阅读说明：本技术 沟槽气孔叠加的低串扰多芯少模光纤 (Groove air hole superimposed low-crosstalk multi-core few-mode optical fiber ) 是由 李曙光 王璐瑶 李增辉 李建设 孟潇剑 于 2021-01-08 设计创作，主要内容包括：本发明公开了一种沟槽气孔叠加的低串扰多芯少模光纤,其包括多个少模单元、包围各个少模单元的多芯光纤包层和完美匹配层；少模单元采用阶跃折射率分布设计,折射率由高到低分别为少模纤芯、第一沟槽、第二沟槽和嵌在第二沟槽中的空气孔,每个少模纤芯在1550nm处能够支持4～6种传输模式；整个光纤有一个少模单元处于光纤包层的中心位置,其余少模单元环绕中心位置排列形成正六边形结构,任意三个两两相邻的少模单元构成一个正三角形结构；本发明设计的沟槽和空气孔叠加辅助结构,使纤芯在更低的掺杂浓度条件下就可以实现与主流技术结构同等的低串扰性能；且结合气孔个数、掺杂浓度等参数的优化,使光纤在提高系统通信容量的同时具有良好的传输性能。(The invention discloses a low-crosstalk multi-core few-mode fiber with overlapped grooves and air holes, which comprises a plurality of few-mode units, a multi-core fiber cladding surrounding each few-mode unit and a perfect matching layer, wherein the multi-core fiber cladding surrounds each few-mode unit; the few-mode unit is designed by adopting step refractive index distribution, the refractive indexes of the few-mode unit are respectively a few-mode fiber core, a first groove, a second groove and an air hole embedded in the second groove from high to low, and each few-mode fiber core can support 4-6 transmission modes at 1550 nm; the whole optical fiber is provided with one few-mode unit at the central position of an optical fiber cladding, the other few-mode units are arranged around the central position to form a regular hexagon structure, and any three few-mode units which are adjacent in pairs form a regular triangle structure; the groove and air hole superposition auxiliary structure designed by the invention enables the fiber core to realize the low crosstalk performance equivalent to that of a main flow technical structure under the condition of lower doping concentration; and the optimization of parameters such as the number of air holes and doping concentration is combined, so that the optical fiber has good transmission performance while the communication capacity of the system is improved.)

1. A low-crosstalk multi-core few-mode optical fiber with overlapped grooves and air holes is characterized by comprising a plurality of few-mode units, a multi-core optical fiber cladding surrounding each few-mode unit and a perfect matching layer; the number of the few-mode units is 7, 13 or 19;

when the number of the few-mode units is 7, one few-mode unit is positioned at the central position of the multi-core optical fiber cladding, the remaining 6 few-mode units are arranged into a regular hexagon structure around the few-mode units at the central position, and any three few-mode units adjacent to each other in the optical fiber form a regular triangle structure;

when the number of the few-mode units is 13, the few-mode units are composed of one few-mode unit positioned at the central position of the multi-core optical fiber cladding and 12 few-mode units uniformly arranged at the outer two layers surrounding the central position, each layer comprises 6 few-mode units, wherein the 6 few-mode units of the first layer are arranged in a regular hexagon structure, the 6 few-mode units of the second layer are arranged at the periphery of the few-mode units of the first layer in a hexagram manner, and any three few-mode units adjacent to each other in every two optical fibers can form a regular triangle structure;

when the number of the few-mode units is 19, the few-mode units are formed by one few-mode unit located at the central position of the multi-core optical fiber cladding and 18 few-mode units which are uniformly arranged at the outer two layers around the central position, the first layer comprises 6 few-mode units, the second layer comprises 12 few-mode units, the 6 few-mode units of the first layer are arranged in a regular hexagon form, the 12 few-mode units of the second layer surround the periphery of the few-mode units of the first layer in a regular hexagon structure, and any three few-mode units which are adjacent in pairs in the optical fiber can form a regular triangle structure;

the refractive index distribution conditions between any two of the few-mode units are the same, and the few-mode unit comprises a few-mode fiber core, a first groove, a second groove and an air hole embedded in the second groove; the radius of the few-mode fiber core is 5.5-7.5 mu m; the thickness of the first groove is 2-4 mu m; the thickness of the second groove and the radius of the air hole are respectively 5-14 mu m and 2-4 mu m; the diameter of the multi-core optical fiber cladding is 125-250 mu m; the core spacing of any two few-mode fiber cores is 30-50 mu m; the multi-core optical fiber cladding is made of pure quartz glass; the perfect matching layer is at the outermost layer of the fiber structure.

