A broadband, amplitude-coordinated terahertz metasurface device

Abstract

This invention relates to a broadband amplitude-coherent terahertz metasurface device, comprising a top metal structure layer, an intermediate flexible polyimide dielectric layer, and a bottom metal plate layer arranged sequentially from top to bottom. The top metal structure layer, the intermediate flexible polyimide dielectric layer, and the bottom metal plate layer form a Fabry-Perot resonator. This invention achieves simultaneous amplitude and phase modulation solely through rotating the top metal structure of the subwavelength unit structure, effectively solving the problems of large size and low precision of Airy beamforming devices. This enables flexible modulation of broadband (0.95-1.8 THz) one-dimensional and two-dimensional Airy beams in the terahertz band, opening up possibilities for its application in high-capacity, obstacle-avoiding wireless communication.

Description

Technical Field

[0001] This invention belongs to the technical field of terahertz metamaterials and electromagnetic functional devices, specifically relating to a broadband amplitude isotropic terahertz metasurface device. Background Technology

[0002] The terahertz (THz) band offers abundant broadband resources for data transmission, potentially meeting the exponentially increasing data rate demands of future wireless communications. However, this high-frequency band requires directional beams to overcome path loss in free space. Airy beams, with their unique characteristics such as non-diffraction, self-bending, and self-healing properties, demonstrate great potential in solving diffraction-free obstacle-around transmission problems in wireless communication systems.

[0003] Traditional Airy beam generation relies on a phase mask formed by a spatial light modulator or diffractive optics element and additional Fourier transform lenses. These conventional methods are bulky, incompatible with on-chip integration of nanophotonic systems, and the pixel size of these methods is typically larger than the operating wavelength, limiting their performance and accuracy.

[0004] Metasurfaces are two-dimensional materials composed of ultrathin subwavelength structures. By cleverly designing the resonant modes and spatial distribution of the structure, multiple degrees of freedom of the electromagnetic field output by the metasurface can be manipulated, providing a smaller and more convenient method for generating Airy beams.

[0005] Currently, there is relatively little research on metasurface devices that can achieve Airy beam control in the terahertz band, and even fewer metasurface devices that can achieve broadband control. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a broadband amplitude-coherent terahertz metasurface device. It can achieve simultaneous amplitude and phase modulation by rotating the top metal structure of the subwavelength unit structure, effectively solving the problems of large size and low precision of Airy beam generation devices. Thus, it realizes flexible modulation of broadband (0.95-1.8THz) one-dimensional and two-dimensional Airy beams in the terahertz band, opening up possibilities for its application in high-capacity, obstacle-avoiding wireless communication.

[0007] The technical problem solved by this invention is achieved through the following technical solution:

[0008] A broadband amplitude-coherent terahertz metasurface device is characterized by comprising a top metal structure layer, an intermediate flexible polyimide dielectric layer, and a bottom metal plate layer arranged sequentially from top to bottom. The top metal structure layer, the intermediate flexible polyimide dielectric layer, and the bottom metal plate layer form a Fabry-Perot resonant cavity. The top metal structure layer can be rotated horizontally within a certain angle range to achieve simultaneous modulation of amplitude and phase.

[0009] Furthermore, the top metal structure layer and the bottom metal plate layer are both made of copper with a thickness of 0.18 to 0.22 μm, and the intermediate flexible polyimide dielectric layer is made of polyimide with a thickness of 24 to 26 μm. The dielectric constant of the intermediate flexible polyimide dielectric layer is 3.5 and the loss tangent is 0.0027.

[0010] Furthermore, the period length of the top metal structure layer is P = 100 μm. The top metal structure layer consists of an "8" shaped structure and two diagonally opposite circular arc structures. The "8" shaped structure is an open ring structure with symmetrical upper and lower parts. The upper open ring structure is cut from two circles with different radii and a rectangle. The centers of the two circles are O1 (0, 15 μm) and O2 (0, 22 μm), and the radii are r1 = 25 μm and r2 = 18 μm, respectively. The width of the rectangle is W1 = 12 μm. The lower open ring is formed by rotating the upper open ring 180 degrees symmetrically.

