Optically reconfigurable metasurface for full-space terahertz beam steering

Abstract

An optical control reconfigurable super surface for full space terahertz beam regulation solves the problem of how to provide ubiquitous full space beam coverage for multi-user wireless communication applications, and belongs to the field of artificial electromagnetic super materials. The present application comprises N super subunits arranged periodically, each super subunit comprising 4*4 identical coding units, the corresponding codes being "0" and "1" when there is no light, and the phase responses of the two kinds of coding units being different by 180° at 0.7 THz. Each super subunit comprises 5 layers, the 3rd layer being used for switching between reflection and transmission, the super surface being in a transmission mode when vanadium dioxide is in a dielectric state, and the super surface being in a reflection mode when vanadium dioxide is in a metallic state. The 1st, 2nd, 4th and 5th layers are used for controlling the amplitude and phase of the full space terahertz wave, the conductivity of the photosensitive silicon pattern being changed under excitation of different intensity light, the phase of the full space terahertz beam being effectively modulated, and one-bit terahertz information coding being realized.

Description

Technical Field

[0001] This invention relates to a light-controlled reconfigurable metasurface for full-space terahertz beam manipulation, belonging to the field of artificial electromagnetic metamaterials. Background Technology

[0002] Achieving dynamic and flexible control over electromagnetic waves has always been a core pursuit in various fields of modern science and technology, especially in the terahertz band. In recent years, terahertz communication has begun to be gradually deployed in 6G and other applications, which will drive the rapid progress of core devices, signal processing technology, and antenna technology, and will also play a strong role in promoting terahertz space communication. Full-space control of electromagnetic waves has become an increasingly important issue. Integrated reflection-transmission is a solution for achieving ubiquitous full-space service coverage and full-space resource development, but achieving full-space metasurfaces for dynamic terahertz beam control remains extremely challenging. With the rapid development of advanced military technologies, detection and tracking technologies in various countries are becoming increasingly sophisticated, posing a serious threat to the survivability of weapon platforms such as missiles, fighter jets, and satellites, and placing more stringent requirements on the stealth of important military equipment. Therefore, how to effectively ensure the security of sensitive sensing equipment and military equipment has become an important issue in maintaining national security. To address this challenge, electromagnetic stealth technology has emerged and become a key research direction for many research teams both domestically and internationally. Taking unmanned aerial vehicles (UAVs) as an example, when performing autonomous strike missions in high-threat environments, they require both full-space communication capabilities and stealth characteristics to counter enemy radar electromagnetic wave detection and improve their ability to cope with diverse threats in complex electromagnetic environments. To meet these conflicting technical requirements, we need to integrate reconfigurable electromagnetic devices and equipment with multiple electromagnetic wave manipulation functions, dynamically switching between different functions to handle various mission requirements. Therefore, in complex multi-dimensional reconnaissance environments, there is an urgent need to equip devices that integrate stealth and communication functions to achieve dynamic modulation of terahertz beams throughout space.

[0003] In 2014, Professor Cui Tiejun proposed digitally coded metamaterials, creatively employing digital coding to characterize metamaterials and metasurfaces. A digitally coded metasurface is composed of a finite number of basic units arranged according to a specific coding sequence. For example, a 1-bit digitally coded metasurface consists of units with opposite phases, "0" and "1"; a 2-bit digitally coded metasurface consists of units with a 90-degree phase difference, "00", "01", "10", and "11"; and so on for higher bit levels. This discretized digital coding representation can be viewed as "digital modulation," where the radiation or scattering characteristics of electromagnetic waves can be efficiently controlled by changing the coding sequence arrangement, greatly simplifying the design process and facilitating optimization simulation and fabrication testing. Introducing the concept of digital coding into metasurfaces is also highly applicable to combining adjustable devices or materials such as diodes and MEMS switches to form digitally programmable metasurfaces under the control of field-programmable gate arrays (FPGAs), enabling dynamic control of electromagnetic waves and real-time switching between different functions. Currently, digital coding and programmable metasurfaces are widely used in beamforming, scattering reduction, holographic imaging, microwave imaging, information processing, and wireless communication. More importantly, digitally encoded metasurfaces build a bridge between the physical world and the digital world.

