Electric control terahertz electromagnetic wave reconfigurable metasurface device based on graphene

Abstract

The invention relates to the field of terahertz technology and design and manufacturing of metasurface devices, in particular to a graphene-based electrically-controlled terahertz electromagnetic wave reconfigurable metasurface device which is configured in the mode that the conductivity of the reconfigurable metasurface device is controlled by adjusting the voltage applied to graphene in the reconfigurable metasurface device. The opening direction of the metal resonant ring on each unit cell in the reconfigurable metasurface device is actively controlled; and dynamically modulating the compensation phase of the incident light wave of the reconfigurable metasurface device to realize the dynamic regulation and control of the full phase of the reflected wave of the reconfigurable metasurface device. The conductivity and insulativity of graphene are controlled through voltage, the opening direction of the metal resonant ring is actively adjusted, and the compensation phase of incident light waves is dynamically modulated. Therefore, the metasurface can quickly carry out coding and function switching, the operation process is simplified, the production cost is reduced, the stability and reliability of equipment are improved, and the requirements of a high-performance photoelectric system and a communication technology are met.

Description

Technical Field

[0001] The present invention relates to the field of terahertz technology and the design and manufacture of metasurface devices, and in particular to a graphene-based electrically controlled terahertz electromagnetic wave reconfigurable metasurface device. Background Art

[0002] In recent years, terahertz (THz) technology has attracted widespread attention due to its wide application prospects in the fields of imaging, sensing and communication. In particular, metasurface technology, as an artificial two-dimensional material composed of subwavelength unit structures, has shown excellent application potential in various THz devices such as polarization converters, orbital angular momentum generators, absorbers, focusing lenses and filters. The performance of metasurfaces usually depends on their structural parameters. However, the performance of traditional THz metasurfaces is fixed after manufacturing, which limits their application in areas that require real-time control of wavefronts, such as active beam deflection and dynamic vortex beam generation.

[0003] With the advancement of materials science, the introduction of controllable materials has brought new possibilities to the design of metasurfaces. Researchers have tried to use materials such as vanadium oxide (VO2) and photosensitive silicon to develop dynamically adjustable metasurface structures by changing temperature or light conditions. Among many controllable materials, graphene has become an ideal candidate material for THz metasurfaces due to its ultra-thin, compact structure, low loss and electrical tunability. Based on the electrical tuning characteristics of graphene, THz functional devices with adjustable performance have been developed, such as adjustable focal length super lenses, adjustable efficiency focusing lenses and multi-frequency absorbers.

[0004] However, existing graphene-based metasurface designs still have limitations in achieving full phase coverage and multifunctional switching. In particular, the limited tuning range of graphene's Fermi level makes it difficult to achieve full 360-degree coverage of the phase, which poses a challenge to full wavefront compensation. Summary of the invention

[0005] The embodiment of the present invention provides a graphene-based electrically controlled terahertz electromagnetic wave reconfigurable metasurface device to significantly improve the application flexibility of the metasurface.

[0006] According to an embodiment of the present invention, a graphene-based electrically controlled terahertz electromagnetic wave reconfigurable metasurface device is provided, and the reconfigurable metasurface device is configured as follows:

[0007] By adjusting the voltage applied to graphene in the reconfigurable metasurface device to control its conductivity, the opening direction of the metal resonant ring on each unit cell in the reconfigurable metasurface device is actively controlled;

[0008] Dynamically modulate the compensation phase of the incident light wave of the reconfigurable metasurface device to achieve dynamic control of the full phase of the reflected wave of the reconfigurable metasurface device.

[0009] Furthermore, the reconfigurable metasurface device is composed of periodically arranged unit structures, each unit structure is the same; each unit structure is composed of three layers: a top structural layer, a middle polyimide layer, and a bottom metal plate.

[0010] Furthermore, the top structural layer includes a bimetallic resonant ring and a graphene component embedded in the bimetallic resonant ring; the bimetallic resonant ring is placed concentrically, and four pairs of graphene components are correspondingly distributed at azimuth positions of 0°, 45°, 90° and 135° of the bimetallic resonant ring, where 0° is the positive direction of the x-axis; each pair of graphene components has a suitable opening angle.

[0011] Furthermore, the Fermi level of the graphene component is adjusted by a voltage signal generated by the FPGA controller, thereby controlling its conductivity; each pair of graphene components is connected to the positive and negative poles of the same electrode, and the electrodes are controlled by the FPGA integrated circuit; the high voltage makes the graphene component exhibit strong conductivity and present a metallic state; when there is no voltage, the graphene component is in an insulating state, causing the bimetallic resonant ring to lose conductivity in this area and form an opening.

[0012] Furthermore, at the control end, the FPGA controller generates a "1" or "0" signal, and generates a corresponding high voltage or zero voltage through a circuit amplifier to control the on or off of each pair of graphene components.

