Mode field adapter for coupling rectangular waveguide and terahertz hollow-core dielectric fiber

Abstract

The embodiment of the invention provides a mode field adapter for coupling a rectangular waveguide and a terahertz hollow-core dielectric fiber, and relates to the technical field of fiber laser. The mode field adapter comprises a uniform rectangular section, a rectangular-circular transition section, a conical section and a uniform cylindrical section, and is made of a low-loss polymer within an electromagnetic wave band frequency range; the uniform rectangular section is of a cuboid structure, the rectangular-circle transition section is of a smooth transition structure with the cross section continuously and smoothly gradually changing from a rectangle to a circle in the axial direction, the conical section is of a concentric circular truncated cone structure, and the uniform cylindrical section is of a cylindrical structure; one end of the uniform rectangular section is inserted into the rectangular metal waveguide, the size of the end face is the same as the size of the inner section of the rectangular metal waveguide, one end of the uniform cylindrical section is used for being inserted into a terahertz hollow-core medium optical fiber core, and the diameter of the uniform cylindrical section is smaller than that of the terahertz hollow-core medium optical fiber core. And efficient coupling of the rectangular metal waveguide and the terahertz hollow-core dielectric fiber can be realized.

Description

Technical Field

[0001] This application relates to the field of fiber laser technology, and in particular to a mode field adapter for coupling rectangular waveguides to terahertz hollow-core dielectric optical fibers. Background Technology

[0002] In terahertz communication systems, achieving efficient coupling between the dielectric fiber and the device is a core prerequisite for realizing terahertz communication. Currently, the widely used dielectric terahertz hollow-core anti-resonance fiber (HC-ARF) has a circular core, with a core size approximately three times the wavelength, and transmits HE as its dominant mode. 11 The mode field intensity exhibits a Gaussian distribution; however, in existing terahertz communication systems, the interface is typically a rectangular waveguide, with the long side of the core region being approximately half the wavelength, and the dominant transmission mode is TE. 10 The mode field intensity exhibits a rectangular distribution. It is evident that there are significant inconsistencies between dielectric terahertz hollow-core antiresonant fiber (HC-ARF) and rectangular metallic waveguides in terms of dominant mode type, mode field distribution morphology, and mode field area.

[0003] To achieve coupling between the dielectric fiber and the device, related technologies typically employ metal connectors with a direct insertion method. This involves connecting a rectangular metal waveguide followed by a metal rectangular-to-circular transition waveguide / horn, and then directly inserting the core of the solid-core dielectric terahertz fiber into the metal aperture. However, since the HC-ARF conduction region is air, this method is not suitable for hollow-core dielectric fibers. Therefore, achieving efficient coupling between a rectangular metal waveguide and a terahertz hollow-core dielectric fiber is a crucial problem that urgently needs to be solved. Summary of the Invention

[0004] The purpose of this application is to provide a mode field adapter for coupling rectangular waveguides to terahertz hollow-core dielectric fibers, so as to achieve efficient coupling between rectangular metallic waveguides and terahertz hollow-core dielectric fibers. The specific technical solution is as follows:

[0005] In a first aspect, this application provides a mode field adapter for coupling a rectangular waveguide to a terahertz hollow-core dielectric fiber. The mode field adapter includes a uniform rectangular segment, a rectangular-circular transition segment, a tapered segment, and a uniform cylindrical segment. The uniform rectangular segment, the rectangular-circular transition segment, the tapered segment, and the uniform cylindrical segment are made of the same material, which is a low-loss polymer in the electromagnetic band frequency range.

[0006] The uniform rectangular segment is a cuboid structure, the rectangular-circular transition segment is a smooth transition structure in which the cross-sectional shape gradually changes from rectangular to circular along the axial direction, the conical segment is a concentric frustum structure, and the uniform cylindrical segment is a cylindrical structure.

[0007] The end face dimensions of the uniform rectangular segment are the same as the inner cross-sectional dimensions of the rectangular metal waveguide. One end of the uniform rectangular segment is inserted into the rectangular metal waveguide, and the other end is coaxially connected to the rectangular end of the rectangular-circular transition segment. The rectangular end of the rectangular-circular transition segment has the same end face dimensions as the uniform rectangular segment. The circular end of the rectangular-circular transition segment is coaxially connected to the small end of the conical segment, and the circular end has the same end face dimensions as the small end. The large end of the conical segment is coaxially connected to one end of the uniform cylindrical segment, and the large end has the same end face dimensions as the uniform cylindrical segment, satisfying the single-mode transmission conditions. The other end of the uniform cylindrical segment is inserted into the core of the terahertz hollow dielectric fiber, and the diameter of the uniform cylindrical segment is smaller than that of the terahertz hollow dielectric fiber core.

[0008] The length of the uniform rectangular segment satisfy: The length of the rectangular-circular transition section satisfy: The length of the tapered segment satisfies: , The length of the cone segment is the length between the basic mold and the higher-order mold; the total length of the uniform rectangular segment, the rectangular-circular transition segment, the cone segment, and the uniform cylindrical segment satisfies: , The length of the uniform cylindrical segment is given. It can be any integer greater than 0. The operating wavelength of the mode field adapter. The refractive index of the mode field adapter is... .

[0009] In one possible implementation, the end face of the uniform rectangular segment inserted into the rectangular metal waveguide and the end face of the uniform cylindrical segment inserted into the core of the terahertz hollow dielectric fiber are both coated with a terahertz antireflection film.

[0010] In one possible implementation, the mold field adapter further includes a focusing section with a circular end face. The circular end face of the focusing section is connected to the other end of the uniform cylindrical segment, and the size of the circular end face is the same as the end face size of the uniform cylindrical segment.

[0011] In one possible implementation, the light-concentrating part is a spherical cap structure, and the circular end face is the plane of the spherical cap structure.

[0012] In one possible implementation, the light-concentrating part is a conical structure, the circular end face is the plane where the large end of the conical structure is located, and the large end is the bottom of the conical structure.

[0013] In one possible implementation, the mold field adapter further includes an outer protective wall and a support arm, wherein the outer protective wall and the support arm are made of the same material, namely the low-loss polymer;

[0014] The outer protective wall is disposed on the outside of the rectangular-circular transition section, the conical section, the portion of the uniform rectangular section that does not require the insertion of the rectangular metal waveguide, and the portion of the uniform cylindrical section that does not require the insertion of the terahertz hollow dielectric fiber. The outer protective wall is connected to the uniform rectangular section, the rectangular-circular transition section, the conical section, and the uniform cylindrical section through the support arm.

