Programmable metasurface based on modulo addition operation for terahertz beam steering

Abstract

The application discloses a programmable metasurface for realizing terahertz beam control based on modulo addition operation, comprising an upper quartz substrate, a lower quartz substrate, a metal structure grown on the upper and lower quartz substrates, and liquid crystal material sealed between the upper and lower metal structures. The application further discloses a method for preparing the above-mentioned terahertz liquid crystal metasurface and a method for realizing beam control through 1-bit modulo addition operation by using the above-mentioned terahertz liquid crystal metasurface. The programmable metasurface realizes half-space control of terahertz beams through modulo addition operation after separately coding rows and columns, and has the characteristics of simple device structure, flexible and convenient control method and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of terahertz wave regulation, and particularly relates to a programmable super surface for realizing terahertz beam regulation based on mode addition operation, and particularly relates to preparation and application of a programmable super surface (also known as super material, super structured material, super structured surface, artificial electromagnetic medium) with liquid crystal material as a tuning unit and realizing dynamic half-space beam regulation. BACKGROUND

[0002] Terahertz communication technology with rich spectrum resources, large capacity and strong security is increasingly becoming a key technology of the next generation of wireless communication. Due to the strong directivity and large path loss of terahertz beams, beam regulation technology is essential. Compared with the widely used active phased array technology in the microwave band, the lack of terahertz phase shifters makes the development of phased array technology challenging. In recent years, passive phased array technology based on programmable super surfaces has received extensive attention in the terahertz band, but due to the need for independent control lines for each unit of the traditional programmable super surface, the complex feed network makes it difficult to improve the array size, and the realization of high-precision terahertz beam regulation is challenging. SUMMARY

[0003] The application aims to solve the problems in the prior art. The application provides a programmable super surface for realizing terahertz beam regulation based on mode addition operation, which greatly reduces the number of control lines and can be used to develop large-scale array programmable super surfaces to improve beam regulation accuracy. Meanwhile, based on the programmable super surface, a method for realizing two-dimensional space dynamic regulation of terahertz beams through mode addition operation is provided, which demonstrates the ability to realize half-space beam regulation through row and column coding.

[0004] To achieve the above-mentioned application purposes, the first technical solution of the application is a liquid crystal programmable super surface suitable for mode addition operation,

[0005] which comprises a first layer of quartz substrate, a second layer of quartz substrate, a first layer of metal structure grown on the first layer of quartz substrate, a second layer of metal structure grown on the second layer of quartz substrate, and liquid crystal material sealed between the first layer of metal structure and the second layer of metal structure.

[0006] The first layer of metal structure is a wafer, and the same column of other wafers is connected by a metal wire to realize column control; the second layer of metal structure is a rectangle.

[0007] Further, the first layer of metal structure and the second layer of metal structure of the super surface respectively consist of 32 wire arrays that are perpendicular to each other, wherein the first layer of metal wire array is arranged along the y-axis, and the second layer of metal wire array is arranged along the x-axis direction.

[0008] Further, the first linear array and the second linear array selectively load a threshold voltage (coding value "1") or do not load a voltage (coding value "0"), and a difference voltage applied to the programmable metasurface drives the liquid crystal molecules to reorient, the refractive index of the liquid crystal changes, and the programmable metasurface unit coding value is equal to the result of adding the corresponding first linear array and second linear array coding values and taking the modulus (operator ) of the result.

[0009] The second scheme adopted by the present application is a preparation method of a programmable metasurface based on modulo addition operation for realizing terahertz beam control, comprising the following steps:

