An eight-mode mode division multiplexer based on multi-core optical fiber

Abstract

The present invention belongs to the field of optical fiber communication technology and relates to an eight-mode mode division multiplexer based on multi-core optical fiber, comprising a substrate material and a central few-mode fiber core; a high refractive index ring is provided in the central few-mode fiber core; and a peripheral single-mode fiber core includes a plurality of optical fibers for transmitting LP to the central few-mode fiber core. 11a The first single-mode core of the mode conversion is used for LP to the central few-mode core 31 The second single-mode core for mode conversion is used to conduct LP to the central few-mode core 11b The third single-mode core for mode conversion is used to conduct LP to the central few-mode core 21b The fourth single-mode core for mode conversion is used to conduct LP to the central few-mode core 12 The fifth single-mode core for mode conversion is used to conduct LP to the central few-mode core 21a The sixth single-mode core for mode conversion and the LP to the central few-mode core 02 The seventh single-mode fiber core of the mode conversion has the characteristics of a large number of conversion modes, high space utilization, low insertion loss and high flux.

Description

Technical Field

[0001] The invention belongs to the technical field of optical fiber communication and relates to an eight-mode mode division multiplexer based on multi-core optical fiber. Background Art

[0002] As a key signal processing component, mode-division multiplexers (ADCs) are widely used in modern communication systems, data acquisition, automated control, and audio and video processing. With the rapid development of information technology, particularly the widespread adoption of the Internet and the Internet of Things (IoT), the demand for efficient and flexible signal processing is increasing, making the research and application of ADCs increasingly important. The concept of ADCs first emerged in the 1960s, initially used for simple signal switching and selection. With the continuous advancement of integrated circuit technology, the performance of ADCs has been significantly improved, gradually evolving towards high frequency, high speed, and low power consumption. Entering the 21st century, with the rise of emerging applications such as wireless communications, video surveillance, and smart homes, the design and manufacture of ADCs face higher requirements, driving continuous technological innovation.

[0003] In recent years, researchers have made significant progress in optimizing the structure, switching speed, insertion loss, and interference resistance of mode division multiplexers. Currently, the most common method for mode conversion is to fuse two optical fibers together to achieve refractive index matching, thereby achieving mode conversion. While this method is easy to manufacture, the damage to the fiber structure during the process makes it difficult to multiplex multiple high-order modes, significantly limiting the improvement of optical fiber communication capabilities achieved by mode division multiplexing technology.

[0004] All-fiber mode division multiplexers based on coupled-mode theory, such as those based on long-period fiber Bragg gratings (LPBs), photonic lanterns, tapered fibers, and all-fiber fused-taper structures, have made significant progress. However, these approaches also present challenges. These solutions require disrupting the fiber waveguide structure (such as by adiabatic tapering and cladding polishing) to achieve mode conversion, resulting in poor flexibility, non-reconfigurability, and high fabrication complexity. Furthermore, when transmitting multiple modes, significant interference between signals occurs, and mode coupling severely limits system capacity. Furthermore, multiplexing multiple modes through cascading is cumbersome, and the cumulative insertion loss of multiple stages can have a significant impact. When multiplexing multiple modes, the excessive use of higher-order modes to transmit information makes it difficult to match single-mode fiber parameters. These factors significantly limit the information capacity gains of mode division multiplexing technology, making breakthroughs urgent. Summary of the Invention

[0005] In order to overcome the problems existing in the above-mentioned prior art, the present invention proposes an all-fiber mode division multiplexer with the characteristics of high space utilization, low insertion loss and low inter-mode crosstalk.

[0006] The technical solution of the present invention to solve the above problems is: an eight-mode mode division multiplexer based on multi-core optical fiber, which is special in that:

[0007] Including base material, central few-mode fiber core and peripheral single-mode fiber core,

[0008] The central few-mode fiber core and the peripheral single-mode fiber core are located in the base material;

[0009] The central few-mode core includes a core base and a high refractive index ring;

[0010] The peripheral single-mode fiber core includes a fiber for transmitting LP to the central few-mode fiber core. 11a The first single-mode core of the mode conversion is used for LP to the central few-mode core 31 The second single-mode core for mode conversion is used to conduct LP to the central few-mode core 11b The third single-mode core for mode conversion is used to conduct LP to the central few-mode core 21b The fourth single-mode core for mode conversion is used to conduct LP to the central few-mode core 12 The fifth single-mode core for mode conversion is used to conduct LP to the central few-mode core 21a The sixth single-mode core for mode conversion and the LP to the central few-mode core 02 Seventh single-mode core for mode conversion.