2. The trench-air-hole-stacked low-crosstalk multi-core few-mode optical fiber according to claim 1, wherein the first trench is made of pure quartz glass and has a value of n₀From sellmeier formulaIs calculated to obtain, wherein B₁＝0.6961663；B₂＝0.4079426；B₃＝0.8974794；λ₁＝0.0684043μm，λ₂＝0.1162414μm；λ₃9.896161 μm; the unit of the working wavelength lambda is mum;

the few-mode fiber core is made of germanium-doped quartz glass, and the relative refractive index difference (n) between the few-mode fiber core and the first groove₁-n₀)/n₀Controlling the content within 1 percent; the second trench is made of fluorine-doped quartz glass, and the relative refractive index difference (n) between the second trench and the first trench₂-n₀)/n₀Controlling the content within-0.7%; the air holes are formed by pure quartz glass capillaries.

3. The trench-air-hole-stacked low-crosstalk multi-core few-mode optical fiber according to claim 1, wherein the first trench has a refractive index n₀Said first trench to confine a light beam within said few-mode core by total internal reflection; the refractive index of the few-mode fiber core is n₁The refractive index of the few-mode fiber core is larger than the refractive index n of the first groove₀Thereby realizing that the required number of high-order modes is obtained by improving the refractive index of the few-mode fiber core; the refractive index of the second groove is n₂The second groove refractive index is smaller than the first groove refractive index n₀So as to inhibit mode coupling of signal modes transmitted by adjacent fiber cores and cladding leakage modes and reduce crosstalk between cores; the air holes are used for further reducing the refractive index around the fiber core and are used for being adjusted together with the second grooves, so that the doping concentration and the core spacing of the fiber core in the multi-core fiber are reduced.

4. The trench-air-hole-stacked low-crosstalk multi-core few-mode optical fiber according to claim 1, wherein the number of the air holes in each few-mode unit is set to be 8, 9 or 12, and a plurality of the air holes are uniformly distributed in the second trench at intervals.

5. The trench-void superimposed low crosstalk multicore few mode fiber of claim 1, wherein the few mode fiber is obtained by mixing the doping concentration of the few mode fiber core with the fiberThe core radius is adjusted in the range of less than 1% and less than 7.5 μm to ensure an effective refractive index difference between the modes of less than 10^-3And ensures that each few-mode fiber core can stably transmit LP at the wavelength of 1550nm₀₁、LP₁₁、LP₂₁、LP₀₂、LP₃₁、LP₁₂4-6 transmission modes.

6. The trench air hole superimposed low-crosstalk multi-core few-mode optical fiber as claimed in claim 1, wherein the design of trench air hole superimposition ensures that the crosstalk value between two adjacent few-mode optical cores is lower than-50 dB/100km in a C + L waveband under the condition of 7 cores, 13 cores and 19 cores of the optical fiber.

7. The trench-air-hole-stacked low-crosstalk multi-core few-mode optical fiber as claimed in claim 1, wherein in the case of 7 cores, 13 cores and 19 cores, the differential mode group delay between each transmission mode in each few-mode unit and the fundamental mode is lower than 25ps/m, LP in the C + L band₀₁The dispersion coefficients of the modes are all below 42ps/(nm km) in the C + L band.

8. The trench-air-hole-stacked low-crosstalk multi-core few-mode optical fiber according to claim 1, wherein the optical fiber has a LP (Low-pass Linear) performance in the case of 7 cores, 13 cores and 19 cores₀₁The effective mode field areas of the modes are all larger than 100 mu m in the C + L wave band²The nonlinear coefficients are all lower than 1.5W^-1*km^-1。

Technical Field

The invention belongs to the field of optical fiber communication, relates to a low-crosstalk multi-core few-mode optical fiber with overlapped grooves and air holes, and is particularly suitable for low crosstalk conditions required in optical fiber transmission.

Background

With the advent of the 5G era, information-based network transmission is becoming important. In the age of internet information big data, through the breakthrough of researchers from time to time, the transmission capacity of the single mode fiber has reached 100TB/s, and almost reached the transmission capacity limit of the standard single mode fiber. For the communication industry, increasing the transmission channel of the optical fiber and improving the communication capacity of the optical fiber are necessary requirements of the era, and the existing multi-core few-mode optical fiber based on the space division multiplexing technology, which is relatively hot in the market of the optical fiber, is considered to be one of the best choices for breaking through the transmission limit of the single-mode optical fiber.

The multi-core few-mode optical fiber reserves the appearance of a common single-mode optical fiber, and expands the transmission capacity of the optical fiber from two aspects: firstly, a plurality of fiber core structures can be designed in the cladding of the single-mode fiber, and the transmission channel of the fiber is increased, so that the transmission capacity of the fiber is improved; and secondly, each fiber core can support multiple different transmission modes to work simultaneously, the mode field area of the optical fiber is increased, the nonlinear effect of the optical fiber is reduced, and the transmission capacity of the optical fiber is multiplied along with the increase of the number of the modes.

