A coding metasurface and terahertz beam modulation and signal processing device

Abstract

This invention provides a coded metasurface and a terahertz beam modulation and signal processing device, comprising at least one metasurface structural unit, wherein each metasurface structural unit includes a silicon pillar, a polytetrafluoroethylene (PTFE) layer, and a vanadium dioxide layer from top to bottom. The silicon pillar includes two cross arms orthogonally arranged along the central axis of the PTFE layer. The endpoints of the cross arms on the upper and lower sides are connected to each other through extension arms. The sides of the cross arms on the left and right sides are provided with surrounding arms at intervals, and a rectangular hollow area is opened at the intersection of the two cross arms, realizing four phase states of 0°, 90°, 180°, and 270°. In addition, by combining the correlation between the coded pattern and the far-field radiation pattern under Fourier transform, signal processing is directly completed in the terahertz frequency band through dynamic convolution operation. Furthermore, a 2-bit coded metasurface is constructed to generate an OAM beam, further improving the detail capture capability during the imaging process.

Description

Technical Field

[0001] This invention relates to the field of terahertz communication and metasurface technology, and particularly to an coded metasurface and a terahertz beam modulation and signal processing device, which can be widely used in terahertz high-speed communication, high-resolution imaging, radar stealth, quantum information processing and other fields to realize dynamic switching of terahertz beams, convolution operation and orbital angular momentum (OAM) modulation, and solve the core bottlenecks of existing devices in dynamic control, functional integration and space utilization. Background Technology

[0002] Terahertz imaging, with its unique advantages of "penetrating non-metallic materials" and "non-ionizing radiation," has shown irreplaceable application value in key scenarios such as security inspection and contraband detection. However, it has long been hampered by technical bottlenecks such as low resolution and poor real-time performance, which has become the core obstacle restricting its commercialization.

[0003] Specifically, in security inspection scenarios, airports, train stations, and other venues have an increasingly urgent need for rapid and accurate identification of dangerous goods. Terahertz waves can penetrate materials such as clothing and plastics, and should be able to effectively detect contraband such as small knives and explosive residues. However, due to technical bottlenecks such as insufficient beam control capabilities and low imaging resolution, it is difficult to capture the details of dangerous goods. The core problem of this detection challenge stems from the significant defects of traditional beam control schemes: First, mechanical control relies on mechanical structures to adjust the beam direction, which is not only slow in response speed but also difficult to achieve integrated design, failing to meet the needs of real-time dynamic control; second, although phased array systems can achieve beam scanning, they are complex in structure, expensive, and face technical bottlenecks such as high component losses and low integration in the terahertz band; third, once traditional analog metasurfaces are fabricated, their topology remains fixed, and they can only achieve a single or a few specific electromagnetic functions, unable to dynamically adjust functions according to the actual scenario.

[0004] In other words, from the overall perspective of terahertz sensor research, there are currently three key technical problems that urgently need to be solved:

[0005] 1. Lack of dynamic control capabilities, unable to meet real-time requirements of scenarios: On the one hand, mechanical control solutions have slow response speeds and are difficult to integrate, making it impossible to adjust the beam in real time according to dynamic situations such as baggage movement and changes in the position of prohibited items in security inspection scenarios, making it difficult to quickly capture details of prohibited items; on the other hand, the topology of traditional analog metasurfaces is fixed after preparation, and it cannot switch transmission / reflection modes according to changes in detection angle and target position; in addition, most existing digitally coded metasurfaces are static designs, lacking efficient dynamic control methods, which cannot meet the needs of security inspection for real-time and accurate detection of dangerous items, further exacerbating the problem of poor imaging real-time performance.

[0006] 2. Low functional integration: Existing terahertz metasurface devices mostly focus on a single function and cannot achieve the collaborative integration of multiple core functions. They are difficult to simultaneously achieve multi-functional integration such as dynamic beam switching, convolution operation, and OAM modulation, and cannot meet the integrated requirements of complex systems.

[0007] 3. Single function and low space utilization: Traditional metasurfaces are mostly single reflective or transmissive structures. Reflective types cannot control electromagnetic waves in the space opposite the source, while transmissive types can cover the space on both sides of the source, but their functions are completely fixed after fabrication and cannot be dynamically adjusted according to the scenario.

