An elliptical ring assisted light field controlled graded-index non-degenerate mode fiber

Abstract

The application provides a gradually changed non-degenerate mode few-mode optical fiber assisted by an elliptical ring and light field regulation, which is composed of an elliptical core with gradually changed pure silica refractive index as a center, a high refractive index elliptical ring, a trench region and a cladding. x The horizontal radius of the elliptical core, i.e., the long semi-axis a y = 4.64 μm, the ellipticity ρ = a x / a y = 1.5; the core has a high refractive index elliptical ring auxiliary structure; the elliptical core is used to preliminarily break mode degeneration; the high refractive index elliptical ring is used for mode light field regulation, further breaking high-order mode degeneration and further improving the effective refractive index difference between modes, solving the problem of degeneration of high-order spatial modes and realizing low crosstalk; the elliptical core with gradually changed pure silica refractive index as a center realizes low loss; the trench structure is used to realize low bending loss; and finally, the mode-preserving operation with low intrinsic loss, low crosstalk and low bending loss is realized, providing support for a new generation of information technology.

Description

Technical Field

[0001] This patent application relates to a novel optical fiber, proposing a graded non-degenerate mode few-mode optical fiber with elliptical ring-assisted 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 (MDM) technology based on few-mode fibers has significantly improved the transmission capacity and spectral efficiency of single-mode fibers, becoming a hot topic in the field of optical fiber communication. As the transmission carrier of information in optical fiber communication systems, how to improve the transmission performance of few-mode fibers and reduce their loss and crosstalk is a pressing problem to be solved in optical transmission technology.

[0003] To address the issue of single-mode fiber capacity approaching its limit, current research on traditional round-core few-mode fibers is continuously breaking through the transmission capacity or spectral efficiency limits of optical fibers [RADEMACHER G, PUTTNAM BJ, ]. RS, et al.10.66 Peta-Bit / s Transmission over a 38-Core-Three-Mode Fiber.In Optical FiberCommunication Conference(OFC), OSA Technical Digest(Optical Society of America), 2020, Paper Th3H.1; BEPPU S, SOMA D, SUMITA S, et al.402.7-Tb / s MDM-WDM transmission over weakly coupled 10-mode fiber using rate-adaptive PS-16QAMsignals[J]. Journal of Lightwave Technology, 2020, 38: 2835-2841; WAKAYAMA Y, SOMAD, BEPPU S.266.1-Tbit / s transmission over 90.4-km 6-mode fiber with inlinedual C+L-Band 6-mode EDFA[J]. Journal of Lightwave Technology, 2019, 37: 404-410; SOMA D, BEPPU S, WAKAYAMA Y, et al. 257-Tbit / s weakly coupled 10-mode C+L-Band WDM transmission[J]. Journal of Lightwave Technology, 2018, 36: 1375-1381; WEERDENBURG J, RYF R, ALVARADO-ZACARIAS J, et al. 138-Tb / s mode-and wavelength-multiplexed transmission over six-mode graded-index fiber[J]. Journal of Lightwave Technology, 2018, 36: 1369-1374;], however, these round-core few-mode fibers suffer from mode degeneracy and crosstalk problems. Mode degeneracy and crosstalk require the use of multiple-input multiple-output digital signal processing (MIMO-DSP). As the number of modes increases, the complexity, computational load, and cost of MIMO-DSP systems increase rapidly.To address this issue, a mode-preserving few-mode fiber was proposed. Mode-preserving few-mode fiber breaks mode degeneracy and effectively reduces mode crosstalk. Its system can operate without MIMO-DSP, eliminating the need for multiple-input multiple-output digital signal processing. It is called a MIMO-FREE or MIMO-LESS system [Ezra Ip, Giovanni Milione, Ming-Jun Li, Neda Cvijetic, Konstantinos Kanonakis, Jeffery Stone, Gaozhu Peng, Xesús Prieto, Carlos Montero, Vicente Moreno, and Jesús]. ″SDM transmission of real-time 10GbE traffic using commercial SFP+transceivers over 0.5km elliptical-core few-mode fiber,″Opt.Express 23,17120-17126(2015);G.Milione,E.Ip,P.Ji,Y Huang,T.Wang,M.Li,J.Stone,and G.Peng,″MIMO-less space division multiplexing with elliptical core optical fibers,″inOptical Fiber Communication Conference,OSA Technical Digest(online)(OpticaPublishing Group,2017),paper Tu2J.1]。In recent years, the research on mode-preserving few-mode fibers for MIMO-FREE systems has received widespread attention [Yan G, Yanlei L, Xin L, et al. An Elliptical-Core Few-Mode Fiber with Low Loss and Low Crosstalk for the MIMO-FREE Applications[J]. Frontiers in Physics, 2022, 9; Li M, Li X, Li H, et al. Bow-tie holes-aided elliptical-core polarization-maintaining fiber with high birefringence[J]. Optical Fiber Technology, 2022, 73: 103073; Gougeon S, Ung B, LaRochelle S. Semi-analytical modeling and design of PANDA-type highly-elliptical-core few-mode fibers[J]. Journal of Lightwave Technology, 2025, 43(22): 10302-10311; Peng Z, Zheng J, Zheng H, et al. A novel supermode-maintaining optical fiber with low intrinsic loss and low crosstalk[J]. Fiber and Integrated Optics, 2025, 44(2): 101-123].

