1-bit light-operated terahertz metasurface based on phase change material

Abstract

The invention discloses a 1-bit light-operated terahertz metasurface based on a phase change material, and belongs to the field of metasurface design. According to the invention, the phase-change material is irradiated by adopting proper laser, so that the crystal phase of the phase-change material can be converted between a crystalline state and an amorphous state, and then the metasurface unit generates a 180-degree reflection phase difference. And the 1-bit units form an array, so that the directional regulation and control of incident terahertz electromagnetic waves can be realized in combination with a coding matrix. The design can greatly reduce the size while reducing the electric signal interference caused by the traditional circuit switch control so as to be suitable for the terahertz frequency band.

Description

Technical Field

[0001] The present invention relates to the technical field of metasurface design, and in particular to a 1-bit light-controlled terahertz metasurface based on phase change materials. Background Art

[0002] As society enters the information age, the generation of massive amounts of data places higher demands on existing communications systems and presents greater challenges. Whether in civilian applications like wireless communications and navigation, or in defense fields like radar and electromagnetic stealth, electromagnetic waves, as carriers of information, continue to be explored for their regulation. The emergence of electromagnetic metamaterials offers new avenues for regulating electromagnetic waves.

[0003] Electromagnetic metamaterials, also known as artificial electromagnetic metamaterials, refer to a class of artificial composite structures or materials that possess extraordinary physical properties not possessed by natural materials. They are typically composed of a large number of subwavelength structural units arranged in a specific periodic or aperiodic pattern in space. With the advancement of metamaterial theory, electromagnetic metamaterials have transitioned from three-dimensional to two-dimensional, namely electromagnetic metasurfaces. These metamaterials offer advantages such as small size, simple unit structures, ease of processing, and ease of testing, making the manipulation of electromagnetic waves more flexible and convenient. The introduction of digitally coded electromagnetic metamaterials bridges the gap between physical parameters and the digital world, laying the hardware foundation for the integration of electromagnetic information theory and communications. This new framework offers broad development potential for future communications.

[0004] With the continuous development of wireless communications, there is a need for electromagnetic metamaterial units that can meet the transmission of higher information capacity and higher information rate, and the communication spectrum moves towards high frequencies. Summary of the Invention

[0005] The present invention provides a 1-bit light-controlled terahertz metasurface based on phase-change material. A reflective metasurface operating in the terahertz band is designed. By adding phase-change material to the unit, the state of the unit can be quickly controlled under the control of a laser source. Through the spatial arrangement and combination of the unit states, the metasurface can effectively control the direction of the electromagnetic wave, providing a potential electromagnetic wave control method and hardware foundation for new communication systems.

[0006] An embodiment of the present invention provides a 1-bit optically controlled terahertz metasurface based on phase change material. The metasurface includes multiple metasurface units. Each metasurface unit includes, from top to bottom, a metal patch layer, a phase change material layer, a substrate, and a metal backplane layer. The size of the germanium telluride layer is larger than that of the metal patch layer.

[0007] By irradiating the phase change material layer with laser, the crystal phase of the phase change material layer is converted between the crystalline state and the amorphous state, so that the metasurface unit produces a reflection phase difference of 180°. By spatially arranging and combining the states of multiple metasurface units, the incident terahertz electromagnetic wave is directional controlled.

[0008] Optionally, in one embodiment of the present invention, when the phase change material layer is in an amorphous state, it is approximately transparent to terahertz waves, and the resonant structure of the metasurface unit is determined by the size of the metal patch; when the phase change material is transformed into a crystalline state by receiving specific laser irradiation, the phase change material has metal-like properties, and the phase change material layer is approximately regarded as a large metal patch to realize two square metal microstrip structures of different sizes. By adjusting the size of the metal patch layer and the phase change material layer, the reflection phase of the metasurface unit in the crystalline state and the amorphous state differs by 180°, thereby realizing 1-bit phase modulation, and then combining the generalized Snell's law to control the direction of the electromagnetic wave.

[0009] Optionally, in one embodiment of the present invention, the phase change material is germanium telluride.

