A multi-core optical fiber with a double-doped concentration core

Abstract

The present invention discloses a multi-core optical fiber with a double-doped concentration core. From the inside to the outside, it sequentially includes a core ring with 50% ± 3.0% doping material at the center of the optical fiber. Three core rings with 50% ± 3.0% doping material and three core rings with 70% ± 3.0% doping material are evenly distributed around the central core ring. Moreover, the core rings with these two different doping concentrations around the central core ring are arranged in a staggered manner. The center of each core ring is a circular air hole, and the rest of the optical fiber except for the above is the cladding. The present invention can effectively avoid signal crosstalk between the cores, reduce the confinement loss of the optical fiber, thereby making the signal transmission quality higher, the transmission distance farther, and the applicable range wider.

Description

Technical Field

[0001] The present invention relates to fiber optic design technology, and particularly to a multi-core optical fiber with a double-doping concentration core. Background Art

[0002] With the rapid development of information technology, fiber optic communication, as a communication technology with high bandwidth and low transmission loss, can meet people's needs for large-capacity and high-rate data transmission, enabling a large amount of data to be transmitted quickly and stably. However, the communication capacity has shown exponential growth in recent years, and traditional communication methods can no longer meet the development needs of current large-data transmission. Recently, a new multiplexing method using the orbital angular momentum (OAM) of light beams as an information carrier has been proposed to improve the communication capacity.

[0003] Research has found that light beams contain angular momentum, which includes two parts: spin angular momentum (SAM) and orbital angular momentum (OAM). Spin angular momentum is related to the polarization state of light, and any type of light, whether linearly polarized, circularly polarized or elliptically polarized, has spin angular momentum. Orbital angular momentum (OAM) is related to the spatial structure of the light wavefront, and not all light beams carry significant orbital angular momentum, which shows the particularity of light beams carrying orbital angular momentum. The orbital angular momentum modes have an orthogonal relationship in space, showing a new degree of freedom, and theoretically its topological charge number is infinite. Using OAM light beams as the information carrier of a communication system can ideally infinitely improve the transmission capacity and efficiency of optical communication. The OAM mode can be transmitted in atmospheric turbulence and optical fibers. However, compared with atmospheric turbulence, optical fibers are more suitable for the transmission of the OAM mode because they can avoid interference from many external factors and are a good transmission medium.

[0004] However, traditional fiber optic structures cannot better support the transmission of the OAM mode. For example, in multi-core optical fibers, in previous studies, most of the multi-core optical fibers designed by people have cores made of only one material, which makes multi-core optical fibers vulnerable to inter-core crosstalk, limited loss, and dispersion when transmitting optical signals, resulting in low transmission quality of the OAM mode and increased inter-mode crosstalk. Therefore, it is necessary to consider the fiber optic structure design and material selection to better support the transmission of the OAM mode. Summary of the Invention

[0005] Object of the Invention: The object of the embodiments of the present invention is to provide a multi-core optical fiber with a double-doping concentration core that has a wider application range, higher transmission quality, and lower signal attenuation in view of the problems existing in the prior art.

[0006] Technical solution: The multi-core optical fiber with a double-doped concentration core in the present invention is different from most traditional optical fibers that only use one material to prepare the core. Instead, it uses two materials with different doping concentrations to prepare the core. The optical fiber structure from the inside to the outside is a core ring with a doping concentration of 50% ± 3.0% placed at the center of the optical fiber. Three core rings of 50% ± 3.0% doped material and three core rings of 70% ± 3.0% doped material are evenly distributed around the central core ring. Moreover, the core rings of 50% ± 3.0% doped material and the three core rings of 70% ± 3.0% doped material around the central core ring are arranged in a uniform staggered pattern, that is, one core ring of 50% ± 3.0% doped material and one core ring of 70% ± 3.0% doped material are arranged in such a cyclic alternating pattern. The centers of the seven core rings in the optical fiber are all circular air holes, and the periphery of all the core rings is the cladding part.

[0007] Furthermore, the core ring material with a doping concentration of 50% ± 3.0% is a material prepared by doping 50% ± 3.0% of germanium dioxide into silicon dioxide.

[0008] Furthermore, the core ring material with a doping concentration of 70% ± 3.0% is a material prepared by doping 70% ± 3.0% of germanium dioxide into silicon dioxide.

[0009] The cladding material is silicon dioxide, and its Sellmeier equation is as follows:

[0010]

[0011] Where λ is the working wavelength, n is the refractive index of the cladding material, and Bi and Ci are the coefficients of the Sellmeier equation. Specifically, Bi is the coefficient related to the specific wavelength dependence of the material, and Ci is the coefficient related to the specific resonance frequency of the material. In an embodiment of the present invention, B1 = 0.6961663, B2 = 0.4079426, B3 = 0.8974794, C1 = 0.0684043, C2 = 0.1162414, and C3 = 9.896161 in the above formula.