[0004] However, when the number of modes in a mode-preserving few-mode fiber in a MIMO-FREE system further increases, for example to eight modes (using Hermigass modes corresponding to elliptical cores to describe HG00, HG10, HG01, HG20, HG11, HG30, HG02, and HG21), such fibers will suffer from severe mode degeneracy. For example, modes HG10 and HG01, and modes HG20 and HG11, exhibit severe degeneracy problems. Exploring mode optical field modulation methods to further solve the mode degeneracy problem, eliminate complex multiple-input multiple-output digital signal processing (MIMO-DSP), and realize MIMO-FREE applications has significant academic and application value, with great research significance and broad application prospects. 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 mode few-mode fiber with elliptical ring-assisted optical field modulation. This fiber integrates the advantages of elliptical core with pure silica, graded core and Trench structure, and adopts a high refractive index elliptical ring structure to realize mode optical field modulation, further solving the problem of spatial mode degeneracy, eliminating complex MIMO-DSP processing, realizing mode preservation, low loss and low crosstalk MIMO-FREE application, and providing 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.

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

[0007] A graded-ratio non-degenerate few-mode fiber with elliptical ring-assisted optical field modulation is characterized by: the fiber consisting of an elliptical core with a graded refractive index of pure silica, a high-refractive-index elliptical ring, a trench region, and a cladding; the horizontal radius of the elliptical core, i.e., its semi-major axis a, is... x = 6.96μm, vertical radius is the minor semi-axis a y =4.64μm, ellipticity ρ=a x / a y =1.5; where the Trench cross-section is an elliptical ring structure, and the horizontal radius of the inner ellipse is the semi-major axis b. x=14.46μm, vertical radius is the minor semi-axis b y = 9.64μm, its outer ellipse horizontal radius is also known as the semi-major axis c x = 29.46 μm, vertical radius is the minor semi-axis c y =19.64μm; the core has a high-refractive-index elliptical ring auxiliary structure, and the horizontal radius of the inner ellipse of the high-refractive-index elliptical ring is the semi-major axis d. x = 4.2μm, vertical radius is the minor semi-axis d y =2.8μm, the horizontal radius of the outer ellipse of the high refractive index elliptical ring, i.e., the semi-major axis e x =6μm, vertical radius is the minor semi-axis e y =4μm; the remaining part is the cladding, and its outer cladding radius is R = 62.5μm; the center coordinates of the fiber core are (0, 0); the refractive index distribution of the gradient elliptical fiber core follows the formula n(r) = n1*[1-2Δ(r / a)] α ] 1 / 2 In the formula, r ≤ a, where n1 is the refractive index of pure silica at the center of the elliptical fiber core (1.4440), r represents the distance from any point in the fiber core to the axis, a represents the semi-major axis of the fiber core (6.96 μm), and α is the gradient parameter 2. The refractive indices of the cladding, trench region, and high-refractive-index elliptical ring are n2 = 1.41380, n3 = 1.40474, and n4 = 1.43480, respectively. The mode field characteristics of the spatial modes in this fiber can be altered by changing the size, position, and refractive index distribution of the core, cladding, trench, and high-refractive-index elliptical ring. The elliptical core is used to initially break mode degeneracy; the high-refractive-index elliptical ring is used for mode optical field modulation, further breaking higher-order mode degeneracy and increasing the effective refractive index difference between modes, thus solving the degeneracy problem of higher-order spatial modes and achieving low crosstalk. The elliptical core, with its pure silica core and gradually varying refractive index distribution at the center, achieves low loss. The trench structure achieves low bending loss. Ultimately, mode-preserving operation with low intrinsic loss, low crosstalk, and low bending loss is achieved, 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 use of an elliptical fiber core initially breaks mode degeneracy; the use of a high-refractive-index elliptical ring for mode optical field modulation further breaks mode degeneracy, further increases the effective refractive index difference between modes, realizes mode preservation function and low crosstalk characteristics, solves the degeneracy problem of higher-order spatial modes, eliminates complex MIMO-DSP processing, realizes good transmission in MIMO-FREE applications, and further improves fiber optic transmission performance.

