Vortex light multi-concentric ring core non-zero dispersion shifted optical fiber

Abstract

The invention discloses a vortex light multi-concentric ring core non-zero dispersion shifted optical fiber. The vortex light multi-concentric ring core non-zero dispersion shifted optical fiber comprises three nested ring-shaped fiber cores and an optical fiber cladding, the annular fiber core is divided into an annular fiber core inner layer, an annular fiber core middle layer and an annular fiber core outer layer; the optical fiber cladding comprises a circular area, a first interlayer, a second interlayer and an outer optical fiber cladding; the optical fiber sequentially comprises a circular area, an annular fiber core inner layer, a first interlayer, an annular fiber core middle layer, a second interlayer, an annular fiber core outer layer and an outer optical fiber wrapping layer from inside to outside. The three high-refractive-index annular fiber cores are matched with the annular intensity profile of vortex light, and the outer-layer annular fiber core can support transmission of more OAM modes. According to the invention, low dispersion can be provided for a plurality of OAM modes in the C wave band to suppress the nonlinear effect.

Description

Technical Field

[0001] The invention relates to the technical field of non-zero dispersion shifted ring core optical fiber, and in particular to a vortex light multi-concentric ring core non-zero dispersion shifted optical fiber. Background Art

[0002] To meet the challenge of long-distance high-capacity communication, orbital angular momentum (OAM)-based mode division multiplexing has emerged as a promising technology that can significantly increase the data transmission capacity of communication systems. By combining OAM mode division multiplexing technology with wavelength division multiplexing technology, researchers can achieve significant improvements in data rate and spectral efficiency.

[0003] An OAM beam is a special beam that carries orbital angular momentum and has the characteristics of a spiral phase wavefront and a central phase singularity. Since OAM-based mode division multiplexing (MDM) and wavelength division multiplexing (WDM) are mutually orthogonal, they can be combined to further improve data transmission rate and spectrum efficiency. OAM modes can be synthesized from eigenvector modes:

[0004]

[0005] Among them, l is the topological charge number, which theoretically has infinite values ​​and orthogonal characteristics, and can be used as a new dimension and data carrier. The value of l can be zero, a positive integer, and a negative integer, corresponding to the Laguerre-Gaussian beam, clockwise phase spiral, and counterclockwise phase spiral, respectively.

[0006] In high-speed optical communication systems, dispersion management plays a vital role in eliminating inter-symbol interference, ultimately reducing the bit error rate. Although close to zero dispersion can reduce pulse broadening, when the dispersion is small enough to meet the phase matching condition, four-wave mixing effect will occur, resulting in reduced signal quality. Non-zero dispersion-shifted fiber can effectively solve this problem by providing strictly controlled dispersion characteristics. However, single-ring core non-zero dispersion-shifted fiber usually limits the number of OAM modes supported for transmission. Designing and studying multi-core optical fibers with innovative structures is a current research direction.

[0007] In order to realize a large-capacity, long-distance OAM mode multiplexing system, it is necessary to design optical fibers that can transmit various OAM modes. Currently, there are few studies on low-dispersion, low-nonlinear non-zero dispersion-shifted optical fibers. Summary of the invention

[0008] In order to overcome the defects of the above prior art, the present invention provides a vortex optical multi-concentric ring core non-zero dispersion shifted optical fiber, which is designed to meet the needs of low-dispersion transmission of multiple orbital angular momentum modes. The optical fiber can provide lower dispersion for multiple OAM modes in the C band to suppress nonlinear effects.

[0009] In order to achieve the above object, the technical solution adopted by the present invention is:

[0010] A vortex optical multi-concentric ring core non-zero dispersion shifted optical fiber, comprising a ring core and an optical fiber cladding that are mutually nested and spaced apart;

[0011] Wherein, the annular fiber core has at least two layers, and the innermost layer and the outermost layer are the optical fiber cladding;

[0012] The high refractive index annular core matches the annular intensity profile of the vortex light, and the outer annular core can support the transmission of more OAM modes.

[0013] When there are three ring fiber cores;

[0014] The annular fiber core is divided into an annular fiber core inner layer 5, an annular fiber core middle layer 6 and an annular fiber core outer layer 7;

[0015] The optical fiber cladding includes a circular area 1, a first interlayer 2, a second interlayer 3, and an outer optical fiber cladding 4; from the inside to the outside, they are the circular area 1, the inner layer of the annular core 5, the first interlayer 2, the middle layer of the annular core 6, the second interlayer 3, the outer layer of the annular core 7, and the outer optical fiber cladding 4; the three high-refractive-index annular cores match the annular intensity profile of the vortex light, and the outer annular core can support the transmission of more OAM modes.

