A graded non-degenerate supermode fiber based on light field modulation

Abstract

A kind of based on light field regulation's gradual change type four circle core supermode optical fiber, its characterized in that: optical fiber is composed of four circle core of gradually changing refractive index distribution, Trench trench area, cladding;The radius of its four core is a x =3.0 μm The coordinates of the center of four core are and respectively x =14.4 μm, outer circle radius c x =23.4 μm;The rest is cladding, the radius of outermost cladding R=62.5 μm;The center refractive index of two core in X direction is same, the center refractive index of two core in Y direction is same, the center refractive index of core in X, Y direction is different;The center refractive index of two core in X direction adopts pure silica n1=1.44402, the center refractive index of two core in Y direction n2=1.44302, the refractive index of cladding n3=n CL =1.42805, the refractive index of Trench trench area n4=1.42482;The refractive index of four circle core is gradually changed distribution.Using light field regulation method, the mode degeneracy of four circle core supermode optical fiber is broken, and low intrinsic loss, low crosstalk operation is realized.

Description

Technical Field

[0001] This patent application relates to a novel optical fiber, proposing a graded non-degenerate supermode optical fiber based on optical field modulation, which can be applied to next-generation information technology fields such as mode division multiplexing. Background Technology

[0002] With the rapid development of various communication services, traditional single-mode optical fibers, limited by the nonlinear Shannon limit, can no longer meet the demands of more communication services. Mode division multiplexing technology based on few-mode fibers can significantly improve the transmission capacity and spectral efficiency of single-mode fibers, becoming a hot topic in the current field of optical fiber communication. For example, the paper [K. Shibahara, M. Hoshi, and Y. Miyamoto, "10-spatial-mode 1300-km transmission over 6-LP graded index few-mode fiber with 36-ns modal dispersion," J. Lightw. Technol., vol.42, no.4, pp.1257-1268, Feb.15, 2024. doi:] proposes an MDM transmission system with 10 spatial modes and an FMF of 1300km over 6-LP few-mode fiber; the paper [Georg Rademacher, Benjamin J. Puttnam, Ruben S. Luís, et al. "10.66 Peta-Bit / t / s Transmission over a 38-Core-Three-Mode Fiber," [C]. 2020 Optical Fiber Communications Conference and Exhibition (OFC), San Diego, CA, USA] proposes a system that implements 10 spatial modes over 1300km over 6-LP few-mode fiber; [Th3H.1, 1-3, 2020] proposed a few-mode fiber MDM transmission system, which achieved a net transmission capacity of 10.66 Pb / s over 13 km of few-mode fiber.

[0003] Meanwhile, the literature [Cen Xia, Neng Bai, Ibrahim Ozdur, et al. "Supermodes for optical transmission", [J]. Optics express, 2011, 19(17)] introduced the concept of supermode and proposed the advantages of supermode fiber (special few-mode fiber), which can achieve strong coupling between different cores, has a larger effective area, lower fiber nonlinearity, higher mode density and additional design freedom; the literature [Jin Luo, Mei Sang, Ningbo Zhao, et al. "A Supermode Fiber with Strong Mode Coupling for Space-Division Multiplexing." Asia Communications and Photonics Conference 2015] proposed a supermode fiber design to achieve strong mode coupling to reduce differential mode delay (DMD) in SDM; the literature [Lin Sun, Junwei Zhang, Gai Zhou, et al. "Theoretical investigations of weakly and strongly-coupled multi-core fibers for the applications of optical submarine communications under power and fiber count limits", [J]. Optics [Express, 2023, 31(3)] studied the application of weakly coupled and strongly coupled multicore optical fibers (WC-MCF, SC-MCF) in submarine communication. Among them, SC-MCF optical cable can improve the Q factor by 0.75-2dB compared with WC-MCF optical cable. The literature [Sergey Alyshev, Alexander Vakhrushev, Andrey Umnikov, et al. "Supermode lasing and light amplification in multicore bismuth-doped fiber", Opt. Express 32, 29214-29226 (2024)] verified numerically and experimentally that using bismuth-doped multicore optical fiber to excite supermodes can achieve optical amplification and stable laser output in the E-band telecommunications field.The above research shows that multi-core supermode fiber has good transmission performance and broad application prospects in optical communication, fiber lasers and fiber amplifiers, fiber sensors and other fields, bringing better performance to mode division multiplexing systems. Therefore, strong coupling supermode operation is the current research focus and has great advantages. This is the initial consideration factor in the fiber design of this patent.