[0010] 2. The elliptical fiber core achieves low loss by using a gradually varying refractive index centered on pure silicon dioxide.

[0011] 3. This optical fiber adopts a Trench structure, which can effectively reduce bending loss.

[0012] 4. The mode field characteristics of the Hermitian Gaussian mode in this optical fiber can be altered by changing the size, position, and refractive index distribution of the core, cladding, high-refractive-index elliptical ring, and trench. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the cross-section of a graded non-degenerate few-mode fiber with elliptical ring-assisted optical field modulation according to this patent application. The fiber consists of an elliptical core (shaded part) with a gradually changing refractive index centered on pure silicon dioxide, a Trench (left diagonal line part), a high refractive index elliptical ring (right diagonal line part), and a cladding (white part).

[0014] Figure 2 This displays the variation of effective refractive index with wavelength for eight modes without optical field modulation. Solid lines with squares, asterisks, rhombuses, circles, triangles, pentagrams, hexagons, crosses, and vertical lines represent the variations for modes HG00, HG10, HG01, HG20, HG11, HG02, HG30, HG21, and Cladding, respectively. Only this [image / description] is displayed. Figure 2 The first graph is the one without light field manipulation, while the other graphs are the ones with light field manipulation.

[0015] Figure 3 The electric field distribution of X-polarization for each mode is presented under optical field modulation and a wavelength of 1.55 μm. Figure 3 (a), (b), (c), (d), (e), (f), (g), and (h) correspond to modes HG21, HG30, HG02, HG11, HG20, HG01, HG10, and HG00, respectively. The equipotential lines in the figure represent the strength of the incident electric field; the greater the density, the stronger the electric field.

[0016] Figure 4 This displays the variation of the effective refractive index with incident wavelength for eight modes under optical field manipulation. The solid lines, marked with squares, asterisks, rhombuses, circles, triangles, pentagrams, hexagons, crosses, and vertical lines, represent the variations for modes HG00, HG10, HG01, HG20, HG11, HG02, HG30, HG21, and Cladding, respectively.

[0017] Figure 5 This shows the variation of the effective refractive index difference with incident wavelength for eight modes under light field manipulation. The solid lines representing squares, asterisks, rhombuses, circles, triangles, pentagrams, hexagons, and crosses represent n, respectively.HG00 -n HG10 n HG10 -n HG01 n HG01 -n HG20 n HG20 -n HG11 n HG11 -n HG02 n HG02 -n HG30 n HG30 -n HG21 and n HG21 -n Cladding The variation with incident wavelength.

[0018] Figure 6 The differential mode group delay (DMGD) of modes HG21, HG30, HG02, HG11, HG20, HG01, and HG10 is shown as a function of incident wavelength. Solid lines with crosses, hexagons, pentagrams, triangles, circles, diamonds, and asterisks represent the DMGD variations for modes HG21, HG02, HG30, HG11, HG20, HG01, and HG10, respectively.

[0019] Figure 7 The intrinsic loss of eight Hermitian Gaussian modes varies with incident wavelength. The solid lines with squares, asterisks, rhombuses, circles, triangles, pentagrams, hexagons, and crosses represent the intrinsic loss of modes HG00, HG10, HG01, HG20, HG11, HG02, HG30, and HG21, respectively, as a function of incident wavelength.

[0020] Figure 8 The diagram shows how the bending loss of the HG21 mode changes with the bending radius. The solid lines with squares, asterisks, rhombuses, circles, and diagonals represent the changes in bending loss with the bending radius when the angle θ between the major axis and the X-axis of the ellipse is 0°, 30°, 45°, 60°, and 90°, respectively.