[0011] The first single-mode fiber core, the second single-mode fiber core, the third single-mode fiber core, the fourth single-mode fiber core, the fifth single-mode fiber core, the sixth single-mode fiber core and the seventh single-mode fiber core are sequentially distributed around the central few-mode fiber core.

[0012] Further, the center line of the first single-mode fiber core and the central few-mode fiber core and the center line of the second single-mode fiber core and the central few-mode fiber core are at an angle of 60°, the center line of the second single-mode fiber core and the central few-mode fiber core and the center line of the third single-mode fiber core and the central few-mode fiber core are at an angle of 30°, the center line of the third single-mode fiber core and the central few-mode fiber core and the center line of the fourth single-mode fiber core and the central few-mode fiber core are at an angle of 45°, the center line of the fourth single-mode fiber core and the central few-mode fiber core are at an angle of 60°, the center line of the second single-mode fiber core and the central few-mode fiber core are at an angle of 30°, the center line of the third single-mode fiber core and the central few-mode fiber core are at an angle of 45°, and the center line of the fourth single-mode fiber core and the central few-mode fiber core are at an angle of 60°. The angle between the line and the center line of the fifth single-mode fiber core and the central minority-mode fiber core is 45°, the angle between the center line of the fifth single-mode fiber core and the central minority-mode fiber core and the center line of the sixth single-mode fiber core and the central minority-mode fiber core is 90°, the angle between the center line of the sixth single-mode fiber core and the central minority-mode fiber core and the center line of the seventh mode fiber core and the central minority-mode fiber core is 45°, and the angle between the center line of the seventh mode fiber core and the central minority-mode fiber core and the center line of the first single-mode fiber core and the central minority-mode fiber core is 45°.

[0013] Furthermore, the distances from the centers of the first single-mode core, the second single-mode core, the third single-mode core, the fourth single-mode core, the fifth single-mode core, the sixth single-mode core, and the seventh single-mode core to the center of the central few-mode core are L1, L2, L3, L4, L5, L6, and L7, respectively, where L1 = L3 and L4 = L6.

[0014] Furthermore, the above-mentioned L1 and L3 are both 13.39 μm, L4 and L6 are both 14.14 μm, L2 is 15.10 μm, L5 is 19.35 μm, and L7 is 14.78 μm.

[0015] Furthermore, the diameter of the first single-mode fiber core and the third single-mode fiber core is 5 μm, and the core refractive index is 1.4624 at a wavelength of 1550 nm.

[0016] Furthermore, the diameter of the second single-mode fiber core is 5 μm, and the core refractive index is 1.4537 at a wavelength of 1550 nm.

[0017] Furthermore, the diameter of the fourth single-mode fiber core and the sixth single-mode fiber core is 5 μm, and the core refractive index is 1.4588 at a wavelength of 1550 nm.

[0018] Furthermore, the diameter of the fifth single-mode fiber core is 5 μm, and the core refractive index is 1.4493 at a wavelength of 1550 nm.

[0019] Furthermore, the diameter of the seventh single-mode fiber core is 5 μm, and the core refractive index is 1.4555 at a wavelength of 1550 nm.

[0020] Furthermore, the diameter of the above-mentioned central few-mode fiber core is 16μm, the base refractive index is 1.4549 at a wavelength of 1550nm, the center of the high refractive index ring is the center of the optical fiber, the inner diameter of the high refractive index ring is 8μm, the ring width is 3μm, and the refractive index of the high refractive index ring is 1.4602 at a wavelength of 1550nm.

[0021] Furthermore, the base material is made of silicon dioxide, and its refractive index is 1.444 at a wavelength of 1550 nm.

[0022] Furthermore, the length of the mode division multiplexer is 5000 μm.

