A focal point space adjustable reconfigurable terahertz coding metasurface plane mirror

Abstract

The application discloses a reconfigurable terahertz coding metasurface plane mirror with adjustable focal point space, aims to provide a controllable adjustment method for electromagnetic wave focusing, and solves the problems of poor reconfigurability, unadjustable focal point position and rigid adjustment of an existing metasurface mirror. The unit structure of the metasurface plane mirror comprises a metal-graphene layer, a dielectric layer and a metal layer arranged in sequence from top to bottom, and the metasurface mirror is designed according to a theoretical phase value. Different coding units are obtained by changing the Fermi energy level of graphene, and the spatial position regulation and control function of reflected electromagnetic wave focusing is realized by combining the coding sequence with the coding metasurface plane mirror.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of artificial electromagnetic super surface, and particularly relates to a focal point space adjustable reconfigurable terahertz coded super surface plane mirror which can realize real-time adjustment of the spatial position of the focal point in the terahertz band. BACKGROUND

[0002] Terahertz waves refer to electromagnetic radiation with a frequency range of about 0.1 THz-10 THz, and the corresponding wavelength range is about 0.03 mm-3 mm. A thin plane with resonant sub-wavelength units arranged in a periodic manner, i.e. a super surface, can control electromagnetic fields. In recent years, terahertz devices have been continuously researched and developed, including modulators, filters, super surface mirrors and absorbers, sensors and other high-performance terahertz devices, which are of great significance to the research and application of terahertz systems. Terahertz super surface mirrors are widely used in imaging, communication, miniaturized cavities, adjustable frequency focusing materials and many other application research fields related to the development of national economy and national defense. Therefore, it is of great value to design a high-performance adjustable terahertz super surface plane mirror in the terahertz band.

[0003] In recent years, the functions of various super surface mirrors have been widened from single to multi-function and from fixed to adjustable. Related researchers have also explored in the direction of dynamic super surface mirrors. In the microwave and visible light bands, the existing solutions for dynamically changing the focal point of the super surface mirror mainly use micro-electromechanical systems, special elastic materials and liquid metals. However, these methods are not suitable for the terahertz band. Moreover, the super surface mirrors using related dielectric structures have the disadvantages of poor reconfigurability, complex structure and the like. In view of the above problems, the application provides a focal point space adjustable reconfigurable terahertz coded super surface plane mirror, which realizes adjustable focusing of reflected waves in the terahertz band.

[0004] Graphene is a two-dimensional material with excellent performance. Because of the low carrier density near the Dirac point, the Fermi level of graphene can be adjusted. This phenomenon provides a new method for manipulating the interaction between electromagnetic waves and matter for the adjustability of super surface mirrors. Graphene combined with metamaterials can produce adjustable characteristics, and the speed of electromagnetic control is superior to temperature control, micro-electromechanical control and the like. In addition, the key of the coded super surface mirror lies in that it is composed of four coding units of "0", "1", "2" and "3", and the coding units have a phase difference of 90°, and the placement position and quantity of the units can be designed flexibly. SUMMARY

[0005] The application aims to provide a focal point space adjustable reconfigurable terahertz coded super surface plane mirror. The application solves the problems of poor reconfigurability, complex structure, unadjustable focal point position and rigid adjustment of existing terahertz super surface mirrors.

[0006] The technical scheme adopted by the present application is as follows:

[0007] The reconfigurable terahertz coded metasurface plane mirror with adjustable focal point space comprises, from top to bottom, a metal-graphene layer, a dielectric layer, and a metal layer.

[0008] Further, the focal point space adjustable mode is to use a coded sequence to guide the focal point to a pre-designed direction.

[0009] Further, the material of the metal in the uppermost metal-graphene layer is gold.

[0010] Further, the material of the intermediate dielectric layer is cyclic olefin copolymer (COC), and the relative dielectric constant ε of the intermediate dielectric layer is r = 2.35.

[0011] Further, the material of the metal in the bottom metal layer is gold.