[0004] Although preliminary attempts have been made with all-space metasurfaces in the microwave band, their design in the terahertz band cannot utilize electronic components such as diodes. Traditional electronic control methods typically involve directly connecting the metasurface to an external power supply and control circuit using physical wires. This method easily introduces crosstalk between DC and microwave signals, affecting metasurface performance and increasing the overall system size. Furthermore, real-time dynamic control capabilities are weak. Therefore, the lack of dynamic tunability is an obstacle to the development of terahertz-coded metasurfaces and limits their practical application. In practical applications, it is often necessary to integrate different electromagnetic wave control functions simultaneously. Therefore, achieving dynamic modulation of all-space terahertz beams, especially multifunctional metasurfaces with both communication and stealth capabilities, remains extremely challenging. Summary of the Invention

[0005] To address the problem of providing ubiquitous, full-space beam coverage for multi-user wireless communication applications, this invention provides an optically controllable reconfigurable metasurface for full-space terahertz beam modulation.

[0006] The present invention provides an optically reconfigurable metasurface for full-space terahertz beam modulation, comprising N periodically arranged super sub-units, each super sub-unit comprising 4×4 identical coding units, the corresponding codes being "0" and "1" when there is no illumination, respectively, the two coding units having a phase response difference of 180° at the operating frequency, and each super sub-unit being a 1-bit unit.

[0007] Preferably, each coding unit includes five layers arranged in sequence: the first layer includes a first metal pattern layer, a first active material photosensitive silicon hybrid layer, and a first dielectric layer arranged in sequence; the second layer includes a second metal pattern layer and a second dielectric layer arranged in sequence; the third layer includes a third metal pattern layer and a vanadium dioxide hybrid layer arranged in sequence; the fourth layer includes a fourth metal pattern layer and a third dielectric layer arranged in sequence; and the fifth layer includes a fourth dielectric layer, a fifth metal pattern layer, and a second active material photosensitive silicon hybrid layer arranged in sequence.

[0008] Preferably, when the vanadium dioxide in the third layer is in a dielectric state, the metasurface is in a transmission mode; when the vanadium dioxide mixed layer is in a metallic state, the metasurface unit is in a reflection mode.

[0009] Layers 1, 2, 4, and 5 are used to control the amplitude and phase of the full-space terahertz wave. Specifically, the conductivity of the metal pattern layer changes under different light intensities, and the phase of the full-space terahertz wave beam is modulated to achieve one bit of terahertz information encoding.

[0010] Preferably, the first to fourth dielectric layers are all made of polyimide material with a dielectric constant of 3.5, a tangent loss of 0.0027, and a thickness of 10 μm.

[0011] Preferably, the metasurface operates at the same frequency of 0.7 THz in both reflection and transmission modes.

[0012] Preferred methods for encoding metasurfaces include:

[0013] S1. Initialize the period and metasurface parameters of the super subunit;

[0014] S2. Randomly generate an initial population, wherein the individuals in the initial population are random encoded sequences of the optically controlled reconfigurable metasurface used for full-space terahertz beam modulation.

[0015] S3. Calculate the objective function value for the corresponding coding sequence of each individual in the current population, and determine whether the termination condition is met. If it is met, output the optimal coding sequence and end; otherwise, go to S4. The objective function is set as follows: 360° and 90° are the azimuth angle θ and the elevation angle, respectively. Scope This represents the far-field scattering of the encoded sequence under normal incidence.

[0016] S4. Perform selection, crossover, and mutation operations on the population, and then proceed to S3.

[0017] Preferably, the metasurface can achieve dual-beam and multi-beam modulation in reflection and transmission modes at the operating frequency. By dynamically modulating the quantization code distribution on the metasurface, a multimode OAM beam can be constructed.

[0018] Preferably, the quantization code distribution on the metasurface is dynamically modulated using wireless optical control. The beneficial effects of this invention include its simple structure, ease of design, polarization insensitivity, and low cost, giving it enormous application potential and driving the development of electromagnetic metasurfaces. This invention achieves full-space terahertz beam control by changing the state of vanadium dioxide, improving the utilization efficiency of electromagnetic space resources by the metasurface, and is expected to be applied to next-generation multifunctional, highly integrated, and reconfigurable terahertz functional devices. This invention achieves RCS reduction in the terahertz band by reverse-engineering the coding array using a genetic algorithm, thus giving the proposed metasurface stealth capabilities. The reconfigurable full-space metasurface proposed in this invention employs a wireless optical control scheme, which enriches the control methods of dynamic metasurfaces, provides some reference for the design of multiphysics metasurfaces, and the optical control method has the advantages of ultrafast response time and contactless operation. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of a light-controlled reconfigurable multifunctional full-space metasurface unit structure according to an embodiment of the present invention. The dielectric layer is polyimide with a dielectric constant of 3.5, a tangent loss of 0.0027, and a thickness of 10 μm.