[0008] To address the aforementioned technical bottlenecks, the emergence of digitally coded metasurfaces has provided a new direction for terahertz beam manipulation. By quantizing the electromagnetic response of metasurface units into digital codes such as "0" and "1", it enables flexible control of electromagnetic waves. However, existing digitally coded metasurfaces still lack efficient and non-contact dynamic control mechanisms. Especially in the terahertz band, how to achieve rapid beam switching and complete convolution operation design remains a key problem that urgently needs to be solved. Summary of the Invention

[0009] The purpose of this invention is to provide a coded metasurface and a terahertz beam modulation and signal processing device. By combining phase change material with a digital coded metasurface, dynamic and non-contact modulation of the terahertz beam is achieved using temperature control, while solving the problems of slow response, easy crosstalk, and limited functionality in the prior art.

[0010] To achieve the above objectives, this technical solution provides a terahertz coded metasurface for multi-phase modulation, comprising:

[0011] At least one metasurface structure unit, wherein each metasurface structure unit includes a silicon pillar, a polytetrafluoroethylene layer and a vanadium dioxide layer from top to bottom. The silicon pillar includes two cross arms orthogonally arranged along the central axis of the polytetrafluoroethylene layer. The endpoints of the cross arms on the upper and lower sides are connected to each other through extension arms. The sides of the cross arms on the left and right sides are provided with surrounding arms at intervals, and a rectangular hollow area is opened at the intersection of the two cross arms.

[0012] Secondly, this solution provides a terahertz beam modulation and signal processing device based on a coded metasurface, which is implemented using a terahertz coded metasurface to achieve multi-phase modulation, including:

[0013] Gradient coding sequences in the x-direction are formed by alternating metasurface structural units of different phases as basic units along the x-direction;

[0014] Gradient coding sequences in the L direction are formed by alternating metasurface structural units of different phases as basic units along the L direction;

[0015] Dynamic convolution is performed by superimposing gradient encoding sequences in the x-direction and gradient encoding sequences in the L-direction.

[0016] Thirdly, this solution provides a terahertz beam modulation and signal processing device based on a coded metasurface, which is based on a terahertz coded metasurface to achieve multi-phase modulation, including: setting four metasurface structural units with a phase difference of π / 2 in a spiral phase distribution manner.

[0017] Compared with existing technologies, this technical solution has the following characteristics and beneficial effects:

[0018] 1. Improve beam control precision and dimensionality: By using four phase coding units of “0”, “1”, “2”, and “3”, the limitation of traditional 1-bit coding with only 180° phase control is broken, realizing fine adjustment of terahertz beam phase, and the four-state reflection amplitude is maintained above 0.95, providing a stable electromagnetic response basis for complex beam shape design.

[0019] 2. Real-time convolution operation at the physical layer: Based on the Fourier transform principle, the encoded sequences are spatially superimposed, and the beam pattern convolution operation is directly completed in the terahertz band. This eliminates the need for the analog-to-digital conversion process of traditional digital signal processing, significantly reducing signal delay and providing a hardware-level computing platform for high-speed photonic computing.

[0020] 3. Expanding the lossless scanning range in half-space: By dynamically adjusting the period of the coding sequence, the deflection angle of the reflected beam can be precisely controlled (e.g., the 01230123 sequence achieves a deflection of ~2°, and the 00-1122-33 sequence achieves a deflection of ~4.4°). Combined with convolution operations, multi-beam scanning in any direction in half-space can be achieved, solving the loss and speed bottlenecks of traditional mechanical scanning and improving the coverage capability of communication and imaging systems.

[0021] 4. Supports multi-functional dynamic reuse: The same metasurface can be reconstructed through coding sequences to achieve multiple scene function switching such as beam deflection, vortex beam generation (l=±1) mode purity exceeding 60%. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the unit structure and surface pattern of the coded metasurface of the present invention.

[0023] Figure 2 These are the electromagnetic response curves of different units of the coded metasurface in reflection mode, as presented in this invention.

[0024] Figure 3 These are the electromagnetic response curves of different units of the coded metasurface in transmission mode, as presented in this invention.

[0025] Figure 4This invention provides two sets of 1-bit encoded three-dimensional images of the coded metasurface in a reflective state at 1.0 THz, including two sets of two-beam and four-beam three-dimensional images.