[0013] Furthermore, there are four pairs of graphene components on the bimetallic resonant ring, three pairs of which are controlled to be in a metallic conductive state, and the other pair is in an insulating state, forming an open resonant ring; the conductivity of the graphene components at different positions is controlled by voltage, and the opening direction and size of the bimetallic resonant ring are dynamically adjusted, thereby changing the phase compensation of the incident wave.

[0014] Furthermore, each unit structure corresponds to a four-bit code, and the code is quickly changed according to functional requirements to control the phase to be compensated for each unit structure on the reconfigurable metasurface device.

[0015] Furthermore, for the four pairs of graphene building blocks on the same unit structure, a 4-bit code is assigned, representing their respective positions from right to left.

[0016] Furthermore, only one pair of graphene components in the unit structure is in an insulating state, causing the bimetallic resonant ring at that position to be disconnected. At this time, the state of the graphene component is marked as "1", while the other three pairs of graphene components remain in a metallic state, marked as "0"; the unit structure can autonomously switch between four configurations.

[0017] Furthermore, when the graphene components located at 0°, 45°, 90° and 135° on the bimetallic resonant ring are in an insulating state respectively, phase compensations of 0°, 90°, 180° and 270° are introduced for the reflected waves respectively.

[0018] The graphene-based electrically controlled terahertz electromagnetic wave reconfigurable metasurface device in the embodiment of the present invention controls the conductivity and insulation of graphene by voltage, and the present invention actively adjusts the opening direction of the metal resonant ring to dynamically modulate the compensation phase of the incident light wave. This enables the metasurface to quickly perform encoding and function switching, simplifies the operation process, reduces production costs, and improves the stability and reliability of the device to meet the needs of high-performance optoelectronic systems and communication technologies. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of this application. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0020] Figure 1 A schematic diagram of a supersurface of a graphene-based electrically controlled terahertz electromagnetic wave reconfigurable supersurface device of the present invention;

[0021] Figure 2 A layered structure diagram of a supersurface unit cell of a graphene-based electrically controlled terahertz electromagnetic wave reconfigurable supersurface device of the present invention;

[0022] Figure 3 A top view of a unit cell of a graphene-based electrically controlled terahertz electromagnetic wave reconfigurable metasurface device of the present invention;

[0023] Figure 4 Four coding forms of the supersurface unit structure of the electrically controlled terahertz electromagnetic wave reconfigurable supersurface device based on graphene of the present invention;

[0024] FIG5( a ) is a reflection amplitude diagram of unit cells of different coding sequences of the graphene-based electrically controlled terahertz electromagnetic wave reconfigurable metasurface device of the present invention;

[0025] FIG5( b ) is a reflection phase diagram of unit cells of different coding sequences of the graphene-based electrically controlled terahertz electromagnetic wave reconfigurable metasurface device of the present invention;

[0026] FIG6( a ) is a diagram of a supersurface coding sequence of a graphene-based electrically controlled terahertz electromagnetic wave reconfigurable supersurface device according to the present invention;

[0027] FIG6( b ) is a diagram showing the variation of the normalized electric field intensity of the graphene-based electrically controlled terahertz electromagnetic wave reconfigurable metasurface device with the deflection angle;

[0028] FIG6( c ) is a three-dimensional far-field diagram of the deflected light beam of the graphene-based electrically controlled terahertz electromagnetic wave reconfigurable metasurface device of the present invention;

[0029] FIG. 7( a ) is a vector superposition diagram of the metasurface coding sequence of the electrically controlled terahertz electromagnetic wave reconfigurable metasurface device based on graphene according to the present invention;

[0030] FIG7( b ) is a schematic diagram of bidirectional deflection of reflected waves of the graphene-based electrically controlled terahertz electromagnetic wave reconfigurable metasurface device of the present invention;

[0031] FIG7( c ) is a diagram showing the variation of the electric field intensity of the graphene-based electrically controlled terahertz electromagnetic wave reconfigurable metasurface device with angle;

[0032] FIG8( a ) is a diagram showing the coding mode of the superlens of the graphene-based electrically controlled terahertz electromagnetic wave reconfigurable metasurface device of the present invention;

[0033] FIG8( b ) is a near-field distribution diagram in the xy and xz planes of the graphene-based electrically controlled terahertz electromagnetic wave reconfigurable metasurface device of the present invention;

[0034] FIG8( c ) is a diagram showing the electric field variation along the x and z dimensions of the graphene-based electrically controlled terahertz electromagnetic wave reconfigurable metasurface device of the present invention;

[0035] FIG9( a ) is a diagram showing a combined coding mode of a rotating lens of a graphene-based electrically controlled terahertz electromagnetic wave reconfigurable metasurface device according to the present invention;

[0036] FIG9( b ) is a near-field distribution diagram in the xy and xz planes of the graphene-based electrically controlled terahertz electromagnetic wave reconfigurable metasurface device of the present invention;

[0037] FIG9( c ) is a diagram showing the electric field variation along the xyz dimension of the graphene-based electrically controlled terahertz electromagnetic wave reconfigurable metasurface device of the present invention;

