Terahertz wave directional coupler

Abstract

The utility model provides a terahertz wave directional coupler, which is suitable for coupling terahertz waves from a free space to a waveguide device, and comprises a base, an opening is formed on the base, and the waveguide device is arranged on one side of the base; the two waveguide assemblies extend from the side, opposite to the waveguide device, of the base and are oppositely arranged on the base, a transmission channel communicated with the opening is defined between the two waveguide assemblies, and the minimum gap between the two waveguide assemblies is not smaller than a preset value; the terahertz waves are propagated in the first direction facing the opening along the transmission channel, and in the propagation process, the gap between the two groups of waveguide assemblies is configured to influence the energy distribution of the terahertz waves in the transmission channel, so that the energy distribution of the terahertz waves is matched with the transmission mode of the waveguide device.

Description

TECHNICAL FIELD

[0001] The at least one embodiment of the utility model relates to the field of terahertz technology, and particularly relates to a terahertz directional coupler. BACKGROUND

[0002] Terahertz frequency refers to electromagnetic waves between 0.1THz and 10THz, between microwaves and infrared, and the special frequency range makes it not only have the properties of electromagnetic spectrum, but also have unique advantages superior to other frequency electromagnetic waves, such as low photon energy, strong penetration, good coherence, etc. Thus, terahertz technology is widely concerned by researchers in the fields of life medicine, material chemical industry, communication security, quality security, etc.

[0003] Current research on terahertz technology mainly focuses on the generation and detection of terahertz, transmission and coupling, the generation and detection technology of terahertz waves has gradually matured, and it has also realized low loss, low dispersion and strong stability of transmission by limiting terahertz waves in the waveguide or the surface. As a kind of passive device with directionality, the terahertz coupler is mainly used for the distribution and synthesis of terahertz power, and is one of the key devices in the terahertz system.

[0004] In the near-infrared waveband, the coupler based on microstructured optical fiber has been maturely applied, and theoretically, the coupler in the near-infrared waveband can also be used for THz wave coupling by equal-proportion magnification. However, equal-proportion magnification of size will inevitably increase the coupling length, and the longer the transmission distance in the terahertz waveband, the greater the loss. The microstrip line coupler widely used at present has a narrow applicable bandwidth range, the waveguide coupler is prone to deformation, which affects the coupling efficiency, the photonic crystal coupler and the terahertz coupling based on surface plasmon have problems such as complex design process, complicated preparation process, etc., and the applicable frequency range is single. UTILITY MODEL CONTENT

[0005] Therefore, the utility model provides a terahertz directional coupler, which can improve the coupling efficiency of terahertz waves.

[0006] As an aspect of the embodiments of the present application, a terahertz directional coupler is provided, which is suitable for coupling terahertz waves from free space to a waveguide device, and is characterized in that the terahertz directional coupler comprises: a base, an opening is formed on the base, and the waveguide device is mounted on one side of the base; two groups of waveguide assemblies extend from the side of the base opposite to the waveguide device, and are oppositely arranged on the base, a transmission channel communicating with the opening is defined between the two groups of waveguide assemblies, and the minimum gap between the two groups of waveguide assemblies is not less than a predetermined value; the terahertz waves propagate in a first direction towards the opening along the transmission channel, and in the process of propagation, the gap between the two groups of waveguide assemblies is configured to affect the energy distribution of the terahertz waves in the transmission channel, so that the energy distribution of the terahertz waves matches the transmission mode of the waveguide device.

[0007] According to the embodiments of the present application, each of the waveguide assemblies comprises: a first waveguide extending from the base towards a second direction opposite to the first direction, the first waveguides of the two waveguide assemblies are parallel to each other and have the minimum gap; and a second waveguide extending obliquely from an end of the first waveguide away from the base towards the second direction, the spacing between the second waveguide and the second waveguide of the other waveguide assembly gradually increases along the second direction, and in the extension plane, the dimension of the second waveguide perpendicular to the second direction gradually increases along the second direction, and the second waveguide is suitable for guiding the terahertz waves to gradually adapt to the propagation mode of the flat plate.

[0008] According to the embodiments of the present application, each of the first waveguides comprises: a body portion; and two extension portions extending from both sides of the body portion towards the other first waveguide; and the minimum gap is located between the two facing extension portions of the two first waveguides.

