Dual-frequency terahertz amplitude modulation unit and dual-frequency terahertz amplitude modulator

Abstract

The application discloses a dual-frequency terahertz amplitude modulation unit and a dual-frequency terahertz amplitude modulator, and relates to the technical field of terahertz wave modulation. The unit structure comprises a dielectric layer and a metal metasurface structure located on the surface of the dielectric layer, wherein the metal metasurface structure is formed by a cross-shaped metal sheet, U-shaped metal sheets and vanadium dioxide patches; four U-shaped metal sheets are arranged in four quadrants formed by the cross-shaped metal sheet in a center-symmetrical pattern; and each U-shaped metal sheet is connected with the cross-shaped metal sheet through a vanadium dioxide patch. By taking the vanadium dioxide patch as a switch, two resonant frequencies of high and low frequency bands are formed between low conductivity and high conductivity of the vanadium dioxide patch, amplitude adjustment of high and low dual-frequency terahertz waves is realized, and close modulation depth is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of terahertz wave modulation, and in particular to a dual-frequency terahertz amplitude modulation unit and a dual-frequency terahertz amplitude modulator. BACKGROUND

[0002] Terahertz waves are electromagnetic waves with a frequency range of 0.1 THz-10 THz, which coincide with millimeter waves in the long-wave band and coincide with infrared light in the short-wave band. This frequency band is a transition zone from macroscopic classical theory to microscopic quantum theory and a transition zone from electronics to photonics, and has attracted more and more attention in the past 20 years. Terahertz waves have many advantages, such as low photon energy, which can ensure high safety of imaging compared with X-rays. Terahertz waves have strong penetration ability and can be used for non-destructive testing of material structures. Terahertz waves have many spectral properties and are suitable for material characterization. Communication is one of the important applications of this technology. A standard terahertz communication system is composed of different terahertz functional devices, including a terahertz radiation source using a photoconductive antenna or based on an electronic method, a terahertz modulator, a terahertz mixer, a terahertz power divider, and a terahertz coupler. Among them, the terahertz modulator has a significant impact on the overall performance of the system and plays a crucial role in the system.

[0003] The performance of a terahertz amplitude modulator usually includes parameters such as terahertz modulation depth, modulation rate, and dynamic modulation characteristics. A temperature-controlled terahertz modulator modulates incident terahertz waves by changing the temperature, which changes the electrical conductivity or dielectric constant of the controllable semiconductor, thereby causing changes in the resonance frequency or strength of the metamaterial structure. At present, many studies on terahertz amplitude modulators are based on improving the modulation depth, terahertz wave incident angle insensitivity, and polarization insensitivity. However, the structures of many dual-frequency or multi-frequency terahertz amplitude modulators are repetitive and nested, with small structure sizes corresponding to high frequency points and weak local ability to incident waves, resulting in low resonance strength. Large structure sizes corresponding to low frequency points have strong local ability to incident waves, resulting in high resonance strength. Therefore, it is difficult to make the modulation depths of different resonance peaks equal or close, thereby making the modulation effect unsatisfactory. In addition, due to the asymmetry of the structure, the modulation performance is affected by the terahertz wave incident angle or polarization characteristics. Therefore, designing a terahertz amplitude modulator with dual-frequency modulation depths close to each other and insensitive to incident angles and polarization has great application potential and value for terahertz communication. SUMMARY

[0004] The present application provides a dual-frequency terahertz amplitude modulation unit and a dual-frequency terahertz amplitude modulator to solve the problem that existing terahertz amplitude modulation techniques cannot achieve equal or close dual-frequency modulation depths.

[0005] The present application is achieved by the following technical solutions:

[0006] Provided is a dual-frequency terahertz amplitude modulator, comprising a dielectric layer and a metal metasurface structure located on the surface of the dielectric layer, wherein the metal metasurface structure is formed by a cross-shaped metal sheet, a U-shaped metal sheet and a vanadium dioxide patch.

[0007] The U-shaped metal sheet has four U-shaped metal sheets, which are respectively arranged in the four quadrants formed by the cross-shaped metal sheet.

[0008] In each of the quadrants, the opening direction of the U-shaped metal sheet is towards one side of the cross-shaped metal sheet, and the pattern formed by the cross-shaped metal sheet and the U-shaped metal sheet is centrosymmetric.

[0009] Each of the U-shaped metal sheets is connected to the cross-shaped metal sheet through a vanadium dioxide patch, so that the amplitude modulation of high-frequency or low-frequency terahertz waves is realized through the change of the conductivity of the vanadium dioxide patch.