[0011] The upper arc structure is formed by cutting two ellipses with different major axis sizes and a rectangle. The two ellipses are concentric and have equal minor axis sizes. The major axis radii of the ellipses are r3 = 31 μm and r4 = 35 μm, respectively, and the minor axis radius is r5 = 21 μm. The center is O1 (0, 15 μm). The width of the rectangular structure is W2 = 50 μm. The lower arc structure is formed by rotating the upper arc structure 180 degrees symmetrically.

[0012] Furthermore, the rotation angle α of the top metal structure layer around the center of the structure ranges from -45 ≤ α ≤ 45, with clockwise rotation of the top metal structure layer being a positive angle direction and counterclockwise rotation being a negative angle direction. Under the illumination of a linearly polarized incident wave, the reflection Jones matrix of the anisotropic metasurface unit is expressed as:

[0013]

[0014] The Jones matrix reflecting the image after the top metal structure is rotated by an angle α is:

[0015]

[0016] in: For the rotation matrix of the metasurface device;

[0017] The cross-polarization reflection coefficient is calculated as: r yx =r xy =sin2α·(r xx -r yy ) / 2, by changing the rotation angle α, the full amplitude modulation of the cross-polarized reflected wave is achieved.

[0018] The advantages and beneficial effects of this invention are as follows:

[0019] 1. The terahertz metasurface device proposed in this invention can achieve simultaneous control of amplitude and phase by simply rotating the top metal structure of the device.

[0020] 2. The terahertz metasurface device proposed in this invention can achieve one-dimensional and two-dimensional Airy beam modulation in a broadband range of 0.95-1.8THz.

[0021] 3. The broadband one-dimensional and two-dimensional Airy beams realized by the terahertz metasurface device proposed in this invention exhibit excellent diffraction-free, self-bending, and self-healing properties. Attached Figure Description

[0022] Figure 1 (a) is a schematic diagram of the structure of the present invention. Figure 1 (b) is a schematic diagram of the top metal structure layer of the present invention;

[0023] Figure 2 (a) is a simulation curve of the reflection amplitude of the metasurface device of the present invention. Figure 2 (b) is a simulation curve of the reflection phase of the metasurface device of the present invention; Figure 2 (c) shows the phase and amplitude values ​​and the sin2α function of the metasurface device of the present invention at a frequency of 1 THz;

[0024] Figure 3 (a) and (b) are the theoretical amplitude and phase distribution diagrams along the x-axis of the one-dimensional Airy beam metasurface device with 40 sampling points according to the present invention.

[0025] Figure 4 (a) is the normalized electric field diagram of the one-dimensional Airy beam in the xoz plane generated by the reflection of the beam in the y-polarized direction when incident in the x-polarized direction according to the present invention. Figure 4 (b) shows the normalized electric field plots of the xoz surface of a one-dimensional Airy beam metasurface device with 40 sampling points under the incidence of waves of different frequencies. Figure 4 (c) is a diagram showing the self-healing characteristics of a one-dimensional Airy beam with different curvatures;

[0026] Figure 5 (a) and (b) are respectively the amplitude and phase distribution diagrams required by the present invention to generate the two-dimensional Airy beam metasurface device;

[0027] Figure 6 (a) is the normalized electric field diagram of the two-dimensional Airy beam in the xoy plane generated by the reflection of the x-polarized wave when the x-polarized wave of the present invention is incident. Figure 6 (b) is a diagram of the self-healing characteristics of a two-dimensional Airy beam. Detailed Implementation

[0028] The present invention will be further described in detail below through specific embodiments. The following embodiments are merely descriptive and not limiting, and should not be used to limit the scope of protection of the present invention.

