, and these modifications and substitutions should also be regarded as the protection scope of the present invention.