Two-way beam steering metasurfaces based on broken inversion symmetry and uses thereof

Abstract

The application discloses a bidirectional beam regulation metasurface unit structure based on inversion symmetry breaking and a metasurface and application, and relates to a bidirectional beam regulation metasurface unit based on inversion symmetry breaking, which comprises a cylinder and a metal film disc, wherein the metal film disc is located on one side of the cylinder, and cross beams are arranged between metasurface unit structures to play a fixing role. The bidirectional beam regulation metasurface comprises in-phase unit structures and out-of-phase unit structures, wherein the in-phase unit structures and the out-of-phase unit structures are distributed longitudinally and transversely according to predetermined rules, so that the metasurface has different phase responses to electromagnetic waves in forward incidence and reverse incidence. The application has the characteristics of flexibility and multifunction, and specifically, the application can have different regulation functions for electromagnetic waves in forward incidence and reverse incidence.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic waves and novel artificial electromagnetic materials, specifically relating to a bidirectional beam-tunable metasurface based on inversion symmetry breaking and its applications. Background Technology

[0002] In 2011, Capasso et al. proposed the generalized Snell's law, which theoretically explains the anomalous reflection and refraction phenomena that occur when discontinuous phases are introduced onto the surface of metamaterials. Subsequently, other research groups, based on the generalized Snell's law, designed more complex phase distributions on two-dimensional metasurfaces, thereby achieving arbitrary control over reflected and refracted waves, such as vortex beams and Bessel beams. It is even possible to design random phase distributions, causing the incident beam to be randomly scattered in various directions, forming diffuse reflection, thus effectively reducing the radar cross-section of the target and achieving stealth. More extensive applications have been proven, such as radomes, metalenses, waveplates, and holographic imaging. Well-designed microstructured metasurfaces offer unprecedented solutions for controlling light and hold great promise for the future.

[0003] Metasurfaces are able to achieve these different functions because they exhibit superior performance compared to traditional natural materials. By designing unit structures, they can control the characteristics of electromagnetic waves, such as polarization, amplitude, phase, polarization direction, and propagation mode.

[0004] However, in the design of multifunctional metasurfaces, there is an important wave characteristic that is rarely utilized: the propagation direction. Currently, this characteristic is mainly utilized by using external bias, nonlinear materials, and time-varying materials to break time-reversal symmetry. This places requirements on factors such as material properties, external bias, and the characteristics of the incident wave. Summary of the Invention

[0005] Purpose of the invention: To address the problems of existing metasurface materials for achieving bidirectional beam control having high requirements, needing external bias, and having requirements for incident waves, which are not conducive to integration, this invention proposes a bidirectional beam control metasurface based on inversion symmetry breaking, which can realize bidirectional beam deflection, focal length adjustment, and holographic imaging functions.

[0006] Technical solution:

[0007] To achieve the above-mentioned objectives, the present invention provides a first technical solution: a bidirectional beam-controlled metasurface unit based on inversion symmetry breaking, comprising: a cylinder, a metal thin film disk, and a cross-shaped beam; the metal thin film disk is located on the front side of the cylinder; the cross-shaped beam is located between the metasurface unit structures and serves a fixing function.

[0008] Furthermore, the cylinder is a silicon cylinder with a height of 100 micrometers; the metal thin film disk is a gold thin film disk with a thickness of 200 nanometers; and the cross-shaped beam is 10 micrometers wide.

[0009] The second technical solution provided by this invention is a bidirectional beam-tunable metasurface based on inversion symmetry breaking, comprising in-phase unit structures and out-of-phase unit structures; the in-phase unit structures exhibit the same reflection phase under illumination by forward and reverse perpendicular incident electromagnetic waves, while the out-of-phase unit structures exhibit different reflection phases under illumination by forward and reverse perpendicular incident electromagnetic waves; the in-phase unit structures include four structures, which exhibit reflection phases of 0 degrees / 0 degrees, 90 degrees / 90 degrees, 180 degrees / 180 degrees, and 270 degrees / 270 degrees under illumination by forward and reverse perpendicular incident electromagnetic waves, respectively; the out-of-phase unit structures include 12 structures, which exhibit reflection phases of any two different reflection phases among 0 degrees, 90 degrees, 180 degrees, and 270 degrees under illumination by forward and reverse perpendicular incident electromagnetic waves, respectively. The in-phase and out-of-phase unit structures are metasurface units with different radii of cylinders and metal thin-film disks; in the four in-phase unit structures, the metal thin-film disks are located on the front side of the cylinder; in the twelve out-of-phase unit structures, the metal thin-film disks in six structures are located on the front side of the cylinder, and the other six structures are located on the back side of the cylinder; when the cylinder radius of the metasurface composed of the same unit changes while the radius of the metal thin-film disk on one side of the cylinder array remains unchanged, the reflection phase of the vertically incident electromagnetic wave on one side of the metal thin-film layer changes significantly while the reflection phase of the reverse vertically incident electromagnetic wave remains essentially unchanged; when the radius of the metal thin-film disk of the metasurface composed of the same unit changes while the cylinder radius remains unchanged, the reflection phase of the vertically incident electromagnetic wave on one side of the metal thin-film disk remains essentially unchanged while the reflection phase of the reverse vertically incident electromagnetic wave changes significantly.