[0015] In one possible implementation, the low-loss polymer includes one or more of the following: high-density polyethylene, low-density polyethylene, polyethylene, cyclic olefin copolymers, cyclic olefin polymers, polytetrafluoroethylene, 4-methylpentene polymers, polyurethane, polypropylene, polystyrene, polycarbonate, polyester film, polymethyl methacrylate, polyvinyl chloride compounds, polychlorinated compounds, ethylene polymers, nylon, acrylonitrile butadiene styrene, polylactic acid, and high-purity resin materials.

[0016] In one possible implementation, the mold field adapter is made of a flexible, bendable material.

[0017] In one possible implementation, the length of the tapered segment satisfies:

[0018] ;

[0019] in, The length of the conical segment, For tapered proportions, , The diameter of the large end of the tapered segment is... The diameter of the small end of the tapered segment; The beat length is the distance between the fundamental mode and the higher-order mode of the conical segment. , Let be the propagation constant of the fundamental mode. is the propagation constant of the higher-order mode.

[0020] A second aspect of this application provides a terahertz communication signal transmission system, the transmission system comprising a rectangular metallic waveguide, a terahertz hollow-core dielectric fiber, and a mode field adapter as described in the first aspect, wherein the mode field area of ​​the uniform rectangular segment master mode of the mode field adapter is the same as the mode field area of ​​the master mode of the rectangular metallic waveguide, and the mode field area of ​​the uniform cylindrical segment master mode of the mode field adapter is the same as the mode field area of ​​the master mode of the terahertz hollow-core dielectric fiber.

[0021] The rectangular metal waveguide is used to transmit TE signals.10 The electromagnetic waves of the mode are transmitted to the mode field adapter;

[0022] The mode field adapter is used to transfer TE 10 The electromagnetic waves of the mode are converted into HE. 11 The electromagnetic waves of the mode, and HE 11 The electromagnetic wave of the mode is transmitted to the terahertz hollow-core optical fiber;

[0023] The terahertz hollow-core dielectric fiber is used for HE 11 Transmit electromagnetic waves in a pattern.

[0024] Beneficial effects of the embodiments in this application:

[0025] The mode field adapter for coupling a rectangular metallic waveguide to a terahertz hollow-core dielectric fiber provided in this application embodiment connects a uniform rectangular segment to the rectangular end of a rectangular-circular transition segment, connects the circular end of the rectangular-circular transition segment to the small end of a tapered segment, and connects the large end of the tapered end to a uniform cylindrical segment. 10 When the electromagnetic wave of the mode enters the rectangular metal waveguide, because the end face dimensions of the uniform rectangular segment are the same as the inner cross-sectional dimensions of the rectangular metal waveguide, TE 10 The electromagnetic waves of the mode can be transmitted to the mode field adapter without disturbance. Furthermore, since the end face of the uniform rectangular segment has the same dimensions as the rectangular end of the rectangular transition segment, and the cross-section of the rectangular transition segment gradually and smoothly changes from rectangular to circular, the field pattern can also change from the TE of the rectangular waveguide as the boundary shape of the rectangular transition segment slowly changes. 10 The mode smoothly transitions to the HE of the circular waveguide. 11 However, because the mode field area is not yet matched, the mode field diameter of the circular waveguide output from the rectangular-circular transition section may be smaller than the HE waveguide that hollow-core dielectric fiber can support. 11 If the mode field diameter is directly coupled, loss will occur due to mode field area mismatch. However, since the circular end of the rectangular transition section has the same end face size as the small end of the tapered section, and the large end of the tapered section has the same end face size as the uniform cylindrical section, by gradually increasing the diameter, the smaller mode field can be effectively stretched to a size that better matches the hollow-core optical fiber. Furthermore, because the end face size of the uniform cylindrical section satisfies the single-mode transmission condition, even if high-mode excitation occurs before the electromagnetic wave reaches the uniform cylindrical section, it can be eliminated or attenuated within the uniform cylindrical section, resulting in only HE mode transmission. 11 The mode can be transmitted stably, and because the end face size of the uniform cylindrical segment is smaller than that of the hollow fiber core, energy leakage mode field caused by contact between the mode field adapter and the hollow fiber cladding is avoided, thus realizing efficient coupling between the rectangular metal waveguide and the terahertz hollow fiber.

[0026] Of course, implementing any product or method of the present invention does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other embodiments can be obtained based on these drawings.

[0028] Figure 1 A schematic diagram of a first structure of the mode field adapter provided in the embodiments of this application;

[0029] Figure 2a A schematic diagram of the structure of a mode field adapter coupling a rectangular metallic waveguide and a terahertz hollow dielectric fiber provided in an embodiment of this application;

[0030] Figure 2b for Figure 2a A cross-sectional view of the coupling structure shown;

[0031] Figure 3a A schematic diagram of a second structure of the mode field adapter provided in the embodiments of this application;

[0032] Figure 3b for Figure 3a The cross-sectional view of the mold field adapter shown;

[0033] Figure 3c A schematic diagram of a third structure of the mold field adapter provided in the embodiments of this application;

[0034] Figure 3d for Figure 3c The cross-sectional view of the mold field adapter shown;

[0035] Figure 3e A schematic diagram of a fourth structure of the mold field adapter provided in the embodiments of this application;

[0036] Figure 3f for Figure 3e The cross-sectional view of the mold field adapter shown;

[0037] Figure 4a A schematic diagram of a fifth structure of the mode field adapter provided in an embodiment of this application;

[0038] Figure 4b for Figure 4a The cross-sectional view of the mold field adapter shown;

[0039] Figure 5a Simulation results of the dominant mode field intensity distribution of the WR1.5 metallic waveguide provided in the embodiments of this application;

[0040] Figure 5bSimulation results of the principal mode field intensity distribution of the terahertz hollow-core dielectric fiber provided in the embodiments of this application;

[0041] Figure 5c for Figure 5a A schematic diagram of the simulation results is shown.

[0042] Figure 5d for Figure 5b A schematic diagram of the simulation results is shown.

