Total-space four-channel holographic imaging technology based on asymmetric transmission multilayer metasurface

Abstract

The invention relates to full-space electromagnetic holographic imaging based on a multi-layer metasurface, and relates to the technical field of coding metasurfaces. The invention aims to solve the problem that a metasurface holographic unit realized by an existing multilayer dielectric cascade structure is complex in structure and has symmetrical transmission limitation. The multi-layer coding metasurface unit for four-channel holographic imaging comprises a top layer, a dielectric layer, a grating layer, a dielectric layer and a bottom layer in sequence, the top layer and the bottom layer are of a metal two-way arrow structure and are symmetrical about the x axis and the y axis, and the middle layer is the grating layer composed of metal strips which are vertically arranged at equal intervals. As a basic structure unit, the spatial symmetry in the electromagnetic wave propagation direction is broken, and full-range phase modulation is achieved while the asymmetric transmission characteristic is obtained. The method has the advantages of being easy to design, easy to process and the like, has the asymmetric property and is applied to the fields of information encryption, multi-channel information processing and the like.

Description

Technical Field

[0001] The present invention relates to a full-space four-channel holographic imaging technology based on an asymmetric transmission multi-layer metasurface, and relates to the design of a metasurface capable of simultaneously generating different holographic imaging effects in two directions, belonging to the application technical fields of holographic display, polarization optics, and information encryption. Background Art

[0002] Due to its potential uses in future optical applications, holographic technology has attracted great interest in a wide range of optical fields, such as holographic imaging and optical data storage. Although considerable efforts have been made to develop holographic technology using traditional optical techniques, key problems still hinder their future development. As an emerging multifunctional device, a metasurface can manipulate the phase, amplitude, polarization, and resonance characteristics of electromagnetic fields in the sub-wavelength range, opening up an alternative for compact holographic structures and high imaging quality. However, currently, most metasurface holographic imaging regulations involve less exploration of the incident direction and are usually achieved in half of the imaging space (transmission space or reflection space), while the other half of the space is not utilized, resulting in a waste of electromagnetic wave resources and limiting the metasurface holographic view to half-space imaging. Therefore, the further application of metasurfaces is restricted. Thus, the full-space regulation design of a bidirectional metasurface is worthy of exploration. Our design has important application scenarios in the fields of low-cost and miniaturized communication. The present invention breaks the symmetry of space and realizes the phase modulation of asymmetric transmission in the full space. Summary of the Invention

[0003] The purpose of the present invention is to overcome the problems of symmetrically transmitted electromagnetic waves existing in traditional metasurfaces and the waste of electromagnetic wave space resources caused by only half-space regulation methods, and to provide an all-space electromagnetic regulation metasurface and metasurface unit with asymmetric transmission. The present invention can regulate the cross-polarization transmission phase and cross-polarization reflection phase of electromagnetic waves incident from two opposite directions, and the tunability of the full-space phase of electromagnetic waves incident in a specific direction can be achieved through this method. At the same frequency point, independent regulation of the cross-polarization wave transmission of the same polarization wave incident from two directions is realized. When the electromagnetic wave incident in the forward direction is transmitted, the holographic image letter "HIT" is generated, while when the electromagnetic wave incident in the reverse direction is transmitted, the holographic number "100" is generated. In addition, the corresponding cross-polarization reflection channels respectively generate the holographic images "HIT" and "100" for the electromagnetic waves incident from two directions.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] The full-space four-channel holographic imaging technology based on an asymmetric transmission multi-layer metasurface includes a top layer A, a dielectric layer, a grating layer B, a dielectric layer, and a bottom layer C stacked in sequence. The top and bottom layers are metal "bidirectional arrow" structures, which are symmetric about the x and y axes. The middle layer is a grating layer composed of vertically arranged metal strips with the same interval. The angles between the centers of the metal patches A and C and the positive x-axis are θ1 and θ2.

