Eight-mode mode division multiplexer based on multi-core optical fiber

Abstract

The invention belongs to the technical field of optical fiber communication, and relates to an eight-mode mode division multiplexer based on a multi-core optical fiber, which comprises a substrate material and a central few-mode fiber core, a high-refractive-index ring is arranged in the central few-mode fiber core; the peripheral single-mode fiber core comprises a first single-mode fiber core used for carrying out LP11a mode conversion on the central few-mode fiber core, a second single-mode fiber core used for carrying out LP31 mode conversion on the central few-mode fiber core, a third single-mode fiber core used for carrying out LP11b mode conversion on the central few-mode fiber core, and a fourth single-mode fiber core used for carrying out LP21b mode conversion on the central few-mode fiber core; the fifth single-mode fiber core is used for carrying out LP12 mode conversion on the central few-mode fiber core; the sixth single-mode fiber core is used for carrying out LP21a mode conversion on the central few-mode fiber core; and the seventh single-mode fiber core is used for carrying out LP02 mode conversion on the central few-mode fiber core. The invention has the characteristics of large number of conversion modes, high space utilization rate, low insertion loss, high flux and the like.

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 device, the mode division multiplexer is widely used in modern communication systems, data acquisition, automatic control, audio and video processing and other fields. With the rapid development of information technology, especially the popularization of the Internet and the Internet of Things, the demand for efficient and flexible signal processing is increasing, making the research and application of mode division multiplexers more important. The concept of mode division multiplexer first appeared in the 1960s and was originally used for simple signal switching and selection. With the continuous advancement of integrated circuit technology, the performance of mode division multiplexers has been significantly improved, and gradually evolved 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 mode division multiplexers face higher requirements, which has promoted the continuous innovation of their technology.

[0003] In recent years, researchers have made significant progress in the structural optimization, switching speed, insertion loss and anti-interference ability of mode division multiplexers. Currently, the most common mode conversion method is to fuse two optical fibers to achieve a refractive index matching point, thereby achieving mode conversion. Although this method is easy to manufacture, the damage to the optical fiber structure during the process makes it difficult to achieve multiplexing of multiple high-order modes, which greatly limits the improvement of optical fiber communication capabilities by mode division multiplexing technology.

[0004] All-fiber mode division multiplexers based on coupled mode theory, such as long-period fiber grating mode converters, photon lantern mode converters, tapered fiber mode converters, and all-fiber fused taper structure mode converters, have made a lot of progress, but there are also some problems. The premise of these schemes to achieve mode conversion is to destroy the fiber waveguide structure (adiabatic taper, polished cladding, etc.), which leads to these schemes having difficulties such as poor flexibility, non-reconfiguration, and high difficulty in production. In addition, when transmitting multiple modes, there will be great interference between signals, and mode coupling seriously limits the capacity of the system. In addition, it is cumbersome to multiplex multiple modes through cascading, and the accumulation of insertion loss at multiple levels may cause a more obvious impact; when multiplexing multiple modes, using too many high-order modes to transmit information makes it difficult to match the parameters of single-mode optical fibers. These have greatly limited the improvement of information capacity by mode division multiplexing technology, and it is urgent to seek breakthroughs. 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 problem 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 to conduct 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 on the periphery of 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°, and the center line of the fourth single-mode fiber core and the central few-mode fiber core are at an angle of 50°. 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 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 center 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 few-mode core to the exact center of the central few-mode core are respectively: L 1 , L 2 , L 3 , L 4 , L 5 , L 6 and L 7 . Where L 1 =L 3 , L 4 =L 6 .

[0014] Furthermore, the above L 1 , L 3 Both are 13.39μm, L 4 , L 6 Both are 14.14μm, L 2 15.10μm, L 5 19.35μm, L 7 It is 14.78μm.

[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 diameters of the fourth single-mode fiber core and the sixth single-mode fiber core are 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 circle 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 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 optical fiber structure, the peripheral single-mode fiber core can realize LP 11a LP 11b LP 21a LP 21b LP 31 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 using a smaller number of high-order modes to achieve simultaneous multiplexing of eight modes;

[0026] ③ The present invention effectively converts LP into 02 and LP 21 The effective refractive index difference of the modes can be distinguished to avoid serious crosstalk during mode conversion, which is very useful for the high-purity conversion of eight modes of multiplexing in the multiplexer.