[0016] The outer annular core region refers to the annular core middle layer 6 or the annular core outer layer 7, and the annular core middle layer 6 can transmit more OAM modes than the annular core inner layer 5. The annular core outer layer 7 can transmit more OAM modes than the annular core inner layer 5 and the annular core middle layer 6.

[0017] The refractive index of the optical fiber cladding is n0, and the refractive index of the annular core is n1, satisfying that n1 is greater than n0, that is, the refractive index in the annular core region is greater than that of the optical fiber cladding. The high refractive index can confine the light field in the annular core to achieve a larger effective mode field area and a smaller nonlinear coefficient. The three-layer annular core uses the same doping concentration, which can reduce the cost of optical fiber drawing.

[0018] Each layer of the optical fiber cladding material is any one of pure silica, germanium-doped silica, fluorine-doped silica, air, Schott glass, fluoride or sulfide;

[0019] When it is pure silicon dioxide, when the communication wavelength λ=1550nm, n0=1.4440;

[0020] The three ring fiber core materials are any one of pure silica, germanium-doped silica, fluorine-doped silica, air, Schott glass, fluoride or sulfide;

[0021] When it is germanium-doped silica with the same doping concentration and the communication wavelength λ = 1550 nm, n1 = 1.4605; the inner diameters of the three inner ring cores 5, the middle ring core 6, and the outer ring core 7 are r1, r2, and r3 respectively, and the widths are w1, w2, and w3 respectively. The three ring cores are nested from the inside to the outside, and r1 < r2 < r3. To ensure that the OAM modes of each ring core can be transmitted independently, the width of the outer ring core needs to be greater than that of the inner ring core, that is, w1 < w2 < w3. The range of the doping concentration is 8 - 14 mol%. Increasing the doping concentration, the dispersion of the OAM mode decreases significantly. When the doping concentration increases from 8 mol% to 14 mol%, the dispersions of the HE 2,1 modes of the inner ring core 5, the middle ring core 6, and the outer ring core 7 at the wavelength of 1550 nm are reduced from 6.85 ps / nm / km to 0.41 ps / nm / km, from 6.53 ps / nm / km to 1.44 ps / nm / km, and from 6.99 ps / nm / km to 2.84 ps / nm / km respectively.

[0022] The width w1 of the inner ring core 5 is greater than 2 μm, the width of the outer ring core 7 is less than 2.6 μm, and w1 < w2 < w3 is maintained;

[0023] When the widths w1, w2, and w3 of the three ring cores are 2.2 μm, 2.3 μm, and 2.4 μm respectively, the dispersions of the HE 2,1 modes of the inner ring core 5, the middle ring core 6, and the outer ring core 7 at the wavelength of 1550 nm are 3.46 ps / nm / km, 6.58 ps / nm / km, and 5.21 ps / nm / km respectively;

[0024] When w1, w2, and w3 are 2.3 μm, 2.4 μm, and 2.5 μm respectively, the dispersions of the HE 2,1 modes of the inner ring core 5, the middle ring core 6, and the outer ring core 7 at the wavelength of 1550 nm are 4.32 ps / nm / km, 7.43 ps / nm / km, and 5.99 ps / nm / km respectively;

[0025] On the premise of ensuring w1 < w2 < w3, increasing the width of the ring core, the dispersion value of the OAM mode increases. In addition, when the width of the outer ring core 7 is 2.3 μm, the effective mode field area of the HE 2,1 mode at the wavelength of 1550 nm is 906.9 μm 2 , when the width of the outer ring core 7 is 2.5 μm, the effective mode field area is 915.2 μm 2 , and on the premise of not appearing radial high-order modes, increasing the width of the ring core can increase the effective mode field area.