[0004] The aforementioned research focuses on circular-core few-mode fiber and circular-core supermode fiber. Although these technologies can address capacity limitations in fiber optic communication systems to some extent, they still suffer from significant mode degeneracy, mode crosstalk, and loss. Mode degeneracy and crosstalk require multiple-input multiple-output digital signal processing (MIMO-DSP) to resolve these issues. However, as the number of modes increases, the complexity, computational burden, and cost of MIMO-DSP become more severe, necessitating the exploration of new solutions. Summary of the Invention

[0005] With the support of the National Natural Science Foundation of China (No. 61671227 and 61431009), the graded-index few-mode fiber system has obvious advantages and is widely used in the two major categories of fiber transmission systems: step-index and graded-index fiber transmission systems. [1 Pierre Sillard, Marianne Bigot-Astruc, and Denis Molin, Few-Mode Fibers for Mode-Division-Multiplexed Systems[J]. Journal of Lightwave Technology, 2014, 32(16): 2824-2829; 2 Zheng Hongjun, Li Xin, Bai Chenglin, Chirped Pulse Transmission in Fiber, Beijing: Science Press, 2018, 1-184; 3 Zhiguo Peng, Jindong Zheng, Hongjun Zheng, Xin Li, Chenglin Bai, Weisheng Hu, A novel supermode-maintaining optical fiber with low intrinsic loss and low crosstalk, Fiber and Integrated [Optics, 2025, 44(2), 101-123]; This patent application proposes a graded non-degenerate supermode fiber based on optical field modulation. This fiber integrates the advantages of supermode fiber and the graded distribution of refractive index at the center of pure silica fiber core. It proposes to use optical field modulation method to break the spatial mode degeneracy of circular core supermode fiber, realize the MIMO-FREE application of four circular core supermode fiber with low loss and low crosstalk, eliminate the complex MIMO-DSP processing, and provide important support for in-depth research in the fields of fiber optics, fiber optic communication, fiber optic wireless access, optical information processing and new generation information technology. It has important academic value and also shows broad application prospects. The research significance is very important.

[0006] The technical solution adopted by this patent application to solve its technical problem is:

[0007] A graded-index non-degenerate supermode fiber based on optical field manipulation is characterized in that: the fiber consists of four circular cores with graded-index distribution, a Trench trench region, and a cladding; the radius of each of the four cores is a. x The center coordinates of the four fiber cores with a diameter of 3.0 μm are respectively and The inner radius b of the Trench refractive index groove region x =14.4μm, outer circle radius c x=23.4μm; the rest is cladding, with the outermost cladding radius R = 62.5μm; the two core centers in the X direction have the same refractive index, the two core centers in the Y direction have the same refractive index, and the core centers in the X and Y directions have different refractive indices; the two core centers in the X direction are made of pure silicon dioxide with refractive indices n1 = 1.44402, the two core centers in the Y direction have refractive indices n2 = 1.44302, and the cladding has a refractive index n3 = n CL =1.42805, the refractive index of the Trench groove region n4 = 1.42482; the refractive index distribution of the left and right cores of the gradient four-circle fiber core follows the formula n(r) = n x *[1-2Δ(r / a) α ] 1 / 2 , r≤a; where n x The refractive index of the pure silicon dioxide at the center of the left and right fiber cores is 1.44402, r represents the distance from any point in the fiber core to the axis, a represents the radius of the fiber core as 3.0 μm, and α is a gradient parameter of 2. n(r) = n CL =1.42805, r>a; the refractive index distribution of the upper and lower cores of the gradually changing four-circular fiber core follows the formula; n(r) = n y *[1-2Δ(r / a) α ] 1 / 2 r≤a; where n y The refractive index of the fluorinated silica at the center of the upper and lower fiber cores is 1.44302, r represents the distance from any point in the fiber core to the axis, a represents the radius of the fiber core as 3.0 μm, and α is a gradient parameter of 2. n(r) = n CL =1.42805, r>a; The mode field characteristics of spatial modes in optical fibers can be changed by altering the size, position, and refractive index distribution of the core, cladding, and trench regions; By employing optical field modulation, the mode degeneracy of four-core supermode fibers is broken, achieving low intrinsic loss and low crosstalk operation, thereby eliminating complex MIMO-DSP processing and enabling good transmission for MIMO-FREE applications.