[0021] Figure 9 The figure shows the variation of dispersion of HG21, HG30, HG02, HG11, HG20, HG01, HG10, and HG00 Hermitian Gaussian modes with incident wavelength. The solid lines with circles, asterisks, and triangles in the figure represent the variations of material dispersion, waveguide dispersion, and total dispersion for each Hermitian Gaussian mode, 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 This patent application discloses a graded-ratio non-degenerate few-mode fiber with elliptical ring-assisted optical field modulation. The fiber is characterized by comprising an elliptical core (dark), a high-refractive-index elliptical ring (right-hand shading), a Trench region (left-hand shading), and a cladding (white), all with a graded refractive index centered on pure silica. The horizontal radius of the elliptical core, i.e., its semi-major axis a, is... x = 6.96μm, vertical radius is the minor semi-axis a y =4.64μm, ellipticity ρ=a x / a y =1.5; where the Trench cross-section is an elliptical ring structure (left-side shading), and the horizontal radius of the inner ellipse is the semi-major axis b. x =14.46μm, vertical radius is the minor semi-axis b y = 9.64μm, its outer ellipse horizontal radius is also known as the semi-major axis c x = 29.46 μm, vertical radius is the minor semi-axis c y =19.64μm; the core has a high-refractive-index elliptical ring auxiliary structure (right-side shading), and the horizontal radius of the inner ellipse of the high-refractive-index elliptical ring is the semi-major axis d. x = 4.2μm, vertical radius is the minor semi-axis d y =2.8μm, the horizontal radius of the outer ellipse of the high refractive index elliptical ring, i.e., the semi-major axis e x =6μm, vertical radius is the minor semi-axis e y =4μm; the remaining part is the cladding, and its outer cladding radius is R = 62.5μm; the center coordinates of the fiber core are (0, 0); the refractive index distribution of the gradient elliptical fiber core follows the formula n(r) = n1*[1-2Δ(r / a)] a ] 1 / 2 , r≤a; where n1 is the refractive index of pure silica at the center of the elliptical fiber core (1.4440), r represents the distance from any point in the fiber core to the axis, a represents the semi-major axis of the fiber core (6.96 μm), and α is the gradient parameter 2. The refractive indices of the cladding, trench region, and high-refractive-index elliptical ring are n2 = 1.41380, n3 = 1.40474, and n4 = 1.43480, respectively. The mode field characteristics of the spatial modes in this fiber can be altered by changing the size, position, and refractive index distribution of the core, cladding, trench, and high-refractive-index elliptical ring. The elliptical core is used to initially break mode degeneracy; the high-refractive-index elliptical ring is used for mode optical field modulation, further breaking higher-order mode degeneracy and increasing the effective refractive index difference between modes, thus solving the degeneracy problem of higher-order spatial modes and achieving low crosstalk. The elliptical core, with its pure silica core and gradually varying refractive index distribution at the center, achieves low loss. The trench structure achieves low bending loss. Ultimately, mode-preserving operation with low intrinsic loss, low crosstalk, and low bending loss is achieved, thereby eliminating complex MIMO-DSP processing and enabling good transmission for MIMO-FREE applications.

[0025] Figure 2 This displays the variation of effective refractive index with wavelength for eight modes without optical field modulation. Solid lines with squares, asterisks, rhombuses, circles, triangles, pentagrams, hexagons, crosses, and vertical lines represent the variations for modes HG00, HG10, HG01, HG20, HG11, HG02, HG30, HG21, and Cladding, respectively. Only this [image / description] is displayed. Figure 2 The first figure shows the result under uncontrolled optical field conditions; all other figures show the result under controlled optical field conditions. The literature [Yan Gao, Yanlei Li, Xin Li, Hongjun Zheng, Chenglin Bai, Weishen g Hu, et al., An elliptical-core few-mode fiber with low loss and low crosstalk for the MIMO-FREE applications, Frontiers in Physics, 2022, 9, 796549, 1-13] describes the transmission of five modes in an elliptical core few-mode fiber, with an effective refractive index difference between modes reaching 1.8E-03. However, in the case of core ellipticity ρ = a... x / a y When the incident wavelength is 1.5 μm and the optical wavelength is 1.55 μm, the effective refractive index difference between some modes is significantly reduced when this type of elliptical core fiber reaches eight modes, such as the effective refractive index difference n. HG10 -n HG01 n HG20 -n HG11 n HG30 -n HG21 and n HG21 -n CladdingThe corresponding wavelengths are 5.31E-04, 7.11E-04, 9.69E-04, and 5.24E-04; for wavelengths of 1.555μm and above, n HG21 -n Cladding The effective refractive index difference is 4.48E-04 or less, which is smaller than the adjacent mode effective refractive index difference transmission standard 5E-04 [Sillard P. Few-Mode Fibers for SpaceDivision Multiplexing[C], Optical Fiber Communication Conference, 2016]. This is significantly smaller than the 1.8E-03 effective refractive index difference of five-mode elliptical core few-mode fiber, leading to a serious problem of high-order mode degeneracy, necessitating the exploration of new solutions. This patent application proposes a method to solve the high-order mode degeneracy problem by using a high-refractive-index elliptical ring and Trench region for mode optical field modulation, further breaking mode degeneracy and further increasing the effective refractive index difference between modes. After modulation, n... HG10 -n HG01 n HG20 -n HG11 n HG30 -n HG21 and n HG21 -n Cladding The effective refractive index difference of all modes is greater than 1.596E-03, and the degeneracy problem of higher-order modes is solved. In order to reduce the actual production difficulty of optical fibers, the horizontal radius of the outer ellipse of the high-refractive-index elliptical ring, i.e., the semi-major axis e, is... x =6μm, vertical radius is the minor semi-axis e y =4μm; This patent application selects a core ellipticity ρ of 1.5 for the following discussion.

