Optical fiber signal mode conversion device, conversion method and optical fiber transmission system

Abstract

The embodiments of the present application provide an optical fiber signal mode conversion device, an optical fiber signal mode conversion method, and an optical fiber transmission system, which relate to the field of optical communication technology. The optical fiber signal mode conversion device includes a non-single-mode optical fiber and a single-mode optical fiber, wherein the non-single-mode optical fiber includes a first mode channel and a second mode channel; the single-mode optical fiber forms a first coupling region and a second coupling region with the non-single-mode optical fiber along the transmission direction of the signal in the non-single-mode optical fiber; wherein the effective refractive index of the fundamental mode signal of the single-mode optical fiber in the first coupling region is equal to the effective refractive index of the first mode signal, and the first mode signal can be coupled to the fundamental mode channel of the single-mode optical fiber; wherein the effective refractive index of the fundamental mode signal of the single-mode optical fiber in the second coupling region is equal to the effective refractive index of the second mode signal, and the fundamental mode signal of the single-mode optical fiber can be coupled to the second mode channel. Thus, mode conversion is achieved, and the long-distance optical transmission capability is improved.

Description

Technical Field

[0001] The present application relates to the field of optical communication technology, and in particular to an optical fiber signal mode conversion device, an optical fiber signal mode conversion method, and an optical fiber transmission system. Background Art

[0002] With the explosive growth of information transmission demand, traditional single-mode optical fiber is gradually approaching its transmission limit. New methods represented by few-mode multiplexing and multi-mode multiplexing have received widespread attention. For example, few-mode multiplexing technology uses independent orthogonal modes in few-mode optical fiber as transmission channels, which can exponentially increase the optical transmission capacity.

[0003] One of the core issues in few-mode fiber communication is mode conversion, which mainly includes two categories: one is mode multiplexing and demultiplexing. Mode multiplexing is to multiplex the basemode signals in multiple single-mode fibers into a single-mode fiber as basemode and high-order mode signals for transmission (the basemode and high-order mode signals in the few-mode fiber are combined into a few-mode multiplexed signal). Mode demultiplexing is to demultiplex the few-mode multiplexed signal into the basemode signal in multiple single-mode fibers for transmission. The other is to convert any mode in the few-mode multiplexed signal into another mode for transmission, or to convert multiple modes in the few-mode multiplexed signal into multiple other modes for transmission. Among them, the second type of mode conversion has important applications in scenarios such as mode cyclic conversion and mode add-drop multiplexing. Summary of the Invention

[0004] The embodiments of the present application provide an optical fiber signal mode conversion device, an optical fiber signal mode conversion method, and an optical fiber transmission system. The main purpose is to provide an optical fiber signal mode conversion device that can realize conversion from one mode to another mode.

[0005] To achieve the above objectives, the embodiments of the present application adopt the following technical solutions:

[0006] In a first aspect, the present application provides an optical fiber signal mode conversion device for converting a first mode into a second mode, comprising: a non-single-mode optical fiber, the non-single-mode optical fiber comprising a first mode channel and a second mode channel, the first mode channel being used to transmit a first mode signal, and the second mode channel being used to transmit a second mode signal; a single-mode optical fiber, forming a first coupling region and a second coupling region with the non-single-mode optical fiber along the transmission direction of the signal in the non-single-mode optical fiber; wherein the effective refractive index of the fundamental mode signal of the single-mode optical fiber in the first coupling region is equal to the effective refractive index of the first mode signal, and the first mode signal can be coupled to the fundamental mode channel of the single-mode optical fiber; and the effective refractive index of the fundamental mode signal of the single-mode optical fiber in the second coupling region is equal to the effective refractive index of the second mode signal, and the fundamental mode signal of the single-mode optical fiber can be coupled to the second mode channel.

[0007] In an optical fiber signal mode conversion device provided in an embodiment of the present application, a single-mode optical fiber and an optical fiber are formed with a first coupling region and a second coupling region. Because the effective refractive index of the fundamental mode signal of the single-mode optical fiber in the first coupling region is equal to the effective refractive index of the first mode signal, the first mode signal of the non-single-mode optical fiber can be coupled to the fundamental mode channel of the single-mode optical fiber; and because the effective refractive index of the fundamental mode signal of the single-mode optical fiber in the second coupling region is equal to the effective refractive index of the second mode signal, the fundamental mode signal of the single-mode optical fiber can be coupled to the second mode channel of the optical fiber. Therefore, in an embodiment of the present application, by setting the effective refractive index of the fundamental mode signal in the first coupling region and the second coupling region of the single-mode optical fiber to be different, the effective refractive index of the fundamental mode signal decoupled from the single-mode optical fiber changes when it is transmitted to the second coupling region, and ultimately the fundamental mode signal coupled with the second mode is coupled to the second mode channel of the optical fiber, thereby achieving conversion from the first mode to the second mode.

[0008] In a possible implementation of the first aspect, the non-single-mode optical fiber includes a first optical fiber, a first coupling region is formed between the single-mode optical fiber and the first optical fiber, and a second coupling region is formed between the single-mode optical fiber and the first optical fiber. In other words, the first mode can be converted to the second mode on the same optical fiber.

[0009] In a possible implementation of the first aspect, the non-single-mode optical fiber includes a first optical fiber and a second optical fiber. A first coupling region is formed between the single-mode optical fiber and the first optical fiber, and a second coupling region is formed between the single-mode optical fiber and the second optical fiber. In other words, the converted second mode can be transferred to another optical fiber, which can be used in mode add-drop multiplexing scenarios.

[0010] In a possible implementation of the first aspect, the length of the first coupling region is equal to the coupling length of the first mode signal coupled to the fundamental mode channel of the single-mode optical fiber. Because the length of the first coupling region is equal to the coupling length of the first mode signal coupled to the fundamental mode channel of the single-mode optical fiber, compared to setting the length of the first coupling region equal to an integer multiple greater than 1 of the coupling length of the first mode signal coupled to the fundamental mode channel of the single-mode optical fiber, the length of the optical fiber is significantly reduced. For an all-optical fiber transmission system, the length of the entire all-optical fiber transmission system is also effectively reduced.

[0011] In a possible implementation of the first aspect, the length of the second coupling region is equal to the coupling length between the fundamental mode signal of the single-mode optical fiber and the second mode channel. Because the length of the second coupling region is equal to the coupling length between the fundamental mode signal of the single-mode optical fiber and the second mode channel, compared to setting the length of the second coupling region equal to an integer multiple greater than 1 of the coupling length between the fundamental mode signal of the single-mode optical fiber and the second mode channel, the length of the optical fiber is significantly reduced. For an all-optical fiber transmission system, the length of the entire all-optical fiber transmission system is also effectively reduced.

[0012] In a possible implementation of the first aspect, in the first coupling region, the non-single-mode optical fiber and the single-mode optical fiber are arranged in parallel and the cladding of the optical fiber is fused to the cladding of the single-mode optical fiber. In the second coupling region, the non-single-mode optical fiber and the single-mode optical fiber are arranged in parallel and the cladding of the optical fiber is fused to the cladding of the single-mode optical fiber. The value range of the distance d between the core center of the non-single-mode optical fiber and the core center of the single-mode optical fiber is: d∈[R f1 +R s1 ,R f2 +R s2 ]; where: R f1 is the radius of the core of the non-single-mode optical fiber; R s1 is the radius of the core of the single-mode optical fiber; R f2 is the radius of the cladding of non-single-mode optical fiber; R s2 is the radius of the cladding of a single-mode optical fiber.