[0038] FIG10( a ) is a coding mode diagram of a first-order vortex beam generator of a graphene-based electrically controlled terahertz electromagnetic wave reconfigurable metasurface device according to the present invention;

[0039] FIG10( b ) is a normalized electric field intensity distribution diagram of the graphene-based electrically controlled terahertz electromagnetic wave reconfigurable metasurface device according to the present invention as the deflection angle changes;

[0040] FIG10( c ) is a diagram showing the intensity distribution and phase distribution of the graphene-based electrically controlled terahertz electromagnetic wave reconfigurable metasurface device of the present invention;

[0041] Fig.11 These are the models and characteristic diagrams of the second-order (left) and fourth-order (right) vortex beam generators of the graphene-based electrically controlled terahertz electromagnetic wave reconfigurable metasurface device of the present invention. DETAILED DESCRIPTION

[0042] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0043] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0044] The present invention relates to a metasurface device that utilizes the adjustable electrical properties of graphene to achieve dynamic modulation of the polarization, phase and wavefront of terahertz electromagnetic waves by means of electrical control. The present invention aims to address the limitations of existing terahertz metasurface technologies in terms of dynamic control functions, phase coverage integrity and operational complexity. Although existing metasurface technologies can achieve a certain degree of wavefront control, they are usually static and have significant limitations in achieving full phase control and rapid function conversion:

[0045] Limitations of dynamic control: Most existing terahertz metasurfaces are statically designed, that is, once manufactured, their functions and performance parameters are fixed and cannot adapt to changing application requirements, such as real-time adjustment of beam deflection, dynamic focusing or waveform modulation.

[0046] Limited phase compensation range: Although existing graphene-based metasurfaces provide some electrical control capabilities, their versatility and phase coverage and versatility are still limited. In particular, it is difficult to achieve full 360-degree dynamic adjustment of the phase, which limits its application in full wavefront compensation and complex waveform generation.

[0047] Complexity of operation and manufacturing: In the prior art, the method of full phase coverage based on geometric phase theory usually requires manual or other relatively passive methods to adjust the structure of each unit, which increases the complexity of operation, manufacturing, and cost, while reducing the reliability and stability of the equipment.

[0048] In order to solve the technical defects of the prior art, the present invention proposes a metasurface composed of a composite structure of graphene and a bimetallic resonant ring. By controlling the conductivity and insulation of graphene by voltage, the opening direction of the metal resonant ring can be actively and dynamically adjusted, thereby realizing the encoding of the unit structure. This design does not require manual changes in the shape, size or direction of the unit, and can achieve full phase 2π compensation of the light wavefront, meet multifunctional requirements, and significantly improve the application flexibility of the metasurface.

[0049] Therefore, the purpose of the present invention is to provide a graphene-based electrically controlled terahertz electromagnetic wave reconfigurable metasurface device with a simple structure, dynamically adjustable functions, and full phase control. By controlling the conductivity and insulation of graphene by voltage, the present invention actively adjusts the opening direction of the metal resonant ring and dynamically modulates the compensation phase of the incident light wave. This enables the metasurface to quickly perform encoding and function switching, simplify the operation process, reduce production costs, and improve the stability and reliability of the equipment to meet the needs of high-performance optoelectronic systems and communication technologies.

[0050] The present invention proposes a graphene-based electrically controlled terahertz electromagnetic wave reconfigurable metasurface device, the core principle of which is to utilize the electrically controlled characteristics of graphene to control its conductivity by adjusting the voltage applied to graphene, thereby actively and flexibly controlling the opening direction of the metal resonant ring on each unit cell. This design enables the metasurface to achieve dynamic regulation of the full phase of the reflected wave to meet various functional requirements. The following describes its specific implementation in detail:

[0051] (1) Metasurface structure composition

[0052] like Figure 1 As shown in FIG. 1 , the terahertz metasurface designed by the present invention is composed of periodically arranged unit structures, each unit structure is the same. Each unit structure is composed of three layers: a top structural layer, a middle polyimide layer, and a bottom metal plate, such as Figure 2 As shown, the thickness of the top structural layer and the bottom metal plate are both 0.2 μm, the thickness of the middle polyimide layer is 30 μm, and the side length is 100 μm×100 μm.

[0053] In particular, the top structural layer includes a bimetallic resonant ring and a graphene component embedded in the ring. The bimetallic resonant ring is placed concentrically, and four pairs of graphenes are correspondingly distributed at azimuth positions of 0°, 45°, 90° and 135° of the bimetallic resonant ring (0° is the positive direction of the x-axis). Each pair of graphene components has a suitable opening angle, such as 15°.

[0054] Specifically, the structural layer includes concentric bimetallic resonant rings and four pairs of graphene components embedded therein. The inner and outer ring sizes of the bimetallic resonant rings are ri=23.25μm and ro=30μm (inner ring), Ri=35.75μm and Ro=42μm (outer ring), respectively. The graphene components are distributed at positions of 0°, 45°, 90° and 135° around the resonant ring (the x-axis direction is defined as 0°). Each pair of graphene components has an opening angle of 15°, such as Figure 3 shown.