[0026] Figure 3 The electric field distribution of X-polarization for each mode is presented under optical field modulation and a wavelength of 1.55 μm. Figure 3(a), (b), (c), (d), (e), (f), (g), and (h) correspond to modes HG21, HG30, HG02, HG11, HG20, HG01, HG10, and HG00, respectively. The equipotential lines in the figure represent the strength of the incident electric field; the greater the density, the stronger the electric field. The eight modes corresponding to this fiber are represented by Hermetic Gaussian modes. The fiber we proposed achieves mode-preserving operation of eight Hermetic Gaussian modes: HG21, HG30, HG02, HG11, HG20, HG01, HG10, and HG00. Based on the pure silica elliptical core and Trench structure, we have initially broken the mode degeneracy by using a high-refractive-index elliptical ring for mode optical field modulation, further breaking the degeneracy of higher-order spatial modes, obtaining a larger effective refractive index difference, and achieving mode-preserving operation with low intrinsic loss, low bending loss, and low crosstalk. This eliminates the complex MIMO-DSP processing and achieves good performance for MIMO-FREE applications.

[0027] Figure 4 This figure shows the variation of the effective refractive index of eight modes with incident wavelength under optical field manipulation. The squares, asterisks, rhombuses, circles, triangles, pentagrams, hexagons, crosses, and vertical lines represent the variations of HG00, HG10, HG01, HG20, HG11, HG02, HG30, HG21 modes and Cladding mode with incident wavelength, respectively. This is done when the fiber core ellipticity is ρ = a. x / a y Based on 1.5, a high-refractive-index elliptical ring is further used for mode optical field modulation. At an incident wavelength of 1.55 μm, the refractive indices of each mode HG00, HG10, HG01, HG20, HG11, HG02, HG30, HG21 and Cladding are 1.43664, 1.43012, 1.42852, 1.42412, 1.42200, 1.41971, 1.41764, 1.41560 and 1.41380, respectively. Figure 4 As can be seen, the effective refractive index of all eight modes decreases with increasing incident wavelength, and the change in effective refractive index is slow. In the C-band range, the effective refractive indices of modes HG00, HG10, HG01, HG20, HG11, HG02, HG30, and HG21 decrease with increasing wavelength from 1.43673, 1.43029, 1.42873, 1.42438, 1.42229, 1.42003, 1.41800, and 1.41598 at 1.53 μm to 1.43657, 1.42998, 1.42836, 1.42393, 1.42178, 1.41946, 1.41737, and 1.41533 at 1.565 μm, while the effective refractive index of Cladding remains unchanged at 1.41380.

[0028] Figure 5 This shows the variation of the effective refractive index difference with incident wavelength for eight modes under light field manipulation. The solid lines representing squares, asterisks, rhombuses, circles, triangles, pentagrams, hexagons, and crosses represent n, respectively. HG00 -n HG10 n HG10 -n HG01 n HG01 -n HG20 n HG20 -n HG11 n HG11 -n HG02 n HG02 -n HG30 n HG30 -n HG21 and n HG21 -n Cldding The variation with incident wavelength. After optical field modulation, at a wavelength of 1.55 μm, the effective refractive index difference n of the mode. HG00 -n HG10 n HG10 -n HG01 n HG01 -n HG20 n HG20 -n HG11 n HG11 -n HG02 n HG02 -n HG30 n HG30 -n HG21 and n HG21 -n Cladding The refractive indexes reached 6.525E-03, 1.596E-03, 4.397E-03, 2.126E-03, 2.290E-03, 2.067E-03, 2.037E-03, and 1.805E-03, respectively. At a wavelength of 1.55 μm, compared to the uncontrolled case, the refractive index difference between modes in the controlled case was greater than or equal to 1.596E-03, with the latter case showing an effective refractive index difference n... HG10 -n HG01 It is approximately 3.01 times that of the former case, n HG20 -n HG11 It is approximately 2.99 times that of the former case, n HG30 -n HG21 It is approximately 2.10 times that of the former case, n HG21 -n Cladding It is about 3.44 times that of the former case. The mode light field modulation method further breaks the degeneracy of higher-order modes and realizes MIMO-FREE application.