[0029] like Figure 1 As shown in a), a broadband amplitude-coherent terahertz metasurface device is innovative in that it includes a top metal structure layer, an intermediate flexible polyimide dielectric layer, and a bottom metal plate layer arranged sequentially from top to bottom. The top metal structure layer, the intermediate flexible polyimide dielectric layer, and the bottom metal plate layer form a Fabry-Perot resonant cavity. The top metal structure layer can be rotated horizontally within a certain angle range to achieve simultaneous modulation of amplitude and phase.

[0030] The top metal structure layer and the bottom metal plate layer are both made of copper with a thickness of 0.18 to 0.22 μm, and the intermediate flexible polyimide dielectric layer is made of polyimide with a thickness of 24 to 26 μm. The dielectric constant of the intermediate flexible polyimide dielectric layer is 3.5 and the loss tangent is 0.0027.

[0031] like Figure 1 As shown in b), the periodic length of the top metal structure layer is P = 100 μm. The top metal structure layer consists of an "8" shaped structure and two diagonally opposite circular arc structures. The "8" shaped structure is an open ring structure with symmetrical upper and lower parts. The upper open ring structure is cut from two circles with different radii and a rectangle. The centers of the two circles are O1 (0, 15 μm) and O2 (0, 22 μm), and the radii are r1 = 25 μm and r2 = 18 μm, respectively. The width of the rectangle is W1 = 12 μm. The lower open ring is formed by rotating the upper open ring 180 degrees symmetrically.

[0032] The upper arc structure is formed by cutting two ellipses with different major axis sizes and a rectangle. The two ellipses are concentric and have equal minor axis sizes. The major axis radii of the ellipses are r3 = 31 μm and r4 = 35 μm, respectively, and the minor axis radius is r5 = 21 μm. The center is O1 (0, 15 μm). The width of the rectangular structure is W2 = 50 μm. The lower arc structure is formed by rotating the upper arc structure 180 degrees symmetrically.

[0033] Furthermore, the rotation angle α of the top metal structure layer around the center of the structure ranges from -45 ≤ α ≤ 45, with clockwise rotation of the top metal structure layer being a positive angle direction and counterclockwise rotation being a negative angle direction. Under the illumination of a linearly polarized incident wave, the reflection Jones matrix of the anisotropic metasurface unit is expressed as:

[0034]

[0035] The Jones matrix reflecting the image after the top metal structure is rotated by an angle α is:

[0036]

[0037] in: For the rotation matrix of the metasurface device;

[0038] The cross-polarization reflection coefficient is calculated as: r yx =r xy =sin2α·(r xx -r yy ) / 2, by changing the rotation angle α, the full amplitude modulation of the cross-polarized reflected wave is achieved.

[0039] like Figure 2 As shown in (a) and (b), the electromagnetic characteristics of the metasurface device of the present invention are illustrated by the cross-polarization reflection coefficient. Under X-ray polarized wave irradiation, full amplitude modulation under binary phase is achieved by rotating the metasurface unit from -45° to 45°, where α = ±45° corresponds to the highest reflection amplitude and α = 0° corresponds to the lowest reflection amplitude. The highest reflection amplitude is greater than 0.9 in the broadband operating frequency range of 0.95 to 1.8 THz.

[0040] Figure 2 (c) Further demonstrates the approximate sin2α functional relationship between the amplitude at the 1THz frequency and the rotation angle α, which is consistent with the above theoretical derivation results. Figure 2 (c) shows a binary phase with a phase difference of 180° at the 1 THz frequency point. The electromagnetic properties of the metasurface unit of this invention can meet the requirements for generating Airy beams with the same amplitude and coherence over a wide frequency band.