[0026] Figure 5 This invention provides two sets of 1-bit encoded three-dimensional images of the encoded metasurface in a transmission state at 1.1 THz, including two sets of two-beam and four-beam coded images.

[0027] Figure 6 This is a three-dimensional far-field map of the encoding sequences of "segmented gradient" and "continuous gradient" of the encoded metasurface in the reflection state at 1.0 THz according to the present invention.

[0028] Figure 7 This is a three-dimensional far-field map of the encoding sequences of "segmented gradient" and "continuous gradient" of the encoded metasurface in the transmission state at 1.1 THz, according to the present invention.

[0029] Figure 8 The present invention enables the superposition of encoded sequences through dynamic convolution operations using encoded metasurfaces.

[0030] Figure 9 This invention provides a three-dimensional far-field map of the dynamic convolution operation of the encoded metasurface in a reflective state at 1.0 THz.

[0031] Figure 10 This is a three-dimensional far-field map of the encoded metasurface under dynamic convolution operation at 1.1 THz in the transmission state, as described in this invention.

[0032] Figure 11 This invention provides a phase distribution diagram and surface schematic of a vortex wave metasurface with topological charge l = +1 at 1.0 THz.

[0033] Figure 12 This invention provides the simulated beam image and electric field phase distribution of a vortex wave metasurface at 1.0 THz. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0035] Those skilled in the art should understand that, in the disclosure of this invention, the terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the above terms should not be construed as limiting this invention.

[0036] Example 1

[0037] This scheme addresses the issues of low resolution and poor real-time performance in terahertz imaging by altering the properties of vanadium dioxide through temperature control, thereby achieving ultra-fast dynamic switching of the terahertz beam and enabling dynamic switching between transmission and reflection functions. Simultaneously, 1-bit and 2-bit coding units are designed. The 1-bit coding unit uses two different structural units to achieve specific phase modulation to support basic beam switching, while the 2-bit coding unit expands to four different structural units to achieve finer phase modulation, thus supporting precise multi-directional beam deflection. Furthermore, by combining the correlation between the coded pattern and the far-field radiation pattern under Fourier transform, dynamic convolution operations are performed through a 2-bit coded metasurface, directly completing signal processing in the terahertz band. In addition, a 2-bit coded metasurface is constructed to generate an OAM beam, further enhancing the detail capture capability during the imaging process.

[0038] Specifically, such as Figure 1 As shown, this scheme provides a terahertz coded metasurface for realizing multi-phase modulation, comprising:

[0039] At least one metasurface structure unit, wherein each metasurface structure unit includes a silicon pillar, a polytetrafluoroethylene layer and a vanadium dioxide layer from top to bottom. The silicon pillar includes two cross arms orthogonally arranged along the central axis of the polytetrafluoroethylene layer. The endpoints of the cross arms on the upper and lower sides are connected to each other through extension arms. The sides of the cross arms on the left and right sides are provided with surrounding arms at intervals, and a rectangular hollow area is opened at the intersection of the two cross arms.

[0040] The silicon pillars of the terahertz coded metasurface provided by this solution are cross-symmetrical and have extension characteristics. By adjusting the length of the cross arms, four phase states of 0°, 90°, 180°, and 270° can be achieved, thereby realizing the 2-bit encoding requirement. Compared with 1-bit encoding (only 2 phase states), the degree of freedom and accuracy of phase control are increased by orders of magnitude. By increasing the number of phase states, 2-bit encoding makes the metasurface more precise and flexible in controlling the phase of electromagnetic waves, thus becoming the core of high-precision beam control.

[0041] Regarding silicon pillars:

[0042] Specifically, the two intersecting arms are identical rectangular strip structures, and are orthogonally symmetrically arranged with the central axis of the polytetrafluoroethylene layer as the center, forming a rectangular hollow area at the intersection.

[0043] In some embodiments, the length of the rectangular strip of the cross arm is defined as the arm length L, then the width x of the rectangular strip of the cross arm is L / 24. Correspondingly, rectangular sub-units with a width of x and a length of L / 2 are symmetrically arranged on both sides of the rectangular cutout area.

[0044] Regarding the rectangular cutout area at the intersection of the two cross arms, the rectangular cutout area is also symmetrically arranged with the central axis as the center, and the rectangular side of the rectangular cutout area is parallel to the side of the polytetrafluoroethylene layer.