[0055] (2) Electrically controlled graphene modulation

[0056] The Fermi level of the graphene component is adjusted by a voltage signal generated by the FPGA controller, thereby controlling its conductivity. Each pair of graphene is connected to the positive and negative poles of the same electrode, which is controlled by the FPGA integrated circuit. The high voltage makes the graphene exhibit strong conductivity and present a metallic state. When there is no voltage, the graphene is in an insulating state, causing the metal resonant ring to lose conductivity in this area and form an opening. This electrical control method allows precise control of the graphene component of each unit cell, achieving dynamic adjustment and rapid function switching.

[0057] Specifically, the Fermi level of graphene is adjusted by electrical control, thereby affecting its conductivity. The four pairs of graphene components in each unit are connected to independent electrodes, such as Figure 3 As shown. At the control end, the FPGA generates a "1" or "0" signal, which generates a corresponding high voltage or zero voltage through the circuit amplifier to achieve the on or off control of each pair of graphene components. When a high voltage (such as 25V) is applied, the graphene exhibits strong metallic conductivity; in the absence of voltage, the graphene is in an insulating state, causing the metal resonant ring to lose conductivity in this area and form an opening.

[0058] It should be noted that each unit cell requires four parallel circuits for control. In the metasurface functional demonstration, 729 (27×27) unit cells need to be controlled, so a total of 2916 (729×4) independent switches need to be controlled. Therefore, the FPGA on the control side should choose a model with sufficient I / O ports and logic units, such as Xilinx's Artix-7 series or the higher-end Virtex series to meet the control requirements.

[0059] (3) Phase modulation principle

[0060] There are four pairs of graphene on the metal resonant ring, three of which are controlled to be in a metallic conductive state, and the other pair is in an insulating state, thus forming an open resonant ring. By controlling the conductivity of graphene at different positions through voltage, the opening direction and size of the resonant ring can be dynamically adjusted, thereby changing the phase compensation of the incident wave. This phase modulation theory can be explained by the following geometric phase theory.

[0061] When a plane wave is incident vertically on the metasurface, the complex reflection coefficient of circularly polarized light can be expressed by the transfer matrix RCP:

[0062]

[0063] Where rij is the polarization reflection coefficient, the first subscript is the incident polarization, and the second subscript is the reflected polarization. When the insulating position of graphene changes, it is similar to rotating the unit structure around the z-axis. Assuming a counterclockwise rotation of an angle θ, the transfer matrix becomes:

[0064]

[0065] In the above formula, is the rotation matrix. Define the electric field of left-handed polarized light wave After incident on the metasurface, the reflected electric field can be described as:

[0066]

[0067] In the above formula, the second term on the right side has a phase factor 2θ, which is the cross-polarization component, while the first term lacks this component. Therefore, based on the principle of geometric phase, the metasurface unit can convert the incident circularly polarized wave into a cross-polarized wave and achieve a 2-fold compensation for the reflected phase by rotating the unit structure.

[0068] In summary, the phase angle of unit cell compensation is equal to the opening azimuth, that is, twice the azimuth of the graphene pair in an insulating state. Specifically, the azimuth of the graphene pair determines the phase angle of compensation. In this implementation case, the four pairs of graphene are located at 0°, 45°, 90° and 135°, respectively, so the achievable phase compensation can be 0°, 90°, 180° and 270°. Therefore, the design of the present invention can cover 360° phase requirements.

[0069] (4) Metasurface unit encoding and phase modulation

[0070] Each unit cell corresponds to a four-bit code. According to functional requirements, the code is changed rapidly to control the phase to be compensated for each unit cell on the metasurface.

[0071] For the four pairs of graphene on the same unit cell, the present invention assigns a 4-bit code, representing their respective positions from right to left. In actual application, only one pair of graphene on the unit structure is in an insulating state, causing the metal resonant ring at that position to be disconnected. This graphene state is marked as "1", while the other three pairs of graphene remain in a metallic state, marked as "0". This design enables the unit to autonomously switch between four configurations, marked as "1000", "0100", "0010" and "0001" respectively.

[0072] Specifically, according to the geometric phase theory, when the graphene at the positions of 0°, 45°, 90° and 135° on the resonant ring is in an insulating state in turn, phase compensation of 0°, 90°, 180° and 270° can be introduced for the reflected wave respectively. In order to simplify the operation, the present invention assigns a 4-bit code to the four pairs of graphene, which represents the different positions of the graphene from right to left. In practical applications, only one pair of graphene is in an insulating state on each unit structure, thereby disconnecting the metal resonant ring at this position. The present invention uses "1" to mark this graphene state, while the other three pairs of graphene remain in a conductive state and are marked with "0". This allows each unit to switch between four configurations, and the corresponding codes are "1000", "0100", "0010" and "0001".