[0043] Figure 6a Simulation results of the modulus intensity distribution at the rectangular end port of the modulus adapter provided in the embodiments of this application;

[0044] Figure 6b Simulation results of the electric field distribution at the circular end port of the mode field adapter provided in the embodiments of this application;

[0045] Figure 6c for Figure 6a A schematic diagram of the simulation results is shown.

[0046] Figure 6d for Figure 6b A schematic diagram of the simulation results is shown.

[0047] Figure 7a Simulation results of the mode field intensity distribution at the circular end port of the mode field adapter provided in the embodiments of this application;

[0048] Figure 7b Simulation results of a first electric field distribution for the circular port of the mode field adapter provided in the embodiments of this application;

[0049] Figure 7c Simulation results of a second electric field distribution for the circular port of the mode field adapter provided in the embodiments of this application;

[0050] Figure 7d for Figure 7a A schematic diagram of the simulation results is shown.

[0051] Figure 7e for Figure 7b A schematic diagram of the simulation results is shown.

[0052] Figure 7f for Figure 7c A schematic diagram of the simulation results is shown.

[0053] Figure 8a Simulation results of the modulus field intensity distribution at different locations of the modulus field adapter provided in the embodiments of this application;

[0054] Figure 8b for Figure 8a A schematic diagram of the simulation results is shown.

[0055] Figure 9 Simulation results of the transmission coefficient of the mode field adapter from a rectangular metallic waveguide to a terahertz hollow-core dielectric fiber when applying the mode field adapter provided in the embodiments of this application;

[0056] Figure 10 This is a schematic diagram of the structure when a metallic rectangular waveguide is directly coupled to a hollow dielectric optical fiber.

[0057] Figure 11 for Figure 10 The simulation results show the transmission coefficient of a rectangular metallic waveguide directly to a terahertz hollow-core optical fiber in the case shown. Detailed Implementation

[0058] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0059] With the explosive growth of high-bandwidth services such as artificial intelligence, cloud computing, and the Internet of Things, the demand for data traffic is increasing exponentially. Microwave and millimeter-wave bands can no longer meet the network capability requirements of terahertz ultra-high-speed connectivity and full coverage, and carrier frequency bands will expand to higher frequencies. The terahertz (THz) band (0.1~10 THz) is considered a new frequency band for next-generation ultra-wideband communication systems. It is dozens of times longer than the millimeter-wave band (typically 1-2 GHz bandwidth), and the wavelength of terahertz is extremely short, between 0.3 and 3 millimeters. Therefore, terahertz communication systems have the characteristics of high communication speed, good directionality, high security, and abundant spectrum resources.

[0060] Waveguides, as key components in terahertz communication systems, enable efficient and enclosed transmission of terahertz waves between different functional devices. Among them, dielectric terahertz waveguides (also known as dielectric terahertz optical fibers) are considered an alternative to classic metallic waveguides / transmission lines in the terahertz band due to their advantages such as low loss, wide bandwidth, low cost, high flexibility, and lightweight.

[0061] Dielectric terahertz fibers are classified into three main categories based on their core structure: solid-core dielectric fiber, porous-core dielectric fiber, and hollow-core dielectric fiber. Hollow-core dielectric fiber, benefiting from its inherent low-loss, low-latency, and high-bandwidth characteristics, has become a research hotspot in recent years. In terahertz communication systems, efficient coupling between the dielectric fiber and the equipment is essential. The dielectric terahertz HC-ARF fiber has a circular core, with a core size approximately three times the wavelength, and its dominant transmission mode is HE. 11The mode field intensity exhibits a Gaussian distribution; however, existing terahertz communication systems typically use rectangular waveguides for their interfaces, with the long side of the core region being approximately half the wavelength, and the dominant transmission mode being TE. 10 The mode field intensity exhibits a rectangular distribution. There is a severe mismatch in the transmission dominant mode, mode field shape, and mode field area between the two. Therefore, it is essential to develop a mode field adaptation scheme between a rectangular metallic waveguide and a terahertz hollow-core dielectric fiber to achieve efficient coupling between them.

[0062] Currently, coupling between terahertz HC-ARF and rectangular metallic waveguides is mainly achieved through free-space optical path coupling. This method is not only bulky and requires high alignment accuracy, but also prone to exciting higher-order modes, leading to mode crosstalk. Furthermore, the exposed fiber endfaces are susceptible to mechanical damage or the effects of humid environments. To meet the needs of subsequent system integration, enclosed coupling devices are urgently needed. For example, the current connection between rectangular metallic waveguides and solid-core dielectric terahertz fibers typically uses metal connectors with a direct insertion method: a metal rectangular-circular transition waveguide / horn is connected after the rectangular metallic waveguide, and then the core of the solid-core dielectric terahertz fiber is directly inserted into the metal hole. However, since the HC-ARF conduction region is air, this method is not suitable for hollow-core dielectric fibers. Therefore, how to achieve efficient coupling between rectangular metallic waveguides and terahertz hollow-core dielectric fibers is a core problem that urgently needs to be solved.

[0063] To achieve efficient coupling between a rectangular metallic waveguide and a terahertz hollow-core dielectric fiber, a first aspect of this application provides a mode field adapter for coupling a rectangular waveguide to a terahertz hollow-core dielectric fiber, such as... Figure 1 The diagram shown is a schematic representation of a first structure of the mode field adapter provided in this application embodiment. The mode field adapter includes a uniform rectangular segment 1, a rectangular-circular transition segment 2, a conical segment 3, and a uniform cylindrical segment 4. The uniform rectangular segment 1, the rectangular-circular transition segment 2, the conical segment 3, and the uniform cylindrical segment 4 are all made of the same material, namely, a low-loss polymer within the electromagnetic frequency range. It is understood that, in this application, a low-loss polymer within the electromagnetic frequency range refers to a polymer material with low dielectric loss and low conductor loss in terahertz waves, which can effectively reduce energy attenuation during signal transmission.

[0064] In one possible implementation, the low-loss polymer includes one or more of the following: high-density polyethylene, low-density polyethylene, polyethylene, cyclic olefin copolymers, cyclic olefin polymers, polytetrafluoroethylene, 4-methylpentene polymers, polyurethane, polypropylene, polystyrene, polycarbonate, polyester film, polymethyl methacrylate, polyvinyl chloride compounds, polychlorinated compounds, ethylene polymers, nylon, acrylonitrile butadiene styrene, polylactic acid, and high-purity resin materials.