[0013] In a possible implementation of the first aspect, the refractive index of the core of the single-mode optical fiber in the first coupling region is a first refractive index, the refractive index of the core of the single-mode optical fiber in the second coupling region is a second refractive index, and the refractive index of the core of the single-mode optical fiber in a non-coupling region between the first coupling region and the second coupling region is a third refractive index, where the third refractive index is between the first refractive index and the second refractive index.

[0014] Since the third refractive index is between the first and second refractive indices, when processing and manufacturing single-mode optical fibers, the processing difficulty of single-mode optical fibers is significantly reduced compared to when the third refractive index sometimes exceeds the first refractive index and sometimes exceeds the second refractive index.

[0015] In a possible implementation of the first aspect, the first mode and the second mode are two modes within a degenerate mode; the effective refractive index of the fundamental mode signal of the single-mode optical fiber in the first coupling region is equal to the effective refractive index of the fundamental mode signal of the single-mode optical fiber in the second coupling region; in the first coupling region, along the cross section of the non-single-mode optical fiber, the core center of the non-single-mode optical fiber and the core center of the single-mode optical fiber are on a first straight line; in the second coupling region, along the cross section of the non-single-mode optical fiber, the core center of the non-single-mode optical fiber and the core center of the single-mode optical fiber are on a second straight line, and the angle between the first straight line and the second straight line is equal to the phase difference between the first mode and the second mode.

[0016] When the first mode and the second mode are two modes within the degenerate mode, the first mode and the second mode, which are degenerate modes, can be converted by making the effective refractive index of the fundamental mode signal of the single-mode optical fiber in the first coupling region equal to the effective refractive index of the fundamental mode signal of the single-mode optical fiber in the second coupling region, and the angle between the first straight line and the second straight line equal to the phase difference between the first mode and the second mode. Therefore, the embodiment of the present application realizes the conversion of modes within the degenerate mode, expanding the application scenarios of the optical fiber signal mode conversion device.

[0017] In a possible implementation of the first aspect, the second mode is a degenerate mode, and the second mode includes a first submode and a second submode; the optical fiber signal mode conversion device is used to convert the first mode into the first submode, and the effective refractive index of the fundamental mode signal of the single-mode optical fiber in the second coupling region is n1. The optical fiber signal mode conversion device is further used to convert the first mode into the second submode, and the effective refractive index of the fundamental mode signal of the single-mode optical fiber in the second coupling region is n2, and n1=n2; the optical fiber signal mode conversion device is used to convert the first mode into the first submode, and along the cross section of the non-single-mode optical fiber in the second coupling region, the core center of the non-single-mode optical fiber and the core center of the single-mode optical fiber are on a third straight line; the optical fiber signal mode conversion device is further used to convert the first mode into the second submode, and along the cross section of the non-single-mode optical fiber in the second coupling region, the core center of the non-single-mode optical fiber and the core center of the single-mode optical fiber are on a fourth straight line, and the angle between the third straight line and the fourth straight line is equal to the phase difference between the first submode and the second submode.

[0018] When the second mode includes two sub-modes of a degenerate mode, by setting n1=n2 in the second coupling region and the angle between the third straight line and the fourth straight line being equal to the phase difference between the first sub-mode and the second sub-mode, the first mode can be converted into the first sub-mode of the degenerate mode or the first mode can be converted into the second sub-mode, thereby achieving discrimination between the modes within the degenerate mode.

[0019] In a possible implementation of the first aspect, the optical fiber signal mode conversion device is used to convert N modes, where N is an integer greater than or equal to 2; the non-single-mode optical fiber includes N mode channels, and the N mode channels correspond one-to-one to the N modes; there are N single-mode optical fibers, and any single-mode optical fiber and non-single-mode optical fiber are formed with a first coupling region and a second coupling region; the mode of the non-single-mode optical fiber coupled to any single-mode optical fiber is one of the N modes; the mode of any single-mode optical fiber coupled to the non-single-mode optical fiber is one of the N modes, and the mode of the non-single-mode optical fiber coupled to any single-mode optical fiber is different from the mode of the single-mode optical fiber coupled to the non-single-mode optical fiber.

[0020] When the optical fiber signal mode conversion device of the above technical solution is adopted, the optical fiber signal mode conversion device can form a cyclic mode conversion device. When it is suitable for an optical fiber transmission system, it can realize the cyclic conversion of the signal mode. If it is applied to the mode cyclic conversion, it can realize the compensation of the differential mode group delay and reduce the signal crosstalk.

[0021] In a possible implementation of the first aspect, the plurality of first coupling regions are sequentially arranged along the axial direction of the optical fiber, and the plurality of second coupling regions are sequentially arranged along the axial direction of the optical fiber.

[0022] In a second aspect, the present application also provides a method for converting an optical fiber signal mode, which is applied to the above-mentioned optical fiber signal mode conversion device, comprising: when the signal of the first mode in the non-single-mode optical fiber is transmitted to the first coupling region, the signal of the first mode is decoupled to the fundamental mode channel of the single-mode optical fiber and transmitted as a fundamental mode signal in the single-mode optical fiber; when the fundamental mode signal in the single-mode optical fiber is transmitted to the second coupling region, the fundamental mode signal of the single-mode optical fiber is coupled to the second mode channel of the non-single-mode optical fiber and transmitted as a second mode in the non-single-mode optical fiber.

[0023] In the optical fiber signal mode conversion method provided in the embodiments of the present application, since the effective refractive index of the fundamental mode signal of the single-mode optical fiber in the first coupling region is equal to the effective refractive index of the first mode signal, when the first mode signal transmitted in the optical fiber is transmitted into the first coupling region, the first mode signal is decoupled into the fundamental mode channel of the single-mode optical fiber according to the mode matching condition and transmitted together with the fundamental mode signal within the single-mode optical fiber. Furthermore, since the effective refractive index of the fundamental mode signal of the single-mode optical fiber in the second coupling region is equal to the effective refractive index of the second mode signal, when the fundamental mode signal in the single-mode optical fiber is transmitted into the second coupling region, the fundamental mode signal of the single-mode optical fiber is coupled to the second mode channel of the optical fiber according to the mode matching condition, thereby converting the first mode into the second mode.

[0024] In a third aspect, the present application also provides an optical fiber transmission system, comprising: a transmission optical fiber, the transmission optical fiber comprising a first transmission optical fiber and a second transmission optical fiber, the first transmission optical fiber and the second transmission optical fiber both comprising a first mode channel and a second mode channel; the aforementioned optical fiber signal mode conversion device is provided at the node between the first transmission optical fiber and the second transmission optical fiber; the light inlet of the non-single-mode optical fiber is opposite to the light outlet of the first transmission optical fiber, and the light outlet of the non-single-mode optical fiber is opposite to the light inlet of the second transmission optical fiber.

[0025] The optical fiber transmission system provided in the embodiment of the present application includes the optical fiber signal mode conversion device of any of the above-mentioned technical solutions. In this way, the optical fiber signal mode conversion device can convert the first mode signal on the first transmission optical fiber into the second mode channel of the second transmission optical fiber and transmit it in the second mode in the second transmission optical fiber. The optical fiber transmission system provided in the embodiment of the present application and the optical fiber signal mode conversion device described in the above-mentioned technical solutions can solve the same technical problems and achieve the same expected effects.