[0023] Advantages of the present invention

[0024] ① Based on the multi-core optical fiber structure, the present invention proposes a mode division multiplexer that couples eight modes. In the same section of optical fiber structure, the peripheral single-mode fiber core can realize LP 11a LP 11b LP 21a LP 21b LP31 LP 12 and LP 02 Simultaneous conversion of seven higher-order modes and direct input to the central few-mode core LP 01 The mode can multiplex eight modes at the same time. Compared with the traditional cascade mode multiplexer, it can multiplex eight modes at the same time, which greatly improves the number of modes and space utilization;

[0025] ② The present invention effectively avoids using too high-order modes to transmit information by multiplexing degenerate modes, thereby achieving simultaneous multiplexing of eight modes using a smaller number of high-order modes;

[0026] ③ The present invention effectively converts LP into 02 and LP 21 The effective refractive index difference of the modes is distinguished to avoid serious crosstalk during mode conversion, which is extremely effective for the high-purity conversion of eight modes simultaneously multiplexed by the multiplexer;

[0027] ④ The present invention adopts a mode division multiplexer length of 5000μm, which provides sufficient coupling distance and enhances the coupling efficiency between different modes, thereby improving the overall performance of the mode division multiplexing system. At the same time, this length brings greater design flexibility, enabling the system to better adapt to diverse transmission requirements and environmental conditions;

[0028] ⑤ The eight-mode mode division multiplexer designed by the present invention has a wavelength of 1550nm, LP 01 LP 11a LP 11b LP 21a LP 21b LP 02 LP 31 and LP 12 The mode conversion efficiencies are 99.9%, 99.6%, 99.6%, 97.6%, 99.3%, 96.5%, 87.1% and 76.8% respectively, suitable for high-purity mode conversion. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic diagram of the cross-sectional structure and mode conversion of the mode division multiplexer proposed in the present invention;

[0030] Figure 2 This is a schematic diagram of a cross-sectional structure of the mode division multiplexer proposed in the present invention after adding annotations;

[0031] Figure 3 The second schematic diagram of the cross-sectional structure of the mode division multiplexer proposed by the present invention after adding annotations;

[0032] Figure 4This is a schematic diagram of the method of using the mode division multiplexer proposed by the present invention in actual operation;

[0033] Figure 5 The mode division multiplexer proposed by the present invention is LP at a wavelength of 1550nm 01 LP 21 LP 02 LP 11 LP 12 and LP 31 Variation of mode coupling efficiency with coupling length;

[0034] Figure 6 This is a diagram of the device insertion loss of the mode division multiplexer proposed in the present invention at a wavelength of 1.50 to 1.60 μm.

[0035] Among them: 1. base material, 2. fiber core base, 3. high refractive index ring, 4. first single-mode fiber core, 5. second single-mode fiber core, 6. third single-mode fiber core, 7. fourth single-mode fiber core, 8. fifth single-mode fiber core, 9. sixth single-mode fiber core, 10. seventh single-mode fiber core. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the invention for which protection is sought, but merely represents selected embodiments of the present invention.

[0037] The present invention provides an eight-mode mode division multiplexer based on multi-core optical fiber, such as Figure 1 and Figure 4 As shown, it includes a base material 1, a central few-mode core and a peripheral single-mode core. The central few-mode core includes a core base 2 and a high-refractive-index ring 3. The core base 2 is the main material of the few-mode core. The high-refractive-index ring 3 is located inside the central few-mode core base 2. The high-refractive-index ring 3 is used to increase the LP in the few-mode core. 21 and LP 02 The effective refractive index difference between the modes.

[0038] The peripheral single-mode fiber core includes a fiber for transmitting LP to the central few-mode fiber core. 11a The first single-mode fiber core 4 of the mode conversion is used to conduct LP to the central few-mode fiber core 31The second single-mode fiber core 5 of mode conversion is used to conduct LP to the central few-mode fiber core 11b The third single-mode fiber core 6 for mode conversion is used to conduct LP to the central few-mode fiber core 21b The fourth single-mode fiber core 7 of mode conversion is used to conduct LP to the central few-mode fiber core 12 The fifth single-mode fiber core 8 of mode conversion is used to conduct LP to the central few-mode fiber core 21a The sixth single-mode fiber core 9 for mode conversion and the LP fiber core for the central few-mode fiber core 02 The seventh single-mode fiber core 10 for mode conversion has seven fiber cores in total. The first single-mode fiber core 4, the second single-mode fiber core 5, the third single-mode fiber core 6, the fourth single-mode fiber core 7, the fifth single-mode fiber core 8, the sixth single-mode fiber core 9, and the seventh single-mode fiber core 10 are sequentially distributed around the central minority-mode fiber core.