[0010] For general reconfigurable metasurfaces, the unit control method is often to use varactor diodes, PIN diodes, etc., which will face problems such as complex control circuit design for outputting electrical signals, difficult layout design, and certain coupling and interference between electrical signals and electromagnetic wave signals that transmit information. The 1-bit optically controlled terahertz metasurface based on phase change materials in the embodiments of the present invention has the following beneficial effects:

[0011] 1. The unit structure adopted by the metasurface designed by the present invention is simple, and the control mechanism of electromagnetic waves is not complicated, which enables designers to design the required metasurface structure according to functional requirements.

[0012] 2. The structural processing process proposed in the present invention is not complicated and has a small size. It can be applied to the terahertz frequency band and is easy to integrate.

[0013] 3. The laser control signal used in the present invention does not interfere with the electromagnetic waves that transmit information while dynamically controlling the structure of the unit, and has a fast response speed, which can achieve faster electromagnetic wave control function.

[0014] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0016] Figure 1This is a side view of a 1-bit light-controlled terahertz metasurface according to an embodiment of the present invention;

[0017] Figure 2 A top view of a 1-bit light-controlled terahertz metasurface according to an embodiment of the present invention;

[0018] Figure 3 The super surface unit S of the embodiment of the present invention 11 Simulation results, where (a) is the amplitude response and (b) is the phase response;

[0019] Figure 4 The simulated directional pattern of the embodiment of the present invention when the reflection angle is 10°, where (a) is the 3D directional pattern and (b) is the xoz plane directional pattern;

[0020] Figure 5 The simulated directional pattern of the embodiment of the present invention when the reflection angle is 30°, where (a) is the 3D directional pattern and (b) is the xoz plane directional pattern;

[0021] Figure 6 The simulated directional pattern of the embodiment of the present invention when the reflection angle is 50°, where (a) is the 3D directional pattern and (b) is the xoz plane directional pattern;

[0022] Figure 7 A coding matrix of a 25×25 array for two-dimensional beam steering according to an embodiment of the present invention;

[0023] Figure 8 It is the normalized yoz plane pattern of the two-dimensional beam steering in an embodiment of the present invention. DETAILED DESCRIPTION

[0024] The following describes in detail embodiments of the present application, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present application, and should not be construed as limiting the present application.

[0025] With the continuous development of wireless communications, in order to meet the transmission needs of higher information capacity and higher information rate, the communication spectrum is constantly moving towards high frequency. The present invention designs an electromagnetic metamaterial unit operating in the terahertz frequency band. Different from the previous digital coding metamaterials that use electrical control such as varactor diodes or PIN diodes, the present invention chooses to use optical control, which has the advantages of small interference of control signals on electromagnetic wave signals, fast response speed, and easy integration. It can not only improve the reliability of the antenna, but also effectively reduce the size of the antenna. This research direction shows broad application prospects.

[0026] like Figure 1As shown, the metasurface includes multiple metasurface units, each of which includes, from top to bottom, a metal patch layer, a phase change material layer, a substrate, and a metal backplane layer, and the size of the germanium telluride layer is larger than that of the metal patch layer.

[0027] By irradiating the phase change material layer with laser, the crystal phase of the phase change material layer is converted between the crystalline state and the amorphous state, so that the metasurface unit produces a reflection phase difference of 180°. By spatially arranging and combining the states of multiple metasurface units, the incident terahertz electromagnetic wave is directional controlled.

[0028] In an embodiment of the present invention, the phase change material is germanium telluride (GeTe).

[0029] In one specific implementation, Figure 2 As shown, the reflective light-control metasurface based on the square metal patch structure includes: a smaller upper metal patch, a larger lower germanium telluride layer, a sapphire substrate and a metal backplane layer.

[0030] The metasurface unit utilizes the resonant properties of a microstrip structure. When the underlying GeTe layer is in an amorphous state, it is nearly transparent to terahertz waves, and the unit's resonant structure is primarily determined by the size of the metal patch. However, when transformed into a crystalline state by specific illumination, the GeTe layer exhibits metal-like properties, allowing the GeTe layer to be treated as a larger metal patch, creating two square metal microstrip structures of different sizes. By adjusting their size, the unit's reflection phase in the two states differs by 180°, achieving 1-bit phase modulation. This allows the directionality of the electromagnetic wave to be controlled by combining the generalized Snell's law.