[0026] In a possible implementation of the third aspect, a fiber optic transmission system is configured to transmit signals in N modes, where N is an integer greater than or equal to 2. The transmission optical fiber comprises N segments, each having equal axial length, and each segment having N mode channels, each corresponding one-to-one to the N modes. The fiber optic signal mode conversion device comprises N-1 optical fiber signal mode conversion devices, with one optical fiber signal mode conversion device being disposed at a node between two segments of the transmission optical fiber. The fiber optic transmission system can compensate for differential mode group delay. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a structural block diagram of the optical fiber transmission system according to an embodiment of the present application;

[0028] Figure 2 This is a schematic structural diagram of an optical fiber signal mode conversion device according to an embodiment of the present application;

[0029] Figure 3a This is a schematic structural diagram of an optical fiber signal mode conversion device according to an embodiment of the present application;

[0030] Figure 3b This is a schematic structural diagram of an optical fiber signal mode conversion device according to an embodiment of the present application;

[0031] Figure 4a A schematic diagram of the refractive index distribution of a single-mode optical fiber according to an embodiment of the present application;

[0032] Figure 4b A schematic diagram of the refractive index distribution of a single-mode optical fiber according to an embodiment of the present application;

[0033] Figure 5a This is a partial schematic diagram of the optical fiber signal mode conversion device according to an embodiment of the present application;

[0034] Figure 5b for Figure 5a A schematic cross-sectional view of the coupling region;

[0035] Figure 6a This is a schematic structural diagram of an optical fiber signal mode conversion device according to an embodiment of the present application;

[0036] Figure 6b This is a schematic structural diagram of an optical fiber signal mode conversion device according to an embodiment of the present application;

[0037] Figure 7a This is a schematic structural diagram of an optical fiber signal mode conversion device according to an embodiment of the present application;

[0038] Figure 7b for Figure 7a A schematic cross-sectional view of the first coupling region;

[0039] Figure 7c for Figure 7a A schematic cross-sectional view of the second coupling region;

[0040] Figure 8a This is a schematic structural diagram of an optical fiber signal mode conversion device according to an embodiment of the present application;

[0041] Figure 8b for Figure 8a A schematic cross-sectional view of the second coupling region;

[0042] Figure 9aThis is a schematic structural diagram of an optical fiber signal mode conversion device according to an embodiment of the present application;

[0043] Figure 9b for Figure 9a A schematic cross-sectional view of the second coupling region;

[0044] Figure 10 This is a structural block diagram of the optical fiber transmission system according to an embodiment of the present application;

[0045] Figure 11 for Figure 10 A schematic diagram of the structure of the optical fiber signal mode conversion device;

[0046] Figure 12 This is a structural block diagram of the optical fiber transmission system according to an embodiment of the present application;

[0047] Figure 13 for Figure 12 A schematic diagram of the structure of the optical fiber signal mode conversion device;

[0048] Figure 14 This is a structural block diagram of the optical fiber transmission system according to an embodiment of the present application;

[0049] Figure 15a for Figure 14 A schematic diagram of the structure of the optical fiber signal mode conversion device;

[0050] Figure 15b for Figure 15a Schematic diagram of the cross section of the coupling region;

[0051] Figure 15c for Figure 15a Schematic diagram of the cross section of the coupling region;

[0052] Figure 16 This is a structural block diagram of the optical fiber transmission system according to an embodiment of the present application;

[0053] Figure 17 for Figure 16 A schematic diagram of the structure of the optical fiber signal mode conversion device;

[0054] Figure 18 Schematic diagram of the structure of the optical fiber signal mode conversion device according to an embodiment of the present application. DETAILED DESCRIPTION

[0055] The embodiments of the present application relate to an optical fiber transmission system, an optical fiber signal mode conversion device, and an optical fiber signal mode conversion method. The optical fiber transmission system, the optical fiber signal mode conversion device, and the optical fiber signal mode conversion method are described in detail below with reference to the accompanying drawings.

[0056] In the embodiments of the present invention, non-single-mode includes few-mode and multi-mode. The following embodiments take few-mode optical fiber and few-mode signal transmission as examples.

[0057] The present application provides an optical fiber transmission system. Figure 1 The optical fiber transmission system includes a first transmission optical fiber 21 and a second transmission optical fiber 22. The first transmission optical fiber 21 and the second transmission optical fiber 22 both include a first mode channel and a second mode channel. The first mode channel is used to transmit a first mode signal, and the second mode channel is used to transmit a second mode signal. An optical fiber signal mode conversion device 1 is provided at the node between the first transmission optical fiber 21 and the second transmission optical fiber 22. The optical fiber signal mode conversion device 1 is used to convert the first mode into the second mode.

[0058] The present invention provides a device for converting optical fiber signal mode. Figure 2 The optical fiber signal mode conversion device 1 includes: a few-mode optical fiber 11 and a single-mode optical fiber 12. The few-mode optical fiber 11 includes a first mode channel and a second mode channel. The first mode channel is used to transmit a first mode signal, and the second mode channel is used to transmit a second mode signal. Along the transmission direction of the signal in the few-mode optical fiber 11, the single-mode optical fiber 12 and the few-mode optical fiber 11 form a first coupling region 13 and a second coupling region 14. In the first coupling region 13, the effective refractive index of the fundamental mode signal of the single-mode optical fiber 12 is equal to the effective refractive index of the first mode signal, and the first mode signal can be coupled to the fundamental mode channel of the single-mode optical fiber 12. In the second coupling region 14, the effective refractive index of the fundamental mode signal of the single-mode optical fiber 12 is equal to the effective refractive index of the second mode signal, and the fundamental mode signal of the single-mode optical fiber 12 can be coupled to the second mode channel.

[0059] Since the effective refractive index of the fundamental mode signal of the single-mode fiber 12 in the first coupling region 13 is equal to the effective refractive index of the first mode signal, the first mode signal can be coupled to the fundamental mode channel of the single-mode fiber 12. In this way, the first mode of the few-mode fiber 11 and the fundamental mode of the single-mode fiber 12 meet the mode matching condition in the first coupling region 13. The first mode signal in the few-mode fiber 11 can be decoupled to the single-mode fiber 12 and transmitted in the fundamental mode in the single-mode fiber 12. Moreover, because the effective refractive index of the fundamental mode signal in the first coupling region 13 of the single-mode fiber 12 is different from the effective refractive index of the fundamental mode signal in the second coupling region 14, and the effective refractive index of the fundamental mode signal of the single-mode fiber 12 in the second coupling region 14 is equal to the effective refractive index of the second mode signal, the fundamental mode of the single-mode fiber 12 and the second mode of the few-mode fiber 11 meet the mode matching condition in the second coupling region 14. As a result, the fundamental mode signal in the single-mode fiber 12 is coupled to the second mode channel of the few-mode fiber 11 and transmitted in the second mode in the few-mode fiber 11, thereby achieving conversion of the first mode into the second mode.

[0060] When used in an optical fiber transmission system, the optical fiber signal mode conversion device provided in this embodiment can achieve all-fiber transmission (both the transmission fiber and the mode conversion device are optical fibers) and is highly compatible with optical fiber transmission systems. It can convert one mode into another using only one few-mode fiber 11 and one single-mode fiber 12. This simple structure significantly reduces the cost of the transmission system. Furthermore, the few-mode fiber 11 and the single-mode fiber 12 form only two coupling regions, resulting in low insertion loss.