[0012] As described above, due to the adoption of the above technical scheme, the present application has the following beneficial effects:

[0013] In the present application, the terahertz coded metasurface plane mirror has a simple and unified structure, and the opening structure design further enhances the response of electromagnetic waves and the structure. By adjusting the graphene Fermi level, the reflection phase requirements of different coding units, i.e., 0°, 90°, 180°, and 270°, can be met, which are correspondingly coded as "0", "1", "2", and "3", thereby meeting the design requirements of the coded metasurface mirror. The y-polarized electromagnetic waves can be focused on the focal plane. Meanwhile, the focal point can be effectively adjusted to a pre-designed position by using the constructed coded sequence. Unlike other dielectric or other fixed structure coded metasurface mirrors, once the structure is fixed, the coding state cannot be changed. By loading different Fermi levels in the same unit structure, different coding states can be achieved, and real-time coded metasurface mirrors can be realized, thereby flexibly adjusting the spatial position of the focal point of the metasurface plane mirror. This flexible coding method solves the problems of poor reconfigurability, complex structure, unadjustable focal point position, and rigid adjustment of existing metasurface mirror devices. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 FIG. 1 is a schematic diagram of a reconfigurable terahertz coded metasurface plane mirror;

[0015] Figure 2 FIG. 2 is a schematic diagram of a unit structure of a reconfigurable terahertz coded metasurface plane mirror;

[0016] Figure 3The reflection phase of four coding units "0", "1", "2" and "3" of the reconfigurable terahertz coding metasurface planar mirror;

[0017] Figure 4 (a) is a coding schematic diagram of the reconfigurable terahertz coding metasurface planar mirror; Figure 4 (b) is an electric field distribution in the Z-Y (X=0mm) plane; Figure 4 (c) is an electric field distribution in the X-Y (Z=1mm) plane;

[0018] Figure 5 The reconfigurable terahertz coding metasurface planar mirror formed by superimposing the Sx3 coding sequence is shown in the figure;

[0019] Figure 6 The electric field distribution of the reconfigurable terahertz coding metasurface planar mirror formed by superimposing the Sx3 coding sequence is shown in the figure;

[0020] Figure 7 The reconfigurable terahertz coding metasurface planar mirror formed by superimposing the Sy2 and Sx3 coding sequences is shown in the figure;

[0021] Figure 8 (a) is the electric field distribution of the reconfigurable terahertz coding metasurface planar mirror formed by superimposing the Sy2 and Sx3 coding sequences, and the pitch angle deflection schematic diagram is shown in the figure; Figure 8 (b) is the electric field distribution in the X-Y (Z=0.88mm) plane and the azimuth angle deflection schematic diagram. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application, and are not used to limit the present application. Based on the examples of the present application, all other examples obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0023] The reconfigurable terahertz coding metasurface planar mirror with adjustable focal point space comprises a metal-graphene layer, a dielectric layer and a metal layer arranged from top to bottom.

[0024] Further, the adjustable focal point space mode is to guide the focal point to a pre-designed direction by using a coding sequence.

[0025] Further, the material of the metal in the uppermost metal-graphene layer is gold.

[0026] Further, the material of the intermediate dielectric layer is cyclic olefin copolymer (COC), and the relative dielectric constant ε r =2.35.

[0027] Further, the material of the metal in the bottom metal layer is gold.

[0028] Figure 1 It is a schematic diagram of a reconfigurable terahertz coded metasurface plane mirror. Based on the unit structure at different positions, the phase design of the metasurface mirror should meet the following formula:

[0029]

[0030] Where F represents the focal length of the super lens, (x, y) is the position coordinate of the unit structure with the center of the metasurface as the origin, and λ is the incident wavelength of the super lens.

[0031] Figure 2 It is a schematic diagram of a reconfigurable terahertz coded metasurface plane mirror unit structure. The metasurface unit structure includes a metal-graphene layer, a dielectric layer, and a metal layer from top to bottom. The thickness of the top elliptical split ring resonator is t1=1μm, the thickness of the intermediate spaced dielectric layer is t1=9μm, and the bottom metal layer has a thickness of t1=1μm, which reduces the loss caused by the transmission of the incident wave. The designed terahertz metasurface mirror unit period is P=50μm, and the uppermost layer is an elliptical split ring resonator, which contains two elliptical split rings separated by a graphene strip. The major axis of the elliptical split ring is a=20μm, the minor axis is b=14μm, the width is w=2μm, and the width of the graphene strip is w x =6μm, and the length is w y =32μm.

[0032] Figure 3 It is the reflection phase of four coded units "0", "1", "2" and "3" of a reconfigurable terahertz coded metasurface plane mirror. The phase of the coded metasurface mirror unit structure changes continuously in the frequency range of 1.8THz-2THz under different Fermi energy levels, and the coverage range of the phase is as high as 270°. Therefore, the constructed phase distribution is feasible and flexible. For example, by loading 0.28eV, 0.38eV, 0.52eV and 1.15eV Fermi energy levels on the graphene strips of the four coded units respectively, a 2-bit coded phase distribution of 0°, 90°, 180° and 270° can be realized, and the working frequency point of this embodiment is located at 1.86THz.