[0065] It is understood that when the low-loss polymer includes one of the above materials, the uniform rectangular segment 1, the rectangular-circular transition segment 2, the conical segment 3, and the uniform cylindrical segment 4 are all selected low-loss polymers; when the low-loss polymer includes multiple of the above materials, it means that multiple materials are mixed in a preset ratio to obtain a new mixed material, and the uniform rectangular segment 1, the rectangular-circular transition segment 2, the conical segment 3, and the uniform cylindrical segment 4 are all composed of the new mixed material.

[0066] In one possible implementation, when determining the material of the mold field adapter from the aforementioned low-loss polymer, a flexible and bendable material can be selected. This allows the mold field adapter to bend to a certain extent, improving its layout flexibility within a limited space. It is understood that when the mold field adapter only includes a uniform rectangular segment 1, a rectangular-circular transition segment 2, a conical segment 3, and a uniform cylindrical segment 4, the material of the mold field adapter being a bendable material means that the materials of the uniform rectangular segment 1, the rectangular-circular transition segment 2, the conical segment 3, and the uniform cylindrical segment 4 are all made of the same bendable low-loss polymer. When the mold field adapter includes a uniform rectangular segment 1, a rectangular-circular transition segment 2, a conical segment 3, a uniform cylindrical segment 4, and a focusing section 5, the material of the mold field adapter being a bendable material means that the materials of the uniform rectangular segment 1, the rectangular-circular transition segment 2, the conical segment 3, the uniform cylindrical segment 4, and the focusing section 5 are all made of the same flexible low-loss polymer. The material of the light section 5 is the same flexible, low-loss polymer. Similarly, when the mode field adapter includes a uniform rectangular section 1, a rectangular-circular transition section 2, a conical section 3, a uniform cylindrical section 4, a light-concentrating section 5, an outer protective wall 6, and a support arm 7, the material of the mode field adapter being flexible means that the materials of the uniform rectangular section 1, the rectangular-circular transition section 2, the conical section 3, the uniform cylindrical section 4, and the light-concentrating section 5 are the same flexible, low-loss polymer. The materials of the outer protective wall 6 and the support arm 7 can be flexible, bendable, low-loss polymers, or they can be non-flexible, bendable, low-loss polymers.

[0067] Uniform rectangular segment 1 has a cuboid structure, and its length is... satisfy: The rectangular-circular transition segment 2 is a smooth transition structure in which the cross-sectional shape gradually changes from rectangular to circular along the axial direction. The length of the rectangular-circular transition segment 2 is... satisfy: Conical segment 3 is a concentric frustum structure, and the length of conical segment 3 is... satisfy: , The length of the cone segment is the length between the basic mold and the higher-order mold; the uniform cylindrical segment 4 is a cylindrical structure, and the total length of the uniform rectangular segment 1, the rectangular-circular transition segment 2, the cone segment 3, and the uniform cylindrical segment 4 satisfies: That is, the total length of the uniform rectangular segment 1, the rectangular-circular transition segment 2, the conical segment 3, and the uniform cylindrical segment 4 is an integer multiple of half the equivalent wavelength. The length of the uniform cylindrical segment, It can be any integer greater than 0. For the operating wavelength of the mode field adapter, The refractive index of the mode field adapter, .

[0068] In one possible implementation, the length of the tapered segment 3 specifically satisfies:

[0069]

[0070] in, For tapered proportions, , The diameter of the large end of the conical segment 3 is... The diameter of the small end of the tapered segment 3; , Let be the propagation constant of the fundamental mode. is the propagation constant of the higher-order mode. Using this formula, the length of the conical segment 3 can be accurately calculated.

[0071] The end face dimensions of the uniform rectangular segment 1 are the same as the inner cross-sectional dimensions of the rectangular metal waveguide. One end of the uniform rectangular segment 1 is used for insertion into the rectangular metal waveguide. The end face of the uniform rectangular segment 1 refers to the cross-section of the end 11 used for insertion into the rectangular metal waveguide. The other end 12 of the uniform rectangular segment 1 is coaxially connected to the rectangular end 21 of the rectangular-circular transition segment 2. The rectangular end 21 of the rectangular-circular transition segment 2 has the same end face dimensions as the uniform rectangular segment 1.

[0072] The rectangular-circular transition section 2 is used to realize the dominant mode TE of the rectangular metal waveguide. 10 With terahertz hollow-core dielectric fiber dominant mode HE 11 Mode conversion of the component. The circular end 22 of the rectangular-circular transition section 2 is coaxially connected to the small end 31 of the conical section 3, and the end face dimensions of the circular end 22 and the small end 31 are the same, and the end face dimensions satisfy the single-mode transmission conditions. Specifically, the end face diameter R of the circular end 22 and the small end 31 satisfies:

[0073]

[0074] in, For the normalized cutoff frequency, , Let R be the numerical aperture of the dielectric waveguide.

[0075] The large end 32 of the tapered segment 3 is coaxially connected to one end 41 of the uniform cylindrical segment 4, and the large end 32 and the end face size of the uniform cylindrical segment 4 are the same; the other end 42 of the uniform cylindrical segment 4 is used to insert into the core of the terahertz hollow medium fiber, and its mode field is the same as that of the terahertz hollow medium fiber, and the diameter of the uniform cylindrical segment 4 is smaller than that of the terahertz hollow medium fiber core.

[0076] like Figure 2a The diagram shown is a schematic representation of the structure of a mode field adapter coupling a rectangular metallic waveguide and a terahertz hollow-core dielectric fiber according to an embodiment of this application. Figure 2b for Figure 2a The cross-sectional view of the coupling structure shown is shown. Figure 2b The dashed line indicates the mode field adapter 200. The TE in the rectangular metal waveguide 100... 10 The mode input mode field adapter 200 has a uniform rectangular segment 1, whose mode field shape and area are the same as those of the rectangular metal waveguide 100; subsequently, TE 10 The pattern is injected into rectangular-circular transition segment 2, and after passing through rectangular-circular transition segment 2, it is converted into HE. 11 The mode, which is the transmission master mode of terahertz hollow-core fiber 300; then HE 11 The mode is injected into the terahertz hollow medium fiber 300 for transmission through the tapered segment 3 and the uniform cylindrical segment 4. The mode field shape and mode field area of ​​the uniform cylindrical segment 4 are the same as those of the terahertz hollow medium fiber 300.