[0061] like Figure 2 The optical fiber signal mode conversion device is used to convert the M1 mode into the M2 mode (the light inlet of the few-mode optical fiber 11 is M1+M3+···+M n The light outlet of the few-mode fiber 11 is M2+M3+···+M n ), the few-mode fiber 11 includes an M1 mode channel, an M2 mode channel, an M3 mode channel, and so on, until the Mn mode channel. The effective refractive index of the fundamental mode signal of the single-mode fiber 12 in the first coupling region 13 is equal to the effective refractive index of the M1 mode signal n M1 The effective refractive index of the fundamental mode signal of the single-mode optical fiber 12 in the second coupling region 14 is equal to the effective refractive index of the M2 mode signal n M2 The fundamental mode signal of the single-mode optical fiber 12 can be coupled to the M2 mode channel. In this way, the optical fiber signal mode conversion device can convert the M1 mode into the M2 mode.

[0062] In some scenarios, it is necessary to convert multiple modes into multiple modes. The embodiment of the present application provides a fiber optic signal mode conversion device, such as Figure 3a The business requirement is to convert the M1, M2 and M3 modes into M4, M5 and M6 modes (the light inlet of the few-mode fiber 11 is M1+M2+M3+M7····+M n The light outlet of the few-mode fiber 11 is M4+M5+M6+M7···+M n ), the few-mode fiber 11 includes M1, M2, M3, and even Mn mode channels. The single-mode fiber includes single-mode fiber 12a, single-mode fiber 12b, and single-mode fiber 12c. The single-mode fiber 12a, single-mode fiber 12b, and single-mode fiber 12c form a first coupling region and a second coupling region with the few-mode fiber 11. The effective refractive index of the fundamental mode signal of the single-mode fiber 12a in the first coupling region is the same as the effective refractive index of the M1 mode signal. M1 The effective refractive index of the fundamental mode signal of the single-mode optical fiber 12a in the second coupling region is equal to the effective refractive index of the M4 mode signal n M4equal, and the fundamental mode signal of the single-mode optical fiber 12a can be coupled to the M4 mode channel; the effective refractive index of the fundamental mode signal of the single-mode optical fiber 12b in the first coupling region is equal to the effective refractive index n of the M2 mode signal M2 The effective refractive index of the fundamental mode signal of the single-mode fiber 12b in the second coupling region is equal to the effective refractive index of the M5 mode signal n M5 The effective refractive index of the fundamental mode signal of the single-mode fiber 12c in the first coupling region is equal to the effective refractive index of the M3 mode signal n M3 The effective refractive index of the fundamental mode signal of the single-mode optical fiber 12c in the second coupling region is equal to the effective refractive index of the M6 ​​mode signal n M6 The fundamental mode signal of the single-mode optical fiber 12c can be coupled to the M6 ​​mode channel, so that the optical fiber signal mode conversion device can convert the M1 mode, M2 mode and M3 mode into the M4 mode, M5 mode and M6 mode.

[0063] It should be noted that: Figure 3a The optical fiber signal mode conversion device shown is not limited to the above-mentioned conversion method, and can also be: the effective refractive index of the fundamental mode signal of the single-mode optical fibers 12a, 12b, and 12c in the first coupling region is equal to the effective refractive index of the signals in the M1, M2, and M3 modes, respectively, and the effective refractive index of the fundamental mode signal of the single-mode optical fibers 12a, 12b, and 12c in the second coupling region is equal to the effective refractive index of the signals in the M5, M6, and M4 modes, respectively.

[0064] In some scenarios, it is necessary to dynamically convert multiple modes into multiple modes in real time or at a high frequency, and the conversion correspondence between the multiple modes is different during the previous and subsequent dynamic conversions. The embodiment of the present application provides a fiber optic signal mode conversion device, such as Figure 3b The business requirement is to convert the M1, M2 and M3 modes into M4, M5 and M6 modes (the light inlet of the few-mode fiber 11 is M1+M2+M3+M7····+M n The light outlet of the few-mode fiber 11 is M4+M5+M6+M7···+M n ), the few-mode fiber 11 includes M1, M2, M3, and M nMode channel. The single-mode optical fiber includes single-mode optical fiber 12a, single-mode optical fiber 12b, single-mode optical fiber 12c, single-mode optical fiber 12d, single-mode optical fiber 12e and single-mode optical fiber 12f. The single-mode optical fiber 12a, single-mode optical fiber 12b and single-mode optical fiber 12c form a first coupling region with the few-mode optical fiber 11, and the single-mode optical fiber 12d, single-mode optical fiber 12e and single-mode optical fiber 12f form a second coupling region with the few-mode optical fiber 11. The effective refractive index of the fundamental mode signal of the single-mode optical fiber 12a in the first coupling region is the same as the effective refractive index of the M1 mode signal n M1 equal, and the M1 mode signal can be coupled to the fundamental mode channel of the single-mode optical fiber 12a; the effective refractive index of the fundamental mode signal of the single-mode optical fiber 12b in the first coupling region is equal to the effective refractive index n of the M2 mode signal M2 equal, and the M2 mode signal can be coupled to the fundamental mode channel of the single-mode optical fiber 12b; the effective refractive index of the fundamental mode signal of the single-mode optical fiber 12c in the first coupling region is equal to the effective refractive index n of the M3 mode signal M3 The effective refractive index of the fundamental mode signal of the single-mode fiber 12d in the second coupling region is equal to the effective refractive index of the M4 mode signal n M4 The effective refractive index of the fundamental mode signal of the single-mode fiber 12e in the second coupling region is equal to the effective refractive index of the M5 mode signal n M5 The effective refractive index of the fundamental mode signal of the single-mode fiber 12f in the second coupling region is equal to the effective refractive index of the M6 ​​mode signal n M6 The fundamental mode signal of single-mode optical fiber 12f is equal, and the fundamental mode signal of single-mode optical fiber 12a, 12b, 12c can be coupled to the M6 ​​mode channel. Between single-mode optical fibers 12a, 12b, 12c and single-mode optical fibers 12d, 12e, 12f is a dynamic optical switching device 31, which functions to switch the optical signal transmitted within each of single-mode optical fibers 12a, 12b, or 12c to single-mode optical fibers 12d, 12e, or 12f, respectively. This switching relationship can be dynamically changed in real time or at a high frequency. In this way, the optical fiber signal mode conversion device can convert the M1 mode, M2 mode, or M3 mode into the M4 mode, M5 mode, or M6 mode, respectively, and the mode conversion relationship can be dynamically changed in real time or at a high frequency. For example, when the dynamic optical switching device 31 is in working state 1, the M1 mode is converted to the M4 mode, the M2 mode is converted to the M5 mode, and the M3 mode is converted to the M6 ​​mode; after the dynamic optical switching device 31 is dynamically switched to working state 2, the M1 mode is converted to the M5 mode, the M2 mode is converted to the M6 ​​mode, and the M3 mode is converted to the M4 mode. Figure 3bThe optical fiber signal mode conversion device shown is not limited to performing conversion between the above three pairs of modes at the same time, but can also perform conversion between two, four or more pairs of modes at the same time.