[0020] Figure 2 These are the amplitude and phase responses of a 1-bit optically reconfigurable multifunctional full-space metasurface unit. (a) shows the simulation results of the reflection amplitude of the 1-bit optically reconfigurable multifunctional full-space metasurface subunit in the 0.4 to 1 THz frequency band; (b) shows the simulation results of the reflection phase of the 1-bit optically reconfigurable multifunctional full-space metasurface subunit in the 0.4 to 1 THz frequency band; (c) shows the simulation results of the transmission amplitude of the 1-bit optically reconfigurable multifunctional full-space metasurface subunit in the 0.4 to 1 THz frequency band; and (d) shows the simulation results of the transmission phase of the 1-bit optically reconfigurable multifunctional full-space metasurface subunit in the 0.4 to 1 THz frequency band.

[0021] Figure 3The diagrams are three-dimensional far-field radiation patterns, where (a) is the three-dimensional far-field radiation pattern (reflection mode and transmission mode) generated by the dual-beam modulation coding sequence (00110011…) at an operating frequency of 0.7THz; (b) is the three-dimensional far-field radiation pattern (reflection mode and transmission mode) generated by the three-beam modulation coding sequence (000111000111…) at an operating frequency of 0.7THz; and (c) is the three-dimensional far-field radiation pattern (reflection mode and transmission mode) generated by the four-beam modulation coding sequence (checkerboard coding) at an operating frequency of 0.7THz.

[0022] Figure 4 The diagram shows the flow and effect of the encoding method, where (a) is the flowchart of the genetic algorithm; and (b) is the RCS curve corresponding to the encoding sequence designed by the reverse of the genetic algorithm.

[0023] Figure 5 The diagrams are shown below, where (a) is the phase distribution diagram of the vortex wave in OAM mode l = -2 (reflection mode and transmission mode), (b) is the phase distribution diagram of OAM mode l = -1 (reflection mode and transmission mode), (c) is the phase distribution diagram of OAM mode l = +1 (reflection mode and transmission mode), and (d) is the phase distribution diagram of OAM mode l = +2 (reflection mode and transmission mode). Detailed Implementation

[0024] 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. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0026] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the scope of the invention.

[0027] This embodiment of a light-controlled reconfigurable metasurface for full-space terahertz beam modulation includes N periodically arranged super sub-units. Each super sub-unit includes 4×4 identical coding units, with the corresponding codes being "0" and "1" when there is no illumination, respectively. The two coding units have a phase response difference of 180° at 0.7THz, and each super sub-unit is a 1-bit unit.

[0028] like Figure 1As shown, each coding unit comprises five layers arranged sequentially. Layer 1 includes a first metal pattern layer, a first active material photosensitive silicon hybrid layer, and a first dielectric layer arranged sequentially. Layer 2 includes a second metal pattern layer and a second dielectric layer arranged sequentially. Layer 3 includes a third metal pattern layer and a vanadium dioxide hybrid layer arranged sequentially. Layer 4 includes a fourth metal pattern layer and a third dielectric layer arranged sequentially. Layer 5 includes a fourth dielectric layer, a fifth metal pattern layer, and a second active material photosensitive silicon hybrid layer arranged sequentially. Specifically, the metal pattern layer and the active material photosensitive silicon hybrid layer are composed of 0.5 mm thick photosensitive silicon and metal. The dielectric layer is polyimide with a dielectric constant of 3.5, a thickness of d = 10 μm, and a unit period p = 100 mm. The photosensitive silicon has a dielectric constant of 11.5 and a radius of r = 10 mm. The conductivity of the tunable photosensitive silicon changes with the pump light energy. When the light energy increases, the carrier concentration within the semiconductor also increases, thereby achieving the purpose of regulating the conductivity. The relationship between the photosensitive silicon conductivity σ and the pump light power I is σ = 4.863 × 10⁻⁶. -4 ×I 2 +0.1856×I+1.569. The conductivity of photosensitive silicon is 0 without pump excitation; when the pump power is 790 μJ / cm... 2 At that time, the conductivity was 5.0 × 10⁻⁶. 5 S / m.

[0029] The third layer is used to switch between reflection and transmission modes very quickly. It is called the reflection and transmission control layer. When vanadium dioxide is in the dielectric state in the reflection and transmission control layer, the metasurface is in the transmission mode. When the vanadium dioxide mixed layer is in the metallic state, the metasurface unit is in the reflection mode.