[0026] When the distance between the inner layer 5 of the annular core and the middle layer 6 of the annular core, and the distance between the middle layer 6 of the annular core and the outer layer 7 of the annular core are both 10 μm, the HE of the inner layer 5 of the annular core, the middle layer 6 of the annular core, and the outer layer 7 of the annular core are 2,1 The dispersion of the modes at a wavelength of 1550nm is 3.29ps / nm / km, 3.40ps / nm / km, and 3.96ps / nm / km respectively; when the spacing between the inner layer 5 of the ring core and the middle layer 6 of the ring core, and the spacing between the middle layer 6 of the ring core and the outer layer 7 of the ring core are all 18μm, the HE of the inner layer 5 of the ring core, the middle layer 6 of the ring core, and the outer layer 7 of the ring core are 2,1 The dispersions of the modes at a wavelength of 1550 nm are 2.87 ps / nm / km, 3.32 ps / nm / km, and 4.39 ps / nm / km, respectively.

[0027] When the spacing increases, the dispersion of the annular core inner layer 5 and the annular core middle layer 6 decreases, and the dispersion of the annular core outer layer 7 increases.

[0028] Under certain structural parameters, the optical fiber of the present invention can provide lower dispersion while maintaining a larger effective mode field area and a smaller nonlinear coefficient to reduce nonlinear effects.

[0029] Beneficial effects of the present invention:

[0030] In the optical fiber structure design of the present invention, the outer annular core width is greater than the annular core width, which can ensure that the OAM mode of each annular core can be transmitted independently, and a sufficiently large spacing is maintained between the annular cores to reduce mode coupling.

[0031] By selecting the materials of the three annular core regions, adjusting the width and position of the three annular cores, changing the refractive index distribution of the three annular cores, and increasing the number of annular cores, the dispersion value in the C band can be adjusted so that the dispersion of multiple orbital angular momentum modes meets the ITU-T G.655.C standard. By adjusting the above-mentioned optical fiber materials and structural parameters, adjusting the dispersion characteristics, and moving the zero dispersion wavelength to 1550nm, a dispersion-shifted optical fiber that meets the ITU-T G.653 standard can be designed. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of the optical fiber cross section and refractive index distribution of the present invention.

[0033] Figure 2 In the optical fiber structure of the present invention, when the structural parameters are r1 = 12 μm, r2 = 28.1 μm, r3 = 44.3 μm, w1 = 2.1 μm, w2 = 2.2 μm, and w3 = 2.3 μm, the HE corresponding to the inner layer 5 of the annular core is 2,1 , HE 3,1 , HE4,1 , EH 1,1 , EH 2,1 The dispersion of the mode varies with wavelength.

[0034] Figure 3 In the optical fiber structure of the present invention, the HE corresponding to the middle layer 6 of the annular core 2,1 , HE 3,1 , HE 4,1 , HE 5,1 , HE 6,1 , HE 7,1 , HE 8,1 , EH 1,1 , EH 2,1 , EH 3,1 , EH 4,1 , EH 5,1 , EH 6,1 The dispersion of the mode varies with wavelength.

[0035] Figure 4 In the optical fiber structure of the present invention, the outer layer 7 of the annular core corresponds to HE 2,1 , HE 3,1 , HE 4,1 , HE 5,1 , HE 6,1 , HE 7,1 , HE 8,1 , HE 9,1 , HE 10,1 , HE 11,1 , EH 1,1 , EH 2,1 , EH 3,1 , EH 4,1 , EH 5,1 , EH 6,1 , EH 7,1 , EH 8,1 , EH 9,1 The dispersion of the mode varies with wavelength.

[0036] Figure 5 In the optical fiber structure of the present invention, the OAM synthesized by the HE mode corresponding to the inner layer 5 of the annular core 1,1 、OAM 3,1 The effective mode area of ​​the mode changes with wavelength, and the OAM synthesized by the HE mode corresponding to the middle layer 6 of the ring core 1,1 、OAM 3,1 、OAM 5,1 、OAM 7,1 The effective mode area of ​​the mode changes with wavelength, and the OAM synthesized by the HE mode corresponding to the outer layer 7 of the ring core 1,1 、OAM 3,1 、OAM 5,1 、OAM7,1 、OAM 9,1 Variation of the effective mode area of ​​a mode with wavelength.