[0029] Figure 6The figure shows the variation of the differential mode group delay (DMGD) as a function of incident wavelength for modes HG21, HG30, HG02, HG11, HG20, HG01, and HG10. The solid lines marked with crosses, hexagons, pentagrams, triangles, circles, rhombuses, and asterisks represent the DMGD of modes HG21, HG30, HG02, HG11, HG20, HG01, and HG10, respectively, as a function of incident wavelength. Within the wavelength range of 1.3μm to 1.6μm, the HG30 mode exhibits the highest DMGD value. The DMGD values ​​of the HG11, HG01, and HG10 modes show relatively stable changes, while the HG21 mode exhibits a larger variation. The DMGD values ​​of the HG20, HG01, and HG10 modes increase with increasing incident wavelength. Furthermore, within the 1.3μm to 1.6μm wavelength range, the HG10 mode has the lowest DMGD value. At an incident wavelength of 1.55μm, the DMGD values ​​of the HG21, HG30, HG02, HG11, HG20, HG01, and HG10 modes are respectively... The DMGD values ​​for the HG21, HG30, and HG02 modes are 0.6928, 5.3673, 3.3800, 2.8013, 1.4150, 2.5245, and -1.5372 ps / m, respectively. Within the C-band, the DMGD values ​​for these modes gradually decrease with increasing incident wavelength. The HG21 mode has a maximum DMGD of 1.6789 ps / m at an incident wavelength of 1.530 μm and a minimum of -0.1561 ps / m at 1.565 μm. The HG30 mode has a maximum DMGD of 6.0204 ps / m at an incident wavelength of 1.530 μm. The DMGD at 1.565 μm has a minimum value of 4.7863 ps / m; the HG02 mode has a maximum DMGD of 3.8227 ps / m at an incident wavelength of 1.530 μm and a minimum DMGD of 3.0518 ps / m at 1.565 μm; the DMGD of the HG11, HG01, and HG10 modes remains relatively stable with increasing incident wavelength. The HG11 mode has a DMGD value of 2.8223 ps / m at an incident wavelength of 1.530 μm and a DMGD value of 2.7733 ps / m at 1.565 μm; the HG01 mode has a DMGD of 4.7863 ps / m at an incident wavelength of 1.565 μm and a minimum DMGD of 3.0518 ps / m at 1.565 μm. The DMGD value at 30 μm is 2.4775 ps / m, and at 1.565 μm it is 2.5555 ps / m. The DMGD value of the HG10 mode is -1.6041 ps / m at the incident wavelength of 1.530 μm and -1.4918 ps / m at 1.565 μm. The DMGD of the HG20 mode gradually increases with the increase of the incident wavelength. The HG20 mode has a minimum DMGD of 1.2729 ps / m at the incident wavelength of 1.530 μm and a maximum DMGD of 1.5112 ps / m at 1.565 μm.

[0030] Figure 7The figure shows the intrinsic loss of eight Hermitian modes as a function of incident wavelength. The solid lines marked with squares, asterisks, rhombuses, circles, triangles, pentagrams, hexagons, and crosses represent the intrinsic loss of modes HG00, HG10, HG01, HG20, HG11, HG02, HG30, and HG21, respectively. The intrinsic loss of all eight modes initially decreases and then increases with increasing wavelength in the C-band, with each mode reaching a minimum at an incident wavelength of 1.55 μm. The intrinsic loss of the HG00 mode is 0.1523 dB / km at a wavelength of 1.53 μm. The intrinsic loss of this mode first decreases with increasing incident wavelength to 0.1480 dB / km at 1.55 μm, and then increases to 0.1494 dB / km at 1.565 μm. The intrinsic loss of the HG10 mode is 0.1685 dB / km at a wavelength of 1.53 μm. The intrinsic loss of this mode first decreases with increasing incident wavelength to 0.1635 dB / km at 1.55 μm, and then increases to 0.1645 dB / km at 1.565 μm. The HG01 mode exhibits an intrinsic loss of 0.1648 dB / km at a wavelength of 1.53 μm. This intrinsic loss initially decreases with increasing incident wavelength, reaching 0.1601 dB / km at 1.55 μm, before increasing again to 0.1611 dB / km at 1.565 μm. The HG20 mode, on the other hand, has an intrinsic loss of 0.1829 dB / km at 1.53 μm. This intrinsic loss also increases with increasing incident wavelength. The intrinsic loss of the HG11 mode is 0.1802 dB / km at 1.53 μm. This intrinsic loss first decreases to 0.1773 dB / km at 1.55 μm, then increases to 0.1778 dB / km at 1.565 μm. B / km; The intrinsic loss of the HG02 mode at 1.53 μm is 0.1803 dB / km. The intrinsic loss of this mode first decreases with increasing incident wavelength to 0.1753 dB / km at 1.55 μm, then increases to 0.1761 dB / km at 1.565 μm. The intrinsic loss of the HG30 mode at 1.53 μm is 0.1933 dB / km. The intrinsic loss of this mode increases with increasing incident wavelength. The intrinsic loss of the HG21 mode is 0.1953 dB / km at 1.53 μm. The intrinsic loss of this mode first decreases to 0.1897 dB / km at 1.55 μm wavelength, and then increases to 0.1902 dB / km at 1.565 μm wavelength.The intrinsic loss of the optical fiber proposed in this patent is significantly lower than that of other germanium-doped equivalent few-mode optical fibers.