[0045] In some embodiments, the width m of the rectangular cutout area is x, with length n x.

[0046] In some embodiments, the endpoints of the cross arms located on the upper and lower sides are connected to each other by extension arms. Since the two cross arms are orthogonally arranged to each other, the included angle between each cross arm and extension arm is 45°.

[0047] Furthermore, the endpoints of the cross arms located on the upper and lower sides are connected to each other through extension arms; that is, the endpoints of the two upper cross arms are connected through the upper extension arm, and the endpoints of the two lower cross arms are connected through the lower extension arm. For example... Figure 1 As shown, the two cross arms and the extension arms form a symmetrical structure similar to the figure "8".

[0048] Furthermore, the two extension arms are set in parallel.

[0049] In some embodiments, the sides of the cross arms on the left and right sides are provided with surrounding arms at intervals, and the surrounding arms on both sides are symmetrically arranged with respect to the central axis of the polytetrafluoroethylene layer. It should be noted that the surrounding arms and the cross arms are spaced apart, that is, the surrounding arms and the cross arms do not contact each other.

[0050] Furthermore, the two surrounding arms are arranged in parallel.

[0051] Furthermore, the extension arm and the surrounding arm are orthogonally arranged.

[0052] In some embodiments, the width a of the surrounding arm is x, and the length b is L / 2.

[0053] In some embodiments, the silicon pillar adopts a high dielectric constant silicon-based pillar structure with a relative dielectric constant ε of 11.9 and a thickness h3 of 200 μm.

[0054] As previously shown, this scheme can achieve four-phase control (0°, 90°, 180°, 270°) by adjusting the length of the cross arms. The reason this scheme can achieve four-phase control by adjusting the cross arm length stems from the synergistic effect of three aspects: First, based on the PB phase principle, when terahertz waves are incident on the top-layer anisotropic silicon pillar cross structure, the phase change is directly related to the structural geometric parameters. Due to the different cross arm lengths, the "optical path" of the terahertz wave propagating within the silicon pillar, the "electromagnetic coupling strength" with the structure, and the "resonant frequency" differ, causing a regular accumulation and shift in phase. The phase changes regularly with the effective length of the cross arm; different lengths correspond to different optical paths and electromagnetic coupling strengths, resulting in phase shift. Second, the high dielectric constant (ε=11.9) and 200μm thickness of the silicon pillars enhance phase accumulation, and the symmetrical design of the cross arms and the hollowed-out sections eliminates polarization interference, ensuring phase stability. Third, the low-loss characteristics of the polytetrafluoroethylene layer reduce signal distortion, and the fixed thickness maintains electromagnetic coupling stability, ensuring that the phase is determined only by the cross arm length, ultimately achieving precise four-phase control.

[0055] Furthermore, when the length L of the cross arm is 40 μm, the corresponding metasurface structure unit is at a phase of 0°, which is defined as a “0” encoding unit; when the length L of the cross arm is 80 μm, the corresponding metasurface structure unit is at a phase of 90°, which is defined as a “1” encoding unit; when the length L of the cross arm is 112 μm, the corresponding metasurface structure unit is at a phase of 180°, which is defined as a “2” encoding unit; and when the length L of the cross arm is 134 μm, the corresponding metasurface structure unit is at a phase of 270°, which is defined as a “3” encoding unit.

[0056] The corresponding coding units and normalized phases for cross arms of different lengths are shown in Table 1 below:

[0057] Table 1. Encoding units and normalized phase tables for crossarms of different lengths.

[0058] .

[0059] This scheme uses CST to perform parameter scanning (electromagnetic response (amplitude and phase) testing) on ​​cross arms of different lengths (40μm, 80μm, 112μm, 134μm), obtaining the electromagnetic response curves of different coding units in reflection mode, as shown below. Figure 2 As shown, the electromagnetic response curves of different coding units in transmission mode are obtained as follows: Figure 3As shown, four unit sizes with a phase difference of 90° were obtained through screening, and they can be named 0, 1, 2, and 3. It is evident that in reflection mode, the reflection amplitude of different coding units in the target terahertz band remains above 0.95, with low energy loss, and the phase precisely matches the four states of 0°, 90°, 180°, and 270°. In transmission mode, the phase of each coding unit still precisely corresponds to the preset four states, the transmission amplitude is stable without significant fluctuations, and energy loss is controllable. This indicates that the same coding unit can achieve precise phase control and amplitude stability in both modes, confirming that metasurfaces can achieve dynamic switching between reflection and transmission through vanadium dioxide phase transitions, providing a stable electromagnetic response foundation for subsequent functions such as beam deflection and convolution operations.