[0010] The dual-frequency terahertz amplitude modulation unit of the present application is composed of a centrosymmetric metal metasurface structure and a dielectric layer, and the cross-shaped metal sheet and the U-shaped metal sheet in the four quadrants formed thereby form four equivalent LC oscillation circuits, and the vanadium dioxide patch serves as a "switch" for the LC oscillation circuit, and the vanadium dioxide patch has the characteristic that the conductivity changes with temperature, and when the conductivity is low, it is equivalent to a "switch" being closed, and when the conductivity is high, it is equivalent to a "switch" being opened, according to the equivalent circuit theory, the resonance frequency of the amplitude modulation unit in the "switch" closed state is higher than that in the "switch" opened state, and the low and high frequency bands are formed between the low and high conductivity of the vanadium dioxide patch, and the dual-frequency device proposed by the present application has the same level of local ability to the incident electromagnetic wave in the high and low frequency corresponding resonance loop structure size, so as to realize the modulation depth close to each other. According to the experimental data and the calculation results of the dual-frequency modulation depth formula, the adjustment depth of the dual-frequency terahertz amplitude modulation unit of the present application at high and low frequencies is about 70%. And due to the centrosymmetric structure, it is not sensitive to the incident angle and polarization.

[0011] Further, the material of the cross-shaped metal sheet and the U-shaped metal sheet is aluminum.

[0012] Further, the material of the dielectric layer is polyimide, high-resistance silicon or quartz.

[0013] Further, the metal metasurface structure is located in the central region of the dielectric layer.

[0014] Further, the opening direction of the U-shaped metal sheet is perpendicular to one side of the cross-shaped metal sheet.

[0015] Further, the cross-sectional shape of the dielectric layer is polygonal, circular or elliptical.

[0016] Further, the cross-section shape of the dielectric layer is a square with a size of 150 μm x 150 μm; the thickness of the dielectric layer is 25 μm, and the thickness of the metal metasurface structure is 0.2 μm.

[0017] Further, the two mutually perpendicular metal strips of the cross-shaped metal patch are of the same size, and the length of the metal strip is 100 μm and the width is 5 μm.

[0018] Further, the thickness of the bottom of the U-shaped metal patch is 10 μm.

[0019] In a second aspect, the present application provides another dual-frequency terahertz amplitude modulator, which comprises a plurality of dual-frequency terahertz amplitude modulation units according to any one of the first aspect of the present application, and the plurality of dual-frequency terahertz amplitude modulation units are arranged in a periodic arrangement structure.

[0020] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0021] The cross-shaped metal patch and the U-shaped metal patch in the four quadrants formed by the cross-shaped metal patch form four equivalent LC oscillation circuits, the vanadium dioxide patch acts as a "switch" of the LC oscillation circuit, and two resonant frequencies of high and low frequency bands are formed between the low conductivity and the high conductivity of the vanadium dioxide patch, thereby realizing amplitude adjustment of high and low dual-frequency terahertz waves.

[0022] According to the experimental data and the calculation results of the dual-frequency modulation depth formula, the adjustment depth of the dual-frequency terahertz amplitude modulation unit of the present application at high and low frequencies is about 70%, and the dual-frequency modulation depth is close to 70%.

[0023] And because it is a center-symmetric structure, the modulation performance will not be affected by the incident angle or the polarization characteristics of the terahertz wave.

[0024] The dual-frequency terahertz amplitude modulation unit is composed of a dielectric layer and a metal metasurface structure, the metal metasurface structure is a center-symmetric structure formed by a cross-shaped metal patch, a U-shaped metal patch and a vanadium dioxide patch, the structure is simple in structure and preparation, and the amplitude modulation of dual-frequency terahertz waves can be realized. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present application, the following will briefly introduce the drawings needed in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be considered as limiting the scope. For those skilled in the art, other related drawings can also be obtained without creative labor. In the drawings:

[0026] Figure 1is a structural schematic diagram of a dual-frequency terahertz amplitude modulation unit of an embodiment of the present application;

[0027] Figure 2 is a schematic diagram of a vanadium dioxide patch connection of an embodiment of the present application;

[0028] Figure 3 is a dual-frequency terahertz amplitude modulator of a 2x2 unit structure of an embodiment of the present application;

[0029] Figure 4 is a transmission curve diagram of the dual-frequency terahertz amplitude modulation unit of embodiment 1 of the present application under different conductivities of the vanadium dioxide patch;

[0030] Figure 5 is a current distribution diagram of the dual-frequency terahertz amplitude modulation unit of embodiment 1 of the present application;

[0031] Figure 6 is an equivalent circuit diagram of the dual-frequency terahertz amplitude modulation unit of embodiment 1 of the present application;

[0032] Figure 7 is a transmission coefficient of the dual-frequency terahertz amplitude modulation unit of embodiment 1 of the present application at different incident angles when the conductivity g = 40 S / m and g = 1.2x10 7 S / m;

[0033] Figure 8 is a transmission coefficient of the VO2 patch in the on and off states at different azimuth angles.