[0031] Figure 8 The figure shows the bending loss of the HG21 mode at a wavelength of 1.55 μm as a function of the bending radius. The solid lines with squares, asterisks, rhombuses, circles, and triangles in the figure represent the bending loss as a function of the bending radius when the angle θ between the major axis of the ellipse and the X-axis is 0°, 30°, 45°, 60°, and 90°, respectively. As can be seen from the figure, the bending loss of the HG21 mode gradually decreases with the increase of the bending radius at 0°, 30°, 45°, 60° and 90°. When the bending radius is 10mm, the bending loss of the HG21 mode at 0°, 30°, 45°, 60° and 90° are 8.7202E-06, 5.8005E-05, 1.1410E-04, 1.3318E-04 and 1.6387E-04dB / m, respectively, all less than 159.15dB / m, [Han, Jiawei, et al.″Bendperformance analysis of few-mode fibers with high modal multiplicity factors.″Journal of Lightwave Technology 35.13(2017): 2526-2534.] which meets the robustness requirement. The optical fiber proposed in this patent has low bending loss and good robustness.

[0032] Figure 9The figures show the dispersion of HG21, HG30, HG02, HG11, HG20, HG01, HG10, and HG00 Hermitian Gaussian modes as a function of incident wavelength. The solid lines marked with circles, asterisks, and triangles represent the material dispersion, waveguide dispersion, and total dispersion of each Hermitian Gaussian mode, respectively. Figures (a), (b), (c), (d), (e), (f), (g), and (h) show the dispersion of the HG21, HG30, HG02, HG11, HG20, HG01, HG10, and HG00 modes, respectively. As can be seen from the figure, the total dispersion of each mode is relatively small in the wavelength range of 1.3μm to 1.6μm. The total dispersion of modes HG11, HG20, HG01, HG10 and HG00 increases with increasing wavelength, while the total dispersion of modes HG21, HG30 and HG02 decreases with increasing wavelength. The material dispersion of all eight modes increases with increasing incident wavelength. The waveguide dispersion of modes HG21, HG30, HG02, HG11 and HG20 gradually decreases with increasing wavelength, while the waveguide dispersion of modes HG01, HG10 and HG00 changes slowly with increasing wavelength.Within the C-band, the waveguide dispersion of modes HG21, HG30, HG02, HG11, and HG20 gradually decreases with increasing wavelength. Specifically, the waveguide dispersion of mode HG21 decreases from -45.4014 ps / (nm·km) at 1.53 μm to -59.5284 ps / (nm·km) at 1.565 μm, and the waveguide dispersion of mode HG30 decreases from -29.4079 ps / (nm·km) at 1.53 μm to -41.2070 ps / (nm·km) at 1.565 μm. The waveguide dispersion of the HG02 mode decreases from -19.4078 ps / (nm·km) at 1.53 μm to -24.3596 ps / (nm·km) at 1.565 μm with increasing wavelength; the waveguide dispersion of the HG11 mode decreases from -0.4262 ps / (nm·km) at 1.53 μm to -2.1190 ps / (nm·km) at 1.565 μm with increasing wavelength; and the waveguide dispersion of the HG20 mode decreases from 7.6332 ps / (nm·km) at 1.53 μm to -2.1190 ps / (nm·km) at 1.565 μm with increasing wavelength. The waveguide dispersion of the HG01, HG10, and HG00 modes is 6.2116 ps / (nm·km), and the waveguide dispersion changes slowly with increasing wavelength in the C-band. The waveguide dispersion of the HG01 mode changes from 2.5514 ps / (nm·km) at 1.53 μm to 2.2229 ps / (nm·km) at 1.565 μm with increasing wavelength. The waveguide dispersion of the HG10 mode changes from 3.4777 ps / (nm·km) at 1.53 μm to 3.1358 ps / (nm·km) at 1.565 μm with increasing wavelength. The HG00... The waveguide dispersion of mode 0 changes from 0.1176 ps / (nm·km) at 1.53 μm wavelength to 0.1224 ps / (nm·km) at 1.565 μm wavelength as the wavelength increases. The total dispersion of modes HG11, HG20, HG01, HG10 and HG00 all show an increasing trend with increasing incident wavelength. Among them, the total dispersion of mode HG11 increases first and then changes slowly with increasing incident wavelength. The total dispersion of modes HG21, HG30 and HG02 all show a decreasing trend with increasing incident wavelength. Among them, the total dispersion of mode HG02 changes slowly first and then gradually decreases with increasing incident wavelength.Within the C-band, the total dispersion of HG21, HG30, and HG02 modes gradually decreases with increasing wavelength. The total dispersion of the HG21 mode decreases from -24.8152 ps / (nm·km) at 1.53 μm to -36.6747 ps / (nm·km) at 1.565 μm. The total dispersion of the HG30 mode decreases from -8.8217 ps / (nm·km) at 1.53 μm to -1 ps / (nm·km) at 1.565 μm. The total dispersion of the HG02 mode is 8.3533 ps / (nm·km). It decreases from 1.1784 ps / (nm·km) at 1.53 μm wavelength to -1.5060 ps / (nm·km) at 1.565 μm wavelength with increasing wavelength. In the C-band range, the total dispersion of the HG11 and HG20 modes changes slowly with wavelength. The total dispersion of the HG11 mode decreases from 20.16 ps / (nm·km) at 1.53 μm wavelength to 2.3533 ps / (nm·km) at 1.565 μm wavelength with increasing wavelength. The total dispersion of the HG20 mode decreases from 28.2195 ps / (nm·km) at 1.53 μm wavelength to 29.0652 ps / (nm·km) at 1.565 μm wavelength with increasing wavelength. In the C-band range, the total dispersion of the HG01, HG10, and HG00 modes gradually increases with increasing wavelength. The total dispersion of the HG01 mode decreases from 23.1376 ps / (nm·km) at 1.53 μm wavelength to 1.565 μm wavelength with increasing wavelength. The total dispersion of the HG10 mode is 25.0766 ps / (nm·km) at a wavelength of 65 μm, which changes from 24.0639 ps / (nm·km) at a wavelength of 1.53 μm to 25.9894 ps / (nm·km) at a wavelength of 1.565 μm as the wavelength increases. The total dispersion of the HG00 mode changes from 20.7038 ps / (nm·km) at a wavelength of 1.53 μm to 22.9761 ps / (nm·km) at a wavelength of 1.565 μm as the wavelength increases.