[0037] Figure 6 In the optical fiber structure of the present invention, the OAM synthesized by the HE mode corresponding to the inner layer 5 of the annular core 1,1 、OAM 3,1 The nonlinear coefficient of the mode varies with wavelength. The OAM synthesized by the HE mode corresponding to the middle layer 6 of the ring core 1,1 、OAM 3,1 、OAM 5,1 、OAM 7,1 The nonlinear coefficient of the mode varies with wavelength. The OAM synthesized by the HE mode corresponding to the outer layer 7 of the ring core 1,1 、OAM 3,1 、OAM 5,1 、OAM 7,1 、OAM 9,1 Variation of the nonlinear coefficient of the mode with wavelength.

[0038] Figure 7 In the optical fiber structure of the present invention, the OAM synthesized by the HE mode corresponding to the outer layer 7 of the annular core 1,1 、OAM 2,1 、OAM 3,1 、OAM 4,1 、OAM 5,1 、OAM 6,1 、OAM 7,1 、OAM 8,1 、OAM 9,1 、OAM 10,1 The mode confinement loss varies with wavelength. DETAILED DESCRIPTION

[0039] The present invention will be further described in detail below in conjunction with the accompanying drawings.

[0040] Embodiment 1:

[0041] The vortex light multi-concentric ring core non-zero dispersion shifted optical fiber provided by the present invention is as follows Figure 1 As shown, the optical fiber comprises, from inside to outside, a circular region 1, an annular core inner layer 5, a first interlayer 2, an annular core middle layer 6, a second interlayer 3, an annular core outer layer 7, and an outer optical fiber cladding 4.

[0042] The refractive index of the fiber cladding is n0, and the refractive index of the annular core region is n1, where n1 > n0. The widths of the three nested annular cores are w1, w2, and w3 from the inside to the outside, satisfying w1 < w2 < w3. In this embodiment, the circular region 1, the first interlayer 2, the second interlayer 3, and the outer fiber cladding 4 are made of silica, and the material of the annular core region is germanium-doped silica. The above cross-sectional structure remains unchanged along the length direction of the fiber.

[0043] Figure 1 In the figure, the light color represents the fiber cladding region of pure silica with a refractive index of n0, and the dark color represents the annular core region of germanium-doped silica with a refractive index of n1. At a wavelength of 1550 nm, n0 = 1.4440 and n1 = 1.4605.

[0044] Figures 2 to 4 It is the variation of the dispersion of each order of HE mode and EH mode corresponding to the inner annular core 5, the middle annular core 6, and the outer annular core 7 with wavelength when the structural parameters are r1 = 12 μm, r2 = 28.1 μm, r3 = 44.3 μm, w1 = 2.1 μm, w2 = 2.2 μm, and w3 = 2.3 μm. It can be seen from the figure that the three annular cores from the inside to the outside can support the transmission of 10, 26, and 34 OAM modes respectively, that is, the dispersion of the 70 orbital angular momentum modes in the fiber of the present invention is maintained between 1 ps / nm / km and 10 ps / nm / km in the C band, and this dispersion characteristic can meet the ITU-T G.655.C standard of non-zero dispersion shifted fiber.

[0045] Where r1, r2, and r3 are the inner diameters of the inner annular core 5, the middle annular core 6, and the outer annular core 7 of the three annular cores respectively, and w1, w2, and w3 are the widths of the three annular cores respectively.

[0046] Figure 5 It is the variation of the effective mode field area of the odd-order OAM mode synthesized by the HE mode corresponding to the inner annular core 5, the middle annular core 6, and the outer annular core 7 with wavelength. It can be seen from the figure that the inner annular core has a smaller effective mode field area than the outer annular core.

[0047] Figure 6 It is the variation of the nonlinear coefficient of the odd-order OAM mode synthesized by the HE mode corresponding to the inner annular core 5, the middle annular core 6, and the outer annular core 7 with wavelength. It can be seen from the figure that the inner annular core has a larger nonlinear coefficient than the outer annular core.

[0048] Figure 7It is the variation of the confinement loss of each order of OAM mode synthesized by the HE mode corresponding to the outer layer 7 of the annular core with wavelength. It can be seen from the figure that as the wavelength increases, the confinement loss of each order of OAM mode increases, but it can be controlled below 0.35 dB / km.

[0049] The optical fiber cladding material is pure silica. When the communication wavelength λ = 1550 nm, n0 = 1.4440;

[0050] The materials of the three annular cores are all germanium-doped silica, and the doping concentrations are the same. When the communication wavelength λ = 1550 nm, n1 = 1.4605; The inner diameters of the inner layer 5, the middle layer 6, and the outer layer 7 of the three annular cores are r1, r2, and r3 respectively, and the widths are w1, w2, and w3 respectively. The three annular cores are nested from the inside to the outside, and r1 < r2 < r3. To ensure that the OAM modes of each annular core can be transmitted independently, the width of the outer annular core needs to be greater than that of the inner annular core, that is, w1 < w2 < w3.