[0008] The beneficial effects of this patent application are as follows:

[0009] 1. The optical field modulation method breaks the spatial mode degeneracy of four-core supermode fiber, eliminates the complex MIMO-DSP processing, realizes good transmission in MIMO-FREE applications, and further improves the fiber transmission performance.

[0010] 2. This optical fiber adopts a circular core structure and uses different refractive indices in the X and Y directions to achieve mode optical field modulation, increase the effective refractive index difference between modes, and realize low crosstalk transmission characteristics between modes; adjusting the parameters can further increase the effective refractive index difference between modes and improve the low crosstalk performance.

[0011] 3. The refractive index of the fiber core in the X direction is gradually distributed in a pure silica core, achieving low loss. This provides important support for in-depth research in the fields of fiber optics, fiber optic communication, fiber optic wireless access, optical information processing, and next-generation information technology.

[0012] 4. The mode field characteristics of the Hermitian Gaussian mode in this optical fiber can be changed by altering the size, position, and refractive index of the core and cladding. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the cross-section of a graded non-degenerate supermode fiber based on optical field modulation, as per this patent application. The fiber consists of left and right cores with a gradually changing refractive index distribution at the center of a pure silica core (as shown by the vertical shaded area), upper and lower cores with a gradually changing refractive index distribution at the center of a fluorine-doped silica core (as shown by the horizontal shaded area), a trench region (as shown by the diagonal shaded area), and a cladding (as shown by the white area).

[0014] Figure 2 The electric field distributions for X-polarization of each mode are presented under optical field modulation and at a wavelength of 1.55 μm. Figure 2 (a), (b), (c), and (d) correspond to the electric field distribution of X-polarization for the four supermodes LP21b, LP11b, LP11a, and LP01, respectively. The equipotential lines in the figure represent the strength of the incident electric field; the greater the density, the stronger the electric field.

[0015] Figure 3 This displays the variation of the effective refractive index of the four modes with incident wavelength after optical field manipulation. The square, asterisk, rhombus, triangle, and cross represent the variation of the effective refractive index of the four modes LP01, LP11a, LP11b, LP21b, and Trench with incident wavelength, respectively.

[0016] Figure 4 This shows the effective refractive index difference and the change of Trench as a function of incident wavelength for the four modes after optical field manipulation. Squares, asterisks, rhombuses, and triangles represent n, respectively. LP01 -n LP11a n LP11a -n LP11b n LP11b -n LP21b and n LP21b -n Trench The effective refractive index difference.

[0017] Figure 5The figure shows the variation of the differential mode group delay (DMGD) of the LP21b, LP11b, LP11a, and LP01 supermodes with incident wavelength. The solid lines marked with triangles, diamonds, and asterisks represent the DMGD variations of the LP21b, LP11b, and LP11a modes, respectively.

[0018] Figure 6 The intrinsic loss of the four modes varies with the incident wavelength. The solid lines with squares, asterisks, rhombuses, and triangles represent the intrinsic loss of the LP01, LP11a, LP11b, and LP21b modes, respectively, as a function of the incident wavelength.

[0019] Figure 7 The bending loss of the LP21b mode as a function of wavelength is shown with a bending radius of 9 mm and an angle θ of 30°, indicated by a solid line with an asterisk.

[0020] Figure 8 The bending loss of the LP21b mode as a function of the bending radius is shown at an incident wavelength of 1.55 μm and angles θ of 0°, 30°, 45°, 60° and 90°, represented by a red solid line with a circle, a black solid line with a square, a green solid line with a cross, a pink solid line with a diamond, and a blue solid line with a triangle, respectively.

[0021] Figure 9 Figures (a), (b), (c), and (d) show the variation of dispersion of the four modes LP01, LP11a, LP11b, and LP21b with incident wavelength. The solid lines with circles, asterisks, and triangles in the figures represent the variations of material dispersion, waveguide dispersion, and total dispersion of the modes, respectively. Detailed Implementation

[0022] The technical solution of this patent application is described in detail below with reference to the embodiments and accompanying drawings, but the scope of protection is not limited thereto.