[0033] Figure 4(a) is a coding schematic diagram of a reconfigurable terahertz coded metasurface plane mirror. The coded metasurface plane mirror is designed according to formula (1). The ideal focal position is (0,0,1)mm and the focal length is 1mm. Figure 4 (b) shows the electric field distribution in the ZY (X = 0 mm) plane. Figure 4 (c) shows the electric field distribution in the XY (Z = 1 mm) plane. It can be seen that the reflected plane wave converges to the focal point (0,0,1) mm in the Z-axis direction.

[0034] Figure 5 A schematic diagram of the formation process of a reconfigurable terahertz coded metasurface planar reflector constructed by superimposing the Sx3 coding sequence is shown below. The coding unit sequence Sx3 mentioned is represented as a coding sequence formed by arranging the coding sequence in the manner of 0°, 0°, 0°, 90°, 90°, 90°, 180°, 180°, 180°, 270°, 270°, 270°. The characteristic is that the number of units in the coding sequence is 3, and the direction of the coding sequence is the X direction.

[0035]

[0036] Will Figure 4 The encoding schematic diagram of the encoded metasurface plane mirror shown in (a) and the encoding sequence Sx3 can be used to perform Fourier operation to form an encoded metasurface plane mirror that is different from the focal position (0,0,1)mm.

[0037] Figure 6 The figure shows the electric field distribution at the deflection focus in the X-direction of a reconfigurable terahertz coded metasurface plane mirror constructed by superimposing Sx3 coding sequences. As can be seen, the coded metasurface plane mirror constructed by superimposing Sx3 coding sequences retains its focusing characteristics but deviates from the original focal position (0,0,1) mm. The resulting coded metasurface plane mirror has a focal position of (0.29,0,0.96) mm, a deviation angle of 17°, and is located in the X-direction of the coding sequence.

[0038] Figure 7 A schematic diagram illustrating the formation process of a reconfigurable terahertz coded metasurface planar mirror constructed by simultaneously superimposing Sy2 and Sx3 coding sequences. The mentioned coding unit sequence Sx3 is as follows: Figure 5 As shown in the figure, the mentioned coding unit sequence Sy2 is as follows, representing a coding sequence formed by arranging the coding sequence in the pattern of 0°, 0°, 90°, 90°, 180°, 180°, 270°, 270°. The characteristic is that the number of units within the coding sequence is 2, and the direction of the coding sequence is the Y direction.

[0039]

[0040] The code sequence of Sy2 and Sx3 superimposed simultaneously can be expressed as

[0041]

[0042] The code sequence of Sy2 and Sx3 superimposed simultaneously can be expressed as Figure 4 The code sequence of Sy2 and Sx3 superimposed simultaneously can be expressed as

[0043] Figure 8 The code sequence of Sy2 and Sx3 superimposed simultaneously can be expressed as Figure 8 The code sequence of Sy2 and Sx3 superimposed simultaneously can be expressed as

[0044] The code sequence of Sy2 and Sx3 superimposed simultaneously can be expressed as The code sequence of Sy2 and Sx3 superimposed simultaneously can be expressed as

Claims

1. A reconfigurable terahertz-encoded metasurface planar reflector with adjustable focal space, characterized in that, The metasurface reflector array adopts an identical unit structure. Each unit includes, from top to bottom, a gold-graphene composite layer, a cyclic olefin copolymer (COC) dielectric layer, and a gold reflective layer. The gold-graphene composite layer includes an elliptical split-ring resonator, which consists of two elliptical open rings of the same size, separated by a graphene strip. By controlling the Fermi level of the graphene in different units of the array, it can operate in different encoding states and be used to construct a dynamically variable encoding sequence. The encoding sequence is convolved with the wavefront phase distribution corresponding to the preset target focus to dynamically reconstruct the wavefront phase distribution of the reflected wave, thereby achieving precise dynamic control of the three-dimensional position of the reflected wave focus in the upper half-space.

2. The reconfigurable terahertz coded metasurface planar reflector with adjustable focal space according to claim 1, characterized in that, The metasurface mirror operates at a frequency of 1.86 THz. At this frequency, by changing the Fermi level of graphene, the unit structure can generate four discrete phase responses with an interval of 90° required for 2-bit encoding, thereby achieving phase coverage from 0° to 270°.

3. The reconfigurable terahertz coded metasurface planar reflector with adjustable focal space according to claim 1, characterized in that, The period of the unit structure is P = 50 μm, wherein the major axis of the elliptical open ring of the elliptical split ring resonator is a = 20 μm, the minor axis is b = 14 μm, and the width is w = 2 μm; the width of the graphene strip is w_x = 6 μm, and the length is w_y = 32 μm.

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