[0073] Figure 4 The schematic diagrams of these four configurations and their corresponding codes are shown. In actual operation, in order to realize the specific functions required by the metasurface, the present invention designs a corresponding four-bit coding sequence for each unit cell and converts these sequences into FPGA control codes. Through FPGA, the present invention can accurately set these coding sequences, and then accurately control each unit cell to produce the required phase compensation, thereby ensuring that the metasurface achieves the expected functional characteristics.

[0074] (5) Functional verification and simulation analysis

[0075] CST Microwave Studio is used to design and simulate the metasurface unit. By setting different boundary conditions and electromagnetic parameters, the performance of the metasurface is simulated to ensure that the design can achieve the expected effect in practical applications.

[0076] Through the above technical means, the present invention not only solves the limitations of existing metasurface technology in terms of dynamic regulation, phase coverage and operational complexity, but also greatly improves the application flexibility and practicality of metasurface technology. This graphene-based metasurface device is expected to play a key role in high-performance optoelectronic systems and advanced communication technologies.

[0077] Specifically, in the implementation process of the present invention, CST Microwave Studio 2018 was used to simulate the metasurface unit. The x and y directions were defined as periodic boundary conditions to simulate the repeated unit planes. The z direction was set as an open boundary to simulate the propagation of right-handed circularly polarized light. The metal structure was modeled using copper with a conductivity of 5.8×10^7S / m and a thickness of 0.2μm. The intermediate dielectric layer was defined as a polyimide material with a dielectric constant of 3.5 and a loss tangent of 0.0027. .

[0078] (a) Analysis of unit cell reflection performance

[0079] Figure 5 shows the changes in reflection amplitude and phase of unit cells of four different coding structures at different incident light frequencies. As shown in Figure 5(a), in the frequency ranges of 1.47 to 1.51 THz and 1.53 to 1.59 THz, the reflection amplitude of the light wave remains above 0.7, indicating that the proposed composite metasurface exhibits excellent polarization conversion efficiency in these frequency ranges. Figure 5(b) shows the relationship between reflection phase and frequency under different coding sequences. The figure shows that the phase of the same coding unit is roughly linearly related to the frequency, and at any frequency, the phases of the four different coding units differ by 90° in sequence, ensuring that a phase range of 360° can be covered when used in combination.

[0080] Therefore, the metasurface designed in the present invention has excellent reflection properties in the frequency ranges of 1.47-1.51 THz and 1.53-1.59 THz, which ensure the effective manipulation of the light wavefront and the realization of the metasurface functions.

[0081] In the subsequent functional simulation analysis of beam deflection, lens focusing and vortex beam generation, the present invention will use a metasurface composed of 27×27 unit cells for testing.

[0082] (b) Metasurface performance 1: beam deflection

[0083] The unit cells are arranged in sequence along the x-axis according to the coding sequence 0001, 0001, 0010, 0010, 0100, 0100, 1000 and 1000, with every 8 units forming a period, thus generating phase gradients of 0°, 90°, 180° and 270° in the x-direction, effectively changing the propagation direction of the electromagnetic wave. Figure 6(a) shows the distribution of the metasurface units, and the different compensation phases are marked by colors - green, light green, yellow and orange corresponding to the codes 0001, 0010, 0100 and 1000, respectively. It should be noted that the correspondence between the color of the cell and the coding sequence remains consistent throughout the document, but for the sake of simplicity, this relationship will no longer be shown in subsequent charts.

[0084] According to the generalized Snell's law, the theoretical angle of beam deflection is:

[0085]

[0086] In the above formula, p represents the size of the unit structure period, which is 100 microns in the present invention, and λ represents the wavelength of the incident wave. The incident wave of the present invention is 1.5TH of the above working frequency band, so the emitted light will be deflected by about 14°.

[0087] The simulation results are shown in Figure 6(b) and Figure 6(c). Figure 6(b) shows the normalized electric field intensity distribution under the deflection angle, while Figure 6(c) shows the far-field effect of the deflected beam. The results in Figure 6 show that the reflected wave is deflected by 14° when interacting with the metasurface, which is consistent with theoretical predictions.

[0088] According to the superposition principle, two coding modes with different functions are combined in a composite form to obtain a combined coding mode, which has two functions at the same time and does not interfere or couple with each other. Here, the present invention vector-adds the coding mode (0001, 0010, 0100 and 1000) shown in Figure 7 (a) and its reverse coding mode (1000, 0100, 0010 and 0001). The coding mode of each unit on the merged metasurface is shown in Figure 7 (a). This metasurface can deflect the incident right-handed electromagnetic wave to the left and right sides at the same time, as shown in Figure 7 (b). Figure 7 (c) shows the distribution of electric field intensity as the angle changes. The results show that the metasurface divides the reflected wave into two beams, which are deflected 14° to the left and right, respectively, which is consistent with theoretical predictions.