[0023] Example 1

[0024] Figure 1 A graded-index non-degenerate supermode fiber based on optical field manipulation is presented, characterized in that: the fiber consists of four circular cores with graded-index distribution, a Trench trench region, and a cladding; the radius of each of the four cores is a. x The center coordinates of the four fiber cores with a diameter of 3.0 μm are respectively and The inner radius b of the Trench refractive index groove region x =14.4μm, outer circle radius c x=23.4μm; the rest is cladding, with the outermost cladding radius R = 62.5μm; the two core centers in the X direction have the same refractive index, the two core centers in the Y direction have the same refractive index, and the core centers in the X and Y directions have different refractive indices; the two core centers in the X direction are made of pure silicon dioxide with refractive indices n1 = 1.44402, the two core centers in the Y direction have refractive indices n2 = 1.44302, and the cladding has a refractive index n3 = n CL =1.42805, the refractive index of the Trench groove region n4 = 1.42482; the refractive index distribution of the left and right cores of the gradient four-circle fiber core follows the formula n(r) = n x *[1-2Δ(r / a) α ] 1 / 2 , r≤a; where n x The refractive index of the pure silicon dioxide at the center of the left and right fiber cores is 1.44402, r represents the distance from any point in the fiber core to the axis, a represents the radius of the fiber core as 3.0 μm, and α is a gradient parameter of 2. n(r) = n CL =1.42805, r>a; the refractive index distribution of the upper and lower cores of the gradually changing four-circular fiber core follows the formula; n(r) = n y *[1-2Δ(r / a) α ] 1 / 2 , r≤a; where n y The refractive index of the fluorinated silica at the center of the upper and lower fiber cores is 1.44302, r represents the distance from any point in the fiber core to the axis, a represents the radius of the fiber core as 3.0 μm, and α is a gradient parameter of 2. n(r) = n CL =1.42805, r>a; The mode field characteristics of spatial modes in optical fibers can be changed by altering the size, position, and refractive index distribution of the core, cladding, and trench regions; By employing optical field modulation, the mode degeneracy of four-core supermode fibers is broken, achieving low intrinsic loss and low crosstalk operation, thereby eliminating complex MIMO-DSP processing and enabling good transmission for MIMO-FREE applications.

[0025] Figure 2 The electric field distribution of the X-polarization of the four supermodes under optical field modulation and a wavelength of 1.55 μm is presented. Figure 2Figures (a), (b), (c), and (d) show the electric field distributions of X-polarization for the LP21b, LP11b, LP11a, and LP01 supermodes, respectively. The equipotential lines in the figures represent the strength of the incident electric field; a higher density indicates a stronger electric field. Hermitian modes are used to represent the four modes corresponding to this fiber. The proposed fiber achieves mode-preserving operation of these four Hermitian modes: LP21b, LP11b, LP11a, and LP01. Optical field modulation is achieved based on a pure silica circular core and Trench structure, breaking spatial mode degeneracy and better realizing a large effective refractive index difference and low intrinsic loss. This eliminates complex MIMO-DSP processing and achieves excellent performance for MIMO-FREE applications.

[0026] Figure 3 This figure shows the variation of the effective refractive index of four modes with incident wavelength under optical field manipulation. The squares, asterisks, rhombuses, triangles, and crosses in the figure represent the effective refractive indices of modes LP01, LP11a, LP11b, LP21b, and Trench, respectively. Within the illustrated wavelength range (1.50-1.65 μm), the effective refractive index of all four modes decreases with increasing incident wavelength, and the change in effective refractive index is slow. In the C-band (1.53-1.565 μm), the effective refractive index of all four modes decreases with increasing wavelength. At an incident wavelength of 1.53 μm, the effective refractive indices of modes LP01, LP11a, LP11b, LP21b, and Trench are 1.43401, 1.43264, 1.43208, 1.43072, and 1.42482, respectively. At an incident wavelength of 1.55 μm, the effective refractive indices of modes LP01, LP11a, LP11b, LP21b, and Trench are 1.43401, 1.43264, 1.43208, 1.43072, and 1.42482, respectively. The effective refractive indices of LP11b, LP21b, and Trench are 1.43394, 1.43251, 1.43197, 1.43055, and 1.42482, respectively; and the effective refractive indices of each mode LP01, LP11a, LP11b, LP21b, and Trench are 1.43389, 1.43242, 1.43188, 1.43042, and 1.42482, respectively, at an incident wavelength of 1.565 μm.