At present, the transmission experiment of the multi-core optical fiber is widely carried out, and the transmission from the initial short distance to the current thousands of kilometers of distance is realized. In 2012, Takahashi et al transmitted 40 × 128Gbit/s signals over 6160km length, which is also the longest transmission distance achieved in multicore fiber technology. With the progress of technology, the structure types of the multi-core few-mode optical fiber are more and more abundant. The multi-core few-mode optical fiber types currently mainly used for reducing crosstalk between cores include an air hole-assisted type, a groove-assisted type, a heterogeneous type (different refractive indexes or core radii of adjacent cores), and a freely combined type of the three. The air hole-assisted and groove-assisted multicore few-mode fibers weaken the overlapping of electromagnetic fields between the fiber cores by reducing the refractive index of a cladding layer around the fiber cores, and further reduce the crosstalk between the fiber cores; the inhibition type multicore few-mode optical fiber obtains a certain propagation constant difference through the structural difference of the adjacent fiber cores, so that the phase matching imbalance among the fiber cores is caused, and therefore the crosstalk among the fiber cores is reduced, but the heterogeneous optical fiber can bring larger group delay, so that the difficulty of the demultiplexing technology of a receiving end is increased.

In the prior art, although the groove-type and air-hole-type multicore few-mode optical fiber can realize the arrangement of more fiber cores in a limited cladding, the transmission performance problems of serious crosstalk, nonlinear effect, dispersion and the like brought by more fiber cores and modes cannot well meet the communication requirement.

In the structural design aspect of the multi-core few-mode optical fiber, factors such as the number of fiber cores in the optical fiber, the diameter of a fiber cladding, the distance between the fiber cores, the size of the fiber cores, an auxiliary structure, the doping concentration and the like all influence the crosstalk between the cores of the optical fiber. For example, a large core pitch can bring about a low crosstalk core for independent transmission, but the cladding diameter can be increased while the core density is reduced, and a small core pitch can bring about mode field superposition to generate supermodes, increase the effective mode field area, reduce the nonlinear effect, but also cause strong optical coupling between cores, and increase the crosstalk between cores; a high doping concentration may bring too many high order modes and may cause difficulties in the drawing process, while a too low doping concentration may not effectively reduce inter-core crosstalk and the like.

In summary, how to reduce crosstalk in a multicore few-mode fiber, control the number of required transmission modes, increase the mode field area, suppress the nonlinear effect, and reduce the doping concentration of the fiber core is a problem to be studied urgently.

Disclosure of Invention

The invention provides a low-crosstalk multicore few-mode optical fiber with overlapped grooves and air holes, which aims to solve the problems, namely, a superimposed structure of a groove and an air hole is designed around each fiber core, the advantages of an air hole auxiliary structure and a groove auxiliary structure in the prior art are combined, and compared with the mainstream technical structure, the low-crosstalk multicore few-mode optical fiber has the advantages that the strength of reducing the refractive index around the fiber core is higher, and the fiber core can realize the same low-crosstalk performance under the condition of lower doping concentration.

On the basis of the space division multiplexing technology, the doping concentration of the fiber core and the radius of the fiber core are adjusted within the range of less than 1% and less than 7.5 mu m by using an auxiliary structure overlapped by the groove air holes, so that 4-6 LP modes can be independently transmitted by each fiber core, multi-channel large-capacity transmission is realized by increasing the number of the fiber cores, and low crosstalk performance of-50 dB/100km is realized by increasing the core spacing and the number of the air holes. In addition, the multi-core few-Mode optical fiber provided by the invention can bring larger Mode Differential Group Delay (MDGD) and smaller dispersion, so that the crosstalk between the modes is reduced, and various transmission characteristics of the optical fiber are ensured; therefore, the invention is suitable for the optical fiber transmission system in the optical fiber communication field.

The technical scheme adopted by the invention is to provide a low-crosstalk multi-core few-mode optical fiber with overlapped grooves and air holes, which comprises a plurality of few-mode units, a multi-core optical fiber cladding surrounding each few-mode unit and a perfect matching layer; the number of the few-mode units is 7, 13 or 19, and lower crosstalk can be guaranteed; when the number of the few-mode units is 7, one few-mode unit is positioned at the central position of the multi-core optical fiber cladding, the remaining 6 few-mode units are arranged into a regular hexagon structure around the few-mode units at the central position, and any three few-mode units adjacent to each other in the optical fiber form a regular triangle structure; when the number of the few-mode units is 13, the few-mode units are composed of one few-mode unit positioned at the central position of the multi-core optical fiber cladding and 12 few-mode units uniformly arranged at the outer two layers surrounding the central position, each layer comprises 6 few-mode units, wherein the 6 few-mode units at the first layer are arranged in a regular hexagon form, the 6 few-mode units at the second layer are arranged at the periphery of the few-mode units at the first layer in a hexagram form, and any three few-mode units adjacent to each other in the optical fiber form a regular triangle structure; when the number of the few-mode units is 19, the few-mode units are formed by one few-mode unit located at the central position of the multi-core optical fiber cladding and 18 few-mode units which are uniformly arranged at the outer two layers around the central position, the first layer comprises 6 few-mode units, the second layer comprises 12 few-mode units, the 6 few-mode units of the first layer are arranged in a regular hexagon form, the 12 few-mode units of the second layer are also arranged around the periphery of the few-mode units of the first layer in a regular hexagon structure, and any three few-mode units which are adjacent in pairs in the optical fiber form a regular triangle structure; the refractive index distribution situation between any two of the few-mode units is the same; the few-mode unit comprises a few-mode fiber core, a first groove, a second groove and an air hole embedded in the second groove; the radius of the few-mode fiber core is 5.5-7.5 mu m, and the small-mode fiber core is used for obtaining a larger effective mode field area; the thickness of the first groove is 2-4 mu m, and the limiting capacity of the fiber core on the light beam is guaranteed; the thickness of the second groove and the radius of the air hole are respectively 5-14 mu m and 2-4 mu m, so that the low crosstalk characteristic is realized; the diameter of the multi-core optical fiber cladding is 125-250 mu m, so that good mechanical properties of the optical fiber are ensured; the core spacing of any two few-mode fiber cores is equal, the distance is 30-50 mu m, and the few-mode fiber cores are used for adjusting the low crosstalk performance; the multi-core optical fiber cladding is made of pure quartz glass; the perfect matching layer is positioned at the outermost layer of the optical fiber structure and is a calculation boundary and auxiliary setting added when a finite element method is used for carrying out optical fiber performance simulation.