[0089] (c) Metasurface performance 2: Lens function

[0090] By reconstructing the coding sequence of each unit cell of the metasurface, an appropriate phase gradient can be introduced to convert the incident plane wave into a parabolic wave and converge at the focus. The phase compensation of each unit cell is given by the following formula:

[0091]

[0092] Wherein, x and y represent the coordinates of the metasurface unit cell in the xy plane, the center of the metasurface is located at the origin of the coordinates, and f is the preset focal length. In the present invention, the focal length of the lens is set to 1.8 mm, and the above formula can be used to calculate the phase compensation required for each unit structure. The unit coding corresponding to the phase compensation is shown in Figure 8(a). Figures 8(b) and 8(c) respectively depict the electric field distribution in the xy plane and the xz plane, as well as the intensity distribution in the x and z dimensions.

[0093] In the z direction, the maximum value of the electric field appears at a distance of about 1.6 mm from the focus. The simulation results show that by reconstructing the unit structure, the proposed metasurface can realize the function of a focusing lens, which has important application potential for highly integrated optoelectronic systems.

[0094] In addition, by using the Fourier superposition principle, the focus of the lens in the xy plane can be deflected by pre-designing the coding sequence of the metasurface. As shown in Figure 9(a), a coding sequence is applied to deflect the light beam to the left in the x direction, and this phase gradient sequence is superimposed on the initial coding of the lens, thereby reconstructing the metasurface unit structure and realizing the function of adjusting the focal position along the x axis. Figure 9(b) shows the near-field diagram of the deflected lens in the xy and xz planes, while Figure 9(c) depicts the electric field changes in the xyz dimension. The results show that the focal point has moved from 1350 microns at the center position to 822 microns on the x axis. In addition, due to this deflection, the focal position in the z direction is also adjusted from about 1600 mm (as shown in Figure 6(c)) to about 1500 mm.

[0095] (d) Metasurface performance 3: vortex beam

[0096] By designing a specific phase sequence on the metasurface, a compensation phase is provided for the incident wave, thereby generating a vortex beam. The compensation phase can be expressed as:

[0097]

[0098] Here, m represents the topological charge.

[0099] In this case, a vortex beam generator with a topological charge of m = 1 is first designed. The metasurface is divided into four regions along the diagonal, and the cells in each region have the same encoding, thereby compensating the same phase. The phase difference between adjacent regions is 90°, which enables the four regions to achieve a phase coverage of 2π. Figure 10(a) shows the distribution of cell encoding on the metasurface plane, Figure 10(b) describes the change of the electric field with the deflection angle, and Figure 10(c) shows the three-dimensional far-field effect. As shown in the figure, the phase of the reflected wave carries orbital angular momentum and rotates around the z-axis. The electric field intensity is in the shape of a "donut" with zero intensity at the center, representing the characteristic singularity of the vortex beam.

[0100] In addition, the present invention adopts a similar method to design second-order (m=2) and fourth-order (m=4) vortex beam generators, such as Fig.11 As shown in the figure. By reconfiguring the unit structure of the metasurface, the m×4 regions are realigned on the hyperplane with the corresponding coding sequences, ensuring that the phase coverage of m×2π is completed around the center. This progress promotes the generation of higher-order vortex beams, thereby enhancing the versatility and applicability of the metasurface platform in optical manipulation.

[0101] The graphene-based reconfigurable metasurface proposed in the present invention realizes flexible modulation of metasurface units through electrical control means, significantly simplifies the operation process, and at the same time has the capabilities of beam control, focusing, and generating a variety of vortex beams, and has broad application prospects.

[0102] Compared with the prior art, the graphene-based electrically controlled terahertz electromagnetic wave reconfigurable metasurface device of the present invention has the following significant beneficial effects:

[0103] 1. Enhanced dynamic control capabilities:

[0104] Existing terahertz metasurfaces are mostly static in design, and their functions and performance parameters cannot be changed once they are manufactured, which limits their adaptability to rapidly changing application requirements.

[0105] The present invention: By utilizing the electrical tuning properties of graphene, the present invention realizes real-time dynamic adjustment of metasurface performance, such as beam deflection, dynamic focusing or waveform modulation, thereby enhancing the adaptability and flexibility of applications.

[0106] 2. Full phase coverage and complex wavefront control:

[0107] Existing technology: Many existing metasurfaces are difficult to achieve full 360-degree phase control due to material and design limitations, which affects their application in complex wavefront control.

[0108] The present invention: The present invention realizes complete 0 to 360 degree phase control through the composite design of graphene and bimetallic resonant ring, and supports more complex wavefront modulation requirements, such as advanced beamforming and wavefront compensation.

[0109] 3. Operation simplification and cost reduction:

[0110] Existing technology: Traditional metasurfaces require physical adjustments to the unit structure to change their functions, which not only increases manufacturing complexity but also increases costs.

[0111] The present invention: The design of the present invention simplifies the manufacturing and operation process of the metasurface. All unit cells can be manufactured with the same structure, and rapid function switching can be achieved through simple voltage control, which significantly reduces production and maintenance costs.