[0065] Generally, the refractive index of the core of the uncoupling region of the single-mode optical fiber 12 is between the refractive indices of the cores of the two coupling regions. Assume that the refractive index of the core of the single-mode optical fiber 12 in the first coupling region is a first refractive index, the refractive index of the core of the single-mode optical fiber 12 in the second coupling region is a second refractive index, and the refractive index of the core of the single-mode optical fiber 12 in the uncoupling region between the first coupling region and the second coupling region is a third refractive index, which is between the first and second refractive indices.

[0066] The third refractive index is between the first refractive index and the second refractive index, and has various embodiments. Figure 4a and Figure 4b When the first refractive index of the core of the single-mode optical fiber in the first coupling region is greater than the second refractive index of the core of the single-mode optical fiber in the second coupling region, the third refractive index is gradually changed, for example, it can be linearly changed ( Figure 4a Straight line 1), can be a nonlinear gradient ( Figure 4a Curve 2 and curve 3), can also be a step-by-step gradient such as Figure 4b .

[0067] In order to shorten the length of the few-mode fiber 11 and reduce the volume of the conversion device, refer to Figure 5a The length L of the first coupling region 13 is equal to the coupling length for coupling the first mode signal to the fundamental mode channel of the single-mode fiber. The coupling length refers to the shortest coupling length during the first complete transfer of optical signal energy from the few-mode fiber 11 to the single-mode fiber 12. By controlling the length L of the first coupling region 13 to be equal to the coupling length for coupling the first mode signal to the fundamental mode channel of the single-mode fiber, rather than an integer multiple of the coupling length greater than 1, the length of the optical fiber can be shortened. This effect is particularly significant when multiple first coupling regions are provided.

[0068] The length L of the second coupling region 14 should also be controlled to be equal to the coupling length of the fundamental mode signal of the single-mode optical fiber coupled to the second mode channel. The coupling length is the shortest coupling length when the optical signal energy is completely transferred from the single-mode optical fiber 12 to the least mode optical fiber 11 for the first time.

[0069] In the embodiments of the present application, the single-mode optical fiber 12 and few-mode optical fiber 11 involved in the radial direction of the optical fiber include a core, a cladding, and a coating arranged in order from the inside out. The core transmits the optical signal. The cladding has a different refractive index from the core, confining the optical signal within the core for transmission and protecting the core. The coating acts as a protective structure for the core and cladding.

[0070] Embodiments of the present invention also provide a method for forming a coupling zone. Within the first coupling zone, the few-mode fiber 11 and the single-mode fiber 12 are arranged parallel to each other, and the cladding of the few-mode fiber 11 is fused to the cladding of the single-mode fiber 12, or bonded by side-throwing. Within the second coupling zone, the few-mode fiber 11 and the single-mode fiber 12 are also arranged parallel to each other, and the cladding of the few-mode fiber 11 is fused to the cladding of the single-mode fiber 12, or bonded by side-throwing. Of course, the few-mode fiber 11 and the single-mode fiber 12 can also be connected using other structures.

[0071] Reference Figure 5b , is a schematic cross-sectional view of the coupling region. The distance between the center of the core 11-2 of the few-mode fiber 11 and the center of the core 12-2 of the single-mode fiber 12 is d, and its value range is usually: d∈[R f1 +R s1 ,R f2 +R s2 ]; where: R f1 is the radius of the core 11-2 of the few-mode optical fiber 11; R s1 is the radius of the core 12-2 of the single-mode optical fiber 12; R f2 is the radius of the cladding 11-1 of the few-mode fiber 11; R s2 is the radius of the cladding 12 - 1 of the single-mode optical fiber 12 .

[0072] Typically, the maximum coupling efficiency during decoupling within the first coupling region is determined based on the first mode to be converted. The distance d between the core center of the few-mode fiber and the core center of the single-mode fiber within the first coupling region is then determined based on the maximum coupling efficiency. The coupling length of the first coupling region is then determined based on the value of d. Similarly, the maximum coupling efficiency during decoupling within the second coupling region is determined based on the second mode to be converted. The distance d between the core center of the fiber and the core center of the single-mode fiber within the second coupling region is then determined based on the maximum coupling efficiency. The coupling length of the second coupling region is then determined based on the value of d. Specific parameter design is not further elaborated.

[0073] The embodiment of the present invention also provides a mode conversion method, referring to Figure 6a The few-mode fiber includes a first few-mode fiber 111 and a second few-mode fiber 112. The first coupling region 13 is formed between the single-mode fiber 12 and the first few-mode fiber 111, and the second coupling region 14 is formed between the single-mode fiber 12 and the second few-mode fiber 112. In other words, the converted second mode can be transferred to another few-mode fiber, which can be used in mode add-drop multiplexing scenarios.

[0074] Two or more modes in a few-mode fiber can also be dynamically converted to multiple modes in two or more other few-mode fibers. Figure 6bThe few-mode optical fibers include a first few-mode optical fiber 111, a second few-mode optical fiber 112, and a third few-mode optical fiber 113. The single-mode optical fibers include a single-mode optical fiber 121, a single-mode optical fiber 122, a single-mode optical fiber 123, and a single-mode optical fiber 124. Between the single-mode optical fibers 121 and 122 and the single-mode optical fibers 123 and 124 is a dynamic optical switching device 31. Its function is to switch the optical signal transmitted in each optical fiber of the single-mode optical fiber 121 or 122 to the single-mode optical fiber 123 or 124, respectively. The switching correspondence can be dynamically changed in real time or at a high frequency. In this way, the optical fiber signal mode conversion device can convert the M1 mode or M2 mode in the first few-mode optical fiber 111 into the M3 mode in the second few-mode optical fiber 112 or the M4 mode in the third few-mode optical fiber 113, respectively. The mode conversion correspondence can be dynamically changed in real time or at a high frequency. In other words, multiple modes in one few-mode optical fiber can be dynamically converted to multiple modes in multiple other few-mode optical fibers, which can be used in mode add-drop multiplexing scenarios with dynamically adjustable modes.

[0075] When the first mode and the second mode are two modes within a set of degenerate modes, the optical fiber signal mode conversion device provided in the embodiment of the present application can still convert the first mode into the second mode. The effective refractive index of the fundamental mode signal of the single-mode optical fiber 12 in the first coupling region 13 is equal to the effective refractive index of the fundamental mode signal of the single-mode optical fiber 12 in the second coupling region 14. At the same time, along the cross section of the optical fiber in the first coupling region 13, the core center of the few-mode optical fiber 11 and the core center of the single-mode optical fiber 12 are on a first straight line. Along the cross section of the few-mode optical fiber 11 in the second coupling region 14, the core center of the few-mode optical fiber 11 and the core center of the single-mode optical fiber 12 are on a second straight line. The angle between the first straight line and the second straight line is equal to the phase difference between the first mode and the second mode. Thus, the optical fiber signal mode conversion device provided in the embodiment of the present application realizes mode conversion within a degenerate mode.

[0076] It should be noted that: the angle between the first straight line and the second straight line is equal to the phase difference between the first mode and the second mode not only means that the angle between the first straight line and the second straight line is exactly equal to the phase difference between the first mode and the second mode, but also that the angle between the first straight line and the second straight line is close to the phase difference between the first mode and the second mode, which is also within the protection scope of this application.