[0030] Layers 1, 2, 4, and 5 are used to control the amplitude and phase of the full-space terahertz wave and are called the optically controlled terahertz information encoding layer. This layer utilizes the change in conductivity of the metal pattern layer under different intensities of light excitation to modulate the phase of the full-space terahertz wave beam, thereby realizing one bit of terahertz information encoding, which allows for dynamic reconfiguration of the metasurface's functionality.

[0031] like Figure 2 Figures (a)-(d) show the amplitude and phase response curves corresponding to the 1-bit optically reconfigurable multifunctional full-space metasurface unit obtained by simulation using the commercial software CST Microwave Studio.

[0032] In this embodiment, the metasurface operates at the same frequency of 0.7 THz in both reflection and transmission modes. A super-sub-unit arrangement is employed, where 4×4 identical metasurface units are grouped into a single super-sub-unit. The reconfigurable coded metasurface is designed by arranging a coded pattern in space, thereby achieving the specified electromagnetic function. For example... Figure 3 In the middle (a), the three-dimensional far-field radiation pattern (reflection mode and transmission mode) generated by the dual-beam modulated coding sequence at the operating frequency of 0.7 THz is shown. Figure 3 (b) shows the three-dimensional far-field radiation pattern (reflection mode and transmission mode) generated by the three-beam modulated coding sequence at an operating frequency of 0.7 THz; Figure 3 Image (c) shows the three-dimensional far-field radiation pattern (reflection mode and transmission mode) generated by the four-beam modulated coding sequence at an operating frequency of 0.7 THz. The beam deflection angle can be calculated using θ = arcsin(λ / Γ), where λ is the free-space wavelength and Γ represents the period length of the coding sequence.

[0033] To reduce energy consumption, simplify the control system, and accelerate response speed, 1-bit encoding is implemented at 0.7 THz using two states of photosensitive silicon. Furthermore, a metasurface array encoding is designed using a genetic algorithm to achieve RCS reduction. The flowchart of the reverse design of the metasurface array encoding based on the genetic algorithm is shown below. Figure 4 As shown, methods for encoding metasurfaces include:

[0034] Step 1: Initialize parameters such as the period of the super subunit and the size of the metasurface array;

[0035] Step 2: Randomly generate an initial population consisting of 50 individuals. Each individual in the initial population is a random coding sequence of the optically controlled reconfigurable metasurface used for full-space terahertz beam modulation. Each individual is a 32×32 random coding sequence.

[0036] Step 3: Calculate the objective function value for the corresponding encoding sequence of each individual in the current population, and determine whether the termination condition is met, such as reaching the maximum number of iterations of 1500. If the condition is met, output the optimal encoding sequence and end; otherwise, proceed to step 4.

[0037] The objective function for RCS reduction is set as follows: 360° and 90° are the azimuth angle θ and the elevation angle, respectively. Scope This represents the far-field scattering of the encoded sequence under normal incidence.

[0038] Step 4: Perform selection, crossover, and mutation operations on the population, and then proceed to step 3.

[0039] This process is repeated iteratively until the set number of iterations is reached, finally outputting the optimal array coding sequence. First, the coded array obtained through reverse engineering is modeled and simulated in CST to obtain the far-field scattering amplitude. Then, the far-field scattering amplitude of a metal plate of the same size as the coded metasurface is calculated using the same method. Finally, the RCS values ​​of the two are compared to obtain the RCS reduction value. Figure 4 As shown, the metasurface optimized using a genetic algorithm achieved an RCS reduction of over 10 dB in the 0.6–0.78 THz range. In summary, this invention improves RCS reduction by optimizing the metasurface encoding and radiation field using a genetic algorithm.

[0040] Metasurfaces enable a range of dynamic functions at their operating frequencies, including dual-beam and multi-beam manipulation in both reflection and transmission modes. They can also generate electromagnetic waves carrying orbital angular momentum (OAM). By dynamically modulating the quantization code distribution on the metasurface, reconfigurable multimode OAM beams can be constructed. These operations can be performed wirelessly via optical control. The single-vortex beam generation results at 0.7 THz for different topological charge numbers on the coded metasurface are shown below. Figure 5 As shown. Figure 5 (a)-(d) are respectively The far-field scattering and phase results are shown. Observing the phase results, it can be found that when the topological charge number is... and When the phase has 1 and 2 periods respectively in the counterclockwise direction from 0° to 360°; when the topological charge number is and At that time, the phase has 1 and 2 cycles in the clockwise direction from 0° to 360°, which is consistent with the characteristics of a vortex beam.