Further, the first trench is made of pure quartz glass, and has a value of n₀From sellmeier formulaIs calculated to obtain, wherein B₁＝0.6961663；B₂＝0.4079426；B₃＝0.8974794；λ₁＝0.0684043μm；λ₂＝0.1162414μm；λ₃9.896161 μm; the unit of the working wavelength lambda is required to be mum in the formula; the few-mode fiber core is made of germanium-doped quartz glass, and has a relative refractive index difference (n) with the first groove₁-n₀)/n₀Controlling the content within 1 percent; the second trench is made of fluorine-doped quartz glass, and the relative refractive index difference (n) between the second trench and the first trench₂-n₀)/n₀The control is within-0.7%, and the thermodynamic properties of all parts of the optical fiber are easily matched when the optical fiber with low doping concentration is prepared; the air hole is formed by a pure quartz glass capillary; the perfect matching layer can also be referred to as a perfect matching layer, the english name perfect matched layer.

Preferably, the first trench has a refractive index n₀Mainly ofFor confining the light beam within said few-mode core by total internal reflection; the refractive index of the few-mode fiber core is n₁Is greater than the first trench refractive index n₀The required number of high-order modes is obtained by improving the refractive index of the few-mode fiber core; the refractive index of the second groove is n₂Is smaller than the first trench refractive index n₀The optical fiber is mainly used for inhibiting mode coupling of a signal mode transmitted by an adjacent fiber core and a cladding leakage mode and reducing crosstalk between cores; the air holes are used for further reducing the refractive index around the fiber cores and are used for being adjusted together with the second grooves, the doping concentration and the core spacing of the fiber cores in the multi-core optical fiber are reduced, a plurality of transmission channels formed by the fiber cores and a small number of modes are obtained, and high-capacity transmission under the condition of low crosstalk is guaranteed.

Preferably, the number of the air holes in each few-mode unit can be set to be 8, 9 or 12, and the air holes are uniformly distributed in the second grooves at intervals; the refractive index around the few-mode fiber core is further reduced through the arrangement of the air holes, the core distance in the multi-core few-mode fiber and the number of few-mode units in the multi-core fiber cladding can be adjusted, and therefore the communication channel of the fiber is increased; the doping concentration of the few-mode fiber core can be reduced, and unnecessary high-order modes can be prevented from being generated.

Further, the effective refractive index difference between modes is ensured to be less than 10 by adjusting the doping concentration of the few-mode core and the radius of the core within the range of less than 1% and less than 7.5 mu m^-3The cross talk between modes can be ignored, and each few-mode core can be ensured to stably transmit LP at the wavelength of 1550nm₀₁、LP₁₁、LP₂₁、LP₀₂、LP₃₁、LP₁₂And 4-6 transmission modes.

Furthermore, through the design of groove air hole superposition, the optical fiber can ensure that the crosstalk value between two adjacent few-mode fiber cores is lower than-50 dB/100km in a C + L waveband under the conditions of 7 cores, 13 cores and 19 cores.

Preferably, the optical fiber has 7 cores, 13 cores and 19 cores, and the differential mode group delay between each transmission mode and the fundamental mode in each few-mode unit is C + LAll in the wave band are lower than 25ps/m, LP₀₁The dispersion coefficients of the modes are all below 42ps/(nm km) in the C + L band.

Preferably, the optical fiber is LP with 7 cores, 13 cores and 19 cores₀₁The effective mode field areas of the modes are all larger than 100 mu m in the C + L wave band²The nonlinear coefficients are all lower than 1.5W^-1*km^-1。

Due to the adoption of the technical scheme, the invention has the following beneficial effects:

(1) the invention designs a low-crosstalk multicore few-mode optical fiber with overlapped grooves and air holes, and combines the advantages of the grooves and the air hole overlapped structure arranged around each fiber core, thereby effectively reducing the refractive index of the cladding around the fiber core, weakening the overlapping of electric fields between adjacent fiber cores and further effectively inhibiting the crosstalk between the fiber cores.