[0041] According to the Airy solution of the paraxial diffraction equation, the dynamic evolution propagation equation of an arbitrary trajectory of a one-dimensional finite-energy Airy beam is expressed as:

[0042]

[0043] Where: Ai is the Airy function, s = x / x0 is the transverse scale, a is the attenuation coefficient, and ξ is the normalized propagation distance. The attenuation coefficient a and the scaling length x0 determine the size and energy of the Airy beam's main lobe and side lobes. A smaller attenuation coefficient a results in slower side lobe energy attenuation, more pronounced side lobes, and a longer quasi-non-diffraction propagation distance; a larger scaling length x0 results in a wider main lobe and a longer quasi-non-diffraction propagation distance. Changing the scaling length x0 and the attenuation factor a yields an ideal Airy beam. Based on the non-diffraction characteristics of the Airy beam, the amplitude and phase distribution of the metasurface of a one-dimensional Airy beam generator is calculated using a real-valued function as follows:

[0044]

[0045] In fact, by simultaneously considering the Airy envelopes in the orthogonal directions, the propagation equation for a two-dimensional Airy beam can be easily derived, as follows:

[0046]

[0047] To design a metasurface device that generates a one-dimensional Airy beam, the continuous amplitude and phase distributions calculated by formula (2) should be further discretized. To improve accuracy, the perimeter of the unit structure is considered to be P = 100 μm, and the amplitude and phase at the center point of the unit structure are taken as the basis for arranging the metasurface units. Three one-dimensional Airy beam metasurface devices with sampling point numbers of N = 40, 50 and 60 are designed to verify the influence of the number of sampling points on the curvature of the Airy beam. To ensure the consistency of the number and energy of the Airy beam sidelobes, the attenuation coefficient a in formula (2) is uniformly set to 0.07, and the scaling length x0 is set to 0.0003, 0.0004 and 0.0005 respectively.

[0048] Figure 3 The theoretical amplitude and phase distribution along the x-axis of the one-dimensional Airy beam metasurface device with 40 sampling points, as well as the results after sampling, are shown. The sampling range is designed to be 0 to 4 mm, and 40 elements are generated by sampling in the x-axis direction. Open boundary conditions are applied in the x-direction, and periodic boundary conditions are applied in the y-direction to simulate and verify the performance of the metasurface device that generates a one-dimensional Airy beam.

[0049] Simulation of a metasurface device that generates a one-dimensional Airy beam under 1 THz x-polarized wave incidence. Figure 4 (a) shows the normalized electric field plot of the reflected y-polarization direction. The figure shows that even after long-distance propagation, the beam exhibits two distinct characteristics: constant intensity and a parabolic trajectory, demonstrating the diffraction-free and self-bending properties of the generated one-dimensional Airy beam. Furthermore, the beam curvature gradually decreases with increasing sampling points, proving the influence of the sampling point number on the one-dimensional Airy beam curvature. To further quantitatively analyze the reliability of the simulation results, Figure 4 The illustration in (a) shows a comparison between the simulation results and the theoretically predicted normalized electric field amplitude at a propagation distance of z = 1 mm. The results clearly show that the simulated one-dimensional Airy beam agrees well with the theoretical model, proving that the metasurface device of the present invention can achieve the control of one-dimensional Airy beams with different curvatures.

[0050] A one-dimensional Airy-beam metasurface device with 40 sampling points and three different frequencies (0.95 THz, 1.3 THz, and 1.8 THz) of x-polarized wave incident on it was used to verify its broadband performance. Simulation results are as follows: Figure 4As shown in (b), one-dimensional Airy beams can be observed at three different frequencies. Simulation results verify that the metasurface device of the present invention can achieve broadband Airy beam generation in the frequency range of 0.95–1.8 THz.

[0051] Self-healing is a key characteristic for identifying Airy beams, and it is typically verified by placing an obstacle in the propagation path of the main lobe. A 100μm × 100μm metallic obstacle was placed in front of the main lobe at a distance of 1500μm from the metasurface device to verify the self-healing properties of one-dimensional Airy beams with varying curvatures.

[0052] Figure 4 (c) illustrates the self-healing properties of a one-dimensional Airy beam. The figure shows that the energy of the main lobe is almost completely blocked by the obstacle for a certain distance after bypassing it. After this propagation distance, the energy propagation resumes on its original trajectory. Simulation results demonstrate the self-healing properties of a one-dimensional Airy beam with different curvatures.