[0077] In this embodiment of the application, by connecting the rectangular end of the uniform rectangular segment to the rectangular end of the rectangular-circular transition segment, connecting the circular end of the rectangular-circular transition segment to the small end of the conical segment, and connecting the large end of the conical end to the uniform cylindrical segment, TE 10 When the electromagnetic wave of the mode enters the rectangular metal waveguide, because the end face dimensions of the uniform rectangular segment are the same as the inner cross-sectional dimensions of the rectangular metal waveguide, TE 10 The electromagnetic waves of the mode can be transmitted to the mode field adapter without disturbance. Furthermore, since the end face of the uniform rectangular segment has the same dimensions as the rectangular end of the rectangular transition segment, and the cross-section of the rectangular transition segment gradually and smoothly changes from rectangular to circular, the field pattern can also change from the TE of the rectangular waveguide as the boundary shape of the rectangular transition segment slowly changes. 10 The mode smoothly transitions to the HE of the circular waveguide. 11 However, because the mode field area is not yet matched, the mode field diameter of the circular waveguide output from the rectangular-circular transition section may be smaller than the HE waveguide that hollow-core dielectric fiber can support. 11If the mode field diameter is directly coupled, loss will occur due to mode field area mismatch. However, since the circular end of the rectangular transition section has the same end face size as the small end of the tapered section, and the large end of the tapered section has the same end face size as the uniform cylindrical section, by gradually increasing the diameter, the smaller mode field can be effectively stretched to a size that better matches the hollow-core optical fiber. Furthermore, because the end face size of the uniform cylindrical section satisfies the single-mode transmission condition, even if high-mode excitation occurs before the electromagnetic wave reaches the uniform cylindrical section, it can be eliminated or attenuated within the uniform cylindrical section, resulting in only HE mode transmission. 11 The mode can be transmitted stably, and because the end face size of the uniform cylindrical segment is smaller than that of the hollow fiber core, energy leakage mode field caused by contact between the mode field adapter and the hollow fiber cladding is avoided, thus achieving efficient coupling between the rectangular metal waveguide and the terahertz hollow fiber.

[0078] To further improve coupling efficiency, in one possible implementation, a terahertz antireflection coating can be deposited on the end face of the uniform rectangular segment 1 (for insertion into the rectangular metal waveguide) and the end face of the uniform cylindrical segment 4 (for insertion into the core of the terahertz hollow dielectric fiber), thereby reducing reflection loss and improving signal quality.

[0079] The terahertz antireflection film has low absorption loss in the operating band, and this application does not limit the specific material of the terahertz antireflection film.

[0080] In another possible implementation, reflection loss can be reduced by providing a focusing section on the end 42 of the uniform cylindrical segment 4 where the terahertz hollow dielectric fiber 300 core is inserted. The focusing section has a circular end face, which is connected to one end 42 of the uniform cylindrical segment 4, and the size of the circular end face is the same as the end face size of the uniform cylindrical segment.

[0081] The light-gathering part can be a spherical cap structure or a plano-convex lens-like structure, such as... Figure 3a The diagram shown is a second structural schematic of the mold field adapter provided in an embodiment of this application. Figure 3b for Figure 3a The cross-sectional view of the model field adapter shown shows that a light-concentrating part 5 with a spherical cap structure is provided on one end 42 of the uniform cylindrical segment 4, and the end face of the end 42 of the uniform cylindrical segment 4 is connected to the bottom of the spherical cap structure.

[0082] The focusing section can also be a conical structure, such as... Figure 3c The diagram shown is a third structural schematic of the mold field adapter provided in this application embodiment. Figure 3d for Figure 3c The cross-sectional view of the mold field adapter shown shows that a conical light-concentrating part 5 is provided on one end 42 of the uniform cylindrical segment 4, and the end face of the end 42 of the uniform cylindrical segment 4 is connected to the bottom of the conical structure.

[0083] The focusing section can also be a partially ellipsoidal structure, such as... Figure 3e The diagram shown is a fourth structural schematic of the mold field adapter provided in this application embodiment. Figure 3f for Figure 3e The cross-sectional view of the model field adapter shown shows that a light-concentrating part 5 with a partial ellipsoidal structure is provided on one end 42 of the uniform cylindrical segment 4, and the end face of the end 42 of the uniform cylindrical segment 4 is connected to the bottom of the partial ellipsoidal structure.

[0084] In other possible implementations, the light-concentrating part may also be other structures that can reduce reflection loss, which will not be listed in this application.

[0085] With the focusing section 5 provided, the TE in the rectangular metal waveguide 100 10 The mode input field adapter 200 inputs a uniform rectangular segment 1, followed by TE. 10 The pattern is injected into rectangular-circular transition segment 2, and after passing through rectangular-circular transition segment 2, it is converted into HE. 11 The mode, which is the transmission master mode of terahertz hollow-core fiber 300; then HE 11 The pattern will be transmitted through the conical section 3, the uniform cylindrical section 4, and the focusing section 5 to the HE. 11 The mode is injected into a terahertz hollow-core medium fiber 300 for transmission.

[0086] To isolate the mold field adapter from the influence of the external environment, a protective layer can be installed on its exterior. For example... Figure 4a The diagram shows a fifth structural schematic of the mold field adapter provided in this application embodiment. The mold field adapter further includes an outer protective wall 6 and a support arm 7. The outer protective wall 6 and the support arm 7 are made of the same material, which is also a low-loss polymer. It is understood that the materials used for the outer protective wall 6 and the support arm 7 can be the same as or different from the materials used for the uniform rectangular segment 1, the rectangular-circular transition segment 2, the conical segment 3, and the uniform cylindrical segment 4. This application embodiment does not limit this. When the materials used for the outer protective wall 6 and the support arm 7 are different from the materials used for the uniform rectangular segment 1, the rectangular-circular transition segment 2, the conical segment 3, and the uniform cylindrical segment 4, the refractive index of the materials used for the outer protective wall 6 and the support arm 7 should be less than or equal to the refractive index of the materials used for the uniform rectangular segment 1, the rectangular-circular transition segment 2, the conical segment 3, and the uniform cylindrical segment 4.