(2) The low-crosstalk multi-core few-mode optical fiber with the overlapped grooves and air holes can enable the fiber core to simultaneously transmit 4-6 LP modes in a C + L waveband, and the transmission capacity of the optical fiber is multiplied; simultaneously ensures the separation purity of each mode, and ensures that the difference of effective refractive indexes between the modes is more than 10^-3And crosstalk due to coupling between modes can be neglected.

(3) Compared with the conventional air hole or groove auxiliary type multi-core few-mode optical fiber, the low-crosstalk multi-core few-mode optical fiber with overlapped grooves and air holes has obvious advantages in doping concentration; when the parameters such as the diameter of the fiber core, the distance between the fiber cores and the like are the same, the difference between the refractive indexes of the few-mode fiber core and the second groove and the refractive index of the pure quartz is controlled within 1 percent and-0.7 percent, the same crosstalk inhibition effect can be achieved, and meanwhile, the nonlinear effect of the optical fiber can be effectively reduced.

(4) The low-crosstalk multi-core few-mode optical fiber with overlapped grooves and air holes is more flexible in structural arrangement, and can be flexibly regulated and controlled in the aspects of fiber core number, fiber core layout, fiber core diameter, fiber core interval, groove width, diameter and number of air holes, doping concentration and the like, so that ideal optical fiber performance is achieved.

Drawings

FIG. 1 is a schematic cross-sectional view of a seven-core few-mode fiber of a low crosstalk multi-core few-mode fiber stacked with trench air holes according to the present invention;

FIG. 2 is a schematic diagram of refractive index distribution between any two few-mode units of a low-crosstalk multicore few-mode fiber with stacked trench air holes according to the present invention;

fig. 3 is a schematic view of the structure and mode field distribution of a seven-core few-mode optical fiber and a common single-groove auxiliary seven-core few-mode optical fiber provided in embodiment 1 of the trench-air-hole stacked low-crosstalk multi-core few-mode optical fiber of the present invention;

FIG. 4 is a schematic diagram of structural distributions of several multi-core few-mode fibers of a low crosstalk multi-core few-mode fiber stacked with trench air holes according to the present invention;

fig. 5 a-5 b are diagrams illustrating the comparison between the crosstalk and the dispersion coefficient of the fundamental mode in the C + L band in the seven-core few-mode fiber provided in embodiment 1 of the trench-air-hole stacked low-crosstalk multi-core few-mode fiber according to the present invention and the common single-trench auxiliary type seven-core few-mode fiber;

fig. 6 is a graph showing effective refractive index difference variation curves of adjacent modes in a seven-core few-mode optical fiber according to embodiment 1 of the present invention of a trench-air hole stacked low crosstalk multi-core few-mode optical fiber;

fig. 7 is a cross-talk variation curve of a seven-core few-mode optical fiber provided in embodiment 1 of the low cross-talk multi-core few-mode optical fiber with stacked trench air holes of the present invention in a C + L band;

fig. 8 is a differential mode group delay variation situation of a seven-core few-mode optical fiber provided in embodiment 1 of the low crosstalk multi-core few-mode optical fiber with trench air hole superposition according to the present invention;

fig. 9 is a dispersion coefficient curve diagram of a seven-core few-mode optical fiber provided in embodiment 1 of the low-crosstalk multi-core few-mode optical fiber with trench and air hole superposition according to the present invention.

The main reference numbers:

1 is a few-mode fiber core; 2 is a first groove; 3 is a second groove; 4 is an air hole; 5 is a multi-core fiber cladding; 6 is a few-mode unit; and 7 is a perfect matching layer.

a is the radius of the few-mode fiber core; b is the thickness of the first trench; e is the thickness of the second trench; w is the diameter of the air hole; d is two adjacent few-mode fibersThe distance between the cores; d is the diameter of the cladding of the multi-core optical fiber; n is₁And Δ₁The refractive index of the few-mode core and the relative refractive index difference (n) between the few-mode core and the first trench₁-n₀)/n₀；n₂And Δ₂Refractive index of the second trench and relative refractive index difference (n) of the second trench and the first trench, respectively₂-n₀)/n₀(ii) a The refractive indexes of the first groove and the multi-core optical fiber cladding are both the refractive index n of pure quartz₀。

Detailed Description

In order to more clearly illustrate the technical application and the product advantages of the present invention, the technical solution of the present invention will be described in detail with reference to several specific embodiments and the accompanying drawings.

The following examples are specifically described by taking 7-core, 13-core and 19-core multi-core few-mode fibers as examples.