[0009] According to the embodiments of the present application, each of the waveguide assemblies further comprises: a pair of adjustment portions connecting the second waveguide and the two extension portions, the dimension of the adjustment portion in a first plane perpendicular to the second waveguide gradually decreases along the second direction, and the adjustment portion is suitable for cooperating with the second waveguide to gradually guide the terahertz waves to gradually adapt to the propagation mode of the flat plate.

[0010] According to the embodiments of the present application, the extension length of the second waveguide projected in the plane parallel to the body portion is configured to be between 100 μm-1000 μm.

[0011] According to the embodiment of the present application, the cross-sectional dimension of the opening in a second plane perpendicular to the first direction is the same as the cross-sectional dimension of the transmission channel enclosed by the two first waveguides in the second plane.

[0012] According to the embodiment of the present application, the inner surfaces of the two waveguide assemblies are coated with a metal layer to reflect the terahertz waves incident on the surface of the metal layer.

[0013] According to the embodiment of the present application, the base is a flange structure to facilitate connection with the waveguide device.

[0014] According to the embodiment of the present application, the size of the minimum gap is configured to be less than or equal to 900 μm.

[0015] According to the embodiment of the present application, the extension length of the first waveguide is configured to be between 100 μm and 500 μm.

[0016] According to the terahertz wave directional coupler of the embodiment of the present application, the transmission channel is formed between the two sets of opposing waveguide assemblies, and the minimum gap between the two sets of waveguide assemblies is kept not less than a predetermined value, so that the energy distribution of the terahertz wave in the transmission channel is affected by the gap between the two sets of waveguide assemblies during the propagation of the terahertz wave along the transmission channel in the first direction. The energy distribution of the terahertz wave is matched with the transmission mode of the waveguide device, and the coupling efficiency of the terahertz wave in the transmission channel is improved. BRIEF DESCRIPTION OF DRAWINGS

[0017] The above and other objects, features and advantages of the present application will become more apparent from the following description of the embodiments of the present application taken with reference to the accompanying drawings, in which:

[0018] Figure 1 A perspective view of the terahertz wave directional coupler according to the embodiment of the present application is schematically shown;

[0019] Figure 2 A perspective view of the terahertz wave directional coupler according to the embodiment of the present application is schematically shown; Figure 1 A partial enlarged view of part A is shown;

[0020] Figure 3 A side view of the terahertz wave directional coupler according to the embodiment of the present application is schematically shown;

[0021] Figure 4 Another side view of the terahertz wave directional coupler according to the embodiment of the present application is schematically shown;

[0022] Figure 5 A perspective view of the base according to the embodiment of the present application is schematically shown;

[0023] Figure 6 Fig. 2 schematically illustrates a perspective view of a waveguide assembly according to embodiments of the present application;

[0024] Figure 7 Fig. 3 schematically illustrates a perspective view of two second waveguides according to embodiments of the present application;

[0025] Figure 8 Fig. 4 schematically illustrates a perspective view of two first waveguides according to embodiments of the present application;

[0026] Figure 9 Fig. 5 schematically illustrates a perspective view of two pairs of adjustment portions according to embodiments of the present application;

[0027] Figure 10 Fig. 6 schematically illustrates an equivalent diagram of two second waveguides according to embodiments of the present application;

[0028] Figure 11 Fig. 7 schematically illustrates a cross-sectional view of two second waveguides according to embodiments of the present application;

[0029] Figure 12 Fig. 8 schematically illustrates a cross-sectional view of two first waveguides according to embodiments of the present application;

[0030] Figure 13 Fig. 9 schematically illustrates simulation results of the influence of a minimum gap varying from 0-100 pm on the coupling degree;

[0031] Figure 14 Fig. 10 schematically illustrates simulation results of the influence of a minimum gap varying from 100-900 pm on the coupling degree;

[0032] Figure 15 Fig. 11 schematically illustrates simulation results of the influence of I1 being 500 pm and I2 varying from 100 pm -900 pm on the coupling degree; and

[0033] Figure 16 Fig. 12 schematically illustrates simulation results of the influence of I2 being 1000 pm and I1 varying from 100 pm -500 pm on the coupling degree.