[0051] When the doping concentration is 8 mol%, the dispersions of the HE 2,1 modes of the inner layer 5, the middle layer 6, and the outer layer 7 of the annular core at a wavelength of 1550 nm are 6.85 ps / nm / km, 6.53 ps / nm / km, and 6.99 ps / nm / km respectively;

[0052] When the doping concentration is 14 mol%, the dispersions of the HE 2,1 modes of the inner layer 5, the middle layer 6, and the outer layer 7 of the annular core at a wavelength of 1550 nm are 0.41 ps / nm / km, 1.44 ps / nm / km, and 2.84 ps / nm / km respectively;

[0053] When the widths w1, w2, and w3 of the three annular cores are 2.2 μm, 2.3 μm, and 2.4 μm respectively, the dispersions of the HE 2,1 modes of the inner layer 5, the middle layer 6, and the outer layer 7 of the annular core at a wavelength of 1550 nm are 3.46 ps / nm / km, 6.58 ps / nm / km, and 5.21 ps / nm / km respectively; When w1, w2, and w3 are 2.3 μm, 2.4 μm, and 2.5 μm respectively, the dispersions of the HE 2,1 modes of the inner layer 5, the middle layer 6, and the outer layer 7 of the annular core at a wavelength of 1550 nm are 4.32 ps / nm / km, 7.43 ps / nm / km, and 5.99 ps / nm / km respectively.

[0054] When the distance between the inner layer 5 of the annular core and the middle layer 6 of the annular core, and the distance between the middle layer 6 of the annular core and the outer layer 7 of the annular core are both 10 μm, the HE of the inner layer 5 of the annular core, the middle layer 6 of the annular core, and the outer layer 7 of the annular core are 2,1 The dispersion of the modes at a wavelength of 1550nm is 3.29ps / nm / km, 3.40ps / nm / km, and 3.96ps / nm / km respectively; when the spacing between the inner layer 5 of the ring core and the middle layer 6 of the ring core, and the spacing between the middle layer 6 of the ring core and the outer layer 7 of the ring core are all 18μm, the HE of the inner layer 5 of the ring core, the middle layer 6 of the ring core, and the outer layer 7 of the ring core are 2,1 The dispersions of the modes at a wavelength of 1550 nm are 2.87 ps / nm / km, 3.32 ps / nm / km, and 4.39 ps / nm / km, respectively.

Claims

1. A vortex optical multi-concentric ring core non-zero dispersion shifted optical fiber, characterized in that: It includes an annular fiber core and an optical fiber cladding which are mutually nested and spaced apart; Wherein, the annular fiber core has at least two layers, and the innermost layer and the outermost layer are the optical fiber cladding; The high refractive index annular core matches the annular intensity profile of the vortex light, and the outer annular core can support the transmission of more OAM modes.

2. The vortex light multi-concentric ring core non-zero dispersion shifted optical fiber according to claim 1, characterized in that: When the number of ring fiber cores is three; The annular fiber core is divided into an annular fiber core inner layer (5), an annular fiber core middle layer (6) and an annular fiber core outer layer (7); The optical fiber cladding comprises a circular region (1), a first interlayer (2), a second interlayer (3), and an outer optical fiber cladding (4); from the inside to the outside, they are the circular region (1), an inner layer of an annular fiber core (5), the first interlayer (2), an inner layer of an annular fiber core (6), the second interlayer (3), an outer layer of annular fiber core (7), and an outer optical fiber cladding (4); The three high-refractive-index annular cores match the annular intensity profile of the vortex light, and the outer annular core can support the transmission of more OAM modes.

3. The vortex light multi-concentric ring core non-zero dispersion shifted optical fiber according to claim 1, characterized in that: The refractive index of the optical fiber cladding is n0, and the refractive index of the annular core is n1, satisfying that n1 is greater than n0, that is, the refractive index in the annular core is greater than that in the optical fiber cladding. The high refractive index can confine the light field in the annular core to achieve a larger effective mode field area and a smaller nonlinear coefficient.