[0112] 4. Improve system integration and reliability:

[0113] Existing technology: Existing metasurface systems have common stability and reliability issues due to their complex designs.

[0114] The present invention: The electrical control design of the present invention not only optimizes the structural stability of the metasurface, but also improves the reliability and stability of the overall system due to its simplified operation and maintenance requirements.

[0115] The above advantages enable the present invention to not only improve the performance of terahertz metasurface technology, but also broaden its application potential in multiple advanced technology fields such as communication, sensing, and imaging.

[0116] The key points / protection points of the present invention are:

[0117] 1. Design of electrically controlled graphene modulation: According to the principle of geometric phase, traditional phase compensation design usually requires manual or complex passive methods to rotate the resonant ring. By inlaying graphene at different positions on the metal resonant ring, the present invention uses the conductivity of electrically controlled graphene to dynamically adjust the opening direction of the resonant ring to achieve flexible phase regulation. When a specific compensation phase is required, it is only necessary to control the graphene at the corresponding position and control its conductivity by applying or not applying voltage to form the required opening. The flexibility of phase regulation is greatly improved.

[0118] 2. Unified structural design: All units adopt the same structure and size. This consistency simplifies the production and operation process. Functional changes can be achieved through different electronic control strategies, without the need to manually adjust each unit, which simplifies the production and operation process and improves the overall stability and reliability of the system.

[0119] 3. Full phase coverage: Four pairs of graphene are embedded in the metal resonant ring, located at 0°, 45°, 90° and 135° respectively, which can achieve phase compensation of 0°, 90°, 180° and 270°. This design covers the full phase requirements of 360°. In particular, the vibration ring is designed as a concentric double ring. At the same position, the graphene appears in pairs on the large ring and the small ring. When connecting the circuit, the graphene on the large ring and the small ring in this position respectively serve as the positive and negative poles of the electrode circuit. This ingenious design greatly facilitates circuit connection and improves the operability of the system.

[0120] 4. Design and control of coding: A high level is used to turn graphene on (marked as coding 1), while a low level or no voltage turns it off (marked as coding 0). Each unit has four graphene components, forming a 4-bit code (0001, 0010, 0100, 1000). In practical applications, according to the required phase compensation, the coding sequence is input into the FPGA controller, and the conductive state of graphene is controlled by high and low levels, thereby achieving precise control of the metasurface. The graphene state of each unit cell is controlled by four-bit coding, which realizes precise phase adjustment and function switching of the metasurface, improving the flexibility and efficiency of control.

[0121] 5. Use of FPGA controller: The FPGA controller is used to generate and adjust voltage signals to achieve precise control of graphene components, thereby achieving dynamic adjustment of the metasurface. This control method ensures that the function of the metasurface can be quickly adjusted and optimized according to actual needs.

[0122] Modifications, alternatives and other uses of the present invention

[0123] 1. Change the design (alternative solution)

[0124] (1) Material substitution: Graphene can be replaced by other materials with similar electrical control properties, such as vanadium oxide (VO2) and photosensitive silicon. These materials can adjust conductivity by changing temperature or light conditions, thereby achieving similar dynamic control effects, as long as they can provide the required conductive and insulating properties in the terahertz band.

[0125] (2) Control method replacement: In addition to voltage control, temperature control or light control can also achieve material conductivity regulation. For example, vanadium oxide will show a metal-insulator transition under temperature changes, and photosensitive silicon can change its conductivity under light changes. These control methods are also applicable to the modulation needs of terahertz waves.

[0126] (3) Coding extension: The current design uses four-bit coding (0°, 45°, 90°, 135°), and the corresponding phase compensation is 0°, 90°, 180°, and 270°. It can be expanded to 8-bit coding, covering 0°, 22.5°, 45°, 67.5°, 90°, 112.5°, 135°, 157.5°, and the corresponding compensation phase is 0°, 45°, 90°, 135°, 180°, 225°, 270°, and 315°, to achieve more detailed phase control and adapt to more complex terahertz wave applications.

[0127] (4) Size adjustment: The size of the unit cell can be adjusted according to the requirements of specific applications to optimize the performance of the metasurface and ensure its effectiveness and adaptability in the terahertz band.

[0128] 2. Other uses

[0129] (1) Dynamic terahertz lens: Applied to terahertz optical lenses with adjustable focal length to achieve adaptive focusing and image correction of terahertz light waves, thereby improving imaging quality and accuracy.

[0130] (2) Terahertz communication system: In terahertz wireless communication, the signal propagation and reception are optimized by dynamically adjusting the phase, thereby improving the system's flexibility and anti-interference ability.

[0131] (3) Terahertz sensor: used in high-sensitivity terahertz sensors to improve detection accuracy and response speed by adjusting the phase, and is applied to material testing and environmental monitoring.

[0132] (4) Terahertz imaging system: In a terahertz imaging system, dynamically adjusting the phase of light waves helps to enhance the contrast and clarity of the image and improve the performance of the imaging system.