[0034] The following reference signs are used in the drawings:

[0035] 1 - base;

[0036] 11 - opening;

[0037] 12 - mounting hole;

[0038] 2 - waveguide assembly;

[0039] 21 - first waveguide;

[0040] 211 - body portion;

[0041] 212 - extension;

[0042] 22 - second waveguide;

[0043] 23 - adjustment portion;

[0044] 24 - metal layer. DETAILED DESCRIPTION

[0045] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to specific embodiments and drawings.

[0046] The terms used herein are merely used to describe specific embodiments, and are not intended to limit the present application. The terms "include", "comprise" and the like used herein indicate the presence of the described features, steps, operations and / or components, but do not exclude the presence or addition of one or more other features, steps, operations or components.

[0047] All terms used herein, including technical and scientific terms, have meanings commonly understood by one of ordinary skill in the art, unless otherwise defined. It should be noted that the terms used herein should be interpreted as having meanings consistent with the context of the specification, and should not be interpreted in an idealized or overly formal manner.

[0048] In the case of using expressions similar to "at least one of A, B, and C, etc.", it should be generally construed that the expression means at least one of the applicable items selected by a person having ordinary knowledge in the art, unless explicitly stated otherwise. For example, "a system having at least one of A, B, and C" should be construed to include a system having only A, a system having only B, a system having only C, a system having both A and B, a system having both A and C, a system having both B and C, and / or a system having A, B, and C, etc. In the case of using expressions similar to "at least one of A, B, or C, etc.", it should be generally construed that the expression means at least one of the applicable items selected by a person having ordinary knowledge in the art, unless explicitly stated otherwise. For example, "a system having at least one of A, B, or C" should be construed to include a system having only A, a system having only B, a system having only C, a system having both A and B, a system having both A and C, a system having both B and C, and / or a system having A, B, and C, etc.

[0049] It should also be noted that the directional phrases mentioned in the embodiments, such as "upper", "lower", "front", "rear", "left", "right", etc., are only the directions of the drawings, and are not intended to limit the protection scope of the present application. Throughout the drawings, the same elements are represented by the same or similar reference numerals. When the conventional structures or configurations may cause confusion in understanding the present application, the conventional structures or configurations will be omitted.

[0050] Figure 1A perspective view of a terahertz wave directional coupler according to an embodiment of the present application is schematically shown, Figure 2 A perspective view of a terahertz wave directional coupler according to an embodiment of the present application is schematically shown, Figure 1 A partial enlarged view of part A shown, Figure 3 A perspective view of a terahertz wave directional coupler according to an embodiment of the present application is schematically shown, Figure 4 A perspective view of a terahertz wave directional coupler according to an embodiment of the present application is schematically shown.

[0051] As an aspect of the present application, a terahertz wave directional coupler is provided, which is suitable for coupling a terahertz wave from free space to a waveguide device (not shown in the figure). As shown, Figures 1 to 4 The terahertz wave directional coupler includes a base 1 and two sets of waveguide assemblies 2. An opening 11 is formed on the base 1, and a waveguide device is installed on one side of the base 1. The two sets of waveguide assemblies 2 extend from the side of the base 1 opposite to the waveguide device, and are oppositely arranged on the base 1. A transmission channel is defined between the two sets of waveguide assemblies 2 and communicates with the opening 11, and the minimum gap between the two sets of waveguide assemblies 2 is not less than a predetermined value. The terahertz wave propagates along the transmission channel in a first direction (the direction of the arrow in the figure) towards the opening 11, and in the process of propagation, the gap between the two sets of waveguide assemblies 2 is configured to affect the energy distribution of the terahertz wave in the transmission channel, so that the energy distribution of the terahertz wave matches the transmission mode of the waveguide device. Figure 3

[0052] According to the terahertz wave directional coupler of the present application, by forming a transmission channel between the two sets of oppositely arranged waveguide assemblies 2 and keeping the minimum gap between the two sets of waveguide assemblies 2 not less than a predetermined value, the terahertz wave can be made to propagate along the transmission channel in the first direction, and the gap between the two sets of waveguide assemblies 2 can affect the energy distribution of the terahertz wave in the transmission channel, so that the energy distribution of the terahertz wave matches the transmission mode of the waveguide device, and the coupling efficiency of the terahertz wave in the transmission channel is improved.