[0087] The outer protective wall 6 is located on the outer side of the rectangular-circular transition section 2, the conical section 3, the outer side of the portion of the uniform rectangular section 1 where the rectangular metal waveguide 100 does not need to be inserted, and the outer side of the portion of the uniform cylindrical section 4 where the terahertz hollow dielectric fiber 300 does not need to be inserted, such as... Figure 4b As shown Figure 4aThe cross-sectional view of the mold field adapter shown shows that the outer protective wall 6 is connected to the uniform rectangular segment 1, the rectangular-circular transition segment 2, the conical segment 3, and the uniform cylindrical segment 4 through the support arm 7.

[0088] The uniform rectangular segment 1 can be fully inserted into the rectangular metal waveguide 100, or it can be partially inserted into the rectangular metal waveguide 100. That is, the length of the portion of the uniform rectangular segment 1 that does not need to be inserted into the rectangular metal waveguide 100 can be 0 or greater than 0, but the length of the portion of the uniform rectangular segment 1 that does not need to be inserted into the rectangular metal waveguide 100 cannot be greater than or equal to the total length of the uniform rectangular segment 1. For example, the entire uniform rectangular segment 1 can be set for insertion into the rectangular metal waveguide 100, half of the uniform rectangular segment 1 can be set for insertion into the rectangular metal waveguide 100, or one-third of the uniform rectangular segment 1 can be set for insertion into the rectangular metal waveguide 100. Specifically, the length of the portion of the uniform rectangular segment 1 used for insertion into the rectangular metal waveguide 100 can be preset according to actual experience and needs, and this application embodiment does not limit this.

[0089] The following example uses a field adapter made of a cyclic olefin polymer with a dielectric constant of 1.5258. Taking 1.5258, loss tangent 0.000495, terahertz wavelength 0.4285 mm (mode field adapter operating frequency 700 GHz), and terahertz hollow-core medium fiber core diameter 0.986 mm as examples, the mode field adapter provided in this application embodiment will be described in detail with reference to specific embodiments.

[0090] A uniform rectangular segment 1 of the mode field adapter is inserted into a WR1.5 metal waveguide (a type of rectangular metal waveguide). The end face dimensions of the uniform rectangular segment 1 are 0.381 mm × 0.1905 mm, which are the same as the inner cross-sectional dimensions of the WR1.5 metal waveguide. The length of the uniform rectangular segment is... , When the value is 5, .

[0091] The rectangular end 21 of the rectangular-circular transition segment 2 is connected to the uniform rectangular segment 1 and has the same end face dimensions. The radius of the circular end 22 satisfies... That is, the radius of the circular end 22 Let R = 0.1423 mm. The length of the rectangular circular transition section 2. ,Pick .

[0092] The small end 31 of the tapered segment 3 is connected to the circular end 22 of the rectangular-circular transition segment 2, and their end face dimensions are the same, that is, the diameter D of the small end 31 of the tapered segment 3 is the same. t=2R=0.2846 mm, the diameter D1=0.98 mm of the large end 32 of the tapered segment 3 matches the core of the terahertz hollow-core medium fiber and is slightly smaller than the core of the terahertz hollow-core medium fiber. The propagation constant of the fundamental mode (dominant mode) along the tapered segment 3 is obtained through simulation. Higher-order mode propagation constant Corresponding shot length Then the length of the conical segment 3 satisfies ,Pick .

[0093] The uniform cylindrical segment 4 is connected to the large end 32 of the conical segment 3, and their end face dimensions are the same. Since the total length of the uniform rectangular segment 1, the rectangular-circular transition segment 2, the conical segment 3, and the uniform cylindrical segment 4 satisfies: ,Right now The length of the uniform cylindrical segment 4 When N2 is 80, L cir =0.53mm.

[0094] See Figure 5a , Figure 5b , Figure 5c and Figure 5d , Figure 5a The simulation results for the dominant mode field intensity distribution of the WR1.5 metallic waveguide provided in the embodiments of this application are as follows. Figure 5b The simulation results for the principal mode field intensity distribution of the terahertz hollow-core dielectric fiber provided in the embodiments of this application are as follows. Figure 5c for Figure 5a The diagram shows the simulation results. Figure 5d for Figure 5b A schematic diagram of the simulation results is shown. From Figure 5a and Figure 5c It can be seen that the dominant transmission mode of the rectangular metal waveguide WR1.5 is TE. 10 Pattern, from Figure 5b and Figure 5d It can be seen that the energy distribution of the dominant mode field intensity in terahertz hollow-core dielectric fiber is concentrated at the center and attenuates outward along the radius, exhibiting an ideal Gaussian distribution, which is HE. 11 model.

[0095] Figure 6a The simulation results show the modulus intensity distribution at the rectangular end port of the modulus adapter provided in this embodiment of the application. Figure 6b The simulation results show the electric field distribution at the circular end port of the mode field adapter provided in this application embodiment. Figure 6c for Figure 6a The diagram shows the simulation results. Figure 6d for Figure 6b A schematic diagram of the simulation results is shown. From Figure 6a , Figure 6b , Figure 6c and Figure 6d It can be seen that the rectangular segment of the mold field adapter has a TE port. 10 The mode is the same as the main mode transmitted by the connected rectangular metal waveguide 100; Figure 7a The simulation results show the mode field intensity distribution at the circular end port of the mode field adapter provided in this application embodiment. Figure 7d for Figure 7a The schematic diagram of the simulation results shown is from... Figure 7a and Figure 7b It can be seen that the energy at the circular end port is concentrated at the center and decays outward along the radius, exhibiting an ideal Gaussian distribution, indicating that the circular end port is an ideal HE. 11 The mode is consistent with the dominant transmission mode of terahertz hollow-core optical fiber. Figure 6a , Figure 6b and Figure 7a It can be seen that TE 10 The pattern was successfully converted to HE after passing through the pattern field adapter of this application. 11 model.

[0096] It should be noted that, due to the structural symmetry of the circular end, HE 11 The mode undergoes polarization degeneracy (x-pol and y-pol). Figure 7b and Figure 7e Corresponding to y-pol, Figure 7c and Figure 7f Corresponding to x-pol, Figure 7b Simulation results of the first electric field distribution of the circular port of the mode field adapter provided in the embodiments of this application. Figure 7c The simulation results show the second electric field distribution of the circular port of the mode field adapter provided in the embodiments of this application. Figure 7e for Figure 7b The diagram shows the simulation results. Figure 7f for Figure 7c The diagram shows the simulation results.