[0133] The above alternatives and application scenarios demonstrate the wide applicability of the technology in the field of terahertz light waves, which can meet the needs of different applications while maintaining high performance and flexibility.

[0134] The serial numbers of the above embodiments of the present invention are only for description and do not represent the advantages or disadvantages of the embodiments.

[0135] In the above embodiments of the present invention, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0136] In the several embodiments provided in this application, it should be understood that the disclosed technical content can be implemented in other ways. Among them, the system embodiments described above are only schematic. For example, the division of units can be a logical function division. There may be other division methods in actual implementation. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of units or modules, which can be electrical or other forms.

[0137] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed over multiple units. Some or all of the units may be selected according to actual needs to achieve the purpose of the present embodiment.

[0138] In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0139] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product, and the computer software product is stored in a storage medium, including a number of instructions for a computer device (which can be a personal computer, a server or a network device, etc.) to perform all or part of the steps of the methods of each embodiment of the present invention. The aforementioned storage medium includes: U disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), mobile hard disk, magnetic disk or optical disk and other media that can store program codes.

[0140] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A graphene-based electrically controlled terahertz electromagnetic wave reconfigurable metasurface device, characterized in that: The reconfigurable metasurface device is configured as: By adjusting the voltage applied to the graphene in the reconfigurable metasurface device to control its conductivity, the opening direction of the metal resonant ring on each unit cell in the reconfigurable metasurface device is actively controlled; Dynamically modulate the compensation phase of the incident light wave of the reconfigurable metasurface device to achieve dynamic regulation of the full phase of the reflected wave of the reconfigurable metasurface device.

2. The graphene-based electrically controlled terahertz electromagnetic wave reconfigurable metasurface device according to claim 1, characterized in that: The reconfigurable metasurface device is composed of periodically arranged unit structures, each unit structure is the same; each unit structure is composed of three layers: a top structural layer, a middle polyimide layer and a bottom metal plate.

3. The graphene-based electrically controlled terahertz electromagnetic wave reconfigurable metasurface device according to claim 2, characterized in that: The top structural layer includes a bimetallic resonant ring and a graphene component embedded in the bimetallic resonant ring; the bimetallic resonant ring is placed concentrically, and four pairs of graphene components are correspondingly distributed at azimuth positions of 0°, 45°, 90° and 135° of the bimetallic resonant ring, where 0° is the positive direction of the x-axis; each pair of graphene components has a suitable opening angle.

4. The graphene-based electrically controlled terahertz electromagnetic wave reconfigurable metasurface device according to claim 3, characterized in that: The Fermi level of the graphene component is adjusted by the voltage signal generated by the FPGA controller, thereby controlling its conductivity; each pair of graphene components is connected to the positive and negative poles of the same electrode, and the electrodes are controlled by the FPGA integrated circuit; the high voltage makes the graphene component exhibit strong conductivity and present a metallic state; when there is no voltage, the graphene component is in an insulating state, causing the bimetallic resonant ring to lose conductivity in this area and form an opening.

5. The graphene-based electrically controlled terahertz electromagnetic wave reconfigurable metasurface device according to claim 4, characterized in that: On the control side, the FPGA controller generates a "1" or "0" signal, which generates a corresponding high voltage or zero voltage through the circuit amplifier to control the on or off of each pair of graphene components.

6. The graphene-based electrically controlled terahertz electromagnetic wave reconfigurable metasurface device according to claim 2, characterized in that: There are four pairs of graphene components on the bimetallic resonant ring, three of which are controlled to be in a metallic conductive state, and the other pair is in an insulating state, forming an open resonant ring; the conductivity of the graphene components at different positions is controlled by voltage, and the opening direction and size of the bimetallic resonant ring are dynamically adjusted, thereby changing the phase compensation of the incident wave.

7. The graphene-based electrically controlled terahertz electromagnetic wave reconfigurable metasurface device according to claim 2, characterized in that: Each unit structure corresponds to a four-bit code. According to functional requirements, the code is quickly changed to control the phase to be compensated for each unit structure on the reconfigurable metasurface device.

8. The graphene-based electrically controlled terahertz electromagnetic wave reconfigurable metasurface device according to claim 7, characterized in that: For the four pairs of graphene building blocks on the same unit structure, a 4-bit code is assigned, representing their respective positions from right to left.

9. The graphene-based electrically controlled terahertz electromagnetic wave reconfigurable metasurface device according to claim 8, characterized in that: Only one pair of graphene components in the unit structure is in an insulating state, causing the bimetallic resonant ring at that position to be disconnected. At this time, the state of the graphene component is marked as "1", while the other three pairs of graphene components remain in a metallic state, marked as "0"; the unit structure can autonomously switch between four configurations.

10. The graphene-based electrically controlled terahertz electromagnetic wave reconfigurable metasurface device according to claim 9, characterized in that: When the graphene components located at 0°, 45°, 90° and 135° on the bimetallic resonant ring are in an insulating state respectively, phase compensations of 0°, 90°, 180° and 270° are introduced for the reflected waves respectively.

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