[0060] Regarding the polytetrafluoroethylene layer:

[0061] The polytetrafluoroethylene (PTFE) layer in this design has a square structure, and the period of the PTFE layer is P, which is 120 μm.

[0062] It should be noted that this scheme selects a polytetrafluoroethylene (PTFE) layer as an intermediate layer, which can serve as the core functional layer connecting the top silicon pillar structure and the bottom vanadium dioxide film. Its key electromagnetic and geometric parameters are designed as follows: the relative permittivity ε of the PTFE layer is 2.65, the loss tangent is 0.001, and the thickness h2 is 20 μm.

[0063] With its low dielectric constant and extremely low loss tangent, the polytetrafluoroethylene (PTFE) layer can effectively suppress energy dissipation of terahertz electromagnetic waves during cross-layer transmission, reducing transmission losses caused by dielectric absorption and scattering. Simultaneously, its fixed-thickness geometry provides a stable electromagnetic coupling environment for phase modulation of the top silicon pillar and phase transition modulation of the bottom vanadium dioxide layer, ensuring efficient transmission of terahertz waves in the "silicon pillar-F4B-vanadium dioxide" three-layer structure. This lays a low-loss foundation for the realization of subsequent core functions such as dynamic beam switching and fine-tuned phase control.

[0064] Regarding the vanadium dioxide layer:

[0065] The vanadium dioxide layer in this design has a square structure, and the period of the vanadium dioxide layer is P, which is 120 μm.

[0066] In some embodiments, the thickness h1 of the vanadium dioxide layer is 0.5 μm.

[0067] The vanadium dioxide layer in this scheme is the core functional carrier for realizing the dynamic switching of terahertz beam transmission / reflection modes. Its electromagnetic response characteristics can achieve a reversible phase transition from metal to insulator through temperature control. At room temperature, vanadium dioxide is in an insulating state with a conductivity of σ=500S / m and strong electromagnetic penetration. When the ambient temperature rises to the critical phase transition threshold (>68℃), vanadium dioxide undergoes a lattice transformation. Utilizing the metal-insulator phase transition characteristics of vanadium dioxide (VO2) at approximately 68°, combined with the geometric phase mechanism, the configuration changes, transitioning from the insulating state to the metallic state. The conductivity increases sharply to σ=20000S / m, exhibiting strong electromagnetic reflection characteristics.

[0068] The terahertz coded metasurface in this scheme adopts a super-cell design, that is, an N*N encoding method. In a specific embodiment, the terahertz coded metasurface contains a structure composed of 3*3 identical cells.

[0069] The first reflection group is formed by periodically coded three times along the x-axis using the encoding pattern "02020202". Each encoding pattern consists of 24×24 metasurface structure units. The second reflection group is formed by periodically coded along the x-axis using the encoding pattern "0202… / 2020…". In reflection mode at 1.0 THz, the two-beam and four-beam three-dimensional images of the first and second reflection groups under 1-bit encoding are as follows: Figure 4 As shown, the two reflection groups, in transmission mode at 1.0 THz, have two-beam and four-beam three-dimensional images encoded with 1 bit, as shown below. Figure 5 As shown. By Figure 4 and Figure 5 It is evident that in the 1.0THz reflection mode, the first and second reflection groups can stably and flexibly switch between two-beam and four-beam splitting using a 1-bit encoded metasurface, with uniform beam energy distribution and no significant loss. In the 1.0THz transmission mode, the same 1-bit encoding can also successfully generate two-beam and four-beam splitting, with controllable beam shape. This indicates that the metasurface can effectively complete the basic beam splitting function based on 1-bit encoding in both reflection and transmission modes, verifying that mode switching (relying on vanadium dioxide phase transition) does not affect the beam control effect of 1-bit encoding, laying the foundation for beam control in subsequent multi-directional scanning, complex signal processing, and other functions.