[0010] (1) Substrate pretreatment: clean the first layer of quartz substrate and the second layer of quartz substrate; (2) spin coating photoresist: spin coat photoresist LOR10B and AZ1500 on the surfaces of the first layer of quartz substrate and the second layer of quartz substrate and dry; (3) photoetching: form geometric pattern structures on the photoresist layer by exposure and development, and develop with positive photoresist developer after exposure; (4) metal sputtering deposition and stripping: use a magnetron sputtering instrument to sputter and deposit a layer of metal film on the first layer of quartz substrate and the second layer of quartz substrate after the operation of step (3), and strip the sputtered sample in an organic solution; (5) making a liquid crystal cell and filling liquid crystal: use copper foil tape and conductive silver paste to lead out the electrodes of the first layer of metal structure to the back, use Mylar film as a spacer, place the processed first layer of metal structure and the second layer of metal structure face to face, and encapsulate them into a box using AB glue, then fill liquid crystal, and finally use an aluminum wire welding machine to complete the electrical connection between the device and the PCB board by wire bonding.

[0011] The third technical scheme adopted by the present application is a control circuit of a programmable metasurface based on modulo addition operation for realizing terahertz beam control, an FPGA program capable of controlling 64-way port output voltage is written, and DuPont wires are used to connect the FPGA output ports with the input ports of the 64-way amplification circuit; the bias voltage applied to the first linear array and the second linear array is changed by the FPGA program, and independent coding control of the upper and lower two layers of array units is realized.

[0012] The fourth technical scheme adopted by the present application is a test method of a programmable metasurface based on modulo addition operation for realizing terahertz beam control, comprising the following steps: fixing the programmable metasurface at the center position of the rotation table of a terahertz time-domain spectroscopy system, so that the programmable metasurface is located at the light path intersection of a terahertz transceiver module; changing the coding sequence applied to the programmable metasurface by a control circuit, and finally measuring the spatial beam distribution of the programmable metasurface under different coding sequences.

[0013] The fifth technical solution of the present application is a beam steering method of a programmable metasurface based on modulo addition operation for realizing terahertz beam steering, wherein the Fourier transform relationship exists between the electric field distribution E on the programmable metasurface and the far-field radiation F, u=sinθcosφ and v=sinθsinφ, θ and φ are the elevation angle and azimuth angle of an arbitrary direction respectively, the full coverage of the beam in the uv space can be realized by controlling the electric field distribution in the x and y axis directions; the electric field phase response of each unit of the programmable metasurface corresponds to the sum of the row and column phases, therefore the coding state of the unit corresponds to the modulo addition of the row and column coding, which can be expressed as:

[0014]

[0015] Wherein S1 and S2 are the coding matrices along the x and y axis directions respectively, A0 is the amplitude; E(S1) and E(S2) represent the electric field distribution of the metasurface when the S1 and S2 coding matrices are loaded respectively, F(u,v), F(u,0) and F(0,v) represent the far-field radiation of the metasurface under the uv coordinate; therefore the beam deflection control of the u and v axis can be realized respectively by controlling the two orthogonal coding sequences; the modulo addition operation of the two coding sequences forms a two-dimensional phase distribution on the programmable metasurface, when a plane wave is vertically incident, the reflected beam can be deflected along any azimuth angle in the half space.

[0016] Beneficial effects: The present application utilizes the electro-optic effect of liquid crystal material, introduces a new cross architecture, proposes a method for realizing the two-dimensional spatial free steering of terahertz beam based on modulo addition operation, and verifies the coding control method for realizing the half-space steering of terahertz beam by row and column coding separately. The design can realize a large array scale, and the number of control lines is greatly reduced compared with the traditional terahertz programmable metasurface. This method provides an effective way to improve the array scale and beam steering precision of the beam steering device. The modulo addition operation simplifies the design and implementation of dynamic beam steering, and this function can be expanded to other programmable devices and electromagnetic frequency bands. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 The unit structure diagram of the programmable metasurface for realizing terahertz beam steering based on modulo addition operation of the present application;

[0018] Figure 2 The preparation flow chart of the programmable metasurface for realizing terahertz beam steering based on modulo addition operation of the present application;

[0019] Figure 3 The test schematic diagram of the programmable metasurface for realizing terahertz beam steering based on modulo addition operation of the present application;

[0020] Figure 4Beam distribution map of the programmable metasurface for realizing terahertz beam control based on modulo addition operation when only x-axis encoding is applied (a) and beam distribution map when only y-axis encoding is applied (b);