[0077] Reference Figure 7a , the optical fiber signal mode conversion device is used to convert M 1a Mode switched to M 1b Mode, M 1a Mode and M 1b The modes are two modes within the degenerate mode M1, and M 1a Mode and M 1b Phase difference of the mode The effective refractive index of the fundamental mode signal of the single-mode optical fiber 12 in the first coupling region 13 is equal to the effective refractive index of the fundamental mode signal of the single-mode optical fiber 12 in the second coupling region 14, and both are equal to the effective refractive index of the signal in the M1 mode (n M1a =n M1b ); along the cross section of the optical fiber within the first coupling region 13, reference Figure 7b The center of the core 11-2 of the few-mode fiber 11 and the center of the core 12-2 of the single-mode fiber 12 are on the first straight line L3. The cross section of the optical fiber in the second coupling region 14 is shown in FIG. Figure 7c The center of the core 11-2 of the few-mode fiber 11 and the center of the core 12-2 of the single-mode fiber 12 are on the second straight line L4, and the angle α2 between the first straight line L3 and the second straight line L4 is equal to M 1a Mode and M 1b Phase difference of the mode That is, α2=45°.

[0078] In the case where the second mode is a degenerate mode and the second mode includes a first submode and a second submode, when the optical fiber signal mode conversion device is used to convert the first mode into the first submode, the effective refractive index of the fundamental mode signal of the single-mode optical fiber in the second coupling region is n1; when the optical fiber signal mode conversion device is used to convert the first mode into the second submode, the effective refractive index of the fundamental mode signal of the single-mode optical fiber in the second coupling region is n2, and n1=n2; when the optical fiber signal mode conversion device is used to convert the first mode into the first submode, along the cross section of the optical fiber in the second coupling region, the center of the optical fiber core and the center of the single-mode optical fiber core are on a third straight line; when the optical fiber signal mode conversion device is used to convert the first mode into the second submode, along the cross section of the optical fiber in the second coupling region, the center of the optical fiber core and the center of the single-mode optical fiber core are on a fourth straight line, and the angle between the third straight line and the fourth straight line is equal to the phase difference between the first submode and the second submode. Therefore, the optical fiber signal mode conversion device provided in the embodiment of the present application can achieve the distinction between mode conversion within the degenerate mode.

[0079] It should be noted that: the angle between the third straight line and the fourth straight line is equal to the phase difference between the first sub-mode and the second sub-mode not only means that the angle between the third straight line and the fourth straight line is exactly equal to the phase difference between the first sub-mode and the second sub-mode, but also that the angle between the third straight line and the fourth straight line is close to the phase difference between the first sub-mode and the second sub-mode, which is also within the protection scope of this application.

[0080] Reference Figure 8a , the optical fiber signal mode conversion device is used to convert the M1 mode into the M 2a Mode (M 2a Mode and M 2b The modes are two modes within the degenerate mode M2, M 2a Mode and M2b Phase difference of the mode is 90°), the effective refractive index of the fundamental mode signal of the single-mode fiber in the second coupling region is equal to M 2a The effective refractive index n of the mode signal M2a , refer to Figure 9a The optical fiber signal mode conversion device is used to convert the M1 mode into the M 2b mode, the effective refractive index of the fundamental mode signal of the single-mode fiber in the second coupling region is n M2b , n M2a =n M2b .

[0081] Reference Figure 8b , Figure 8a In the second coupling region shown along the cross section of the optical fiber, the center of the optical fiber core 11-2 and the center of the single-mode optical fiber core 12-2 are located on the third straight line L1. Figure 9b , Figure 9a In the cross section of the optical fiber in the second coupling region shown, the center of the optical fiber core 11-2 and the center of the single-mode optical fiber core 12-2 are on the fourth straight line L2, and the angle α1 between the third straight line L1 and the fourth straight line L2 is equal to M 2a Mode and M 2b Phase difference of the mode That is, α1 = 90°.

[0082] The optical fiber signal mode conversion device provided in the embodiment of the present application can also realize mode cyclic conversion applications, and thus be used in few-mode and multi-mode optical fiber transmission systems. For example, the transmission system transmits N modes of signals, where N is greater than 1. In order to compensate for differential mode delay, the transmission optical fiber in the transmission system has N sections, and the axial lengths of the N sections of transmission optical fiber are equal. Each section of the transmission optical fiber has N mode channels, and the N mode channels correspond one-to-one to the N modes. There are N-1 optical fiber signal mode conversion devices in the transmission system, and an optical fiber signal mode conversion device is provided at the node between two sections of transmission optical fiber. The few-mode fiber 11 of each optical fiber signal mode conversion device includes N mode channels, and the N mode channels correspond one-to-one to the N modes; there are N single-mode optical fibers 12, and any single-mode optical fiber and the few-mode optical fiber 11 form a first coupling region and a second coupling region; the mode of the few-mode optical fiber 11 coupled to any single-mode optical fiber is one of the N modes, and the modes of the optical fiber coupled to the N single-mode optical fibers are all different; the mode of any single-mode optical fiber coupled to the optical fiber is one of the N modes, and the modes of the N single-mode optical fibers coupled to the optical fiber are all different, and the mode of the few-mode optical fiber 11 coupled to any single-mode optical fiber is different from the mode of the single-mode optical fiber coupled to the optical fiber, thereby forming a cyclic conversion.

[0083] The following describes an optical fiber transmission system having an optical fiber signal mode conversion device by taking an example.

[0084] like Figure 10 As shown, the optical fiber transmission system is used to transmit LP 01 LP 11 LP 21 and LP 02 mode signal, the transmission optical fiber includes a first transmission optical fiber 211, a second transmission optical fiber 212, a third transmission optical fiber 213 and a second transmission optical fiber 214, and the axial lengths of the first transmission optical fiber 211, the second transmission optical fiber 212, the third transmission optical fiber 213 and the second transmission optical fiber 214 are equal, and there are three optical fiber signal mode conversion devices 1, an optical fiber signal mode conversion device 1 is set at the node of the first transmission optical fiber 211 and the second transmission optical fiber 212, an optical fiber signal mode conversion device 1 is set at the node of the second transmission optical fiber 212 and the third transmission optical fiber 213, and an optical fiber signal mode conversion device 1 is set at the node of the third transmission optical fiber 213 and the fourth transmission optical fiber 214, and the structures of the three optical fiber signal mode conversion devices 1 are the same.

[0085] like Figure 11 The optical fiber signal mode conversion device of one structure is a single-mode optical fiber including single-mode optical fibers 121, 122, 123 and 124, each of which forms a first coupling region and a second coupling region with the few-mode optical fiber 11. The effective refractive index of the fundamental mode signal of the single-mode optical fibers 121, 122, 123 and 124 in the first coupling region is respectively 01 LP 11 LP 21 and LP 02 The effective refractive index n of the mode signal LP01 、n LP11 、n LP21 and n LP02 The effective refractive index of the fundamental mode signal of the single-mode optical fibers 121, 122, 123 and 124 in the second coupling region is equal to LP 11 The effective refractive index n of the mode signal LP11 、n LP21 、n LP02 and n LP01 equal, so the optical fiber signal mode conversion device realizes LP 01 Mode → LP 11 Mode, LP 11 Mode → LP 21 Mode, LP 21 Mode → LP 02 Mode and LP 02 Mode → LP 01 Mode conversion, so, use Figure 11The optical fiber transmission system of the optical fiber signal mode conversion device shown in the figure undergoes three-cycle mode conversion, and the signal of each mode is converted by LP 01 Mode, LP 11 Mode, LP 21 Mode and LP 02 The four modes are transmitted equidistantly, so the optical fiber transmission system can compensate for the differential mode group delay.