As shown in fig. 1-2, the present invention discloses a low crosstalk multicore few-mode fiber with stacked trench air holes, which includes a plurality of few-mode units 6, a multicore fiber cladding 5 surrounding each few-mode unit, and a perfect matching layer 7; the number of the few-mode units 6 can be 7, 13 or 19, and lower crosstalk can be guaranteed; if the number of the few-mode units 6 is 7, one few-mode unit 6 is located at the central position of the multi-core optical fiber cladding 5, the remaining 6 few-mode units 6 are arranged in a regular hexagon structure around the few-mode units at the central position, and any three few-mode units 6 adjacent to each other in the optical fiber form a regular triangle structure; if the number of the few-mode units 6 is 13, the optical fiber is composed of one few-mode unit 6 positioned at the central position of the multi-core optical fiber cladding 5 and 12 few-mode units 6 uniformly arranged at the outer two layers surrounding the central position, wherein the first ring is provided with 6 few-mode units 6 and is arranged in a regular hexagon form, the 6 few-mode units 6 of the second ring are arranged at the periphery of the first few-mode unit 6 in a hexagon form, and any three few-mode units 6 adjacent to each other in pairs in the optical fiber form a regular triangle structure; if the number of the few-mode units 6 is 19, the optical fiber consists of one few-mode unit 6 positioned at the central position of the multi-core optical fiber cladding 5 and 18 few-mode units 6 uniformly arranged around the central position at the outer two layers, wherein the first ring has 6 few-mode unitsThe elements 6 are arranged in a regular hexagon form, the 12 few-mode units 6 of the second ring are also surrounded on the periphery of the first few-mode unit 6 in a regular hexagon structure, and any three few-mode units 6 adjacent to each other in pairs in the optical fiber form a regular triangle structure; the refractive index distribution between any two few-mode units 6 is the same; the few-mode unit 6 comprises a few-mode fiber core 1, a first groove 2, a second groove 3 and an air hole 4 embedded in the second groove; the thickness of the first groove 2 is 2-4 mu m, so that the limiting capacity of the fiber core on the light beam is ensured; the thickness of the second groove 3 and the radius of the air hole 4 are respectively 5-14 mu m and 2-4 mu m, so that the low crosstalk characteristic is realized; the diameter of the multi-core optical fiber cladding 5 is 125-250 mu m, so as to ensure good mechanical property of the optical fiber; the core spacing of any two few-mode fiber cores 1 is equal, the distance is 30-50 mu m, and the few-mode fiber cores are used for adjusting the low crosstalk performance; the refractive index of the first trench 2 is n₀For confining the light beam mainly by total internal reflection within a few-mode core; the refractive index of the few-mode fiber core 1 is n₁And is larger than the refractive index n of the first trench 2₀The required number of high-order modes is obtained by improving the refractive index of the few-mode fiber core; the second trench 3 has a refractive index n₂Smaller than the refractive index n of the first trench 2₀The optical fiber is mainly used for inhibiting mode coupling of a signal mode transmitted by an adjacent fiber core and a cladding leakage mode and reducing crosstalk between cores; the air holes 4 are used for further reducing the refractive index around the fiber core, and are used for regulating and controlling the core distance in the multi-core fiber and reducing the diameter of the multi-core fiber cladding under the coaction with the second grooves 3; the multi-core optical fiber cladding 5 is made of pure quartz glass; the perfect matching layer 7 is located at the outermost layer of the optical fiber structure, and is a calculation boundary and an auxiliary setting added when the finite element method is used for carrying out optical fiber performance simulation.

Example 1

The embodiment provides a trench air hole superposed seven-core few-mode fiber, the structure and mode field distribution of which are shown in fig. 3, one few-mode unit 6 is located at the central position of a multi-core fiber cladding 5, the other six few-mode units 6 are arranged in a regular hexagon structure at the periphery, any three few-mode units 6 adjacent to each other in the fiber form a regular triangle structure, and the number of air holes 4 in each few-mode unit 6 is 12; less mould unit 6 adoptsStep index profile design, as shown in FIG. 2, in which the relative refractive index difference Δ between the few-mode core 1 and the first trench 2₁Set to 1%, the relative refractive index difference Δ of the second trench 3 from the first trench 2₂Set to-0.7%, the core radius a to 7 μm, the core pitch D to 40 μm, the thickness b of the first trench 2 to 2.5 μm, the thickness e of the second trench 3 to 8 μm, the diameter w of the air hole 4 to 5 μm, and the diameter D of the multicore fiber cladding 5 to 140 μm, which was scanned in the C + L band using COMSOL Multiphysics software.