[0053] According to an embodiment of the present application, the predetermined value can be greater than or equal to 0 μm, i.e., the predetermined value ≥ 0 μm. For example, it can be any one of 0 μm, 50 μm, 100 μm, etc.

[0054] In an exemplary embodiment, the size d of the minimum gap is configured to be less than or equal to 900 μm, and greater than or equal to a preset value. That is, 900 μm ≥ d ≥ preset value.

[0055] For example, the size of the minimum gap can be 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm or 900 μm.

[0056] ​According to the embodiments of the present application, the transmission mode of the waveguide device can include any one of a TE mode (Transverse Electric), a TM mode (Transverse Magnetic) and a TEM mode (Transverse Electric and Magnetic). Among them, the TE mode is a transverse electric field mode, that is, the electric field vector is perpendicular to the propagation direction of the wave. The TM mode is a transverse magnetic field mode, that is, the magnetic field vector is perpendicular to the propagation direction of the wave. The TEM mode is a transverse electromagnetic field mode, that is, the electric field and magnetic field vectors are both perpendicular to the propagation direction of the wave.

[0057] In an illustrative embodiment, the cross-sectional shape of the opening 11 on the base 1 can be rectangular.

[0058] Figure 5 The perspective view of the base according to the embodiments of the present application is schematically shown.

[0059] In an illustrative embodiment, as shown in Figure 1 and Figure 5 , the base 1 can be a flange structure to facilitate connection with other components outside.

[0060] In an illustrative embodiment, as shown in Figure 1 and Figure 5 , a mounting hole 12 can be formed on the base 1 near the edge, which can be connected with other components (such as waveguide devices) outside through bolts. It can be understood that the connection of the base 1 with other components can also be welding or riveting, etc., which is not limited here.

[0061] In the process of implementing the present application, it is found that terahertz waves can penetrate non-polar and non-metallic materials such as paper, plastic and ceramic, but it is difficult to penetrate metal materials. When the terahertz wave is transmitted along the metal waveguide structure, only a small amount of electromagnetic energy is distributed in the metal area, and more electromagnetic energy is distributed in the area outside the material. The skin depth of common metal materials such as gold, silver, copper, aluminum and tungsten in the terahertz wave band is only nanometer level, so the metal waveguide has the advantages of low transmission loss and small dispersion.

[0062] In an illustrative embodiment, the two waveguide assemblies 2 and the base 1 can be made of metal materials. The material of the waveguide assembly 2 can be the same as or different from that of the base 1.

[0063] In an illustrative embodiment, the metal material includes but is not limited to gold, silver, copper and alloy.

[0064] In an illustrative implementation, the inner surfaces (i.e. the surfaces facing the transmission channel) of the two waveguide assemblies 2 are coated with a metal layer 24 (e.g. one or more of gold, silver, copper, aluminum, tungsten, etc.) to reflect the terahertz waves incident on the surfaces of the metal layer 24 and improve the coupling efficiency of the terahertz waves. It will be appreciated that in such embodiments the materials of the first waveguide 21, the second waveguide 22 and the adjustment portion 23 can be non-metallic or metallic.

[0065] In the process of implementing the present application, it is found that the parallel flat plate structure has the advantages of low loss and low dispersion, the rectangular waveguide has the advantages of simple structure, high mechanical strength, strong anti-interference ability, low transmission loss, large power capacity, etc., and is widely used in the field of microwave radio frequency transmission.

[0066] Figure 6 Fig. 1 schematically shows a perspective view of a waveguide assembly according to an embodiment of the present application, Figure 7 Fig. 2 schematically shows a perspective view of two second waveguides according to an embodiment of the present application.