[0010] The third technical solution provided by this invention is the application of a bidirectional beam-controlled metasurface based on inversion symmetry breaking. By arranging the in-phase and out-of-phase unit structures, different unit structures can control the electromagnetic wave reflection phase differently, thereby enabling the bidirectional beam-controlled metasurface to be used in bidirectional independent beam deflection, beam focusing, and holographic imaging.

[0011] Beneficial effects: Compared with electromagnetic metamaterials with inversion symmetry, this invention will open up new possibilities for electromagnetic wave manipulation. Specifically, this invention can independently control electromagnetic waves when the incident direction of the incident wave is changed. By adjusting the structural parameters of the metasurface unit, each unit can independently encode the electromagnetic waves incident on the front and back sides, thereby realizing bidirectional independent beam control, such as beam deflection, focusing, holographic imaging, etc. Attached Figure Description

[0012] Figure 1 A schematic diagram of a bidirectional beam-tunable metasurface with inversion symmetry breaking;

[0013] Figures 2(a), 2(b), and 2(c) are schematic diagrams, top views, and front views of the bidirectional beam-controlled metasurface unit with inversion symmetry breaking according to the present invention, respectively.

[0014] Figures 3(a), 3(b), and 3(c) show the reflection phases when the metal thin film disk has a fixed radius of 35 micrometers and the cylindrical radius ranges from 110 micrometers to 153 micrometers, with the incident electromagnetic wave frequency changing from 0.39THz to 0.55THz and 0.4854THz, respectively, when the incident electromagnetic wave is incident perpendicularly from the front and from the back.

[0015] Figures 4(a), 4(b), and 4(c) show the reflection phases when the incident electromagnetic wave frequency is changed from 0.39 THz to 0.55 THz and 0.4854 THz, respectively, with a fixed cylinder radius of 122 micrometers and a metal thin film disk radius ranging from 15 micrometers to 37 micrometers, and when the incident electromagnetic wave frequency is changed from 0.39 THz to 0.55 THz and 0.4854 THz, respectively, when the incident electromagnetic wave is perpendicularly incident from the front and from the back.

[0016] Figures 5(a) and 5(b) are the electric field distribution diagrams of the XZ plane when electromagnetic waves are incident perpendicularly from the front and back sides in Implementation Case 1, respectively, with a frequency of 0.4854 THz.

[0017] Figures 6(a) and 6(b) are schematic diagrams of the front and back structure distribution of the corresponding metasurface in Implementation Case 2, respectively, with a total of 16*16 units;

[0018] Figures 6(c) and 6(d) are the electric field distribution diagrams of the XZ plane when electromagnetic waves are incident perpendicularly on the front and back sides of the corresponding metasurface in Implementation Case 2, respectively, with a frequency of 0.4854 THz.

[0019] Figures 7(a) and 7(b) are schematic diagrams of the front and back structure distribution of the metasurface in Implementation Case 3, respectively, with a total of 40*40 units;

[0020] Figures 7(c) and 7(d) are the phase distribution diagrams of the front and back sides of the corresponding metasurface in Implementation Case 3, respectively, with a frequency of 0.4854 THz;

[0021] Figures 7(e) and 7(f) are the electric field distribution diagrams of the XZ plane with y=0 when the front and back sides are perpendicularly incident, respectively, in Implementation Case 3, with a frequency of 0.4854 THz;

[0022] Figure 8(a) and Figure 8(b) are schematic diagrams of the front and back structure distribution of the metasurface in Implementation Case 4, respectively, with a total of 40*40 units;

[0023] Figures 8(c) and 8(d) are the phase distribution diagrams of the front and back sides of the corresponding metasurface in Implementation Case 4, respectively, with a frequency of 0.4854 THz;

[0024] Figures 8(e) and 8(f) are electric field distribution diagrams of the XY plane with z = 15 mm when the front and back sides of the corresponding metasurface are incident perpendicularly, respectively, with a frequency of 0.4854 THz; Detailed Implementation

[0025] The technical solution of the present invention will now be further described in conjunction with the accompanying drawings and embodiments.