4. The vortex light multi-concentric ring core non-zero dispersion shifted optical fiber according to claim 1, characterized in that: Each layer of the optical fiber cladding is made of any one of pure silica, germanium-doped silica, fluorine-doped silica, air, Schott glass, fluoride or sulfide; when pure silica is used, when the communication wavelength λ=1550nm, n0=1.4440; The three ring fiber core materials are any one of pure silica, germanium-doped silica, fluorine-doped silica, air, Schott glass, fluoride or sulfide; When it is germanium-doped silicon dioxide with the same doping concentration and the communication wavelength λ=1550nm, n1=1.4605; the inner diameters of the three ring core inner layers (5), the ring core middle layer (6) and the ring core outer layer (7) are r1, r2 and r3 respectively, and the widths are w1, w2 and w3 respectively. The three ring cores are nested from the inside to the outside, and there is r1 <r2<r3。 5. The vortex light multi-concentric ring core non-zero dispersion shifted optical fiber according to claim 4, characterized in that: The doping concentration ranges from 8 to 14 mol%. As the doping concentration increases, the dispersion of the OAM mode decreases significantly. When the doping concentration increases from 8 mol% to 14 mol%, the HE of the inner layer (5) of the annular core, the middle layer (6) of the annular core, and the outer layer (7) of the annular core decreases. 2,1 The dispersion of the mode at a wavelength of 1550nm is reduced from 6.85ps / nm / km to 0.41ps / nm / km, from 6.53ps / nm / km to 1.44ps / nm / km, and from 6.99ps / nm / km to 2.84ps / nm / km.

6. The vortex light multi-concentric ring core non-zero dispersion shifted optical fiber according to claim 4, characterized in that: The width w1 of the inner layer (5) of the annular core is greater than 2 μm, and the width of the outer layer (7) of the annular core is less than 2.6 μm.

7. The vortex light multi-concentric ring core non-zero dispersion shifted optical fiber according to claim 6, characterized in that: When the widths w1, w2, and w3 of the three annular cores are 2.2 μm, 2.3 μm, and 2.4 μm, respectively, the HE of the inner layer (5), the middle layer (6), and the outer layer (7) of the annular core is 2,1 The dispersion of the modes at 1550nm wavelength are 3.46ps / nm / km, 6.58ps / nm / km, and 5.21ps / nm / km; When w1, w2, and w3 are 2.3 μm, 2.4 μm, and 2.5 μm, respectively, the HE of the inner layer (5), the middle layer (6), and the outer layer (7) of the annular core is 2,1 The dispersion of the modes at 1550nm wavelength are 4.32ps / nm / km, 7.43ps / nm / km, and 5.99ps / nm / km; On the premise of ensuring w1 < w2 < w3, increasing the width of the annular core, the OAM mode dispersion value increases. In addition, when the width of the outer layer (7) of the annular core is 2.3 μm, the effective mode field area of the HE 2,1 mode at a wavelength of 1550 nm is 906.9 μm 2 , and when the width of the outer layer (7) of the annular core is 2.5 μm, the effective mode field area is 915.2 μm 2 . On the premise of not appearing radial high-order modes, increasing the width of the annular core can increase the effective mode field area.

8. The vortex light multi-concentric ring core non-zero dispersion shifted optical fiber according to claim 4, characterized in that: When the distance between the inner layer (5) of the annular core and the middle layer (6) of the annular core, and the distance between the middle layer (6) of the annular core and the outer layer (7) of the annular core are both 10 μm, the HE of the inner layer (5), the middle layer (6) of the annular core, and the outer layer (7) of the annular core is 2,1 The dispersion of the modes at a wavelength of 1550 nm is 3.29 ps / nm / km, 3.40 ps / nm / km, and 3.96 ps / nm / km respectively. When the spacing between the inner layer (5) of the annular core and the middle layer (6) of the annular core, and the spacing between the middle layer (6) of the annular core and the outer layer (7) of the annular core are all 18 μm, the HE of the inner layer (5), the middle layer (6), and the outer layer (7) of the annular core is 2,1 The dispersion of the modes at 1550nm wavelength are 2.87ps / nm / km, 3.32ps / nm / km, and 4.39ps / nm / km; When the spacing increases, the dispersion of the inner layer (5) of the annular core and the middle layer (6) of the annular core decreases, and the dispersion of the outer layer (7) of the annular core increases.

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