[0034] The reference signs are explained as follows:

[0035] 1 - medium, 2 - metal metasurface structure, 21 - cross-shaped metal sheet, 22 - U-shaped metal sheet, 23 - vanadium dioxide patch. DETAILED DESCRIPTION

[0036] In order to make the objectives, technical solutions and advantages of the present application clearer, further detailed description will be made to the present application in combination with embodiments and drawings, the illustrative embodiments of the present application and the description thereof are only used to explain the present application, and do not limit the present application.

[0037] It should be noted that the terms "include" and "have" and any variations thereof in the specification and claims of the present application and the above drawings are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device containing a series of steps or units does not have to be limited to or inherent to other steps or units.

[0038] The terminology used in the description of the various embodiments herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the various embodiments of the application. As used in this description, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the various embodiments belong. The terms, such as "include," "includes," "including," "contain," "contains," or "containing," are used broadly and encompass the terms "comprising," "comprises," or "comprising," and are not limited. The terms "exemplary," "for example," and "e.g." mean "an example of" and are not intended to convey an exhaustive list.

[0039] In the following description, numerous specific details are set forth to provide a thorough understanding of the application. However, it will be apparent to one skilled in the art that the application can be practiced without the specific details. In other instances, well-known structures, circuits, materials, or processes have not been described in detail in order to avoid obscuring the application.

[0040] The embodiment of the application provides a dual-frequency terahertz amplitude modulation unit and a dual-frequency terahertz amplitude modulator, which are suitable for terahertz wave amplitude modulation, are beneficial to adjusting the amplitudes of incident high-frequency and low-frequency terahertz waves, and have close modulation depths of dual frequencies.

[0041] Embodiment 1

[0042] Referring to Figure 1 As shown in the figure, Figure 1 is a structural schematic diagram of a dual-frequency terahertz amplitude modulation unit of the application, and the basic structure includes a dielectric layer 1 and a metal super surface structure 2. Taking the ground as a reference, the dielectric layer 1 is located in the lower layer, and the metal super surface structure 2 is located on the upper surface of the dielectric layer 1.

[0043] The electromagnetic super surface is an artificial arrangement of composite materials with subwavelength structures, and the electromagnetic characteristics thereof can be arbitrarily designed by changing the geometric parameters. In the application, the metal super surface structure 2 is formed by a cross-shaped metal sheet 21, a U-shaped metal sheet 22 and a vanadium dioxide (VO2) patch 23. The cross-shaped metal sheet 21 forms four quadrants on the surface of the dielectric layer, and the U-shaped metal sheet 22 has four, which are arranged in the four quadrants formed by the cross-shaped metal sheet 21. And in each quadrant, the opening direction of the U-shaped metal sheet 22 is towards one side of the cross-shaped metal sheet 21, and finally the pattern formed by the cross-shaped metal sheet 21 and the U-shaped metal sheet 22 has the property of central symmetry, so that the modulation performance of the terahertz amplitude modulation unit is not sensitive to the incidence angle or polarization characteristics of the terahertz wave.

[0044] In each quadrant, there is a certain spacing between the U-shaped metal sheet 22 and the edge of the cross-shaped metal sheet 21, that is, the U-shaped metal sheet is not directly connected with the cross-shaped metal sheet, but each U-shaped metal sheet 22 is connected with the cross-shaped metal sheet 21 through the vanadium dioxide patch 23. By using the characteristic that the conductivity of vanadium dioxide changes with the ambient temperature, the vanadium dioxide patch acts as a modulation "switch", so as to realize the amplitude modulation of the incident terahertz wave through the change of the conductivity of the vanadium dioxide patch.

[0045] Specifically, according to the relative arrangement position of the U-shaped metal sheet and the cross-shaped metal sheet, it can be distinguished that the two U-shaped edges of the U-shaped metal sheet are located on the outer side or the inner side. As shown in Figure 2 Fig. 4 is a schematic diagram of a vanadium dioxide patch connection, in an optional implementation manner, the four U-shaped metal sheets are connected with one edge of the cross-shaped metal sheet through the U-shaped edge located on the outer side by the vanadium dioxide patch.