[0067] According to embodiments of the present application, as shown in Figures 1 to 4 , Figure 6 and Figure 7 , each waveguide assembly 2 includes a first waveguide 21 and a second waveguide 22. The first waveguide 21 extends from the base 1 towards a second direction opposite to the first direction, and the first waveguides 21 of the two waveguide assemblies 2 are parallel to each other and have a minimum gap. The second waveguide 22 extends obliquely from the end of the first waveguide 21 away from the base 1 towards the second direction, the distance between the second waveguide 22 and the second waveguide 22 of the other waveguide assembly 2 gradually increases along the second direction, and in the extension plane, the dimension of the second waveguide 22 perpendicular to the second direction gradually increases along the second direction. The second waveguide 22 is suitable for guiding terahertz waves and gradually adapting the propagation mode of the flat plate, reducing reflection and scattering caused by mismatched propagation modes, and improving the coupling efficiency of the terahertz waves.

[0068] In such embodiments, as shown in Figure 3 , a gap is formed between the two waveguide assemblies 2, and a minimum gap d is formed between the two parallel first waveguides 21. When the terahertz waves are transmitted along the gap between the two waveguide assemblies 2 towards the first direction, they will be constrained to a certain extent, and the electromagnetic field can be better confined in the transmission channel, effectively reducing the radiation field outside the transmission channel.

[0069] According to embodiments of the present application, as shown in Figure 3 , the extension length I1 of the first waveguide 21 is configured to be between 100 μm - 500 μm, i.e. 100 μm ≤ I1 ≤ 500 μm.

[0070] According to the embodiment of the present application, as shown in Figure 3 The extension length I2 of the second waveguide 22 projected in the plane parallel to the body part 211 is configured to be between 100 μm - 1000 μm, i.e. 100 μm ≤ I2 ≤ 1000 μm.

[0071] According to the embodiment of the present application, the cross-sectional size of the opening 11 in the second plane perpendicular to the first direction is the same as the cross-sectional size of the transmission channel enclosed by the two first waveguides 21 in the second plane. In this way, impedance matching can be achieved to the maximum extent, and reflection of terahertz waves at the interface between the opening 11 and the transmission channel is reduced.

[0072] According to the embodiment of the present application, to better match the waveguide device, the size of the opening 11 can be set to a standard waveguide port (for example, it can be WR08).

[0073] Figure 8 A perspective view of two first waveguides according to an embodiment of the present application is schematically shown.

[0074] According to the embodiment of the present application, as shown in Figure 1 , Figure 2 , Figure 6 and Figure 8 Each first waveguide 21 includes a body part 211 and two extension parts 212. The two extension parts 212 extend from both sides of the body part 211 towards the other first waveguide 21, and the minimum gap is located between the two facing extension parts 212 of the two first waveguides 21.

[0075] Figure 9 A perspective view of two pairs of adjustment parts according to an embodiment of the present application is schematically shown.

[0076] According to the embodiment of the present application, Figures 1 to 3 , Figure 6 and Figure 9 Each waveguide assembly 2 further includes a pair of adjustment parts 23, which connects the second waveguide 22 and the two extension parts 212. The size of the adjustment part 23 in the first plane perpendicular to the second waveguide 22 gradually decreases along the second direction, and the adjustment part 23 is adapted to cooperate with the second waveguide 22 to gradually guide the terahertz waves, so that the terahertz waves gradually adapt to the propagation mode of the slab.

[0077] In such an embodiment, as shown in Figure 3 The gap between the two facing adjustment parts 23 gradually increases along the second direction.

[0078] According to the embodiment of the present application, the body part 211, the extension part 212, the second waveguide 22 and the adjustment part 23 are all slab waveguides.

[0079] In the process of realizing the utility model, it is found that since the rectangular waveguide is a single-conductor hollow structure, only TE mode or TM mode exists, TEM mode cannot exist, it belongs to a dispersive waveguide system, and the rectangular metal waveguide can be analyzed according to Maxwell's equations and related boundary conditions. The electromagnetic field in the rectangular waveguide satisfies Maxwell's equations, when the waveguide metal wall is in ideal conductive condition, at this time, the tangential component of the electric field on the system boundary is 0, the conductivity tends to infinity, first, the constant coefficient of the solution can be determined by using the condition that the tangential component of the electric field on the metal boundary is equal to 0, and the expressions of the field components of the guided wave in the rectangular waveguide can be obtained respectively, at this time, there are infinite solutions that satisfy the boundary conditions, but their linear combination is still the solution of the wave equation.