[0097] Further, see Figure 8a and Figure 8b , Figure 8a The simulation results show the distribution of the mode field intensity at different locations of the mode field adapter provided in this application embodiment. Figure 8b for Figure 8a A schematic diagram of the simulation results is shown. From Figure 8a and Figure 8b As can be seen, through the mode field adapter of this application, the rectangular mode field distribution is converted into a circular mode field distribution, and the mode field area gradually increases, thereby achieving the matching of the mode field shape and mode field area of ​​the transmission master mode of the rectangular metal waveguide and the terahertz hollow medium fiber.

[0098] Furthermore, the simulation results of the transmission coefficient of the mode field adapter from the rectangular metallic waveguide to the terahertz hollow dielectric fiber are also provided (see [reference needed]). Figure 9 , Figure 9 The solid line represented by S2(1),1(1) is the input port TE. 10 Mode to output port HE 11 The transmission coefficients of (y-pol) mode, S2(2),1(1), are represented by dashed lines indicating the input port TE. 10 Mode to output port HE 11 The transmission coefficient of (x-pol) mode, when the output HE 11 polarization direction and input mode TE 10 When the polarization directions are consistent, the transmission coefficient S2(1),1(1) is greater than -2.3 dB in the frequency range of 690-710 GHz, which means that the insertion loss in the 690-710 GHz range is less than 2.3 dB, with the minimum in-band insertion loss being 1.9 dB. This enables terahertz waves to be transmitted in the dominant mode TE of a rectangular metallic waveguide. 10 To the medium terahertz fiber master mode HE 11 Efficient conversion and connection between them.

[0099] For modeless field adapters, i.e. Figure 10 The diagram shows the case of direct coupling between a rectangular metallic waveguide and a hollow-core dielectric fiber. The simulation results for the transmission coefficient from the rectangular metallic waveguide 100 directly to the terahertz hollow-core dielectric fiber 300 in this case are provided in the original text. Figure 11 , Figure 11 The solid line represented by S2(1),1(1) is the input port TE. 10 Mode to output port HE 11 The transmission coefficients of (y-pol) mode, represented by the dashed lines in S2(2),1(1), are the input port TE. 10 Mode to output port HE 11 The transmission coefficient of (x-pol) mode, when the output HE 11 polarization direction and input mode TE 10 When the polarization directions are consistent, the transmission coefficient S2(1),1(1) is greater than -19.4 dB in the frequency range of 690-710 GHz, which means that the insertion loss in the 690-710 GHz range is less than 19.4 dB, which is much greater than the insertion loss after using the mode field adapter provided in the embodiment of this application.

[0100] exist Figure 10 In the case shown, the large insertion loss mainly comes from mode-field mismatch loss, such as at 700 GHz, the dominant mode TE of the WR1.5 in the metallic rectangular waveguide. 10 The area of ​​the mold field is 4.84 × 10. -2 mm2 Hollow-core dielectric fiber master mode HE 11 The mold field area is 2.28 mm. 2 The area of ​​the model field differs by two orders of magnitude.

[0101] Therefore, it can be seen that by applying the mode field adapter of this application, efficient coupling between rectangular metal waveguides and terahertz hollow dielectric optical fibers can be achieved.

[0102] Corresponding to the first aspect mentioned above, the second aspect of this application provides a terahertz communication signal transmission system. The transmission system includes a rectangular metal waveguide 100, a terahertz hollow dielectric fiber 300, and a mode field adapter 200 as described in the first aspect. The mode field area of ​​the dominant mode of the uniform rectangular segment 1 of the mode field adapter 200 is the same as the mode field area of ​​the dominant mode of the rectangular metal waveguide 100, and the mode field area of ​​the dominant mode of the uniform cylindrical segment 4 of the mode field adapter 200 is the same as the mode field area of ​​the dominant mode of the terahertz hollow dielectric fiber 300.

[0103] Rectangular metal waveguide 100, used to transmit TE 10 The electromagnetic waves of the mode are transmitted to the mode field adapter 200;

[0104] Mold field adapter 200, used to connect TE 10 The electromagnetic waves of the mode are converted into HE. 11 The electromagnetic waves of the mode, and HE 11 The electromagnetic wave of the mode is transmitted to the terahertz hollow medium optical fiber 300.

[0105] Terahertz hollow-core dielectric fiber 300, used for HE 11 Transmit electromagnetic waves in a pattern.

[0106] In this embodiment of the application, by connecting the rectangular end of the uniform rectangular segment to the rectangular end of the rectangular-circular transition segment, connecting the circular end of the rectangular-circular transition segment to the small end of the conical segment, and connecting the large end of the conical end to the uniform cylindrical segment, TE 10 When the electromagnetic wave of the mode enters the rectangular metal waveguide, because the end face dimensions of the uniform rectangular segment are the same as the inner cross-sectional dimensions of the rectangular metal waveguide, TE 10 The electromagnetic waves of the mode can be transmitted to the mode field adapter without disturbance. Furthermore, since the end face of the uniform rectangular segment has the same dimensions as the rectangular end of the rectangular transition segment, and the cross-section of the rectangular transition segment gradually and smoothly changes from rectangular to circular, the field pattern can also change from the TE of the rectangular waveguide as the boundary shape of the rectangular transition segment slowly changes. 10 The mode smoothly transitions to the HE of the circular waveguide. 11 However, because the mode field area is not yet matched, the mode field diameter of the circular waveguide output from the rectangular-circular transition section may be smaller than the HE waveguide that hollow-core dielectric fiber can support. 11If the mode field diameter is directly coupled, loss will occur due to mode field area mismatch. However, since the circular end of the rectangular transition section has the same end face size as the small end of the tapered section, and the large end of the tapered section has the same end face size as the uniform cylindrical section, by gradually increasing the diameter, the smaller mode field can be effectively stretched to a size that better matches the hollow-core optical fiber. Furthermore, because the end face size of the uniform cylindrical section satisfies the single-mode transmission condition, even if high-mode excitation occurs before the electromagnetic wave reaches the uniform cylindrical section, it can be eliminated or attenuated within the uniform cylindrical section, resulting in only HE mode transmission. 11 The mode can be transmitted stably, and because the end face size of the uniform cylindrical segment is smaller than that of the hollow fiber core, energy leakage mode field caused by contact between the mode field adapter and the hollow fiber cladding is avoided, thus achieving efficient coupling between the rectangular metal waveguide and the terahertz hollow fiber.