[0086] like Figure 12 As shown, the optical fiber transmission system realizes Figure 10 Cycle through the patterns in different orders. Figure 13 The optical fiber signal mode conversion device shown realizes LP 01 Mode → LP 21 Mode, LP 21 Mode → LP 02 Mode, LP 02 Mode → LP 11 Mode, and LP 11 Mode → LP 01 Mode conversion. Similarly, using Figure 12 and Figure 13 The optical fiber transmission system of the optical fiber signal mode conversion device shown in the figure undergoes three-cycle mode conversion, and the signal of each mode is converted by LP 01 Mode, LP 11 Mode, LP 21 Mode and LP 02 The four modes are transmitted equidistantly, so the optical fiber transmission system can compensate for the differential mode group delay.

[0087] like Figure 14 As shown, the optical fiber transmission system is used to transmit LP 01 Mode signal, LP 11a Mode signal and LP 11b Mode signal, LP 11a Mode and LP 11b The modes are two modes within the degenerate mode. The transmission optical fiber includes a fifth transmission optical fiber 215, a sixth transmission optical fiber 216, and a seventh transmission optical fiber 217, and the axial lengths of the fifth transmission optical fiber 215, the sixth transmission optical fiber 216, and the seventh transmission optical fiber 217 are all equal. There are two optical fiber signal mode conversion devices 1, one optical fiber signal mode conversion device 1 is set at the node between the fifth transmission optical fiber 21 and the sixth transmission optical fiber 216, and one optical fiber signal mode conversion device 1 is set at the node between the sixth transmission optical fiber 216 and the seventh transmission optical fiber 217, and the structures of the two optical fiber signal mode conversion devices 1 are the same.

[0088] like Figure 15aAs shown, the embodiment of the present application provides an optical fiber signal mode conversion device, the single-mode optical fiber includes single-mode optical fibers 125, 126 and 127, all of which form a first coupling region and a second coupling region with the few-mode optical fiber 11, and the effective refractive index of the fundamental mode signal of the single-mode optical fibers 125, 126 and 127 in the first coupling region is respectively 01 LP 11a LP 11b The effective refractive index n of the mode signal LP01 、n LP11a and n LP11b The effective refractive index of the fundamental mode signal of the single-mode optical fibers 125, 126 and 127 in the second coupling region is equal to LP 11a LP 11b LP 01 The effective refractive index n of the mode signal LP11a 、n LP11b and n LP01 The optical fiber signal mode conversion device realizes LP 01 Mode → LP 11a Mode, LP 11a Mode → LP 11b Mode, LP 11b Mode → LP 01 Mode conversion, so, use Figure 14 and Figure 15a The optical fiber transmission system of the optical fiber signal mode conversion device shown in the figure undergoes two cyclic mode conversions, and the signal of each mode is converted by LP 01 Mode, LP 11a Mode and LP 11b The three modes are transmitted equidistantly, so the optical fiber transmission system can compensate for the differential mode group delay.

[0089] Because LP 11a Mode and LP 11b The two modes are degenerate modes, LP 11a Mode and LP 11b The phase difference of the modes is Reference Figure 15b and Figure 15c In the first coupling region of the single-mode optical fiber 126, along the cross section of the few-mode optical fiber 11, the center of the core 11-2 of the few-mode optical fiber 11 and the center of the core 126-2 of the single-mode optical fiber 126 are located on a fifth straight line. In the second coupling region, along the cross section of the few-mode optical fiber 11, the center of the core 11-2 of the few-mode optical fiber 11 and the center of the core 126-2 of the single-mode optical fiber 126 are located on a sixth straight line. The angle between the fifth straight line and the sixth straight line is equal to LP. 11a Mode and LP 11b The phase difference of the mode.

[0090] like Figure 16 As shown, the optical fiber transmission system realizes Figure 14 Cycle through the patterns in different orders. Figure 17 The optical fiber signal mode conversion device shown realizes LP 01 Mode → LP 11b Mode, LP 11b Mode → LP 11a Mode, LP 11a Mode → LP 01 Mode conversion. Similarly, using Figure 16 and Figure 17 The optical fiber transmission system of the optical fiber signal mode conversion device shown in the figure undergoes two cyclic mode conversions, and the signal of each mode is converted by LP 01 Mode, LP 11a Mode and LP 11b The three modes are transmitted equidistantly, so the optical fiber transmission system can compensate for the differential mode group delay.

[0091] The optical fiber signal mode conversion device provided in the embodiment of the present application can also be used in the scenario of mode add / drop multiplexing. Figure 18 , LP transmission of few-mode fiber 111 01 Mode decoupled to single-mode fiber 121, and finally converted to LP in few-mode fiber 112 11 Mode signal transmission, few-mode fiber 111 transmission LP 11 Mode decoupled to single-mode fiber 122, and finally converted to LP in few-mode fiber 113 21 Mode signal transmission, that is, the exchange of mode signals in different optical fibers is realized, and the add-drop multiplexing of mode multiplexing signals is realized.

[0092] The present application also provides a method for converting an optical fiber signal mode. The method is applied to the optical fiber signal mode conversion device described above and includes the following steps:

[0093] S1: When the first mode signal in the few-mode fiber 11 is transmitted to the first coupling region 13, the first mode signal is decoupled to the fundamental mode channel of the single-mode fiber 12 and transmitted in the single-mode fiber 12 as a fundamental mode signal;

[0094] S2: When the fundamental mode signal in the single-mode fiber 12 is transmitted to the second coupling region 14, the fundamental mode signal of the single-mode fiber 12 is coupled to the second mode channel of the few-mode fiber 11 and transmitted in the second mode within the few-mode fiber 11. This achieves conversion from the first mode to the second mode.

[0095] In the description of this specification, specific features, structures, materials or characteristics may be combined in an appropriate manner in any one or more embodiments or examples.

[0096] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. An optical fiber signal mode conversion device, characterized in that: include: a non-single-mode optical fiber, the non-single-mode optical fiber comprising a first mode channel and a second mode channel, the first mode channel being used to transmit a signal in a first mode, and the second mode channel being used to transmit a signal in a second mode; The single-mode optical fiber forms a first coupling region and a second coupling region with the non-single-mode optical fiber along the transmission direction of the signal in the non-single-mode optical fiber; wherein, The effective refractive index of the fundamental mode signal of the single-mode optical fiber in the first coupling region is equal to the effective refractive index of the first mode signal, and the first mode signal can be coupled to the fundamental mode channel of the single-mode optical fiber; The effective refractive index of the fundamental mode signal of the single-mode optical fiber in the second coupling region is equal to the effective refractive index of the second mode signal, and the fundamental mode signal of the single-mode optical fiber can be coupled to the second mode channel to form a second mode signal transmitted in the second mode channel.

2. The optical fiber signal mode conversion device according to claim 1, characterized in that: The non-single-mode optical fiber includes a first optical fiber, the first coupling region is formed between the single-mode optical fiber and the first optical fiber, and the second coupling region is formed between the single-mode optical fiber and the first optical fiber.

3. The optical fiber signal mode conversion device according to claim 1, wherein: The non-single-mode optical fiber includes a first optical fiber and a second optical fiber, the first coupling region is formed between the single-mode optical fiber and the first optical fiber, and the second coupling region is formed between the single-mode optical fiber and the second optical fiber.