[0080] As shown in Figure 3 and Figure 4 , the extension length (length in the second direction) of the first waveguide 21 is I1, and the extension length (length in the second direction) of the second waveguide 22 projected in the plane parallel to the body part 211 is I2, wherein, on the left side shown in the incident port Figure 3 and Figure 4 , the length of the second waveguide 22 in the width direction perpendicular to the second direction in the plane parallel to the body part 211 is L, the maximum gap between the two second waveguides 22 is H, and the size of the first waveguide 21 in the direction perpendicular to the extension direction on the right side shown in the exit port Figure 3 and Figure 4 , the size of the first waveguide 21 in the direction perpendicular to the extension direction on the right side shown in the exit port

[0081] The terahertz wave directional coupler provided by the embodiment of the utility model is composed of a flat plate waveguide and a rectangular transmission channel, has the advantages of simple structure and low insertion loss, and can transmit TE mode, TM mode and TEM mode, which is different from conventional waveguides.

[0082] Figure 10 An equivalent diagram of two second waveguides according to the embodiment of the utility model is schematically shown.

[0083] The two second waveguides 22 are in a non-parallel state, for the purpose of simplifying the analysis process, as shown in Figure 10 , the two second waveguides 22 can be equivalent to an infinite number of parallel flat plate waveguides (P1, P2, P3 …… Pn) with varying intervals. For the passive and uniform region, the Helmholtz equation can be used to obtain:

[0084] (1);

[0085] Wherein, Angular frequency, Permeability, Let be the electric field strength. Since the waveguide region is passive, for a lossless vacuum or air region, the longitudinal electric and magnetic field components of the parallel planar metal waveguide mode are both 0, meaning the transmission mode is the TEM mode. Substituting these equations into Maxwell's equations in Cartesian coordinates yields the following results. , , , The expression is as follows:

[0086] (2);

[0087] in, Let be the propagation constant. Indicates the cutoff wave number, Substituting into Maxwell's equations yields... ,Right now This indicates that the TEM mode has no cutoff wave vector.

[0088] In addition to the TEM mode, planar waveguides also exhibit TE and TM modes. The presence of multiple modes can affect the transmission and coupling of terahertz waves. Therefore, it is necessary to analyze the TE and TM modes of the planar waveguide and calculate their cutoff frequencies.

[0089] Figure 11 A schematic cross-sectional view of two second waveguides according to an embodiment of the present invention is shown. It should be noted that... Figure 11 The cross-sectional view in the diagram is a cross-section of the two second waveguides 22 in a plane perpendicular to the first direction.

[0090] like Figure 3 and Figure 11 As shown, the gap h between the two second waveguides 22 gradually decreases from the maximum gap H to the minimum gap d along the first direction.

[0091] Figure 12 The diagram schematically illustrates cross-sectional views of two first waveguides according to an embodiment of the present invention. It should be noted that... Figure 12 The cross-sectional view in the diagram is a cross-section of the two first waveguides 21 in a plane perpendicular to the first direction.

[0092] like Figure 12 As shown, assuming the planar waveguide (first waveguide 21) is infinitely long along the x-direction and confined along the y-direction, the minimum gap between the first waveguides 21 is... , The characteristics of the pattern are and , the propagation constant and the cutoff frequency can be obtained by substituting Maxwell's equations in the rectangular coordinate system:

[0093] (3);

[0094] (4);

[0095] Similarly, the characteristics of the TM mode are , According to Maxwell's equations, the propagation constant of the TM mode and the cutoff frequency are consistent with those of the TE mode.

[0096] Through the above analysis, it can be seen that when the minimum gap between the first waveguide 21 is smaller, the cutoff frequency of the corresponding mode is higher, and by adjusting the minimum gap between the first waveguide 21, the transmission loss in a certain frequency range can be reduced.

[0097] According to the terahertz wave directional coupler of the embodiment of the utility model, as Figure 11 shown, when the minimum gap between the first waveguide 21 is, that is, the two first waveguides 21 form a rectangular waveguide structure. The rectangular waveguide can avoid external interference and radiation loss to the greatest extent, has large power capacity, and can only transmit TE mode and TM mode. The metal rectangular waveguide (the first waveguide 21) has constraint in the direction as Figure 12 shown and the direction. When the rectangular waveguide can transmit electromagnetic waves, the frequency satisfies:

[0098] (5);

[0099] The cutoff frequency is:

[0100] (6);

[0101] The cutoff wave number of the corresponding mode is:

[0102] (7);

[0103] The propagation constant of the corresponding mode is:

[0104] (8);

[0105] ​​​ is the length of the cross-section medium (e.g., air) domain, is the width of the cross-section medium domain. According to the concept of propagation constant, it is known that when the propagation constant the corresponding mode is a traveling wave, the corresponding mode rapidly attenuates, and when the mode is in a critical state of propagation and cutoff.