[0041] The purpose of this implementation is to propose a light-controlled, reconfigurable, multifunctional all-space metasurface that integrates three modes: reflection communication, transmission communication, and electromagnetic stealth. This provides ubiquitous all-space beam coverage for multi-user wireless communication applications and enhances the survivability of military equipment on the battlefield. The proposed metasurface has already achieved a series of dynamic functions, including dual-beam and multi-beam manipulation in both reflection and transmission modes. Furthermore, the designed reconfigurable metasurface generates electromagnetic waves carrying orbital angular momentum (OAM). By dynamically modulating the quantization code distribution on the metasurface, a reconfigurable multimode OAM beam can be constructed. In electromagnetic stealth mode, a genetic algorithm is used to reverse-design the array arrangement of the encoded metasurface, enabling radar cross-section reduction.

[0042] While the invention has been described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the invention. Therefore, it should be understood that many modifications can be made to the exemplary embodiments, and other arrangements can be designed without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood that different dependent claims and features described herein can be combined in ways different from those described in the original claims. It is also understood that features described in conjunction with individual embodiments can be used in other described embodiments.

Claims

1. A light-controlled reconfigurable metasurface for full-space terahertz beam manipulation, characterized in that, It includes N super subunits arranged in a periodic manner. Each super subunit includes 4×4 identical coding units. The corresponding codes are "0" and "1" when there is no light, respectively. The two coding units are 180° out of phase at the operating frequency. Each super subunit is a 1-bit unit. The encoding unit comprises five layers arranged in sequence. The first layer comprises a first metal pattern layer, a first active material photosensitive silicon hybrid layer, and a first dielectric layer arranged in sequence. The second layer comprises a second metal pattern layer and a second dielectric layer arranged in sequence. The third layer comprises a third metal pattern layer and a vanadium dioxide hybrid layer arranged in sequence. The fourth layer comprises a fourth metal pattern layer and a third dielectric layer arranged in sequence. The fifth layer comprises a fourth dielectric layer, a fifth metal pattern layer, and a second active material photosensitive silicon hybrid layer arranged in sequence.

2. The light-controlled reconfigurable metasurface according to claim 1, characterized in that, When the vanadium dioxide in the third layer is in a dielectric state, the metasurface is in a transmission mode; when the vanadium dioxide mixed layer is in a metallic state, the metasurface unit is in a reflection mode. Layers 1, 2, 4, and 5 are used to control the amplitude and phase of the full-space terahertz wave. Specifically, the conductivity of the metal pattern layer changes under different light intensities, and the phase of the full-space terahertz wave beam is modulated to achieve one bit of terahertz information encoding.

3. The light-controlled reconfigurable metasurface according to claim 2, characterized in that, The first to fourth dielectric layers are all made of polyimide material with a dielectric constant of 3.5, a tangent loss of 0.0027, and a thickness of 10 μm.

4. The light-controlled reconfigurable metasurface according to claim 2, characterized in that, The metasurface operates at the same frequency of 0.7 THz in both reflection and transmission modes.

5. The light-controlled reconfigurable metasurface according to claim 2, characterized in that, Methods for encoding metasurfaces include: S1. Initialize the period and metasurface parameters of the super subunit; S2. Randomly generate an initial population, where each individual in the initial population is a random encoded sequence of the light-controlled reconfigurable metasurface; S3. Calculate the objective function value for the corresponding coding sequence of each individual in the current population, and determine whether the termination condition is met. If it is met, output the optimal coding sequence and end; otherwise, go to S4. The objective function is set as follows: 360° and 90° are the azimuth angle θ and the elevation angle, respectively. Scope This represents the far-field scattering of the encoded sequence under normal incidence. S4. Perform selection, crossover, and mutation operations on the population, and then proceed to S3.

6. The light-controlled reconfigurable metasurface according to claim 2, characterized in that, The metasurface can achieve dual-beam and multi-beam control in reflection and transmission modes at the operating frequency. By dynamically modulating the quantization code distribution on the metasurface, a multimode OAM beam can be constructed.

7. The light-controlled reconfigurable metasurface according to claim 6, characterized in that, The distribution of quantization codes on the metasurface is dynamically modulated using wireless optical control.

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