[0039] As a preferred embodiment of the present invention, the center line of the first single-mode fiber core 4 and the central minority-mode fiber core and the center line of the second single-mode fiber core 5 and the central minority-mode fiber core are at an angle of 60°, the center line of the second single-mode fiber core 5 and the central minority-mode fiber core and the center line of the third single-mode fiber core 6 and the central minority-mode fiber core are at an angle of 30°, the center line of the third single-mode fiber core 6 and the central minority-mode fiber core and the center line of the fourth single-mode fiber core 7 and the central minority-mode fiber core are at an angle of 45°, and the fourth single-mode fiber core 7 and the central minority-mode fiber core are at an angle of 50°. The angle between the center line of and the center line of the fifth single-mode fiber core 8 and the center minority mode fiber core is 45°, the angle between the center line of the fifth single-mode fiber core 8 and the center minority mode fiber core and the center line of the sixth single-mode fiber core 9 and the center minority mode fiber core is 90°, the angle between the center line of the sixth single-mode fiber core 9 and the center minority mode fiber core and the center line of the seventh mode fiber core 10 and the center minority mode fiber core is 45°, and the angle between the center line of the seventh mode fiber core 10 and the center minority mode core and the center line of the first single-mode fiber core 4 and the center minority mode core is 45°.

[0040] As a preferred embodiment of the present invention, the diameters and core refractive indices of the first single-mode fiber core 4 and the third single-mode fiber core 6 are equal, and the diameters and core refractive indices of the fourth single-mode fiber core 7 and the sixth single-mode fiber core 9 are equal.

[0041] See also Figure 3 The distances between the centers of the first single-mode fiber core 4, the second single-mode fiber core 5, the third single-mode fiber core 6, the fourth single-mode fiber core 7, the fifth single-mode fiber core 8, the sixth single-mode fiber core 9, and the seventh single-mode fiber core 10 and the center of the central minority-mode fiber core are L1, L2, L3, L4, L5, L6, and L7, respectively, where L1 = L3 and L4 = L6. As a preferred embodiment, L1 and L3 are both 13.39 μm, L4 and L6 are both 14.14 μm, L2 is 15.10 μm, L5 is 19.35 μm, and L7 is 14.78 μm.

[0042] As a preferred embodiment of the present invention, the base material 1 of the optical fiber is silicon dioxide, and its refractive index is 1.4440 at a wavelength of 1550 nm.

[0043] As a preferred embodiment of the present invention, Figure 2 As shown, the diameter d0 of the central few-mode fiber core is 16 μm, the substrate refractive index n0 is 1.4549 at a wavelength of 1550 nm, the center of the high refractive index ring is the center of the optical fiber, the inner diameter R of the high refractive index ring is 8 μm, the ring width a is 3 μm, and the refractive index n6 of the high refractive index ring is 1.4602 at a wavelength of 1550 nm.

[0044] As a preferred embodiment of the present invention, Figure 2 As shown, the diameters d1 of the first single-mode fiber core 4 and the third single-mode fiber core 6 are both 5 μm, and the core refractive index n1 is 1.4624 at a wavelength of 1550 nm; the diameter d2 of the second single-mode fiber core 5 is 5 μm, and the core refractive index n2 is 1.4537 at a wavelength of 1550 nm; the diameters d3 of the fourth single-mode fiber core 7 and the sixth single-mode fiber core 9 are both 5 μm, and the core refractive index n3 is 1.4588 at a wavelength of 1550 nm; the diameter d4 of the fifth single-mode fiber core 8 is 5 μm, and the core refractive index n4 is 1.4493 at a wavelength of 1550 nm; the diameter d5 of the seventh single-mode fiber core 10 is 5 μm, and the core refractive index n5 is 1.4555 at a wavelength of 1550 nm.