[0012] For the germanium dioxide doped silicon dioxide, the relationship of its material refractive index is as follows:

[0013]

[0014] Where SA i is the coefficient related to the specific wavelength dependence of the silicon dioxide material, SL i is the coefficient related to the specific resonance frequency of the silicon dioxide material, GA i is the coefficient related to the specific wavelength dependence of the germanium dioxide material, GL iIt is a coefficient related to the specific resonance frequency of germanium dioxide material. In one embodiment of the present invention, its values are SA1 = 0.6961663, SA2 = 0.4079426, SA3 = 0.8974794, SL1 = 0.0684043, SL2 = 0.1162414, SL3 = 9.896161, GA1 = 0.80686642, GA2 = 0.71815848, GA3 = 0.85416831, GL1 = 0.068972606, GL2 = 0.15396605, GL3 = 11.841931. X is the doping concentration of germanium dioxide, and λ is the operating wavelength. n(GeO2 - SiO2) is the refractive index of germanium dioxide - doped silica material.

[0015] Furthermore, the material of the cladding part of the optical fiber is silica.

[0016] Furthermore, the seven core rings have the same thickness, which is 1.45 - 1.55 microns.

[0017] Furthermore, the diameter of the optical fiber is 125 microns.

[0018] Furthermore, the center of the innermost core ring of the optical fiber is 35 - 45 microns away from the six core rings of the same size on its periphery.

[0019] Beneficial effects: Compared with the prior art, the significant advantages of the present invention are as follows: Different from most traditional optical fibers that only use one material to prepare the core, the core of the optical fiber of the present invention is prepared with two materials having different doping concentrations. By using materials with different doping concentrations, each core can have unique optical properties, thereby reducing crosstalk, reducing interference between different modes, realizing the transmission of multiple modes, enabling the optical fiber to transmit more data at the same time, and thus improving the bandwidth capacity of the system. And in terms of structure, it is ingeniously designed that the cores made of two materials with different doping concentrations are evenly and alternately distributed, and the seven cores each serve as an independent channel for signal transmission, so that during the transmission of signals in the multi - core optical fiber, inter - core crosstalk is reduced and the quality of signal transmission is improved. At the same time, through experiments, it is measured that its confinement loss is low and the mode quality is high, which is more conducive to long - distance signal transmission. Description of the Drawings

[0020] Figure 1 It is a schematic structural diagram of a multi - core optical fiber with double - doped concentration cores provided by the present invention;

[0021] Figure 2 It is the electric field intensity and phase schematic diagram of the HE 3,1 、HE 5,1 and EH 4,1 mode transmission of the 50% doping concentration core ring;

[0022] Figure 3 is the electric field intensity and phase schematic diagram of the HE 7,1 、HE 8,1 and EH 5,1 modes in a core ring with a 70% doping concentration;

[0023] Figure 4 is the refractive index distribution diagram of the OAM modes supported in a core ring with a 50% doping concentration;

[0024] Figure 5 is the effective refractive index difference distribution diagram between adjacent mode groups in a core ring with a 50% doping concentration;

[0025] Figure 6 is the refractive index distribution diagram of the OAM modes supported in a core ring with a 70% doping concentration;

[0026] Figure 7 is the effective refractive index difference distribution diagram between adjacent mode groups in a core ring with a 70% doping concentration;

[0027] Figure 8 is the confinement loss distribution diagram of the 1st to 7th order OAM modes in a core ring with a 50% doping concentration;

[0028] Figure 9 is the confinement loss distribution diagram of the 2nd to 11th order OAM modes in a core ring with a 70% doping concentration;

[0029] Figure 10 is the OAM in a core ring with a 50% doping concentration 0,1 to OAM 10,1 mode quality distribution diagram of each mode;

[0030] Figure 11 is the OAM in a core ring with a 70% doping concentration 0,1 to OAM 13,1 mode quality distribution diagram of each mode;

[0031] Figure 12 is the dispersion distribution diagram of each mode in a core ring with a 50% doping concentration;

[0032] Figure 13 is the dispersion distribution diagram of each mode in a core ring with a 70% doping concentration;

[0033] Figure 14 is the electric field intensity and phase schematic diagram of the HE 7,1 、HE 8,1 and EH 5,1 modes transmitted in a core ring (core pitch 35 microns, core ring thickness 1.45 microns) with a 70% doping concentration;

[0034] Figure 15It is the core ring with a doping concentration of 50% (core pitch 45 μm, core ring thickness 1.55 μm) transmitting HE 3,1 、HE 5,1 and EH 4,1 mode electric field intensity and phase schematic diagram. Specific implementation mode