In the seven-core few-mode optical fiber prepared by the embodiment, each fiber core supports LP in C + L waveband₀₁、LP₁₁、LP₂₁、LP₀₂、LP₃₁、LP₁₂Six transmission modes; as shown in FIG. 6, the effective refractive index differences between adjacent modes in the same core are greater than 10 in both C + L bands^-3The inter-mode crosstalk can be ignored; FIG. 7 shows LP₀₁、LP₁₁、LP₂₁、LP₀₂、LP₃₁、LP₁₂The crosstalk condition of the six modes when the fiber is transmitted for 100km in a C + L wave band indicates that the fiber can still keep the low crosstalk characteristic after being transmitted for 100 km; as shown in FIG. 8, LP₁₁、LP₂₁、LP₀₂、LP₃₁、LP₁₂The group delay of the differential mode between the five modes and the basic mode is less than 22ps/m in a C + L waveband; as shown in FIG. 9, LP₀₁、LP₁₁、LP₂₁、LP₀₂、LP₃₁、LP₁₂The dispersion coefficients in the six modes of C + L wave bands are all less than 42ps/(nm x km), and the optical fiber keeps good transmission characteristics; LP₀₁The effective mode field area of the mode at 1550nm is 122.5 μm²The nonlinear coefficient is 0.85W^-1*km^-1。

Example 2

The embodiment provides a single-groove auxiliary seven-core few-mode optical fiber compared with the embodiment 1, the structure and the mode field distribution of the fiber are shown in fig. 3, compared with the embodiment 1, the fiber has the same parameters except that the structure of the air hole 4 is not arranged, and the fiber is scanned in the C + L wave band by utilizing COMSOLMULTITIPhysics software; FIGS. 5(a) and (b) are views of the present embodiment, respectivelyAnd example 1 LP in the C + L band₀₁The results of the mode crosstalk comparison diagram and the dispersion coefficient comparison diagram show that the groove air hole superposed auxiliary structure provided by the invention can better inhibit crosstalk under the condition of not increasing optical fiber dispersion.

Example 3

The embodiment provides a trench air hole superposition type thirteen-core few-mode optical fiber, the structural distribution of which is shown in fig. 4, and the optical fiber is composed of a few-mode unit 6 at the central position and twelve few-mode units 6 uniformly arranged at two layers surrounding the central position, wherein the first ring is provided with 6 few-mode units 6 which are arranged in a regular hexagon form, the 6 few-mode units 6 of the second ring are arranged at the periphery of the first layer of few-mode units 6 in a hexagon form, any three few-mode units 6 adjacent to each other in the optical fiber form a regular triangle structure, and the number of air holes 4 in each few-mode unit 6 is 12; the few-mode unit 6 is designed by adopting step-index distribution, as shown in FIG. 2, wherein the relative refractive index difference Delta between the few-mode fiber core 1 and the first trench 2₁Set to 1%, the relative refractive index difference Δ of the second trench 3 from the first trench 2₂The optical fiber is set to be-0.7%, the radius of a fiber core is set to be 7 mu m, the distance D between the fiber cores is set to be 42 mu m, the thickness b of the first groove 2 is set to be 3 mu m, the thickness e of the second groove 3 is set to be 10 mu m, the diameter w of the air hole 4 is set to be 6 mu m, the diameter D of the multi-core optical fiber cladding 5 is set to be 200 mu m, and the wavelength scanning of 1540-1560 nm is carried out by utilizing COMSOLMULTIPYSICS software.

The thirteen-core few-mode optical fiber prepared in the embodiment has each fiber core supporting LP at 1550nm₀₁、LP₁₁、LP₂₁、LP₀₂、LP₃₁、LP₁₂Six modes of transmission; the effective mode index difference between adjacent modes is greater than 10 at 1550nm^-3The inter-mode crosstalk can be ignored; LP₀₁、LP₁₁、LP₂₁、LP₀₂、LP₃₁、LP₁₂The crosstalk values of the six modes at 1550nm are-134.27 dB/100km, -155.21dB/100km, -128.25dB/100km, -136.47dB/100km, -120.47dB/100km and-101.51 dB/100km respectively, and the crosstalk is effectively inhibited; LP₁₁、LP₂₁、LP₀₂、LP₃₁、LP₁₂The differential mode group delay between the five modes and the fundamental mode is respectively 5.95ps/m, 12.99ps/m, 14.16ps/m, 19.97ps/m and 18ps/m at 1550 nm; LP₀₁、LP₁₁、LP₂₁、LP₀₂、LP₃₁、LP₁₂The dispersion coefficients of the six modes at 1550nm are 25.77ps/(nm x km), 30.08ps/(nm x km), 33.35ps/(nm x km), 30.77ps/(nm x km), 32.98ps/(nm x km), 16.11ps/(nm x km), respectively; LP₀₁The effective mode field area of the mode at 1550nm is 121.73 μm²Nonlinear coefficient of 0.86W^-1*km^-1。