4. The optical fiber signal mode conversion device according to claim 3, characterized in that: The optical fiber signal mode conversion device also includes a dynamic optical switching device, wherein the first optical fiber and the M single-mode optical fibers form M first coupling regions, and are connected to the input end of the dynamic optical switching device through the M single-mode optical fibers; the second optical fiber includes M pieces, which respectively form M second coupling regions with the M single-mode optical fibers, and are connected to the output end of the dynamic optical switching device through the M single-mode optical fibers; M is an integer greater than or equal to 2.

5. The optical fiber signal mode conversion device according to any one of claims 1 to 4, characterized in that: The length of the first coupling region is equal to the coupling length of the first mode signal coupled to the fundamental mode channel of the single-mode optical fiber.

6. The optical fiber signal mode conversion device according to any one of claims 1 to 5, characterized in that: The length of the second coupling region is equal to the coupling length of the fundamental mode signal of the single-mode optical fiber coupled to the second mode channel.

7. The optical fiber signal mode conversion device according to any one of claims 1 to 6, characterized in that: In the first coupling region, the non-single-mode optical fiber and the single-mode optical fiber are arranged in parallel and the cladding of the non-single-mode optical fiber is fused to the cladding of the single-mode optical fiber. In the second coupling region, the non-single-mode optical fiber and the single-mode optical fiber are arranged in parallel and the cladding of the non-single-mode optical fiber is fused to the cladding of the single-mode optical fiber. The value range of the distance d between the core center of the non-single-mode optical fiber and the core center of the single-mode optical fiber is: d∈[R f1 +R s1 ,R f2 +R s2 ]; Where: R f1 is the radius of the core of the non-single-mode optical fiber; R s1 is the radius of the core of the single-mode optical fiber; R f2 is the radius of the cladding of the non-single-mode optical fiber; R s2 is the radius of the cladding of the single-mode optical fiber.

8. The optical fiber signal mode conversion device according to any one of claims 1 to 7, characterized in that: The refractive index of the core of the single-mode optical fiber in the first coupling region is a first refractive index, the refractive index of the core of the single-mode optical fiber in the second coupling region is a second refractive index, and the refractive index of the core of the single-mode optical fiber in a non-coupling region between the first coupling region and the second coupling region is a third refractive index, where the third refractive index is between the first refractive index and the second refractive index.

9. The optical fiber signal mode conversion device according to any one of claims 1 to 8, characterized in that: The first mode and the second mode are two modes within a degenerate mode; The effective refractive index of the fundamental mode signal of the single-mode optical fiber in the first coupling region is equal to the effective refractive index of the fundamental mode signal of the single-mode optical fiber in the second coupling region; In the first coupling region, along the cross section of the non-single-mode optical fiber, the core center of the non-single-mode optical fiber and the core center of the single-mode optical fiber are located on a first straight line. In the second coupling region, along the cross section of the non-single-mode optical fiber, the core center of the non-single-mode optical fiber and the core center of the single-mode optical fiber are located on a second straight line. The angle between the first straight line and the second straight line is equal to the phase difference between the first mode and the second mode.

10. The optical fiber signal mode conversion device according to any one of claims 1 to 8, characterized in that: The second mode is a degenerate mode, and the second mode includes a first submode and a second submode; The optical fiber signal mode conversion device is used to convert the first mode into the first sub-mode, the effective refractive index of the fundamental mode signal of the single-mode optical fiber in the second coupling region is n1, and the optical fiber signal mode conversion device is further used to convert the first mode into the second sub-mode, the effective refractive index of the fundamental mode signal of the single-mode optical fiber in the second coupling region is n2, and n1=n2; The optical fiber signal mode conversion device is used to convert the first mode into the first sub-mode, and along the cross section of the non-single-mode optical fiber in the second coupling region, the core center of the non-single-mode optical fiber and the core center of the single-mode optical fiber are located on a third straight line. The optical fiber signal mode conversion device is also used to convert the first mode into the second sub-mode, and along the cross section of the non-single-mode optical fiber in the second coupling region, the core center of the non-single-mode optical fiber and the core center of the single-mode optical fiber are located on a fourth straight line, and the angle between the third straight line and the fourth straight line is equal to the phase difference between the first sub-mode and the second sub-mode.

11. The optical fiber signal mode conversion device according to any one of claims 1 to 10, characterized in that: The optical fiber signal mode conversion device is used to convert N modes, where N is an integer greater than or equal to 2; The non-single-mode optical fiber includes N mode channels, and the N mode channels correspond one-to-one to the N modes; There are N single-mode optical fibers, and any one of the single-mode optical fibers and the non-single-mode optical fibers is formed with the first coupling region and the second coupling region; The mode in which the non-single-mode optical fiber is coupled to any of the single-mode optical fibers is one of the N modes; The mode of any one of the single-mode optical fibers coupled to the non-single-mode optical fiber is one of the N modes, and the mode of the non-single-mode optical fiber coupled to any one of the single-mode optical fibers is different from the mode of the single-mode optical fiber coupled to the non-single-mode optical fiber.

12. The optical fiber signal mode conversion device according to claim 11, characterized in that: A plurality of the first coupling regions are sequentially arranged along the axial direction of the non-single-mode optical fiber, and a plurality of the second coupling regions are sequentially arranged along the axial direction of the non-single-mode optical fiber.

13. The optical fiber signal mode conversion device according to claim 11 or 12, characterized in that: The optical fiber signal mode conversion device also includes a dynamic optical switching device, wherein the N input ends of the dynamic optical switching device are connected to the N first coupling regions through the N single-mode optical fibers, and the N output ends of the dynamic optical switching device are connected to the N second coupling regions through the N single-mode optical fibers.

14. A method for converting optical fiber signal mode, characterized in that: The optical fiber signal mode conversion method is applied to the optical fiber signal mode conversion device according to any one of claims 1 to 13, comprising: When the signal of the first mode in the non-single-mode optical fiber is transmitted to the first coupling region, the signal of the first mode is decoupled to the fundamental mode channel of the single-mode optical fiber and is transmitted as a fundamental mode signal in the single-mode optical fiber; When the fundamental mode signal in the single-mode optical fiber is transmitted to the second coupling region, the fundamental mode signal of the single-mode optical fiber is coupled to the second mode channel of the non-single-mode optical fiber and transmitted in the second mode in the non-single-mode optical fiber.

15. An optical fiber transmission system, characterized in that: include: Transmission optical fibers, the transmission optical fibers comprising a first transmission optical fiber and a second transmission optical fiber, the first transmission optical fiber and the second transmission optical fiber both comprising a first mode channel and a second mode channel; An optical fiber signal mode conversion device according to any one of claims 1 to 13 is provided at a node between the first transmission optical fiber and the second transmission optical fiber; The light inlet of the non-single-mode optical fiber is opposite to the light outlet of the first transmission optical fiber, and the light outlet of the non-single-mode optical fiber is opposite to the light inlet of the second transmission optical fiber.

16. The optical fiber transmission system according to claim 15, wherein: The optical fiber transmission system is used to transmit signals in N modes, where N is an integer greater than or equal to 2; The transmission optical fiber has N sections, the axial lengths of the N sections of the transmission optical fiber are all equal, each section of the transmission optical fiber has N mode channels, and the N mode channels correspond one-to-one to the N modes; The optical fiber signal mode conversion devices include N-1 devices, and one optical fiber signal mode conversion device is provided at a node between two sections of the transmission optical fiber.

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