[0046] In another optional implementation manner, the four U-shaped metal sheets are connected with one edge of the cross-shaped metal sheet through the U-shaped edge located on the inner side by the vanadium dioxide patch. Referring to Figure 1 Fig. 5, or two U-shaped metal sheets are connected with one edge of the cross-shaped metal sheet through the U-shaped edge located on the outer side by the vanadium dioxide patch; two U-shaped metal sheets are connected with one edge of the cross-shaped metal sheet through the U-shaped edge located on the inner side by the vanadium dioxide patch. It can be understood that no matter which connection manner is adopted, only one U-shaped edge of the U-shaped metal sheet is connected with the cross-shaped metal sheet, and the other U-shaped edge of the U-shaped metal sheet is in an open state, and the finally formed pattern is a center-symmetric structure. Thus, the incident terahertz wave resonates on the structure, the opening and closing of the "switch" are realized through the change of the conductivity of the vanadium dioxide patch, the resonance occurs in the low frequency and high frequency bands, so as to realize the regulation of the conductivity of the vanadium dioxide patch through the temperature, and the double-frequency channel modulation effect is achieved.

[0047] In the scheme, the medium layer 1 acts as the substrate of the modulator, which prevents the incident light wave from being transmitted on this layer, so that the transmittance of the absorber approaches zero. The material of the medium layer 1 can be selected from polyimide, high-resistance silicon, quartz and the like.

[0048] The medium layer 1 is a plate structure, and the specific shape of the transverse section thereof is not limited, which can be polygonal such as triangle, quadrilateral, pentagon, hexagon, and circular, elliptical and the like. The metal super surface structure 2 is close to the upper surface of the medium layer 1, and the area occupied by the metal super surface structure 2 is smaller than that of the medium layer 1, that is, in the top view of the modulator, the surface of the part of the medium layer 1 not covered by the metal super surface structure 2 can still be seen.

[0049] The metal super surface structure 2 can be located in the central region of the medium layer 1, or deviate from the center of the medium layer 1.

[0050] In some embodiments, the medium layer 1 is a rectangular plate structure, which is easy to cut and manufacture, and has good symmetry. More preferably, it is a square plate structure, and is made of quartz. Its size is 150 μm x 150 μm, and the thickness is 25 μm.

[0051] In some embodiments, the cross-shaped metal patch and the U-shaped metal patch are made of the same metal material, such as gold, silver, copper, or aluminum. Preferably, both the cross-shaped metal patch and the U-shaped metal patch are made of aluminum.

[0052] In some embodiments, the above-mentioned vanadium dioxide patch can also use a photosensitive material such as photosensitive silicon as the connection between the U-shaped metal patch and the cross-shaped metal patch. By adjusting the conductivity of the photosensitive silicon through light control, a similar modulation effect can be achieved.

[0053] In some embodiments, the opening direction of the U-shaped metal patch is towards one side of the cross-shaped metal patch and is perpendicular to the cross-shaped metal patch, that is, the distance from the two sides of the U-shaped opening of the U-shaped metal patch to the side towards which the distance is equal.

[0054] In some embodiments, taking the case where the opening direction of the U-shaped metal patch is perpendicular to one side of the cross-shaped metal patch as an example, the distance a between the opening of the U-shaped metal patch and the cross-shaped metal patch is 4 μm, and the distance d between the U-shaped side on the inner side of the U-shaped metal patch and the cross-shaped metal patch is 25 μm.

[0055] In some embodiments, the resonant frequency can be adjusted by adjusting the thickness and size of the metal metasurface structure, that is, the size of the cross-shaped metal patch and the U-shaped metal patch, so as to achieve amplitude modulation of terahertz waves in specific low-frequency and high-frequency frequency bands.

[0056] In one embodiment, the cross section of the medium layer is a square with a size of 150 μm x 150 μm, the thickness of the medium layer is 25 μm, and the thickness of the metal metasurface structure is 0.2 μm.

[0057] In one embodiment, the two mutually perpendicular metal strips of the cross-shaped metal patch have the same size, the length of the metal strip is L = 100 μm, and the width is w1 = 5 μm.

[0058] In one embodiment, the thickness of the bottom of the U-shaped metal patch is w2 = 10 μm.