[0106] The terahertz wave coupler has the characteristics of wide coupling bandwidth and high coupling efficiency, and can realize low-loss and efficient terahertz signal coupling transmission of terahertz waves from free space to other devices, thereby improving the transmission and detection efficiency of terahertz waves in the integrated system.

[0107] According to the embodiment of the utility model, the coupling degree is an important index for judging the performance of the coupler, and the strength of the coupling degree and the floating range of the curve determine the advantages and disadvantages of the performance of the coupler. Generally, the coupler with an absolute value of the coupling degree less than 6dB is a strong coupling, and the coupler with strong coupling degree can transmit a large part of power to the coupling output port. The weak coupling type coupler with a coupling degree greater than 20 has very small signal detected from the output port. When the coupling degree is 3dB, the coupler is equivalent to a power divider, and the output power of the coupling end and the output power of the straight-through end are the same, which is half of the input port power.

[0108] For a two-port device, there are four S parameters, which are S11, S12, S21 and S22. Among them, S11 is the reflection coefficient of port 1 when port 2 is matched; S22 is the reflection coefficient of port 2 when port 1 is matched; S12 is the reverse transmission coefficient of port 2 to port 1 when port 1 is matched; and S21 is the forward transmission coefficient of port 1 to port 2 when port 2 is matched.

[0109] Figure 13 The simulation results of the influence of the minimum gap on the coupling degree when the minimum gap changes from 0 to 100μm are schematically shown. Figure 14 The simulation results of the influence of the minimum gap on the coupling degree when the minimum gap changes from 100 to 900μm are schematically shown.

[0110] As shown in Figure 13 and Figure 14 , the abscissa represents the frequency (THz), and the ordinate represents the forward transmission coefficient S21 (dB).

[0111] As shown in Figure 13 and Figure 14As shown, when the minimum gap d changes in the range of 0-100 μm, the forward transmission coefficient S21 is less than 6 dB in the frequency range of 126.2-822.1 GHz, and the coupling bandwidth reaches 695.9 GHz. When the minimum gap is 900 μm, S21 in the range of 0.1-1 THz is less than 6 dB, that is, high-efficiency coupling with an application bandwidth of at least 0.9 THz can be achieved; in the ranges of 0.154-0.533 THz and 0.537-1 THz, S21 is less than 3 dB, at this time, the output power is close to the input power.

[0112] Figure 15 Simulation results showing the influence of I1 being 500 μm and I2 changing in the range of 100 μm-900 μm on the coupling degree are schematically shown. Figure 16 Simulation results showing the influence of I2 being 1000 μm and I1 changing in the range of 100 μm-500 μm on the coupling degree are schematically shown.

[0113] As shown in Figure 15 and Figure 16 the abscissa represents the frequency (THz), and the ordinate represents the forward transmission coefficient S21 (dB).

[0114] As shown in Figure 15 and Figure 16 when the extension length I1 of the first waveguide 21 is 500 μm, the extension length I2 of the second waveguide 22 projected in the plane parallel to the body part 211 changes in the range of 100-900 μm, and as the extension length I2 increases, the resonant frequency gradually decreases;

[0115] when the extension length I2 of the second waveguide 22 projected in the plane parallel to the body part 211 is 1000 μm, the extension length I1 of the first waveguide 21 changes in the range of 100-500 μm, and as the extension length I1 of the first waveguide 21 increases, the resonant frequency gradually decreases, and the forward transmission coefficient S21 in the range of 100-1000 GHz is less than 5.3 dB, which can be used as a strong coupler.