[0006] The full-space four-channel holographic imaging technology based on an asymmetric transmission multi-layer metasurface includes m×n periodically arranged phase mutation units, where both m and n are positive integers; and both m and n are 51.

[0007] For the full-space four-channel holographic imaging technology based on an asymmetric transmission multi-layer metasurface, the metal layer A, the grating layer B, and the metal layer C are all copper layers, and the thickness of the copper sheet is 0.018 mm.

[0008] For the full-space four-channel holographic imaging technology based on an asymmetric transmission multi-layer metasurface, the unit structure is square, with a side length of p = 6 mm. The thickness of the dielectric layer is 1 mm, the relative permittivity is 2.56, and the tangent value of the loss angle is 0.001.

[0009] For the full-space four-channel holographic imaging technology based on an asymmetric transmission multi-layer metasurface, the fixed values of the remaining parameters of the unit structure are: p = 6 mm, b = 0.6 mm, s = 1.2 mm, w = 0.4 mm, l = 5 mm.

[0010] For the full-space four-channel holographic imaging technology based on an asymmetric transmission multi-layer metasurface, a linearly polarized wave is incident perpendicularly on the metasurface in the forward direction. The transmitted cross-polarized wave generates a hologram "HIT", and the reflected cross-polarized wave generates a hologram "HIT".

[0011] For the full-space four-channel holographic imaging technology based on an asymmetric transmission multi-layer metasurface, a linearly polarized wave is incident perpendicularly on the metasurface in the reverse direction. The transmitted cross-polarized wave generates a hologram "100", and the reflected cross-polarized wave generates a hologram "100".

[0012] Beneficial effects:

[0013] The present invention is based on a full-space four-channel holographic imaging technology of an asymmetric transmission multi-layer metasurface. Using multi-layer metal patches, dielectric layers, and grating layers as basic structural units, it breaks the spatial symmetry in the electromagnetic wave propagation direction, enabling the electromagnetic wave to exhibit different reflection and transmission wavefront modulation characteristics according to different transmission channels during forward and reverse transmissions. By adjusting the size of the metal patches, full-phase modulation from 0 to 2π can be achieved, so it can be used to encode different functional phases. Combining the encoded holographic phase distribution map with the asymmetric transmission characteristics of the cascaded multi-layer metasurface further realizes four holographic imaging channels in two directions. The functions in the two directions are relatively independent, so it has a high tolerance for alignment errors in the layer-by-layer preparation process during processing. Description of the Drawings

[0014] Figure 1 It is a three-dimensional view of the unit structure of the full-space four-channel holographic imaging technology of the present invention based on an asymmetric transmission multi-layer metasurface;

[0015] Figure 2 It is the top layer A of the unit structure of the full-space four-channel holographic imaging technology of the present invention based on an asymmetric transmission multi-layer metasurface;

[0016] Figure 3 It is the intermediate grating layer B of the unit structure of the full-space four-channel holographic imaging technology of the present invention based on an asymmetric transmission multi-layer metasurface;

[0017] Figure 4 It is the bottom layer C of the unit structure of the full-space four-channel holographic imaging technology of the present invention based on an asymmetric transmission multi-layer metasurface;

[0018] Figure 5 It is the amplitude and phase modulation effects of 16 different basic constituent units selected for the multi-layer metasurface disclosed by the present invention on each channel. (a) Transmission amplitude spectra of the transmission cross-polarization components of linearly polarized waves incident on the metasurface in the forward and reverse directions. (b) Transmission phase spectra of the transmission cross-polarization components of linearly polarized waves incident on the metasurface in the forward and reverse directions.

[0019] Figure 6 It is the holographic simulation diagram realized by the cross-polarization reflected wave under the forward incidence of linearly polarized waves in the present invention.

[0020] Figure 7 It is the holographic test diagram realized by the cross-polarization reflected wave under the forward incidence of linearly polarized waves in the present invention.