[0035] This embodiment provides a multi-core optical fiber with double-doping concentration cores. As Figure 1 shown, a core ring 2 with a doping concentration of 50% ± 3% is arranged at the center of the optical fiber. The center of the core ring is a circular air hole 1. Three core rings of 50% ± 3% doped material (the black core ring represents 50% ± 3% doping, such as core ring 4) and three core rings of 70% ± 3% doped material (the gray core ring represents 70% ± 3% doping, such as core ring 3) are evenly distributed around the central core ring, and the above two types of core rings are arranged in a uniform staggered pattern, as well as the cladding 5. The seven core rings in the optical fiber have the same size. The radius of the circular air holes in the seven core rings is 7 μm, the core ring thickness is 1.5 μm, and the centers of the six outer core rings are 40 μm away from the center of the core ring 2 in the center of the optical fiber and are evenly distributed. The radius of the cladding 5 is 62.5 μm, and the cladding material is silica. The core ring of 50% ± 3% doped material is prepared by mixing germanium dioxide and silica according to a doping ratio of 1:1. The core ring of 70% ± 3% doped material is prepared by mixing germanium dioxide and silica according to the doping ratio (GeO2:S i O2 = 7:3).

[0036] See Figure 1 , Figure 1Schematic diagram of a multi-core optical fiber with a double-doped concentration core. Each core ring can be used as an independent channel for signal transmission. The core pitch is set to 40 μm, which can reduce the optical signal coupling effect between different cores, helping to reduce the mutual interference between optical signals and the influence of inter-core crosstalk, thereby improving the signal transmission quality in the multi-core optical fiber. At the same time, appropriately increasing the core ring pitch helps to increase the isolation between channels. The higher the isolation, the more stable the performance of the communication system. In other embodiments, it is found that setting the core pitch to any value between 35 μm and 45 μm has basically the same effect. In the present invention, the core ring thickness is set between 1.45 μm and 1.55 μm, and the effect is basically the same. Therefore, the core ring thickness in the embodiment of the present invention is set to 1.5 μm. Appropriately increasing the thickness of the core ring allows the optical fiber to support more propagation modes, which is beneficial to reducing the signal loss in the optical fiber. However, a thicker core ring will lead to an increase in dispersion and interference between modes within the ring, which will reduce the signal transmission quality and transmission distance. In this embodiment, the core ring can achieve multi-mode transmission by using two materials with different doping concentrations, helping to reduce the loss of optical signals during transmission, reduce the interference between different modes, and improve the signal stability and quality.

[0037] The present embodiment is simulated, and modeling, calculation, and analysis are performed using the finite element analysis method. In this embodiment, the optical fiber is analyzed and calculated at a working wavelength of 1.5 μm to 1.6 μm, and the Figure 2 and Figure 3 show the mode field strength and phase supported by the optical fiber. Figure 2 describes the electric field intensity and phase diagram of the HE 3,1 , HE 5,1 and EH 4,1 modes transmitted by the 50% doped concentration core ring; Figure 3 is the electric field intensity and phase diagram of the HE 7,1 , HE 8,1 and EH 5,1 modes transmitted by the 70% doped concentration core ring. The OAM vector mode in the optical fiber is obtained by linearly superimposing the HE mode or the EH mode. The small arrows in the figure represent the electric field direction, and different modes can be judged therefrom. The specific superposition formula is as follows:

[0038]

[0039]

[0040] In the above formula, even represents the even mode, odd represents the odd mode, and j represents the phase difference.