[0070] The three-dimensional far-field plots of the "piecewise gradient" and "continuous gradient" encoded sequences of the encoded metasurface of the present invention at 1.0 THz in the reflection state are shown below. Figure 6 As shown, the three-dimensional far-field plots of the "piecewise gradient" and "continuous gradient" encoded sequences at 1.0 THz in the transmission state are as follows: Figure 7 As shown. Figure 6 and Figure 7The first image in the image uses a coding scheme of "0123-0123" and the codes are arranged periodically along the x-axis. Each coding pattern consists of 24×24 coding units. Figure 6 and Figure 7 The second image shows the encoding pattern "00112233", with the codes arranged periodically along the x-axis. Each encoding pattern consists of 24×24 encoding units. It can be seen that in the three-dimensional far-field plots of the "segmented gradient" and "continuous gradient" encoding sequences under the reflection state of 1.0 THz, the beam can be precisely deflected as designed, with concentrated energy distribution and low loss. Under the transmission state of 1.0 THz, both gradient encoding sequences can also stably control the beam, and the far-field beam shape and deflection effect meet expectations. This indicates that the metasurface can effectively achieve beam control in both reflection and transmission modes using both "segmented gradient" and "continuous gradient" encoding, verifying the reliability of the combination of encoding sequences and mode switching.

[0071] As mentioned earlier, since the vanadium dioxide layer exhibits different electrical conductivities at different temperatures, this scheme can achieve composite control through the phase transition of the vanadium dioxide layer and the adjustment of the arm length of the cross arms. Specifically, when the vanadium dioxide is in the insulating state, i.e., when the metasurface unit is in transmission mode, the phase control of the metasurface unit is dominated by the anisotropic geometry of the top layer. Based on the PB phase principle, by changing the arm length of the cross arms to introduce a dispersive phase gradient, functions such as precise multi-directional beam deflection and vortex beam generation can be achieved. When the vanadium dioxide is in the metallic state, i.e., when the metasurface unit is in reflection mode, the vanadium dioxide layer and the upper silicon pillars generate strong electromagnetic coupling, changing the electromagnetic resonance characteristics of the unit, thereby reconstructing the phase gradient and achieving dynamic switching of functions such as beam deflection direction reversal and vortex topological charge change.

[0072] Furthermore, it is worth mentioning that the top layer of this scheme adopts a cross-symmetric structure composed of silicon pillars with high dielectric constant. The height of 200μm can achieve significant phase accumulation through strong interaction with electromagnetic waves, and can also form a reasonable impedance gradient with the polytetrafluoroethylene layer located in the middle layer to reduce interface reflection loss. The cross-symmetric "X" shape design gives it C4 symmetry, making the unit response to x, L polarization and linearly polarized and circularly polarized incident waves at arbitrary angles completely consistent, fundamentally eliminating the performance fluctuations caused by polarization dependence and adapting to complex polarization environments. The extension characteristics of the cross structure and the matching design of the 120μm period (Px=PL) not only ensure localized electromagnetic control at the subwavelength scale and avoid grating lobe interference, but also make the coupling strength of adjacent units uniform through symmetrical near-field distribution, further suppressing the interference of coupling on the phase response, and ultimately ensuring the stability of the far-field scattering pattern.

[0073] Example 2

[0074] This solution provides a 2-bit encoding scheme based on the terahertz coded metasurface designed in Embodiment 1. Correspondingly, this solution provides a terahertz beam modulation and signal processing device based on the coded metasurface, including:

[0075] Gradient coding sequences in the x-direction are formed by alternating metasurface structural units of different phases as basic units along the x-direction;

[0076] Gradient coding sequences in the y-direction are formed by alternately setting metasurface structural units of different phases as basic units along the y-direction;

[0077] Dynamic convolution is performed by superimposing gradient encoding sequences in the x-direction and gradient encoding sequences in the y-direction.