[0045] Example 1

[0046] An eight-mode mode division multiplexer based on multi-core optical fiber, such as Figure 1 and Figure 4 As shown, it includes a base material 1, a central few-mode core and a peripheral single-mode core. The central few-mode core includes a core base 2 and a high-refractive-index ring 3. The core base 2 is the main material of the few-mode core, and the high-refractive-index ring 3 is used to increase the LP in the few-mode core. 21 and LP 02 The effective refractive index difference between the modes. The mode division multiplexer length x is 5000μm. Using a 5000μm mode division multiplexer length provides sufficient coupling distance, enhances the coupling efficiency between different modes, and thus improves the overall performance of the mode division multiplexing system. At the same time, this length brings greater design flexibility, enabling the system to better adapt to diverse transmission requirements and environmental conditions.

[0047] The positions of the seven outer single-mode fiber cores are distributed in a heptagonal structure, wherein each single-mode fiber core is located at one of the vertices of the heptagonal structure. The angle between the center line of the first single-mode fiber core 4 and the central minority-mode fiber core and the center line of the second single-mode fiber core 5 and the central minority-mode fiber core is 60°, the angle between the center line of the second single-mode fiber core 5 and the central minority-mode fiber core and the center line of the third single-mode fiber core 6 and the central minority-mode fiber core is 30°, the angle between the center line of the third single-mode fiber core 6 and the central minority-mode fiber core and the center line of the fourth single-mode fiber core 7 and the central minority-mode fiber core is 45°, and the angle between the center line of the fourth single-mode fiber core 7 and the central minority-mode fiber core and the center line of the fifth single-mode fiber core is 45°. The angle between the center lines of the single-mode fiber core 8 and the central minority-mode fiber core is 45°, the angle between the center lines of the fifth single-mode fiber core 8 and the central minority-mode fiber core and the center lines of the sixth single-mode fiber core 9 and the central minority-mode fiber core is 90°, the angle between the center lines of the sixth single-mode fiber core 9 and the central minority-mode fiber core and the center lines of the seventh mode fiber core 10 and the central minority-mode fiber core is 45°, and the angle between the center lines of the seventh mode fiber core 10 and the central minority-mode fiber core and the center lines of the first single-mode fiber core 4 and the central minority-mode fiber core is 45°.

[0048] See also Figure 3 The distances between the centers of the first single-mode fiber core 4, the second single-mode fiber core 5, the third single-mode fiber core 6, the fourth single-mode fiber core 7, the fifth single-mode fiber core 8, the sixth single-mode fiber core 9, and the seventh single-mode fiber core 10 and the center of the central minority-mode fiber core are L1, L2, L3, L4, L5, L6, and L7, respectively, where L1 = L3 and L4 = L6. Preferably, L1 and L3 are both 13.39 μm, L4 and L6 are both 14.14 μm, L2 is 15.10 μm, L5 is 19.35 μm, and L7 is 14.78 μm.

[0049] See also Figure 2The optical fiber's base material 1 is silica, with a refractive index of 1.4440 at a wavelength of 1550 nm. The diameter d0 of the central few-mode core is 16 μm, and the base refractive index n0 is 1.4549 at a wavelength of 1550 nm. The center of the high-refractive-index ring is the center of the optical fiber. The inner diameter R of the high-refractive-index ring is 8 μm, the ring width a is 3 μm, and the refractive index n6 of the high-refractive-index ring is 1.4602 at a wavelength of 1550 nm. The diameters d1 of the first single-mode fiber core 4 and the third single-mode fiber core 6 are both 5 μm, and the core refractive index n1 is 1.4624 at a wavelength of 1550 nm; the diameter d2 of the second single-mode fiber core 5 is 5 μm, and the core refractive index n2 is 1.4537 at a wavelength of 1550 nm; the diameters d3 of the fourth single-mode fiber core 7 and the sixth single-mode fiber core 9 are both 5 μm, and the core refractive index n3 is 1.4588 at a wavelength of 1550 nm; the diameter d4 of the fifth single-mode fiber core 8 is 5 μm, and the core refractive index n4 is 1.4493 at a wavelength of 1550 nm; the diameter d5 of the seventh single-mode fiber core 10 is 5 μm, and the core refractive index n5 is 1.4555 at a wavelength of 1550 nm.

[0050] This embodiment calculates the crosstalk and loss problems caused by the mode conversion in the present invention.