[0059] Example 2

[0060] This embodiment provides a dual-frequency terahertz amplitude modulator, which specifically includes a plurality of periodically arranged terahertz amplitude modulation units. As shown in Figure 3 The dual-frequency terahertz amplitude modulator with a 2 x 2 unit structure is shown. In this embodiment, the structure of a single terahertz amplitude modulation unit is described in detail inFigure 1 As shown, the unit structure adopts the dual-frequency terahertz amplitude modulation unit of embodiment 1 of the present invention. The number of unit structures in this embodiment is not limited and can be 3×3, 4×4, etc.

[0061] It should be understood that the terahertz amplitude modulation unit can be used alone as a dual-frequency terahertz amplitude modulator (Example 1), or can be periodically arranged to form an array structure as a dual-frequency terahertz amplitude modulator (Example 2).

[0062] Example 3

[0063] In order to verify the modulation performance of the dual-frequency terahertz amplitude modulator of the present invention, a simulation experiment was conducted on the dual-frequency terahertz amplitude modulation unit structure of Example 1 of the present invention. The structure of the dual-frequency terahertz amplitude modulator used in the simulation experiment is shown in FIG. Figure 1 As shown, the material of the dielectric layer is quartz, and the cross-shaped metal sheet and the U-shaped metal sheet are made of aluminum; the dielectric layer is a square plate with a size of 150μm×150μm and a thickness of 25μm; the length and width of the cross-shaped metal sheet are L=100μm and w1=5μm respectively, and the thickness of the bottom of the U-shaped metal patch is w2=10μm; the distance between the opening of the U-shaped metal patch and the cross-shaped structure in the vertical direction is a=4μm, and the distance between the U-shaped metal patch and the cross-shaped structure in the horizontal direction is d=25μm.

[0064] like Figure 4 The figure shows the transmission curve of the dual-frequency terahertz amplitude modulator of Example 1 of the present invention under different conductivity of the vanadium dioxide patch. Among them, the dotted line ① shows that the vanadium dioxide patch "switch" is in the open state, and the dotted line ② shows that the vanadium dioxide patch "switch" is in the closed state. Figure 5 The figure shows the current distribution of the dual-frequency terahertz amplitude modulator of Example 1 of the present invention, where A shows the current distribution of the vanadium dioxide patch "switch" in the on state, and B shows the current distribution of the vanadium dioxide patch "switch" in the off state. 7 S / m), the “switch” is in the on state, and the current loop related to the low resonant frequency (on state) (such as Figure 5 In contrast, at low conductivity (g = 2S / m), the “switch” is open and the current loop associated with the high resonant frequency (off state) is as follows: Figure 5 As shown in Figure B, the intensity of the high-frequency resonance gradually decreases with increasing conductivity. Conversely, the intensity of the low-frequency resonance increases with increasing conductivity. It has been observed that the current loop of the low-frequency resonance in the on-state is longer than the current loop of the high-frequency resonance in the off-state. According to equivalent circuit theory, the equivalent inductance satisfies: L ∝ l, where l represents the current loop length. The resonant frequency follows the following relationship: L and C represent the equivalent inductance and capacitance of the circuit. Due to the longer length of the current loop related to the resonant frequency, the amplitude modulator has a higher resonant frequency in the off state than in the on state.

[0065] As Figure 6 shown is the equivalent circuit diagram of the dual-frequency terahertz amplitude modulator of Example 1, which corresponds to the formation of an equivalent LC oscillation circuit by coupling of the cross-shaped metal sheet and the U-shaped metal sheet. The incident wave is a vertically polarized wave, and the vanadium dioxide patch acts as a temperature control switch to connect the cross-shaped metal sheet in the middle with the U-shaped metal patch. When the switch is on, the resonant circuit path is shown as a red dashed line in the figure, and when the switch is off, the resonant circuit path is shown as a blue dashed line. The resonance strength of the two circles Figure 6 (top left and bottom right yellow areas) is related to the transmission coefficient of the respective peak. As the switch gradually opens, the resonance strength of the low-frequency resonance increases, while the high-frequency resonance loop is increasingly disturbed, resulting in a decrease in its resonance strength. In this way, by modulating the temperature with the baseband signal, a dual-channel modulation effect is achieved.

[0066] The modulation depth M is used to reflect the modulation performance of the terahertz amplitude modulator, and is defined as the ratio of the difference between the maximum and minimum amplitudes of the modulated wave to the sum of the maximum and minimum amplitudes of the carrier wave, expressed in percentage. It is generally considered that a value of M greater than 70% is a good modulation effect, and the expression of M is:

[0067] M = |V on -V off | / max(V on ,V off )

[0068] where Von represents the modulation wave amplitude in the on state, and Voff represents the modulation wave amplitude in the off state.