Example 4

The embodiment provides a trench air hole superposition type nineteen-core few-mode optical fiber, the structural distribution of which is shown in fig. 4, and the optical fiber is composed of a few-mode unit 6 at the central position and eighteen few-mode units 6 uniformly arranged at two layers around the central position, wherein the 6 few-mode units 6 of the first ring are arranged in a regular hexagon structure, the 12 few-mode units 6 of the second ring are also arranged around the periphery of the few-mode unit 6 of the first layer in a regular hexagon structure, and any three few-mode units 6 adjacent to each other in the optical fiber form a regular triangle structure; the number of the air holes 4 in each less-mold unit 6 is 12; the few-mode unit 6 is designed by adopting step index profile, as shown in FIG. 2, wherein the relative refractive index difference Delta between the few-mode fiber core 1 and the first trench 2₁Set to 1%, the relative refractive index difference Δ of the second trench 3 from the first trench 2₂The optical fiber is set to be-0.7%, the radius a of a fiber core is set to be 6.5 mu m, the distance D between the fiber cores is set to be 44 mu m, the thickness b of the first groove 2 is set to be 3 mu m, the thickness e of the second groove 3 is set to be 10 mu m, the diameter w of the air hole 4 is set to be 6 mu m, the diameter D of the multi-core optical fiber cladding 5 is set to be 240 mu m, and the wavelength scanning of 1540-1560 nm is carried out on the multi-core optical fiber cladding by utilizing COMSOLMULITYSICS software.

In the nineteen-core few-mode optical fiber prepared in the embodiment, each core supports LP₀₁、LP₁₁、LP₂₁、LP₀₂、LP₃₁、LP₁₂Six modes of transmission; the effective mode index difference between adjacent modes is greater than 10 at 1550nm^-3The inter-mode crosstalk can be ignored; LP₀₁、LP₁₁、LP₂₁、LP₀₂、LP₃₁、LP₁₂The crosstalk values of the six modes at 1550nm are-136.17 dB/100km, -135.06dB/100km, -150.84dB/100km, -144.59dB/100km, -127.46dB/100km and-84.13 dB/100km respectively; LP₁₁、LP₂₁、LP₀₂、LP₃₁、LP₁₂The differential mode group delay between the five modes and the fundamental mode is respectively 6.40ps/m, 13.63ps/m, 14.27ps/m, 20.12ps/m and 15.01ps/m at 1550 nm; LP₀₁、LP₁₁、LP₂₁、LP₀₂、LP₃₁、LP₁₂The dispersion coefficients of the six modes at 1550nm are respectively 25.93ps/(nm x km), 30.04ps/(nm x km), 32.08ps/(nm x km), 27.52ps/(nm x km), 28.53ps/(nm x km); LP₀₁The effective mode field area of the mode at 1550nm is 107.79 μm²The nonlinear coefficient is 0.97W^-1*km^-1。

Example 5

The embodiment provides a trench air hole superposed seven-core few-mode fiber, the structural distribution of which is shown in fig. 4, one few-mode unit 6 is located at the central position of a multi-core fiber cladding 5, the other six few-mode units 6 are arranged in a regular hexagon structure at the periphery, any three few-mode units 6 adjacent to each other in the fiber form a regular triangle structure, and the number of air holes 4 in each few-mode unit 6 is 8. The few-mode unit 6 is designed by adopting step index profile, as shown in FIG. 2, wherein the relative refractive index difference Delta between the few-mode fiber core 1 and the first trench 2₁Set to 0.9%, the relative refractive index difference Δ of the second trench 3 from the first trench 2₂The thickness b of the first groove 2 is set to be 3 mu m, the thickness e of the second groove 3 is set to be 10 mu m, the diameter w of the air hole 4 is set to be 6 mu m, the diameter D of the multi-core optical fiber cladding 5 is set to be 150 mu m, and the wavelength scanning is carried out on the multi-core optical fiber cladding 5 at 1540-1560 nm by using COMSOL Multiphysics software.

Each core support LP in the seven-core few-mode fiber prepared in this example₀₁、LP₁₁、LP₂₁、LP₀₂、LP₃₁、LP₁₂Six modes of transmission; at the wavelength of 1550nm, the wavelength of the light,the effective mode refractive index difference between adjacent modes is more than 10^-3The inter-mode crosstalk can be ignored; LP₀₁、LP₁₁、LP₂₁、LP₀₂、LP₃₁、LP₁₂The crosstalk values of the six modes at 1550nm are-130.15 dB/100km, -118.13dB/100km, -101.58dB/100km, -90.73dB/100km, -76.22dB/100km and-54.291 dB/100km respectively; LP₁₁、LP₂₁、LP₀₂、LP₃₁、LP₁₂The differential mode group delay between the five modes and the fundamental mode is respectively 5.29ps/m, 11.62ps/m, 12.81ps/m, 18.09ps/m and 17.21ps/m at 1550 nm; LP₀₁、LP₁₁、LP₂₁、LP₀₂、LP₃₁、LP₁₂The dispersion coefficients of the six modes at 1550nm are respectively 25.37ps/(nm x km), 29.36ps/(nm x km), 32.72ps/(nm x km), 30.99ps/(nm x km), 33.45ps/(nm x km), and 21ps/(nm x km); LP₀₁The effective mode field area of the mode at 1550nm is 139.67 μm²The quasi-nonlinear coefficient is 0.75W^-1*km^-1。

The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and all the changes or substitutions should be covered within the scope of the present invention. Therefore, the protection scope of the present invention should be defined by the appended claims.