[0031] The metasurface unit uses silica glass as the substrate material, and the operating frequency is set at around 0.50THz. In metasurface design, the unit size is usually required to be less than or equal to half the wavelength corresponding to the operating frequency, so the unit period is set to 250um. The unit pattern uses a common square pattern. Figure 1 and Figure 2 As shown, a square GeTe layer is placed at the center of the cell, and a smaller square metal sheet is attached to the GeTe layer. The amorphous and crystalline states of GeTe correspond to the "0" and "1" states of the cell, respectively. When the cell is in the "0" state, the GeTe layer has low conductivity, allowing terahertz electromagnetic waves to easily penetrate the layer. Therefore, the resonant structure of the cell is mainly determined by the size of the small metal sheet. When the GeTe is stimulated to transform into a crystalline state, the cell is in the "1" state, and the high-conductivity GeTe layer exhibits metal-like properties. The resonant response is affected by the area of ​​the GeTe region. By adjusting the size of these two regions, the reflection amplitude and phase of the two states can meet the design requirements of the 1-bit cell.

[0032] CST full-wave simulation was used to scan and optimize various structural parameters. The final values ​​are shown in Table 1. 200μm thick silica glass was used as the substrate material. Because silica materials are not available in the CST material library, a custom material, SiO2, was set to normal with a dielectric constant of 3.82. A metal layer was added to the back of the substrate to reflect electromagnetic waves. The unit period is 250μm, and in the center of the unit there is a square layer of GeTe material with a side length of 162μm and a thickness of 1μm. The material in this area can be set to GT_C or GT_A, corresponding to the two operating states of the unit. Above the GeTe layer, there is also a metal patch with a side length of 74μm, which is represented by PEC material in the simulation.

[0033] Table 1 1-bit metasurface unit structural parameters (μm)

[0034]

[0035] When the GeTe layer is in an amorphous state, that is, the material is set to GT_A, the cell is recorded as the "0" state, and when the GeTe is in a crystalline state and the material is set to GT_C, the cell is recorded as the "1" state. When performing cell simulation, the Floquet feed has two main modes: TE (0, 0) and TM (0, 0). The symmetry of the cell design shows that the simulation results under the two modes are also symmetrical. Therefore, in order to simplify the process, the TE mode is used for simulation, and S 11 Parameters as a result of magnitude and phase response.

[0036] The simulation results of the reflection amplitude and phase of the unit in the "0" and "1" states are as follows: Figure 3 As shown. Figure 3 As shown in (a), the reflection amplitude of the "0" state cell remains above -1dB in the frequency range of 0.40-0.60THz, indicating a high reflectivity. The "1" state cell resonates at 0.455THz, significantly reducing the reflection amplitude. However, in the frequency range above 0.52THz, the reflection amplitude remains above -1.5dB. The amplitude response values ​​of the two cell states are similar in the 0.52-0.60THz range. Figure 3 (b) shows the phase response of the unit in its two states. At 0.53 THz, the reflection phase difference between the "0" unit and the "1" unit is 180°. In the frequency range of 0.525-0.535 THz, the unit phase difference remains between 170° and 190°. Therefore, the reflection amplitude and reflection phase of the unit in its two states can well meet the design requirements of a 1-bit coding metasurface.

[0037] Next, we use this 1-bit metasurface unit array to perform full-wave simulation. First, we use a plane wave as the incident wave, which is incident vertically on the metasurface. Assume that the deflection direction is on the x-axis, that is, the reflection angle is (θ o ,0), taking the 50×50 array as an example, the array operating frequency is set to 0.53THz, θ o We take 10°, 30°, and 50° respectively, and use Matlab to calculate the corresponding 1-bit coding matrix. Based on these matrices, we construct a metasurface model, where the state code of each array element corresponds to the value in the matrix. We use the CST time-domain solver to perform full-wave simulation of the metasurface, setting an x-polarized plane wave propagating along the -z direction as the excitation. The simulated directivity pattern is as follows: Figure 4 、 Figure 5 and Figure 6 shown.