[0078] This scheme is based on the convolution theorem of Fourier transform and introduces the concept of convolution in signal processing into metasurface design: the far-field scattering pattern and the coding pattern of the terahertz beam satisfy the Fourier transform relationship. By superimposing two gradient coding sequences in different directions, a composite sequence S3 is formed. Its far-field scattering pattern is the "convolution superposition" of the scattering patterns in the x and L directions. Dynamic convolution operation is achieved by "superimposing gradient coding sequences of different periods", which can realize the "lossless multi-directional scanning" function of the terahertz beam in half space. Combining the correlation between the coding pattern and the far-field radiation pattern under Fourier transform, dynamic convolution operation is achieved through a 2-bit coding metasurface, and signal processing is completed directly in the terahertz frequency band.

[0079] In some embodiments, the metasurface unit may be in either a reflective or a transmissive mode.

[0080] In some embodiments, the gradient coding sequence in the x-direction may be different from or the same as the gradient coding sequence in the y-direction. That is, the gradient coding sequences in the x-direction and y-direction are not necessarily different, but are determined according to the specific terahertz beam control requirements. Dynamic convolution is performed by superimposing the sequences in the two directions. If the target beam function (i.e., deflection in a specific direction, energy distribution) needs to be achieved, the same gradient coding sequence in the x-direction and the same gradient coding sequence in the y-direction are selected. In this case, the superposition of the same sequences can achieve the target beam function (such as deflection in a specific direction, energy distribution). If it is necessary to adapt to complex beam control requirements, different gradient coding sequences in the x-direction and y-direction are selected.

[0081] In some embodiments, the gradient coding sequence in the x-direction and / or the gradient coding sequence in the y-direction contain metasurface structural units with different phase differences. Dynamic convolution is achieved by superimposing the gradient coding sequences in the x-direction and y-direction. The number of phases in a single-direction sequence needs to match the specific beam control requirements: if only basic beam deflection is required (such as small-angle control), a 1-bit code with two phase differences can be used to achieve a two-beam / four-beam splitting case; when a finer phase gradient is required (such as large-angle precise deflection or complex beam shape), it is necessary to introduce a 2-bit code with four different phases in a single-direction sequence to improve control accuracy.

[0082] In some embodiments, the number of metasurface structural units in the gradient coding sequence in the x-direction and the gradient coding sequence in the L-direction are the same.

[0083] Taking the gradient coding sequence in the x-direction of a periodic sequence such as "01230123" and the gradient coding sequence in the L-direction of a periodic sequence such as "02020202" as examples, the calculation diagram of the superposition operation of the gradient coding sequences in the x-direction and L-direction in dynamic convolution is shown below. Figure 8 As shown, the corresponding three-dimensional far-field plot of dynamic convolution operation at 1.0 THz in the reflection state is as follows: Figure 9 As shown, the three-dimensional far-field plot of dynamic convolution operation at 1.0 THz in the transmission state is as follows. Figure 10 As shown, in the reflection state, convolving the dual-beam coding sequence S2 with the single-beam coding sequence S1 on the coded metasurface can deflect the entire dual beam towards the direction of the single beam. In the transmission state, convolving the dual-beam coding sequence S2 with the single-beam coding sequence S1 on the coded metasurface can deflect the entire beam in a single direction, forming a dual-beam deflection. This confirms the effectiveness of convolution operations in different modes. Furthermore, the mode switching achieved through the vanadium dioxide phase transition allows the same metasurface to flexibly perform beam "integration-split" functional conversion, providing hardware support for diverse beam control requirements in terahertz communication, imaging, and other scenarios.

[0084] Example 3

[0085] This solution provides a 2-bit encoding scheme based on the terahertz coded metasurface designed in Embodiment 1. Correspondingly, this solution provides a terahertz beam modulation and signal processing device based on the coded metasurface, including: setting four metasurface structural units with a phase difference of π / 2 in a spiral phase distribution manner.

[0086] In some embodiments, adjacent metasurface structural units with a phase difference of π / 2 are arranged counterclockwise in a spiral phase distribution to form a vortex wave generator, thereby realizing a vortex beam with a topological charge of 1+1.

[0087] Furthermore, a spiral phase compensation is superimposed to generate a 1+2 spiral vortex wave.

[0088] This scheme can utilize orbital angular momentum (OAM) to expand the communication channel capacity. The phase of the vortex beam is distributed in a 2πl spiral along the azimuth angle (l is the topological charge). The OAM modes of different l are orthogonal, and multiple signals can be transmitted in parallel at the same frequency, breaking through the channel capacity bottleneck of traditional communication and further improving the detail capture capability in the imaging process.