[0051] The present invention is designed around multi-core optical fibers, where inter-core crosstalk is a key quality criterion. This crosstalk is specifically measured as the mode coupling efficiency between the individual cores. In addition, insertion loss and inter-mode extinction ratio are also key performance indicators for mode division multiplexers.

[0052] The present invention is calculated and analyzed by using the beam propagation method, and LP at a wavelength of 1550nm is injected into the peripheral single-mode fiber core. 01 mode, and observe the power changes of all other fiber cores in the mode division multiplexer at the same time, as shown in Table 1. Table 1 shows the output power in other fiber cores when each peripheral single-mode optical fiber performs mode conversion at a wavelength of 1550 nm in Example 1.

[0053]

[0054] We analyze the extinction ratio data given in Table 1. In this invention, the eighth-order linear polarization mode (LP 01 , LP 11a , LP 11b , LP 21a , LP 21b , LP 02 , LP 31 and LP 12) on the desired mode. Through the simulation of mode coupling, it was found that when only one of the cores at the input end of the optical fiber is passed with light, the extinction ratio of the corresponding mode to be converted at the output end of the optical fiber is calculated. The larger the extinction ratio, the smaller the crosstalk of the undesired conversion mode on the desired conversion mode; the smaller the extinction ratio, the greater the crosstalk of all other undesired modes taken into account on the desired mode. As the optical fiber length increases, the extinction ratio of each desired conversion mode shows an upward trend. When the transmission length approaches 5000μm, the mode conversion is basically completed and the ER curve tends to be stable. At a fiber length of 5000μm, each desired conversion mode obtains a high mode extinction ratio.

[0055] By analyzing the conversion efficiency of each mode in Table 1, it is obvious that the present invention has very small crosstalk during each mode conversion process at the working wavelength of 1550nm, and can achieve high mode purity for mode modulation and multiplexing.

[0056] The structural parameters designed by the present invention have a high mode conversion efficiency at a wavelength of 1550nm, but in practical applications, considering the adaptability and tolerance of the device, Figure 5 The conversion efficiency variation curves of each mode of the mode division multiplexer at a wavelength of 1550nm are given.

[0057] The present invention determines the applicable operating frequency band of the mode division multiplexer by calculating the insertion loss (IL) of the device in the C band, such as Figure 6 As shown in FIG, the mode multiplexer can maintain a low IL in the wavelength range of 1.53 μm-1.57 μm, and the IL at 1.55 μm is the lowest, which is 0.2384 dB.

[0058] The eight-mode multiplexer proposed in this paper achieves high-quality mode conversion and multiplexing with low IL and high ER by precisely adjusting the fiber structure and mode coupling characteristics. The CEs of the seven modes to be converted are 99.6%, 99.6%, 97.6%, 99.3%, 96.5%, 87.1%, and 76.8%, respectively. This device offers low manufacturing costs and a high number of modes. This provides greater flexibility for optimizing device performance, reduces complexity, and offers the advantages of high throughput and low loss.

[0059] The above descriptions are merely embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention description and drawings, or directly or indirectly applied to other related system fields, are also included in the scope of protection of the present invention.