[0021] Figure 8 It is the holographic simulation diagram realized by the cross-polarization transmitted wave under the forward incidence of linearly polarized waves in the present invention.

[0022] Figure 9This is the holographic test pattern realized by the cross-polarized transmitted wave under the forward incidence of the on-line polarized wave of the present invention.

[0023] Figure 10 This is the holographic simulation pattern realized by the cross-polarized reflected wave under the reverse incidence of the on-line polarized wave of the present invention.

[0024] Figure 11 This is the holographic test pattern realized by the cross-polarized reflected wave under the reverse incidence of the on-line polarized wave of the present invention.

[0025] Figure 12 This is the holographic simulation pattern realized by the cross-polarized transmitted wave under the forward incidence of the on-line polarized wave of the present invention.

[0026] Figure 13 This is the holographic test pattern realized by the cross-polarized transmitted wave under the forward incidence of the on-line polarized wave of the present invention. Detailed implementation manners

[0027] The present invention is designed through the following steps

[0028] Detailed implementation manner one: Combining Figure 1 , Figure 2 , Figure 3 and Figure 4 Specifically illustrate this implementation manner. The multi-layer coded metasurface for full-space electromagnetic holographic imaging described in this implementation manner includes a plurality of metasurface units arranged in an array. Each metasurface unit includes: a dielectric substrate with a thickness of h = 3 mm and a dielectric constant of 2.65. The top layer A and the bottom layer C are metal "bidirectional arrow" structures, both made of copper, with a thickness of 0.018 mm, having symmetry about the x and y axes. The middle layer is a grating layer composed of vertically arranged metal strips with the same interval. The angles between the centers of the metal patches A and C layers and the positive x-axis are θ1 and θ2. It has the following fixed parameters: p = 6 mm, b = 0.6 mm, s = 1.2 mm, w = 0.4 mm, l = 5 mm.

[0029] Detailed implementation manner two: Set the center frequency of the full-space four-channel holographic imaging technology based on an asymmetric transmission multi-layer metasurface of the present invention to 15 GHz.

[0030] Detailed implementation manner three: Combining Figure 5 Specifically illustrate this implementation manner. We further realize the corresponding change of the unit phase by changing the size and angle of the unit structure. The size change is shown in Table 1. Figure 5 (a) and 5(b) show the amplitude spectra of the transmitted x-polarized waves of all 16 coding units under the forward and reverse incidences of the y-polarized wave. Figure 5Indicates the transmission phase of the transmission cross-polarization components (x-polarized waves) of all 16 coding elements for the forward and backward incidence of y-polarized waves. Additionally, the phase distribution corresponding to the reflection channel is the same as that of Figure 5 is the same.

[0031] Table 1. Structural parameters of the 16 coding units of the metasurface (mm)

[0032]

[0033] Embodiment 4: In the asymmetric transmission full-space wavefront modulation method based on a multi-layer metasurface, the metasurface includes m×n periodically arranged phase mutation units, where both m and n are positive integers; and both m and n are 51. That is, the metasurface consists of 51×51 sub-atoms with a total area of 306×306 mm 2 .

[0034] Embodiment 5: In the full-space four-channel holographic imaging technology based on an asymmetric transmission multi-layer metasurface, the coding units that simultaneously meet the y-polarized electromagnetic wave excitation conditions are combined into the same metasurface and arranged according to image amplitude coding or phase coding to form a coded metasurface, which can achieve holographic imaging.

[0035] When a linearly polarized wave is incident vertically on the metasurface in the forward direction, the transmitted cross-polarized wave in the forward incidence generates a hologram "HIT", and the simulation results are as shown in the appendix Figure 6 shown, and the test results are as shown in Figure 7 shown, and the reflected cross-polarized wave generates a hologram "HIT", and the simulation results are as shown in the appendix Figure 8 shown, and the test results are as shown in Figure 9 shown.

[0036] It can be seen from Figures 6 - 9 that the letter "HIT" is clearly reconstructed in the near-field region.