[0027] ④ The present invention adopts a mode division multiplexer length of 5000 μm, 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, which are suitable for high-purity mode conversion. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1The cross-sectional structure and mode conversion schematic diagram of the mode division multiplexer proposed by the present invention;

[0030] Figure 2 One of the cross-sectional structural schematic diagrams of the mode division multiplexer proposed by 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 4 A schematic diagram of a method for using the mode division multiplexer proposed by the present invention in actual operation;

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

[0034] Figure 6 This is a diagram of 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 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 claimed for protection, 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 4As shown, it includes a substrate material 1, a central few-mode core and a peripheral single-mode core. The central few-mode core includes a core substrate 2 and a high refractive index ring 3. The core substrate 2 is the main material of the few-mode core. The high refractive index ring 3 is located inside the central few-mode core substrate 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 31 The 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 core 6 of mode conversion is used to conduct LP to the central few-mode 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 the mode conversion is used to carry out 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 of 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 on the periphery of the central few-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 central minority mode fiber core is 45°, the angle between the center line of the fifth single-mode fiber core 8 and the central minority mode fiber core and the center line of the sixth single-mode fiber core 9 and the central minority mode fiber core is 90°, the angle between the center line of the sixth single-mode fiber core 9 and the central minority mode fiber core and the center line of the seventh mode fiber core 10 and the central minority mode fiber core is 45°, and the angle between the center line of the seventh mode fiber core 10 and the central minority mode core and the center line of the first single-mode fiber core 4 and the central minority mode core is 45°.

[0040] As a preferred embodiment of the present invention, the diameters and core refractive indexes of the first single-mode fiber core 4 and the third single-mode fiber core 6 are equal, and the diameters and core refractive indexes 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 respectively: L 1 , L 2 , L 3 , L 4 , L 5 , L 6 and L 7 , where L 1 =L 3 , L 4 =L 6 As a preferred solution, L 1 , L 3 Both are 13.39μm, L 4 , L 6 Both are 14.14μm, L 2 15.10μm, L 5 19.35μm, L 7 It is 14.78μm.

[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 d of the central few-mode core 0 The substrate refractive index is n at 16 μm at 1550 nm. 0 is 1.4549, 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 n of the high refractive index ring at a wavelength of 1550 nm is 6 It is 1.4602.

[0044] As a preferred embodiment of the present invention, Figure 2 As shown, the diameters of the first single-mode fiber core 4 and the third single-mode fiber core 6 are both d 1 The core refractive index is n at 5μm and 1550nm wavelength. 1 is 1.4624; the diameter d of the second single-mode core 5 2 The core refractive index n is 5μm and 1550nm. 2 The diameters of the fourth single-mode fiber core 7 and the sixth single-mode fiber core 9 are both d 3 The core refractive index is n at 5μm and 1550nm wavelength.3 is 1.4588; the diameter of the fifth few-mode core 8 is d 4 The core refractive index is n at 5μm and 1550nm wavelength. 4 The diameter d of the seventh few-mode core 10 is 1.4493; 5 The core refractive index n is 5μm and 1550nm. 5 It is 1.4555.

[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 substrate material 1, a central few-mode core and a peripheral single-mode core. The central few-mode core includes a core substrate 2 and a high refractive index ring 3. The core substrate 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. The mode division multiplexer length of 5000μm 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.

[0047] The positions of the seven outer single-mode fiber cores are arranged in a heptagonal structure, wherein each single-mode fiber core is located at one of the vertices of the heptagonal structure. 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 center line of the fourth single-mode fiber core 7 and the central minority-mode fiber core are at an angle of 60°. 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 respectively: L 1 , L 2 , L 3 , L 4 , L 5 , L 6 and L 7 , where L 1 =L 3 , L 4 =L 6 Preferably, L 1 , L 3 Both are 13.39μm, L 4 , L 6 Both are 14.14μm, L 2 15.10μm, L 5 19.35μm, L 7 It is 14.78μm.