[0027] Figure 4This describes the relationship between the effective refractive index difference between different supermodes in the 1.5μm-1.65μm wavelength range of the optical fiber after optical field manipulation, and the change in incident wavelength. Squares, asterisks, rhombuses, and triangles represent the effective refractive index differences between LP01 and LP11a, LP11a and LP11b, LP11b and LP21b, and LP21b and Trench, respectively. In the C-band (1.53μm-1.565μm), the effective refractive index differences between LP01 and LP11a, and between LP11b and LP21b, gradually increase with increasing wavelength. The effective refractive index difference between LP11a and LP11b decreases slightly with increasing wavelength. The effective refractive index difference between LP21b and Trench also decreases gradually with increasing wavelength, and at a relatively rapid rate. At a wavelength of 1.53μm, n... LP01 -n LP11a n LP11a -n LP11b n LP11b -n LP21b and n LP21b -n Trench The effective refractive index difference is 1.37100×10 -3 5.52500×10 -4 1.35850×10 -3 5.90000×10 -3 When the wavelength is 1.55μm, n LP01 -n LP11a n LP11a -n LP11b n LP11b -n LP21b and n LP21b -n Trench The effective refractive index difference is 1.42900×10 -3 5.46500×10 -4 1.41750×10 -3 and 5.72400×10 -3 When the wavelength is 1.565μm, n LP01 -n LP11a n LP11a -n LP11b n LP11b -n LP21b and n LP21b -n Trench The effective refractive index difference is 1.47200×10 -3 5.41500×10 -4 1.46150×10 -3 and 5.59300×10 -3At an incident wavelength of 1.55 μm, the effective refractive index difference between the LP11a and LP11b modes in this four-core supermode fiber is 5.46500 × 10⁻⁶. -4 Furthermore, the effective refractive index difference between other adjacent modes is greater than this value, which is greater than the effective refractive index difference transmission standard 5E0-4 [Sillard P. Few-Mode Fibers for Space Division Multiplexing [C], Optical Fiber Communication Conference, 2016]. Therefore, it can be seen that the optical fiber we studied has a large effective refractive index difference between modes, which can effectively reduce crosstalk or coupling between different modes; adjusting the parameters can further increase the effective refractive index difference between modes and improve the low crosstalk performance.

[0028] Figure 5 The figure shows the variation of the differential mode group delay (DMGD) of the LP21b, LP11b, and LP11a supermodes with incident wavelength. The solid lines marked with triangles, diamonds, and asterisks represent the DMGD variations of the LP21b, LP11b, and LP11a modes, respectively. In the wavelength range of 1.3 μm to 1.65 μm, the LP21b supermode has the highest DMGD value, the LP11b supermode has the lowest, and the LP11a supermode has a moderate DMGD value. The DMGD of both the LP11a and LP11b supermodes increases with increasing input wavelength. The DMGD of the LP21b supermode initially increases with wavelength, then decreases, first increasing to 17.16730 ps / m at 1.565 μm and then decreasing to 16.82590 ps / m at 1.65 μm. Within the C-band (1.53-1.565 μm), the DMGD of the LP11a, LP11b, and LP21b supermodes increases slightly with increasing wavelength. At a wavelength of 1.53 μm, the DMGDs of the LP11a, LP11b, and LP21b supermodes are 10.17730, 6.62026, and 17.06560 ps / m, respectively. At a wavelength of 1.55 μm, the DMGDs of the LP11a, LP11b, and LP21b supermodes are 10.22610, 6.67191, and 17.13810 ps / m, respectively. At a wavelength of 1.565 μm, the DMGDs of the LP11a, LP11b, and LP21b supermodes are 10.25390, 6.70411, and 17.16730 ps / m, respectively.