[0053] The amplitude and phase distributions required for the metasurface device to generate a two-dimensional Airy beam, calculated according to formula (3), are shown in the figure. Figure 5 Similarly, using the sampling method described above for one-dimensional Airy beams, the amplitude and phase of the two-dimensional Airy beam are discretized. Open boundary conditions are applied in the x, y, and z directions to simulate the metasurface device generating the two-dimensional Airy beam. Furthermore, a 100μm × 100μm metal obstacle is placed in front of the main lobe at a distance of 1500μm from the metasurface device to verify the self-healing properties of the two-dimensional Airy beam.

[0054] Figure 6 (a) shows the normalized electric field plots of the xoy plane of the metasurface device generating a two-dimensional Airy beam at different propagation distances under 1 THz x-polarized wave incidence. It is clearly observed from the figure that as the propagation distance increases, the main lobe of the beam gradually shifts towards the positive x and y axes while maintaining its energy. The simulation results demonstrate the diffraction-free and self-bending characteristics of the two-dimensional Airy beam. Figure 6 (b) shows the normalized electric field plots of the two-dimensional Airy beam at different propagation distances after an obstacle is placed in front of the main lobe. The figure shows that the beam resumes energy propagation along its original trajectory after being blocked by the obstacle, confirming the self-healing property of the two-dimensional Airy beam.

[0055] Although embodiments and drawings of the present invention have been disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, variations and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments and drawings.

Claims

1. A broadband, amplitude-coordinated terahertz metasurface device, characterized in that: It includes a top metal structure layer, a middle flexible polyimide dielectric layer and a bottom metal plate layer arranged sequentially from top to bottom. The top metal structure layer, the middle flexible polyimide dielectric layer and the bottom metal plate layer form a Fabry-Perot resonant cavity. The top metal structure layer can be rotated horizontally within the range of -45 to 45 degrees to achieve simultaneous control of amplitude and phase. The periodic length of the top metal structure layer is P = 100 μm. The top metal structure layer consists of an "8" shaped structure and two diagonally opposite circular arc structures. The "8" shaped structure is an open ring structure with symmetrical upper and lower parts. The upper open ring structure is cut from two circles with different radii and a rectangle. The centers of the two circles are O1 (0, 15 μm) and O2 (0, 22 μm), and the radii are r1 = 25 μm and r2 = 18 μm, respectively. The width of the rectangle is W1 = 12 μm. The lower open ring is formed by rotating the upper open ring 180 degrees symmetrically. The upper arc structure is formed by cutting two ellipses with different major axis sizes and a rectangle. The two ellipses are concentric and have equal minor axis sizes. The major axis radii of the ellipses are r3 = 31 μm and r4 = 35 μm, respectively, and the minor axis radius is r5 = 21 μm. The center is O1 (0, 15 μm). The width of the rectangular structure is W2 = 50 μm. The lower arc structure is formed by rotating the upper arc structure 180 degrees symmetrically. The rotation angle α of the top metal structure layer around the center of the structure ranges from -45° ≤ α ≤ 45°. Clockwise rotation of the top metal structure layer is a positive angle direction, and counterclockwise rotation is a negative angle direction. Under the illumination of a linearly polarized incident wave, the reflection Jones matrix of the anisotropic metasurface unit is expressed as: The Jones matrix reflecting the image after the top metal structure layer is rotated by an angle α is: in: For the rotation matrix of the metasurface device; The cross-polarization reflection coefficient is calculated as: r yx =r xy =sin2α·(r xx -r yy ) / 2, by changing the rotation angle α, the full amplitude modulation of the cross-polarized reflected wave is achieved.

2. The broadband amplitude-coherent terahertz metasurface device according to claim 1, characterized in that: The top metal structure layer and the bottom metal plate layer are both made of copper with a thickness of 0.18 to 0.22 μm, and the intermediate flexible polyimide dielectric layer is made of polyimide with a thickness of 24 to 26 μm. The dielectric constant of the intermediate flexible polyimide dielectric layer is 3.5 and the loss tangent is 0.0027.

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