[0026] like Figure 1 The diagram shows a schematic of a bidirectional beam-controlled metasurface with inversion symmetry breaking. Figures 2(a), 2(b), and 2(c) show the structural schematic, top view, and front view of the bidirectional beam-controlled metasurface unit with inversion symmetry breaking of the present invention, respectively. The metasurface unit of the present invention includes: a cylinder 1, a metal thin-film disk 2, and a cross-shaped beam 3. The metal thin-film disk 2 is located on one side of the surface of the cylinder 1 and is in direct contact with the cylindrical unit 1, belonging to a concentric structure. The cylindrical units 1 are connected by the cross-shaped beam 3 to form an array structure. The metasurface array is arranged in the XY plane, and the electromagnetic field is incident perpendicularly to the metasurface along the Z direction. The cylinder is inverted symmetric in the Z direction, and the metal thin-film disk located on one side of the cylinder breaks the inversion symmetry, thereby realizing the breaking of inversion symmetry in the Z direction.

[0027] Figures 3(a) and 3(b) show the reflection phases when the radius of the metal thin-film disk is fixed at 35 micrometers, and the incident electromagnetic wave frequency is changed from 0.39 THz to 0.55 THz while the cylinder radius is changed from 110 micrometers to 153 micrometers, with the incident wave occurring perpendicularly from the front and from the back. Figure 3(c) shows the phase changes under different incident directions when the radius of the metal thin-film disk is fixed at 35 micrometers and the cylinder radius is changed from 110 micrometers to 153 micrometers. Changing the cylinder radius during forward incidence produces a phase change of 2π, but the phase change caused by changing the cylinder radius during reverse incidence is much smaller than 2π.

[0028] Figures 4(a) and 4(b) show the reflection phases when the incident electromagnetic wave frequency is changed from 0.39 THz to 0.55 THz while the radius of the metal thin-film disk changes from 15 micrometers to 37 micrometers, with the cylinder radius fixed at 122 micrometers, and the wave is incident perpendicularly from the front and back. Figure 4(c) shows the phase changes under different incident directions when the cylinder radius is fixed at 122 micrometers and the radius of the metal thin-film disk is changed from 15 micrometers to 37 micrometers. Changing the radius of the metal thin-film disk in the reverse incident direction produces a phase change of 2π, but the phase change caused by changing the radius of the metal thin-film disk in the forward incident direction is much smaller than 2π.

[0029] By changing the cylinder radius and metal thin-film disk radius of the metasurface unit, both in-phase and out-of-phase unit structures can be designed. There are four in-phase unit structures and twelve out-of-phase unit structures. In six out-of-phase unit structures, the metal thin-film disk is located on the front side of the cylinder, while in the other six structures, the metal thin-film disk is located on the back side of the cylinder. Each unit structure can independently generate digital states "00", "01", "10", and "11" under the illumination of electromagnetic waves incident perpendicularly from the front and back, corresponding to reflection phases of 0 degrees, 90 degrees, 180 degrees, and 270 degrees. After permutation and combination, there are 16 different combinations: "00 / 00", "00 / 01", "00 / 10", "00 / 11", "01 / 00", "01 / 01", "01 / 10", "01 / 11", "10 / 00", "10 / 01", "10 / 10", "10 / 11", "11 / 00", "11 / 01", "11 / 10", and "11 / 11". The former is the digital state of the reflection phase when incident perpendicularly from the front, and the latter is the digital state of the reflection phase when incident perpendicularly from the back.

[0030] The geometric parameters of these 16 structures are shown in Table 1. Six of the heterogeneous unit structures can be obtained by translating the front metal film disk from the front of the cylinder along the Z direction to the back of the cylinder. Therefore, only the geometric parameters of four in-phase structures and six heterogeneous structures need to be given in the table.

[0031] Table 1 shows the geometric parameters of 16 basic unit structures of the bidirectional beam-controlled metasurface based on inversion symmetry breaking in this invention. The values ​​before the slashes represent the digital state of the front perpendicular incident reflection phase and the cylinder radius, respectively, while the values ​​after the slashes represent the digital state of the back perpendicular incident reflection phase and the metal thin film disk radius, respectively.

[0032]

[0033]

[0034] Combination Figure 5a to Figure 5b Description of Implementation Case 1

[0035] To demonstrate the functionality of a bidirectional beam-tunable metasurface based on inversion symmetry breaking, in the first example, we use a phase distribution that exhibits a gradient distribution when incident from the front, i.e., “00-01-10-11-00-01-10-11…”, while no phase gradient is generated when incident from the back.