[0029] Figure 6The figure shows the intrinsic loss of four Hermitian Gaussian modes as a function of incident wavelength. The solid lines marked with squares, asterisks, rhombuses, and triangles represent the intrinsic loss of modes LP01, LP11a, LP11b, and LP21b, respectively, as a function of incident wavelength. The intrinsic loss of all four modes initially decreases and then increases with increasing wavelength between 1.5 μm and 1.65 μm. The intrinsic losses of LP01, LP11a, LP11b and LP21b gradually decrease from 0.17449, 0.17059, 0.17483 and 0.17071 dB / km at 1.5 μm to 0.16096, 0.15789, 0.16140 and 0.15819 dB / km at 1.565 μm, and then rapidly increase to 0.20016, 0.19799, 0.20078 and 0.19865 dB / km at 1.65 μm. Within the C-band (1.53-1.565 μm), the intrinsic losses of modes LP21b, LP11b, LP11a, and LP01 decrease with increasing wavelength, decreasing from 0.16245, 0.16614, 0.16225, and 0.16576 dB / km at 1.53 μm to 0.15819, 0.16140, 0.15789, and 0.16096 dB / km at 1.565 μm, respectively. At a wavelength of 1.55 μm, the intrinsic losses of modes LP21b, LP11b, LP11a, and LP01 are 0.15915, 0.16256, 0.15888, and 0.16215 dB / km, respectively. It can be seen that the intrinsic loss of the fiber proposed in this patent is significantly lower than that of other equivalent supermode fibers.

[0030] Figure 7 The bending loss of the LP21b mode with wavelength is shown as a function of wavelength, with a bending radius of 9 mm and an angle θ of 30°, indicated by a solid line with an asterisk. Within the wavelength range of 1.5 μm to 1.65 μm, the bending loss of the LP21b mode with a bending radius of 9 mm and an angle θ of 30° increases continuously with increasing wavelength. The bending losses at wavelengths of 1.5, 1.55, 1.565, and 1.65 μm are 6.02841E-04, 6.55661E-03, 1.27006E-02, and 2.07135E-01 dB / m, respectively. It can be seen that the bending loss of the LP21b mode is relatively small when the angle θ is 30°, the bending radius is 9 mm, and the wavelength is between 1.5 μm and 1.65 μm.

[0031] Figure 8The graph shows the bending loss of the LP21b mode as a function of the bending radius at an incident wavelength of 1.55 μm and angles θ of 0°, 30°, 45°, 60°, and 90°, represented by solid red lines with circles, solid black lines with squares, solid green lines with crosses, solid pink lines with diamonds, and solid blue lines with triangles, respectively. The graph shows that the bending loss of the LP21b mode gradually decreases with increasing bending radius at 0°, 30°, 45°, 60°, and 90°. At a bending radius of 10 mm, the bending loss of the LP21b mode at angles θ of 0°, 30°, 45°, 60°, and 90° are 5.90523E-03, 2.66817E-03, 1.67965E-03, 2.96405E-03, and 6.45132E-03 dB / m, respectively; at a bending radius of 12 mm, the bending loss of the LP21b mode at angle θ... The bending losses at 0°, 30°, 45°, 60°, and 90° are 7.77038E-04, 3.78766E-04, 2.73731E-04, 4.56163E-04, and 8.97552E-04 dB / m, respectively. Furthermore, the bending losses at all angles with R = 10 mm are significantly less than 159.15 dB / m, satisfying the robustness requirement [J. Han, G. Gao, Y. Zhao and S. Hou, "Bend Performance Analysis of Few-Mode Fibers With High Modal Multiplicity Factors," in Journal of Lightwave Technology, vol. 35, no. 13, pp. 2526-2534, 1 July 1, 2017]. This demonstrates that the optical fiber proposed in this patent exhibits low bending loss and good robustness.

[0032] Figure 9 The figure shows the variation of dispersion of Hermitian modes LP01, LP11a, LP11b, and LP21b with incident wavelength. The solid lines marked with circles, asterisks, and triangles represent the variations in material dispersion, waveguide dispersion, and total dispersion for each Hermitian mode, respectively. Figures (a), (b), (c), and (d) show the dispersion of modes LP01, LP11a, LP11b, and LP21b, respectively. It can be seen from the figure that the waveguide dispersion of modes LP11a, LP11b, and LP21b decreases with increasing wavelength; while the waveguide dispersion of mode LP01 increases with increasing wavelength.