[0107] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0108] The various embodiments in this specification are described in a related manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, the system embodiments are basically similar to the mold field adapter embodiments, so the description is relatively simple; relevant parts can be referred to the description of the mold field adapter embodiments.

[0109] The above description is merely a preferred embodiment of this application and is not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application are included within the scope of protection of this application.

Claims

1. A mode field adapter for coupling rectangular waveguides to terahertz hollow-core dielectric optical fibers, characterized in that, The mode field adapter includes a uniform rectangular segment, a rectangular-circular transition segment, a conical segment, and a uniform cylindrical segment. The uniform rectangular segment, the rectangular-circular transition segment, the conical segment, and the uniform cylindrical segment are made of the same material, which is a low-loss polymer in the electromagnetic wave band frequency range. The uniform rectangular segment is a cuboid structure, the rectangular-circular transition segment is a smooth transition structure in which the cross-sectional shape gradually changes from rectangular to circular along the axial direction, the conical segment is a concentric frustum structure, and the uniform cylindrical segment is a cylindrical structure. The end face dimensions of the uniform rectangular segment are the same as the inner cross-sectional dimensions of the rectangular metal waveguide. One end of the uniform rectangular segment is used to insert into the rectangular metal waveguide, and the other end is coaxially connected to the rectangular end of the rectangular-circular transition segment. The rectangular end of the rectangular-circular transition segment has the same end face dimensions as the uniform rectangular segment. The circular end of the rectangular-circular transition segment is coaxially connected to the small end of the conical segment, and the circular end has the same end face dimensions as the small end, satisfying the single-mode transmission condition. The large end of the conical segment is coaxially connected to one end of the uniform cylindrical segment, and the large end has the same end face dimensions as the uniform cylindrical segment. The other end of the uniform cylindrical segment is used to insert into the core of the terahertz hollow dielectric fiber, and the diameter of the uniform cylindrical segment is smaller than that of the terahertz hollow dielectric fiber core. The length of the uniform rectangular segment satisfy: The length of the rectangular-circular transition section satisfy: The length of the tapered segment satisfies: , The length of the cone segment is the length between the basic mold and the higher-order mold; the total length of the uniform rectangular segment, the rectangular-circular transition segment, the cone segment, and the uniform cylindrical segment satisfies: , The length of the uniform cylindrical segment is given. It can be any integer greater than 0. The operating wavelength of the mode field adapter. The refractive index of the mode field adapter is... .

2. The mold field adapter according to claim 1, characterized in that, The end face of the uniform rectangular segment inserted into the rectangular metal waveguide and the end face of the uniform cylindrical segment inserted into the core of the terahertz hollow dielectric fiber are both coated with a terahertz antireflection film.

3. The mold field adapter according to claim 1, characterized in that, The mold field adapter also includes a focusing part with a circular end face. The circular end face of the focusing part is connected to the other end of the uniform cylindrical segment. The size of the circular end face is the same as the size of the end face of the uniform cylindrical segment. The material of the focusing part is the same as the material of the uniform rectangular segment.

4. The mold field adapter according to claim 3, characterized in that, The light-concentrating part is a spherical cap structure, and the circular end face is the plane of the spherical cap structure.

5. The mold field adapter according to claim 3, characterized in that, The light-concentrating part has a conical structure, and the circular end face is the plane where the large end of the conical structure is located. The large end is the bottom of the conical structure.

6. The mold field adapter according to claim 1, characterized in that, The mold field adapter also includes an outer protective wall and a support arm, wherein the outer protective wall and the support arm are made of the same material, namely the low-loss polymer; The outer protective wall is disposed on the outside of the rectangular-circular transition section, the conical section, the portion of the uniform rectangular section that does not require the insertion of the rectangular metal waveguide, and the portion of the uniform cylindrical section that does not require the insertion of the terahertz hollow dielectric fiber. The outer protective wall is connected to the uniform rectangular section, the rectangular-circular transition section, the conical section, and the uniform cylindrical section through the support arm.

7. The mold field adapter according to any one of claims 1-6, characterized in that, The low-loss polymer includes one or more of the following: high-density polyethylene, low-density polyethylene, polyethylene, cyclic olefin copolymers, cyclic olefin polymers, polytetrafluoroethylene, 4-methylpentene polymers, polyurethane, polypropylene, polystyrene, polycarbonate, polyester film, polymethyl methacrylate, polyvinyl chloride compounds, polychlorides, ethylene polymers, nylon, acrylonitrile butadiene styrene, polylactic acid, and high-purity resin materials.

8. The mold field adapter according to claim 1, characterized in that, The material of the mold field adapter is a flexible and bendable material.

9. The mold field adapter according to claim 1, characterized in that, The length of the tapered segment satisfies: ; in, The length of the conical segment, For tapered proportions, , The diameter of the large end of the tapered segment is... The diameter of the small end of the tapered segment; The beat length is the distance between the fundamental mode and the higher-order mode of the conical segment. , Let be the propagation constant of the fundamental mode. is the propagation constant of the higher-order mode.

10. A terahertz communication signal transmission system, characterized in that, The transmission system includes a rectangular metal waveguide, a terahertz hollow-core dielectric fiber, and a mode field adapter as described in any one of claims 1-9. The mode field area of ​​the uniform rectangular segment master mode of the mode field adapter is the same as the mode field area of ​​the master mode of the rectangular metal waveguide, and the mode field area of ​​the uniform cylindrical segment master mode of the mode field adapter is the same as the mode field area of ​​the master mode of the terahertz hollow-core dielectric fiber. The rectangular metal waveguide is used to transmit TE signals. 10 The electromagnetic waves of the mode are transmitted to the mode field adapter; The mode field adapter is used to transfer TE 10 The electromagnetic waves of the mode are converted into HE. 11 The electromagnetic waves of the mode, and HE 11 The electromagnetic wave of the mode is transmitted to the terahertz hollow-core optical fiber; The terahertz hollow-core dielectric fiber is used for HE 11 Transmit electromagnetic waves in a pattern.

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