[0036] Figure 5a and Figure 5bThe electric field distribution diagrams of the XZ plane when electromagnetic waves are incident perpendicularly from the front and back are shown respectively. It can be clearly seen that the beam incident perpendicularly from the front is deflected into the XZ plane at an angle of 24 degrees to the z-axis, while the beam incident perpendicularly from the back is reflected perpendicularly to the XY plane. The results of this calculation are consistent with those calculated by the generalized Snell's law formula θ=arcsin(λ / Γ), where λ represents the wavelength in free space and Γ represents the length of a gradient period.

[0037] Combination Figure 6a to Figure 6d Description of Implementation Case 2

[0038] In the second example, we employ a phase distribution that exhibits a gradient pattern when incident from the front, i.e., "00-01-10-11-00-01-10-11…", and produces the opposite phase gradient when incident from the back, i.e., "11-10-01-00-11-10-01-00…". The front structure of the array is as follows. Figure 6a As shown, the array back structure is distributed as follows Figure 6b As shown, electromagnetic waves incident perpendicularly from the front will have a 24° reflected beam deflection, and electromagnetic waves incident perpendicularly from the back will also have a 24° reflected beam deflection, but in the opposite direction. Figure 6c and Figure 6d The electric field distribution in the XZ plane is shown for both frontal and back perpendicular incident electromagnetic waves. This result is consistent with the calculations based on the generalized Snell's law.

[0039] Combination Figure 7a to Figure 7f Description of Implementation Case 3

[0040] The third example uses different phase arrangements on the front and back of the array to achieve reflective focusing with focal lengths of 15mm and 5mm respectively for vertical incidence from the front and back. Figure 7a and Figure 7b The front and back structures of the array are shown respectively. Figure 7c and Figure 7d The phase distribution is shown for the front and back sides, respectively. Figure 7e and Figure 7f The electric field distribution diagrams for the XZ plane with y=0 when incident perpendicularly from the front and back are shown respectively. It can be seen that reflection focusing was achieved, with focal lengths of 15mm and 5mm respectively, which meets the design target.

[0041] Combination Figure 8a to Figure 8f Description of Implementation Case 4

[0042] The fourth example uses different phase arrangements on the front and back sides of the array to achieve holographic imaging of different patterns. In this example, holographic imaging of the patterns "N" and "E" at a distance of 15mm from the structure is achieved by perpendicular incidence from the front and back sides, respectively. Figure 8a and Figure 8b The front and back structures of the array are shown respectively. Figure 8c and Figure 8d The phase distribution is shown for the front and back sides, respectively. Figure 8e and Figure 8f The electric field distribution diagrams for the XY plane with z=15mm when the light is incident perpendicularly from the front and back are shown respectively. It can be seen that holographic imaging with different patterns has been achieved, with the patterns being "N" and "E" respectively, which basically meet the design goals.

[0043] As demonstrated by the above embodiments, by assigning different encoding matrices to the metasurface, it can independently exhibit different functions under the illumination of electromagnetic waves incident perpendicularly from the front and back sides, such as anomalous reflection, focusing, and holographic imaging. Compared to metamaterials with geometric symmetry relative to their plane, this invention broadens the angle of electromagnetic wave manipulation because it has the same amplitude response and different phase responses to electromagnetic waves incident from the front and back sides. The resulting device is characterized by multifunctionality, flexible design, and high efficiency.

[0044] It should be noted that the above description is only a preferred embodiment of the present invention in the terahertz band. Because this design has the advantages of simple unit structure design and single-layer metal pattern, the same structure can be directly extended to the microwave, infrared, and visible light bands by scaling up the size. It should be pointed out that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A bidirectional beam-tunable metasurface based on inversion symmetry breaking, characterized in that, The system comprises multiple metasurface units arranged in a matrix in the XY plane, with electromagnetic waves incident perpendicularly to the metasurface along the Z-direction. Each metasurface unit includes a silicon cylinder, a metal thin-film disk, and a cross-shaped beam. The metal thin-film disk is located on one side of the silicon cylinder and is concentrically positioned and in direct contact with the silicon cylinder. The cross-shaped beam is located between adjacent metasurface units and connects adjacent silicon cylinders into an array structure. The single-sided arrangement of the metal thin-film disk causes the metasurface unit to form an inversion symmetry broken in the Z-direction. The metasurface unit includes in-phase unit structures and out-of-phase unit structures. The forward and reverse reflection phases of the in-phase unit structure are the same, while the forward and reverse reflection phases of the out-of-phase unit structure are different. Under the condition of a frequency of 0.4854 THz and the metal thin-film disk being located on the front side of the silicon cylinder, when the... When the radius of the metal thin film disk is fixed at 35 micrometers and the radius of the silicon cylinder varies from 110 micrometers to 153 micrometers, the reflection phase of the forward perpendicular incident light covers 2π, while the reflection phase change of the reverse perpendicular incident light is much less than 2π. When the radius of the silicon cylinder is fixed at 122 micrometers and the radius of the metal thin film disk varies from 15 micrometers to 37 micrometers, the reflection phase of the reverse perpendicular incident light covers 2π, while the reflection phase change of the forward perpendicular incident light is much less than 2π. By selecting the radius of the silicon cylinder, the radius of the metal thin film disk, and the position of the metal thin film disk on the front or back of the silicon cylinder, four types of in-phase unit structures and twelve types of out-of-phase unit structures are formed, resulting in 16 forward / reverse reflection phase states formed by orderly pairwise combinations of 0 degrees, 90 degrees, 180 degrees, and 270 degrees.