[0033] In the wavelength range of 1.3 μm to 1.65 μm, the total dispersion of modes LP01, LP11a, and LP11b increases with increasing wavelength; while the total dispersion of mode LP21b first increases and then decreases with increasing wavelength. The total dispersion of LP01, LP11a, and LP11b increases from -18.15790, -5.95665, and -7.79853 ps / (nm·km) at 1.3 μm to 15.11330, 14.36380, and 13.50670 ps / (nm·km) at 1.65 μm, respectively, with increasing wavelength. The total dispersion of LP21b increases from 4.38041 ps / (nm·km) at 1.3 μm to 11.27170 ps / (nm·km) at 1.5 μm, and then decreases with increasing wavelength to 5.66158 ps / (nm·km) at 1.65 μm.

[0034] In the wavelength range of 1.53 μm to 1.565 μm, the total dispersion of modes LP01, LP11a, and LP11b increases with increasing wavelength, from 6.04272, 8.83433, and 9.12472 ps / (nm·km) at 1.53 μm to 8.91203, 10.54260, and 10.68750 ps / (nm·km) at 1.565 μm, respectively; while the total dispersion of mode LP21b decreases with increasing wavelength, from 10.89350 ps / (nm·km) at 1.53 μm to 9.97899 ps / (nm·km) at 1.565 μm.

[0035] At a wavelength of 1.55 μm, the total dispersions of modes LP01, LP11a, LP11b and LP21b are 7.70660, 9.82304, 10.04820 and 10.43320 ps / (nm·km), respectively.

[0036] In summary, the optical fiber proposed in this patent breaks the spatial mode degeneracy of circular core optical fibers, realizing mode optical field modulation and mode preservation functions, and possessing advantages such as low loss, low crosstalk, and low bending loss. It should be noted that the specific embodiments are merely representative examples of this technology, and the technical solution is clearly not limited to the above embodiments; many variations are possible. Those skilled in the art who obtain the technology based on its explicit disclosure or without objection from the written description should consider it to be within the scope of protection of this patent.

Claims

1. A graded-variant non-degenerate supermode optical fiber based on optical field modulation, characterized in that: An optical fiber consists of a four-circular core with a graded refractive index, a trench region, and a cladding; the radius of each of the four cores is α. x The center coordinates of the four fiber cores with a diameter of 3.0 μm are respectively and The inner radius b of the Trench refractive index groove region x =14.4μm, outer circle radius c x =23.4μm; the rest is cladding, with the outermost cladding radius R = 62.5μm; the two core centers in the X direction have the same refractive index, the two core centers in the Y direction have the same refractive index, and the core centers in the X and Y directions have different refractive indices; the two core centers in the X direction are made of pure silicon dioxide with refractive indices n1 = 1.44402, the two core centers in the Y direction have refractive indices n2 = 1.44302, and the cladding has a refractive index n3 = n CL =1.42805, the refractive index of the Trench groove region n4 = 1.42482; the refractive index distribution of the left and right cores of the gradient four-circle fiber core follows the formula n(r) = n x *[1-2Δ(r / a) α ] 1 / 2 , r≤a; where n x The refractive index of the pure silicon dioxide at the center of the left and right fiber cores is 1.44402, r represents the distance from any point in the fiber core to the axis, a represents the radius of the fiber core as 3.0 μm, and α is a gradient parameter of 2. n(r) = n CL =1.42805, r>a; the refractive index distribution of the upper and lower cores of the gradually changing four-circular fiber core follows the formula; n(r) = n y *[1-2Δ(r / a) α ] 1 / 2 , r≤a; where n y The refractive index of the fluorinated silica at the center of the upper and lower fiber cores is 1.44302, r represents the distance from any point in the fiber core to the axis, a represents the radius of the fiber core as 3.0 μm, and α is a gradient parameter of 2. n(r) = n CL =1.42805, r>a; The mode field characteristics of spatial modes in optical fibers can be changed by altering the size, position, and refractive index distribution of the core, cladding, and trench regions; By employing optical field modulation, the mode degeneracy of four-core supermode fibers is broken, achieving low intrinsic loss and low crosstalk operation, thereby eliminating complex MIMO-DSP processing and enabling good transmission for MIMO-FREE applications.

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