[0041] Figure 4 is the variation of the refractive index of the OAM mode supported within the 50% doped concentration core ring with wavelength.Figure 5 is the variation of the effective refractive index difference between adjacent mode groups within the core ring with a 50% doping concentration as a function of wavelength. The effective refractive index difference between each adjacent mode is greater than 10 -4 , and the relatively large refractive index difference can effectively isolate adjacent orbital angular momentum modes and prevent mode coupling between them, which helps to maintain the purity and stability of the modes, and reduce signal loss and distortion during transmission. Figure 6 is the variation of the refractive index of the OAM modes supported within the core ring with a 70% doping concentration as a function of wavelength, Figure 7 is the variation of the effective refractive index difference between adjacent mode groups within the core ring with a 70% doping concentration as a function of wavelength. The effective refractive index difference between each adjacent mode is greater than 10 -4 . Figure 8 is the variation of the confinement loss of the 1st to 7th order OAM modes within the core ring with a 50% doping concentration as a function of wavelength. It can be seen from the figure that the confinement loss of these OAM modes is mainly concentrated around 10 -10 dB / m, Figure 9 is the variation of the confinement loss of the 2nd to 11th order OAM modes within the core ring with a 70% doping concentration as a function of wavelength. It can be seen that the confinement loss is mainly concentrated around 10 -12 dB / m. From Figure 8 and Figure 9 it can be seen that the confinement loss of the said optical fiber is relatively low. The lower confinement loss also reflects lower signal attenuation, which is beneficial to the high-quality transmission of the modes. Figure 10 is the OAM within the core ring with a 50% doping concentration 0,1 to OAM 10,1 The variation of the mode quality of each mode as a function of wavelength. It can be seen that the mode quality transmitted by the core is greater than 75%, Figure 11 is the OAM within the core ring with a 70% doping concentration 0,1 to OAM 13,1 The variation of the mode quality of each mode as a function of wavelength. It can be seen that the mode quality transmitted by the core is greater than 80%. All of these indicate that the said optical fiber is beneficial to the low-loss transmission of the modes. In this application, the mode quality transmitted by the core is greater than 75%, indicating that the transmission loss of the optical fiber in this application is relatively low, thus reflecting low signal attenuation and being conducive to signal transmission. Figure 12 is the variation of the dispersion of each mode within the core ring with a 50% doping concentration as a function of wavelength. The maximum dispersion value is lower than 250 ps / nm / km. At the same time, the dispersion values of some modes are negative, Figure 13 is the variation of the dispersion of each mode within the core ring with a 70% doping concentration as a function of wavelength. The maximum dispersion value is lower than 600 ps / nm / km. The variation of the dispersion of the OAM modes transmitted within the core ring of this application generally tends to be gentle, reducing the influence of dispersion on signal transmission and improving the transmission quality and capacity.

[0042] In other embodiments, by setting the core pitch to 35 microns and the core ring thickness to 1.45 microns, the finite element method is used to perform modeling and analysis of the electric field intensity and phase diagrams of the HE 7,1 、HE 8,1 and EH 5,1 modes, and the effects shown in Figure 14 are obtained; by setting the core pitch to 45 microns and the core ring thickness to 1.55 microns, the finite element method is used to perform modeling and analysis of the electric field intensity and phase diagrams of the HE 3,1 、HE 5,1 and EH 4,1 modes, and the effects shown in Figure 15 are obtained. By comparing the above two other embodiments with Figure 2 Figure 3 in this embodiment (core pitch 40 microns, core ring thickness 1.5 microns), the effects of the electric field intensity and phase diagrams of the same modes transmitted by the core rings with the same doping concentration are basically the same.

[0043] Perform performance parameter simulation on this embodiment. Among them, the core ring with 50% doping concentration supports the stable transmission of the 1st to 10th order OAM modes, and the core ring with 70% doping concentration supports the stable transmission of the 1st to 13th order OAM modes. Also, because there are 4 core rings with 50% doping concentration and 3 core rings with 70% doping concentration in the optical fiber, a total of 302 OAM modes can be transmitted by the two core rings with different doping concentrations (152 in the 4 core rings with 50% doping concentration and 150 in the 3 core rings with 70% doping concentration), and the applicable range is wider; within the communication wavelength range, interference between core rings is avoided, and no radial high-order modes are generated within the core rings, avoiding mode crosstalk, and the confinement loss is lower than that of traditional optical fibers, which is more conducive to the long-distance and high-quality transmission of modes.

[0044] The above-disclosed are only the preferred embodiments of the present invention, and the scope of the rights of the present invention cannot be limited thereby. Therefore, equivalent changes made according to the claims of the present invention still fall within the scope covered by the present invention.

Claims

1. A multi-core optical fiber with a double-doped concentration core, characterized in that, It includes a core ring and a cladding. The core ring includes a central core ring disposed at the center of the optical fiber and core rings with different proportion doped materials evenly distributed around the central core ring; the center of the core ring is a circular air hole; in the multi-core optical fiber, except for the core ring and the air holes inside the core ring, the rest is the cladding. The core rings with different proportion doped materials evenly distributed around the central core ring include a core ring with 50% ± 3.0% doped material and a core ring with 70% ± 3.0% doped material; the material of the core ring with 50% ± 3.0% doped material is the material prepared by doping 50% ± 3.0% germanium dioxide into silica; the material of the core ring with 70% ± 3.0% doped material is the material prepared by doping 70% ± 3.0% germanium dioxide into silica.

2. The multi-core optical fiber with a double-doped concentration core according to claim 1, characterized in that, The material of the central core ring is the same as that of the core ring with 50% ± 3.0% doping around the central core ring.

3. A multi-core optical fiber with a double-doped concentration core according to claim 1, characterized in that, The core rings with different proportion doped materials evenly distributed around the central core ring are arranged in a staggered manner.

4. A multi-core optical fiber with a double-doped concentration core according to claim 1, characterized in that The thickness of the core ring is 1.45 - 1.55 microns.

5. A multi-core optical fiber with a double-doped concentration core according to claim 1, characterized in that, The core pitch is 35 - 45 microns.

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