[0038] When the pointing angle is within the range of 0-50°, the optically controlled 1-bit reflective metasurface can achieve beam pointing in a specified direction and maintain good working characteristics. However, the simulation results also show some problems. For example, when the main beam is pointed at 10° and 30°, except for the mirror beam, the sidelobe intensity of the reflected wave is below -10dB. As the reflection angle increases, the sidelobe intensity increases. Figure 6 As shown, in the simulation with a beam pointing angle of 50°, A vertical reflected beam with an intensity close to the main beam appears in the direction. This may be because the coupling between the array elements is more obvious when the beam deflection angle is large, and the reflectivity of the element in the two states is not strictly equal.

[0039] The advantage of using optically controlled GeTe phase-change properties to control the cell state is that the state of each cell in the array can be independently controlled without complex DC bias circuitry. Compared to column-controlled metasurfaces, independent cell control enables two-dimensional beam modulation. Next, the plane wave is modified from normal incidence to oblique incidence, while the main beam is set on the yoz surface to mitigate the mirror beam problem.

[0040] Set the incident direction to Reflected main beam pointing To simplify the calculation, the array size is set to 25×25, and the array element phase compensation is calculated and discretized into 1-bit to obtain Figure 7 The coding matrix shown in the figure is obtained by full-wave simulation of the metasurface. The direction diagram of the surface (yoz surface), such as Figure 8As shown in the figure, the two mirror beams are effectively preserved as a single beam, and beamforming is achieved from the incident wave on the xoz plane to the reflected wave on the yoz plane. However, due to the large quantization error caused by 1-bit encoding, the reflected wave's pointing angle is (44°, 90°). This problem can be solved by using an optimization algorithm or using a unit with a higher bit count.

[0041] According to an embodiment of the present invention, a 1-bit optically controlled terahertz metasurface based on phase-change material can be fabricated by irradiating the phase-change material with a suitable laser to cause its crystal phase to transition between crystalline and amorphous states, thereby causing the metasurface units to produce a 180° reflection phase difference. Arraying these 1-bit units in conjunction with a coding matrix can achieve directional control of incident terahertz electromagnetic waves. This design can reduce the electrical signal interference caused by traditional circuit switching control while significantly reducing the size, making it suitable for terahertz frequency bands.

[0042] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or N embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0043] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of technical features indicated. Thus, a feature specified as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of this application, "N" means at least two, for example, two, three, etc., unless otherwise specifically defined.

Claims

1. A 1-bit light-controlled terahertz metasurface based on phase change material, characterized in that: The metasurface includes a plurality of metasurface units, each of which includes, from top to bottom, a metal patch layer, a phase change material layer, a substrate, and a metal backplane layer, wherein the size of the germanium telluride layer is larger than the size of the metal patch layer; By irradiating the phase change material layer with laser, the crystal phase of the phase change material layer is converted between the crystalline state and the amorphous state, so that the metasurface unit produces a reflection phase difference of 180°. Through the spatial arrangement and combination of multiple metasurface unit states, the incident terahertz electromagnetic wave is directional controlled.

2. The 1-bit light-controlled terahertz metasurface based on phase change material according to claim 1, characterized in that: When the phase-change material layer is in an amorphous state, it is approximately transparent to terahertz waves, and the resonant structure of the metasurface unit is determined by the size of the metal patch. When the phase-change material is transformed into a crystalline state by receiving specific laser irradiation, the phase-change material has metal-like properties. The phase-change material layer is approximately regarded as a large metal patch, and two square metal microstrip structures of different sizes are realized. By adjusting the size of the metal patch layer and the phase-change material layer, the reflection phase of the metasurface unit in the crystalline state and the amorphous state differs by 180°, realizing 1-bit phase modulation, and then combining the generalized Snell's law to control the direction of the electromagnetic wave.

3. The 1-bit light-controlled terahertz metasurface based on phase change material according to claim 1, characterized in that: The phase change material is germanium telluride.

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