[0021] Figure 5 Beam distribution map of the programmable metasurface for realizing terahertz beam control based on modulo addition operation when x-axis and y-axis encoding are simultaneously applied;

[0022] Figure 6 Beam elevation and azimuth distribution map of the programmable metasurface for realizing terahertz beam control based on modulo addition operation. DETAILED DESCRIPTION

[0023] The present application will be further clarified by the following examples and figures, which should be understood as merely illustrating the present application and not limiting the scope of its use. After reading the present application, those skilled in the art will be able to modify various equivalent forms of the present application, which fall within the scope of the appended claims.

[0024] The present application discloses a liquid crystal terahertz programmable metasurface based on a cross architecture, as shown in Figure 1 The present application discloses a liquid crystal terahertz programmable metasurface based on a cross architecture, as shown in Figure 3 The present application discloses a liquid crystal terahertz programmable metasurface based on a cross architecture, as shown in

[0025] I. Structure of the programmable metasurface for realizing terahertz beam control based on modulo addition operation

[0026] In order to design a liquid crystal beam steering metasurface suitable for modulo addition operation, a new cross architecture is adopted, the first layer metal structure 2 and the second layer metal structure 4 are respectively composed of 32 linear arrays that are perpendicular to each other, wherein the first layer metal linear array is arranged along the y axis, and the second layer metal linear array is arranged along the x axis direction, and in order to better match the cross architecture, the upper layer selects a wafer structure, as shown in Figure 1 , wherein the period size p = 180 μm, the wafer radius r = 75 μm, the line width w = 10 μm, and the liquid crystal layer thickness t = 15 μm.

[0027] II. Preparation of programmable metasurface for realizing terahertz beam steering based on modulo addition operation

[0028] According to the design as shown in Figure 1 , Figure 2 , a mask plate is made by drawing software, and a physical object is made by using it. The main steps of sample preparation are as follows:

[0029] (1) Substrate pretreatment: clean the first layer of quartz substrate 1 and the second layer of quartz substrate 5;

[0030] (2) Spin coating photoresist: spin coating photoresist LOR10B and AZ1500 on the surface of the first layer of quartz substrate 1 and the second layer of quartz substrate 5 and drying;

[0031] (3) Photoetching: forming geometric pattern structure on the photoresist layer by exposure and development, and developing with positive photoresist developer after exposure;

[0032] (4) Metal sputtering deposition and stripping: using a magnetron sputtering instrument, sputtering a layer of metal film on the first layer of quartz substrate 1 and the second layer of quartz substrate 5 after the operation of step (3), and stripping the sputtered sample in an organic solution;

[0033] (5) Making liquid crystal cell and filling liquid crystal: using copper foil tape and conductive silver adhesive to lead out the electrode of the first layer of metal structure 2 to the back, using Mylar film as a spacer, placing the first layer of metal structure 2 and the second layer of metal structure 4 face to face after processing, and using AB adhesive to package into a box and fill liquid crystal, and finally using aluminum wire welding machine to complete the electrical connection between the device and the PCB board by wire bonding.

[0034] III. Steering principle of programmable metasurface for realizing terahertz beam steering based on modulo addition operation

[0035] The first linear array 6 and the second linear array 7 of the coding metasurface are selectively loaded with a threshold voltage (coding value "1") or not loaded with a voltage (coding value "0"), respectively, and the difference voltage applied to the liquid crystal of the programmable metasurface drives the liquid crystal molecules to reorient, and the refractive index of the liquid crystal changes, and the coding value (R) of the programmable metasurface unit is equal to the result of adding the coding values of the corresponding first linear array 6 and second linear array 7 and taking the modulus (operator symbol ).