[0037] Embodiment 6: When a linearly polarized wave is incident vertically on the metasurface in the reverse direction, the transmitted cross-polarized wave generates a hologram "100", and the simulation results are as shown in the appendix Figure 10 shown, and the test results are as shown in Figure 11 shown, and the reflected cross-polarized wave generates a hologram "100", and the simulation results are as shown in the appendix Figure 12 shown, and the test results are as shown in Figure 13 shown. It can be seen from Figures 10 - 13 that the letter "100" is clearly reconstructed in the near-field region. The test results are in good agreement with the simulation results, verifying the effectiveness of using the proposed coded metasurface to achieve full-space holographic imaging.

[0038] This embodiment can achieve electromagnetic wave control of four channels in the whole space through phase encoding under the excitation of y-polarized electromagnetic waves incident in different directions. The proposed coded metasurface can work in reflection and transmission modes when excited by y-polarized waves. By regulating the size and angle of the top layer of the metasurface, phase-coded metasurface holography is realized. At the same time, when excited by the reverse incidence of y-polarized waves, it works in transmission and reflection modes, and different coded metasurface holographies are realized by changing the size and angle of the bottom layer of the metasurface. The present invention realizes the electromagnetic reconstruction of four images in the same coded metasurface, solving the technical bottleneck that the whole-space metasurface is realized by a multi-layer cascade structure, which has a large volume, high cost, difficult processing, and is not conducive to integration with modern electromagnetic devices and systems. The whole-space coded metasurface proposed in this embodiment has good application prospects in the fields of beam control, beamforming, and holographic imaging.

Claims

1. The full-space four-channel holographic imaging technology based on an asymmetric transmission multi-layer metasurface, characterized in that: It includes a top layer A, a dielectric layer, a grating layer B, a dielectric layer, and a bottom layer C stacked in sequence. The top layer and the bottom layer are metal "bidirectional arrow" structures, which are symmetric about the x and y axes. The middle layer is a grating layer composed of vertically arranged metal strips with the same interval. The angles between the centers of the metal patches A and C layers and the positive direction of the x-axis are θ1 and θ2.

2. The all-space four-channel holographic imaging technology based on an asymmetric transmission multi-layer metasurface according to claim 1, wherein: It includes m×n periodically arranged phase mutation units, where both m and n are positive integers; and both m and n are 51.

3. The full-space four-channel holographic imaging technology based on an asymmetric transmission multi-layer metasurface according to claim 1, characterized in that: The metal layer A, the grating layer B, and the metal layer C are all copper layers, and the thickness of the copper sheet is 0.018 mm.

4. The full-space four-channel holographic imaging technology based on an asymmetrically transmitted multi-layer metasurface according to claim 1, characterized in that: The unit structure is square, with a side length of p = 6 mm. The thickness of the dielectric layer is 1 mm, the relative permittivity is 2.56, and the tangent value of the loss angle is 0.

001.

5. The all-space four-channel holographic imaging technology based on an asymmetric transmission multi-layer metasurface according to claim 1, wherein: The fixed values of the remaining parameters of the unit structure are: p = 6 mm, b = 0.6 mm, s = 1.2 mm, w = 0.4 mm, l = 5 mm.

6. The all-space four-channel holographic imaging technology based on the asymmetric transmission multi-layer metasurface according to claims 1-5, wherein: A linearly polarized wave is incident normally in the forward direction on this metasurface. The transmitted cross-polarized wave incident in the forward direction generates a hologram "HIT", and the reflected cross-polarized wave generates a hologram "HIT".

7. The full-space four-channel holographic imaging technology based on the asymmetric transmission multi-layer metasurface according to claims 1-5, characterized in that: A linearly polarized wave is incident normally in the reverse direction on this metasurface. The transmitted cross-polarized wave incident in the forward direction generates a hologram "100", and the reflected cross-polarized wave generates a hologram "100".

Images