[0033] In summary, the optical fiber proposed in this patent further breaks through spatial mode degeneracy, 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. Anything explicitly disclosed in this technology or obtained without objection from the written description in the documents by those skilled in the art should be considered within the scope of protection of this patent.

Claims

1. A graded-gradient non-degenerate few-mode fiber with elliptical ring-assisted optical field modulation, characterized in that: The optical fiber consists of an elliptical core with a gradually decreasing refractive index centered on pure silicon dioxide, a high-refractive-index elliptical ring, a trench region, and a cladding; the horizontal radius of the elliptical core is the semi-major axis a. x = 6.96μm, vertical radius is the minor semi-axis a y =4.64μm, ellipticity ρ=a x / a y =1.5; where the Trench cross-section is an elliptical ring structure, and the horizontal radius of the inner ellipse is the semi-major axis b. x =14.46μm, vertical radius is the minor semi-axis b y = 9.64μm, its outer ellipse horizontal radius is also known as the semi-major axis c x = 29.46 μm, vertical radius is the minor semi-axis c y =19.64μm; the core has a high-refractive-index elliptical ring auxiliary structure, and the horizontal radius of the inner ellipse of the high-refractive-index elliptical ring is the semi-major axis d. x = 4.2μm, vertical radius is the minor semi-axis d y =2.8μm, the horizontal radius of the outer ellipse of the high refractive index elliptical ring, i.e., the semi-major axis e x =6μm, vertical radius is the minor semi-axis e y =4μm; the remaining part is the cladding, and its outer cladding radius is R = 62.5μm; the center coordinates of the fiber core are (0, 0); the refractive index distribution of the gradient elliptical fiber core follows the formula n(r) = n1*[1-2Δ(r / a)] α ] 1 / 2 In the formula, r ≤ a, where n1 is the refractive index of pure silica at the center of the elliptical fiber core (1.4440), r represents the distance from any point in the fiber core to the axis, a represents the semi-major axis of the fiber core (6.96 μm), and α is the gradient parameter 2. The refractive indices of the cladding, trench region, and high-refractive-index elliptical ring are n2 = 1.41380, n3 = 1.40474, and n4 = 1.43480, respectively. The mode field characteristics of the spatial modes in this fiber can be altered by changing the size, position, and refractive index distribution of the core, cladding, trench, and high-refractive-index elliptical ring. The elliptical core is used to initially break mode degeneracy; the high-refractive-index elliptical ring is used for mode optical field modulation, further breaking higher-order mode degeneracy and increasing the effective refractive index difference between modes, thus solving the degeneracy problem of higher-order spatial modes and achieving low crosstalk. The elliptical core, with its pure silica core and gradually varying refractive index distribution at the center, achieves low loss. The trench structure achieves low bending loss. Ultimately, mode-preserving operation with low intrinsic loss, low crosstalk, and low bending loss is achieved, thereby eliminating complex MIMO-DSP processing and enabling good transmission for MIMO-FREE applications.

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