[0089] Correspondingly, the encoding units "0, 1, 2, 3" are arranged counterclockwise with a 90° phase difference to construct a 20×20 vortex wave generator, realizing a vortex beam with topological charge l=+1. The metasurface phase distribution diagram and surface schematic diagram of the 20×20 vortex wave generator with topological charge l=+1 at 1.0THz are shown below. Figure 11 As shown, the simulated beam image and electric field phase distribution of the vortex wave metasurface at 1.0 THz are as follows. Figure 12 As shown.

[0090] Those skilled in the art should understand that the technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments have been described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0091] The above embodiments are merely illustrative of several implementation methods of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A terahertz-encoded metasurface for achieving multi-phase modulation, characterized in that, include: At least one metasurface structure unit, wherein each metasurface structure unit includes, from top to bottom, a silicon pillar, a polytetrafluoroethylene (PTFE) layer, and a vanadium dioxide layer. The PTFE layer and the vanadium dioxide layer are square structures. The silicon pillar includes two cross arms orthogonally arranged along the central axis of the PTFE layer. The endpoints of the two cross arms located on the upper side of the central axis are connected by an upper extension arm, and the endpoints of the two cross arms located on the lower side of the central axis are connected by a lower extension arm. The two cross arms and the two extension arms form a symmetrical structure similar to the figure "8". The upper extension arm and the lower extension arm are arranged in parallel. A surrounding arm is provided at intervals on the sides of the cross arms located on the left and right sides of the central axis. The two surrounding arms are arranged in parallel and symmetrical with respect to the central axis. The extension arm and the surrounding arm are orthogonal. The surrounding arm and the cross arm do not contact each other. A rectangular hollow area is opened at the intersection of the two cross arms. The two cross arms are identical rectangular strip structures. The rectangular hollow area is arranged symmetrically with the central axis as the center, and the rectangular side of the rectangular hollow area is parallel to the side of the PTFE layer. When the length of the cross arm is 40 μm, the corresponding metasurface structure unit is at a phase of 0°; when the length of the cross arm is 80 μm, the corresponding metasurface structure unit is at a phase of 90°; when the length of the cross arm is 112 μm, the corresponding metasurface structure unit is at a phase of 180°; and when the length of the cross arm is 134 μm, the corresponding metasurface structure unit is at a phase of 270°.

2. The terahertz coded metasurface for multi-phase modulation according to claim 1, characterized in that, By adjusting the length of different cross arms, four phase states—0°, 90°, 180°, and 270°—can be achieved.

3. The terahertz coded metasurface for multi-phase modulation according to claim 1, characterized in that, The silicon pillar has a thickness of 200 μm, the polytetrafluoroethylene layer has a thickness of 20 μm, and the vanadium dioxide layer has a thickness h1 of 0.5 μm.

4. A terahertz beam modulation and signal processing device based on a coded metasurface, implemented based on the terahertz coded metasurface for multi-phase modulation as described in any one of claims 1 to 3, characterized in that, include: Gradient coding sequences in the x-direction are formed by alternating metasurface structural units of different phases as basic units along the x-direction; Gradient coding sequences in the y-direction are formed by alternately setting metasurface structural units of different phases as basic units along the y-direction; Dynamic convolution is performed by superimposing gradient encoding sequences in the x-direction and gradient encoding sequences in the y-direction.

5. The terahertz beam modulation and signal processing device based on a coded metasurface according to claim 4, characterized in that, If the target beam function needs to be achieved, the same gradient coding sequence in the x-direction and gradient coding sequence in the y-direction should be selected. If beam control requirements need to be adapted, different gradient coding sequences in the x-direction and gradient coding sequences in the y-direction should be selected.

6. A terahertz beam modulation and signal processing device based on a coded metasurface, implemented based on the terahertz coded metasurface for multi-phase modulation as described in any one of claims 1 to 3, characterized in that, include: The four metasurface structural units with a phase difference of π / 2 are arranged in a spiral phase distribution manner.

7. The terahertz beam modulation and signal processing device based on a coded metasurface according to claim 6, characterized in that, A vortex wave generator is formed by arranging adjacent metasurface structural units with a phase difference of π / 2 counterclockwise in a spiral phase distribution manner to realize a vortex beam with topological charge l=+1.

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