[0116] The terahertz wave coupler according to the embodiments of the present application adopts the concave waveguide formed by the body part 211 and two extension parts 212, the trapezoidal flat plate second waveguide 22, and the triangular flat plate adjustment part 23 to form the waveguide assembly 2, and the two waveguide assemblies 2 are opposite to each other to form a substantially Y-shaped structure. The terahertz wave (for example, a terahertz wave pulse) is input from the longer bottom edge of the trapezoidal flat plate and is output from the rectangular hole at the center of the flange. Compared with the rectangular metal waveguide, the coplanar waveguide, and the microstrip terahertz coupler structure proposed in the related art, the structure is simpler and more compact, is easier to process, and overcomes the problems of high manufacturing process requirement, difficult actual application, and difficult processing of the single structure form terahertz waveguide structure.

[0117] The embodiments of the present application are described above. However, these embodiments are only for the purpose of illustration, and are not intended to limit the scope of the present application. Although each embodiment is described above, this does not mean that the measures in each embodiment cannot be used advantageously in combination. The scope of the present application is defined by the appended claims and their equivalents. Without departing from the scope of the present application, those skilled in the art can make various substitutions and modifications, and these substitutions and modifications should all fall within the scope of the present application.

Claims

1. A terahertz wave directional coupler adapted to couple terahertz waves from free space to a waveguide device, characterized by, The terahertz wave directional coupler comprises: a base having an opening formed thereon, the waveguide device being mounted on one side of the base; two sets of waveguide assemblies extending from the side of the base opposite to the waveguide device, being oppositely arranged on the base, the transmission channel being defined between the two sets of waveguide assemblies and communicating with the opening, the minimum gap between the two sets of waveguide assemblies being not less than a predetermined value; the terahertz wave propagates along the transmission channel in a first direction towards the opening, and in the process of propagation, the gap between the two sets of waveguide assemblies is configured to affect the energy distribution of the terahertz wave in the transmission channel, so that the energy distribution of the terahertz wave matches the transmission mode of the waveguide device.

2. The terahertz wave directional coupler according to claim 1, characterized by, Each set of waveguide assemblies comprises: a first waveguide extending from the base towards a second direction opposite to the first direction, the first waveguides of the two sets of waveguide assemblies being parallel to each other and having the minimum gap; and a second waveguide extending from the end of the first waveguide away from the base towards the second direction obliquely, the distance between the second waveguide and the second waveguide of the other set of waveguide assemblies gradually increases along the second direction, and in the extension plane, the dimension of the second waveguide perpendicular to the second direction gradually increases along the second direction, the second waveguide being adapted to guide the terahertz wave to gradually adapt to the propagation mode of the flat plate.

3. The terahertz wave directional coupler according to claim 2, wherein Each first waveguide comprises: a body portion; and two extension portions extending from both sides of the body portion towards the other first waveguide; the minimum gap is located between the two facing extension portions of the two first waveguides.

4. The terahertz wave directional coupler according to claim 3, wherein Each waveguide assembly further comprises: a pair of adjustment portions connecting the second waveguide and the two extension portions, the dimension of the adjustment portion in a first plane perpendicular to the second waveguide gradually decreases along the second direction, the adjustment portion being adapted to cooperate with the second waveguide to gradually guide the terahertz wave to gradually adapt to the propagation mode of the flat plate.

5. The terahertz wave directional coupler according to claim 3 or 4, characterized in that, The extension length of the second waveguide projected in a plane parallel to the body portion is configured to be between 100 μm - 1000 μm.

6. The terahertz wave directional coupler according to claim 2, wherein The cross-sectional dimension of the opening in a second plane perpendicular to the first direction is the same as the cross-sectional dimension of the transmission channel enclosed by the two first waveguides in the second plane.

7. The terahertz wave directional coupler according to any one of claims 1 to 4, characterized in that, The inner surfaces of the two waveguide assemblies are coated with a metal layer to reflect the terahertz wave incident on the surface of the metal layer.

8. The terahertz wave directional coupler according to any one of claims 1-4, wherein, The base is a flange structure to facilitate connection with the waveguide device.

9. The terahertz wave directional coupler according to any one of claims 1-4, wherein, The size of the minimum gap is configured to be less than or equal to 900 μm.

10. The terahertz wave directional coupler according to any one of claims 2-4, characterized in that, The extension length of the first waveguide is configured to be between 100 μm - 500 μm.

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