[0069] According to Figure 6 the data in the above formula, the modulation depth of the low-frequency component of the dual-frequency terahertz amplitude modulator of the present application is 75.4%, and the modulation depth of the high-frequency component is 73.5%, which are approximately the same.

[0070] Figure 7 shows the transmission coefficient of terahertz waves at different incident angles when the conductivity g = 40 S / m and g = 1.2 x 10 7 S / m. The incident angle of the terahertz wave is 0° to 75°. When the conductivity g = 1.2 x 10 7 S / m, the low-frequency resonance remains stable as the incident angle of the terahertz wave increases. In contrast, as the incident angle of the terahertz wave increases, the high-frequency resonance exhibits a red shift. The dual-frequency terahertz amplitude modulator exhibits angle insensitivity in the range of 0° to 30°.

[0071] Figure 8 The transmission coefficients of the VO2 patch in the on and off states at different azimuth angles are shown, and four VO2 patches are inserted outside between the U-shaped metal patch and the cross-shaped structure. The azimuth angle of the terahertz wave is between 0° and 90°. When the azimuth angle changes between 0° and 90°, the transmission coefficient remains unchanged whether the VO2 is in the on or off state. This result shows that the structure has polarization-insensitive or polarization-invariant characteristics. And its working frequency is located in the two terahertz communication windows of 380 GHz and 850 GHz, respectively, so the designed terahertz amplitude modulator can have certain application value in the terahertz communication field.

[0072] Simulation tests show that the narrow-band and wide-band terahertz perfect absorbers based on the U-shaped metal patch have both a relatively wide absorption band and a narrow-band absorption peak with high absorption rate, and they both have high absorption rate.

[0073] The above specific embodiments further specifically describe the purposes, technical solutions and beneficial effects of the present application, and it should be understood that the above description is only a specific embodiment of the present application and is not used to limit the protection scope of the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A dual-frequency terahertz amplitude modulation unit, characterized by, The metal metasurface structure is formed by a cross-shaped metal sheet, a U-shaped metal sheet and a vanadium dioxide patch. The U-shaped metal sheet has four U-shaped metal sheets, which are arranged in four quadrants formed by the cross-shaped metal sheet. In each quadrant, the opening direction of the U-shaped metal sheet is towards one side of the cross-shaped metal sheet, and the pattern formed by the cross-shaped metal sheet and the U-shaped metal sheet is centrosymmetric. Each U-shaped metal sheet is connected to the cross-shaped metal sheet by a vanadium dioxide patch, so that the amplitude modulation of high-frequency or low-frequency terahertz waves is realized by the change of the conductivity of the vanadium dioxide patch.

2. The dual-frequency terahertz amplitude modulation unit of claim 1, wherein, The material of the cross-shaped metal sheet and the U-shaped metal sheet is aluminum.

3. The dual-frequency terahertz amplitude modulation unit of claim 1, wherein, The material of the medium layer is polyimide, high-resistance silicon or quartz.

4. The dual-frequency terahertz amplitude modulation unit of claim 1, wherein, The metal metasurface structure is located in the central region of the medium layer.

5. The dual-frequency terahertz amplitude modulation unit of claim 1, wherein, The opening direction of the U-shaped metal sheet is perpendicular to one side of the cross-shaped metal sheet.

6. The dual-frequency terahertz amplitude modulation unit of claim 1, wherein, The cross-sectional shape of the medium layer is polygonal, circular or elliptical.

7. The dual-frequency terahertz amplitude modulation unit of claim 1, wherein, The cross-sectional shape of the medium layer is square, and the size is 150μm×150μm; the thickness of the medium layer is 25μm, and the thickness of the metal metasurface structure is 0.2μm.

8. The dual-frequency terahertz amplitude modulation unit of claim 5, wherein, The size of the two mutually perpendicular metal strips of the cross-shaped metal sheet is the same, and the length of the metal strip is 100μm and the width is 5μm.

9. The dual-frequency terahertz amplitude modulation unit of claim 1, wherein, The thickness of the bottom of the U-shaped metal sheet is 10μm.

10. A dual frequency terahertz amplitude modulator characterized by, The double-frequency terahertz amplitude modulation unit comprises a plurality of double-frequency terahertz amplitude modulation units according to any one of claims 1-9, and the plurality of double-frequency terahertz amplitude modulation units are arranged in a periodic arrangement structure.

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