Claims

1. An eight-mode mode division multiplexer based on multi-core optical fiber, characterized by: It comprises a base material (1), a central few-mode fiber core and a peripheral single-mode fiber core, The central few-mode fiber core and the peripheral single-mode fiber core are located in the base material (1); The central few-mode fiber core comprises a fiber core base (2) and a high refractive index ring (3); The peripheral single-mode fiber core includes a fiber for transmitting LP to the central few-mode fiber core. 11a The first single-mode fiber core (4) for mode conversion is used to conduct LP to the central few-mode fiber core 31 The second single-mode fiber core (5) for mode conversion is used to conduct LP to the central few-mode fiber core 11b The third single-mode fiber core (6) for mode conversion is used to conduct LP to the central few-mode fiber core. 21b The fourth single-mode fiber core (7) for mode conversion is used to conduct LP to the central few-mode fiber core 12 The fifth single-mode fiber core (8) for mode conversion is used to conduct LP to the central few-mode fiber core 21a The sixth single-mode fiber core (9) for mode conversion and the LP fiber core for the central few-mode fiber core 02 a seventh single-mode fiber core (10) for mode conversion; The first single-mode fiber core (4), the second single-mode fiber core (5), the third single-mode fiber core (6), the fourth single-mode fiber core (7), the fifth single-mode fiber core (8), the sixth single-mode fiber core (9), and the seventh single-mode fiber core (10) are sequentially distributed on the periphery of the central few-mode fiber core; The angle between the center line of the first single-mode fiber core (4) and the central minority-mode fiber core and the center line of the second single-mode fiber core (5) and the central minority-mode fiber core is 60°, the angle between the center line of the second single-mode fiber core (5) and the central minority-mode fiber core and the center line of the third single-mode fiber core (6) and the central minority-mode fiber core is 30°, the angle between the center line of the third single-mode fiber core (6) and the central minority-mode fiber core and the center line of the fourth single-mode fiber core (7) and the central minority-mode fiber core is 45°, the angle between the center line of the fourth single-mode fiber core (7) and the central minority-mode fiber core and the center line of the fifth single-mode fiber core is 45°. The angle between the center lines of the single-mode fiber core (8) and the central minority-mode fiber core is 45°, the angle between the center lines of the fifth single-mode fiber core (8) and the central minority-mode fiber core and the center lines of the sixth single-mode fiber core (9) and the central minority-mode fiber core is 90°, the angle between the center lines of the sixth single-mode fiber core (9) and the central minority-mode fiber core and the center lines of the seventh single-mode fiber core (10) and the central minority-mode fiber core is 45°, and the angle between the center lines of the seventh single-mode fiber core (10) and the central minority-mode fiber core and the center lines of the first single-mode fiber core (4) and the central minority-mode fiber core is 45°; The distances between the centers of the first single-mode fiber core (4), the second single-mode fiber core (5), the third single-mode fiber core (6), the fourth single-mode fiber core (7), the fifth single-mode fiber core (8), the sixth single-mode fiber core (9), and the seventh single-mode fiber core (10) and the center of the central few-mode fiber core are L1, L2, L3, L4, L5, L6, and L7, respectively, where L1 = L3 and L4 = L6; The L1 and L3 are both 13.39 μm, L4 and L6 are both 14.14 μm, L2 is 15.10 μm, L5 is 19.35 μm, and L7 is 14.78 μm; At a fiber length of 5000μm, each desired conversion mode achieved a high modal extinction ratio, and the insertion loss was lowest at a wavelength of 1.55μm.

2. The eight-mode mode division multiplexer based on multi-core optical fiber according to claim 1, characterized in that: The diameters d1 of the first single-mode fiber core (4) and the third single-mode fiber core (6) are both 5 μm, and the core refractive index n1 is both 1.4624 at a wavelength of 1550 nm; The diameter d2 of the second single-mode fiber core (5) is 5 μm, and the core refractive index n2 is 1.4537 at a wavelength of 1550 nm; The diameters d4 of the fourth single-mode fiber core (7) and the sixth single-mode fiber core (9) are both 5 μm, and the core refractive index n4 at a wavelength of 1550 nm is both 1.4588; The diameter d5 of the fifth single-mode fiber core (8) is 5 μm, and the core refractive index n5 is 1.4493 at a wavelength of 1550 nm; The diameter d7 of the seventh single-mode fiber core (10) is 5 μm, and the core refractive index n7 is 1.4555 at a wavelength of 1550 nm.

3. The eight-mode mode division multiplexer based on multi-core optical fiber according to claim 1, characterized in that: The diameter of the central few-mode fiber core is 16 μm, and the base refractive index is 1.4549 at a wavelength of 1550 nm; the center of the high-refractive-index ring is the center of the optical fiber, the inner diameter of the high-refractive-index ring is 8 μm, the ring width is 3 μm, and the refractive index of the high-refractive-index ring is 1.4602 at a wavelength of 1550 nm.

4. The eight-mode mode division multiplexer based on multi-core optical fiber according to claim 1, characterized in that: The base material (1) of the optical fiber is silicon dioxide, and its refractive index is 1.4440 at a wavelength of 1550 nm.

5. The eight-mode mode division multiplexer based on multi-core optical fiber according to claim 4, characterized in that: The length of the mode division multiplexer is 5000 μm.

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