2. The bidirectional beam-tunable metasurface based on inversion symmetry breaking according to claim 1, characterized in that: The silicon cylinder has a height of 100 micrometers; the metal thin film disk is a gold thin film disk with a thickness of 200 nanometers; and the cross-shaped beam has a width of 10 micrometers.

3. The bidirectional beam-tunable metasurface based on inversion symmetry breaking according to claim 1 or 2, characterized in that, In the four types of in-phase unit structures, the metal thin film disks are all located on the front side of the silicon cylinder; in the twelve types of out-of-phase unit structures, the metal thin film disks in six structures are located on the front side of the silicon cylinder, while the metal thin film disks in the other six structures are located on the back side of the silicon cylinder.

4. The bidirectional beam-tunable metasurface based on inversion symmetry breaking according to any one of claims 1 to 3, characterized in that: The ordered combinations of reflected phases for forward and reverse perpendicular incidence are 0° / 0°, 0° / 90°, 0° / 180°, 0° / 270°, 90° / 0°, 90° / 90°, 90° / 180°, 90° / 270°, 180° / 0°, 180° / 90°, 180° / 180°, 180° / 270°, 270° / 0°, 270° / 90°, 270° / 180°, and 270° / 270°. Among them, the reflected phases of 0°, 90°, 180°, and 270° correspond to 2-bit electromagnetic codes 00, 01, 10, and 11, respectively. The part before the slash is the digital state of the reflected phase for forward perpendicular incidence, and the part after the slash is the digital state of the reflected phase for reverse perpendicular incidence.

5. The bidirectional beam-tunable metasurface based on inversion symmetry breaking according to claim 4, characterized in that: When the metal thin film disk is located on the front side of the silicon cylinder, the correspondence between the forward / backward reflection phase digital states and the silicon cylinder radius / metal thin film disk radius includes: 00 / 00 corresponds to 162 μm / 35 μm, 01 / 00 corresponds to 135 μm / 35 μm, 01 / 01 corresponds to 140 μm / 15 μm, 10 / 00 corresponds to 128 μm / 37 μm, 10 / 10 corresponds to 128 μm / 10 μm, 11 / 00 corresponds to 122 μm / 39 μm, 11 / 01 corresponds to 124 μm / 30 μm, 11 / 10 corresponds to 122 μm / 25 μm, 10 / 01 corresponds to 128 μm / 27 μm, and 11 / 11 corresponds to 120 μm / 10 μm; the remaining 6 heterogeneous unit structures are obtained by translating the corresponding metal thin film disk from the front side of the silicon cylinder along the Z direction to the back side of the silicon cylinder.

6. The use of the bidirectional beam-tunable metasurface based on inversion symmetry breaking as described in any one of claims 1 to 5 in bidirectional independent beam deflection, beam focusing, or holographic imaging, characterized in that, By arranging the in-phase and out-of-phase unit structures according to a predetermined coding matrix, the metasurface provides independent reflection phase distributions for electromagnetic waves incident perpendicularly in the forward and reverse directions, respectively.

7. The use according to claim 6, characterized in that, At a frequency of 0.4854 THz, different phase arrangements are used on the front and back sides of the metasurface, so that forward perpendicular incidence and reverse perpendicular incidence form reflective focusing with focal lengths of 15 mm and 5 mm, respectively.

8. The use according to claim 6, characterized in that, At a frequency of 0.4854 THz, different phase arrangements are used on the front and back sides of the metasurface, so that the forward perpendicular incidence and the reverse perpendicular incidence form holographic images of patterns "N" and "E" at a distance of 15 mm from the metasurface, respectively.

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