[0049] See also Figure 2 The base material 1 of the optical fiber is silicon dioxide, and its refractive index is 1.4440 at a wavelength of 1550 nm. The diameter d of the central few-mode core 0 The substrate refractive index is n at 16 μm at 1550 nm. 0 is 1.4549, 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 n of the high refractive index ring at a wavelength of 1550 nm is 6 The diameters of the first single-mode fiber core 4 and the third single-mode fiber core 6 are both d 1 The core refractive index is n at 5μm and 1550nm wavelength. 1 is 1.4624; the diameter d of the second single-mode core 5 2 The core refractive index n is 5μm and 1550nm. 2 The diameters of the fourth single-mode fiber core 7 and the sixth single-mode fiber core 9 are both d 3 The core refractive index is n at 5μm and 1550nm wavelength. 3 is 1.4588; the diameter of the fifth few-mode core 8 is d 4 The core refractive index is n at 5μm and 1550nm wavelength. 4 The diameter d of the seventh few-mode core 10 is 1.4493; 5 The core refractive index n is 5μm and 1550nm. 5 It is 1.4555.

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

[0051] The main body of the present invention is a multi-core optical fiber. The core-to-core crosstalk in the multi-core optical fiber is one of the important criteria for evaluating the quality of the device. The specific manifestation of the core-to-core crosstalk is the mode coupling efficiency between the modes of each fiber core. In addition, the insertion loss and the inter-mode extinction ratio are also the main indicators for measuring the performance of the mode division multiplexer.

[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 1550nm 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 , L.P. 11a , L.P. 11b , L.P. 21a , L.P. 21b , L.P. 02， LP 31 and LP 12 ) on the desired mode. Through the simulation of mode coupling, it is found that when only one of the cores at the input end of the optical fiber is passed through, 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 non-desired conversion mode on the desired conversion mode; the smaller the extinction ratio, the greater the crosstalk of all other non-desired modes considered on the desired mode. With the increase of the optical fiber length, the extinction ratio of each desired conversion mode shows an upward trend. When the transmission length approaches 5000μm, the ER curve tends to be stable because the mode conversion is basically completed. At a fiber length of 5000μm, each desired conversion mode obtains a higher mode extinction ratio.

[0055] Through the analysis of the conversion efficiency of each mode in Table 1, it is obvious that in the process of each mode conversion at the working wavelength of 1550nm, the crosstalk of the present invention is very small, and a very high mode purity can be obtained 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 5The 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 working 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, the mode multiplexer can maintain a low IL in the wavelength range of 1.53μm-1.57μm, and the IL at 1.55μm is the lowest, which is 0.2384dB.

[0058] The eight-mode multiplexer proposed in the present invention 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 that need to be converted are 99.6%, 99.6%, 97.6%, 99.3%, 96.5%, 87.1%, and 76.8%, respectively. The device has a low manufacturing cost and has more modes. It provides better flexibility for optimizing device performance, can reduce complexity, and has 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 protection scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related system fields, are also included in the protection scope of the present invention.

Claims

1. An eight-mode mode division multiplexer based on multi-core optical fiber, characterized in that: 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) of the mode conversion is used to carry out LP to the central few-mode fiber core 31 The second single-mode fiber core (5) for mode conversion is used to carry out 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 for LP to 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.

2. The eight-mode mode division multiplexer based on multi-core optical fiber according to claim 1, characterized in that: 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 third single-mode fiber core (6) 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 third single-mode fiber core (6) 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 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°.

3. The eight-mode mode division multiplexer based on multi-core optical fiber according to claim 2, characterized in that: The distances from 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) to the exact center of the central few-mode fiber core are L1, L2, L3, L4, L5, L6, and L7, respectively, where L1=L3, L4=L6.

4. The eight-mode mode division multiplexer based on multi-core optical fiber according to claim 3, characterized in that: The L1 and L3 are both 13.39 μm, the L4 and L6 are both 14.14 μm, the L2 is 15.10 μm, the L5 is 19.35 μm, and the L7 is 14.78 μm.

5. An eight-mode mode division multiplexer based on multi-core optical fiber according to any one of claims 1 to 4, 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 indices n1 are 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 few-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 few-mode fiber core (10) is 5 μm, and the fiber core refractive index n7 is 1.4555 at a wavelength of 1550 nm.

6. An eight-mode mode division multiplexer based on multi-core optical fiber according to any one of claims 1 to 4, 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.

7. An eight-mode mode division multiplexer based on multi-core optical fiber according to any one of claims 1 to 4, 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.

8. The eight-mode mode division multiplexer based on multi-core optical fiber according to claim 7, characterized in that: The length of the mode division multiplexer is 5000 μm.

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