[0036] A B R 0 0 0 1 0 1 0 1 1 1 1 0

[0037] Taking a 1-bit coding programmable metasurface containing 32x32 units as an example, different coding units are distributed according to a certain phase gradient. Assuming that the scattering phase of each unit is φ(m, n), where m and n are positive integers less than or equal to 32. Let u = sinθcosφ and v = sinθsinφ, where θ and φ are the elevation angle and azimuth angle of an arbitrary direction, respectively, and in the case of normal incidence of a plane wave, the far-field pattern F(u, v) is:

[0038] where k is the wavelength in vacuum, d is the perimeter of the square coding unit, and N is the number of units in each row

[0039]

[0040] of columns, when the coding matrix is coded along the x-axis, Γ y = ∞, and the far-field pattern F(u, 0) is only related to the physical period length Γ x = ∞ of the coding sequence along the x-axis direction at this time, and by analogy, when the matrix is coded along the y-axis, F(0, v) is only related to Γ y . There is a Fourier transform relationship between the electric field distribution E on the programmable metasurface and the far-field radiation F. By controlling the electric field distribution in the x-axis and y-axis directions, full coverage of the beam in the uv space can be achieved. The electric field phase response of each unit of the programmable metasurface corresponds to the sum of the row and column phases, so the coding state of the unit corresponds to the modulus addition of the row and column coding, which can be expressed as:

[0041] Therefore, by separately controlling two orthogonal coding sequences, beam deflection in the u and v axes can be respectively realized

[0042]

[0043] ; the modulus addition operation of the two coding sequences forms a two-dimensional phase distribution on the programmable metasurface, and when a plane wave is normally incident, the reflected beam can be deflected in any azimuth angle in the half space.

[0044] Four, experimental verification of the programmable metasurface for realizing terahertz beam control based on modulus addition operation

[0045] The programmable metasurface designed based on the modulo addition operation to realize the terahertz beam control is characterized in that: a first linear array 6 and a second linear array 7 of the programmable metasurface are perpendicular to each other, and codes are respectively applied to the two linear arrays; and the code distribution of the programmable metasurface is formed after the modulo addition operation of the two layers of codes, so that the half-space control of the terahertz beam is realized.

[0046] For the programmable metasurface, an FPGA program capable of controlling the output voltage of 64 ports is written, and a DuPont wire is used to connect each output port of the FPGA with an input port of a 64-way amplification circuit; the bias voltage applied to the first linear array 6 and the second linear array 7 is changed respectively by the FPGA program, so that the independent code control of the array units of the two layers of linear arrays perpendicular to each other is realized, as shown in Figure 3 .

[0047] The beam deflection characteristics of the programmable metasurface when the codes are applied along the x-axis or y-axis direction are tested. In order to verify the effect of the beam control, the first layer of metal structure layer A is grounded, that is, set to “0”, and the sequence “10 / 1100 / 111000 / …” of the code is applied to the other layer along the x-axis, and the deflection effect of the reflected terahertz beam is observed, as shown in Figure 4 (a); at this time, the reflected terahertz beam is split into two symmetrical beams along the u-axis; the second layer of metal structure layer B is grounded, and the sequence “10 / 1100 / 111000 / …” of the code is applied to the other layer along the y-axis, and the deflection effect of the reflected terahertz beam is observed, as shown in Figure 4 (b); at this time, the reflected terahertz beam is split into two symmetrical beams along the v-axis. Therefore, when one layer of metal structure is grounded, the beam deflection angle can be dynamically adjusted along the u / v-axis by controlling the code matrix of the other layer.

[0048] When the codes are applied along the x-axis and y-axis at the same time, the beam deflection characteristics of the programmable metasurface are tested. When the same code sequence “101010…” is applied to layer A and layer B at the same time, respectively, after the modulo addition operation of the device, the surface of the device presents a chessboard-like distribution with “1” and “0” alternating, so that the reflected beam is split into four beams along the diagonals of the square, and the four beams are respectively at the azimuth angles of φ1=45°, φ2=135°, φ3=225° and φ4=315°. It can be seen that the elevation angles of the four reflected beams are basically the same, all about 32.3°, and the reflection amplitudes are not much different, and the beam deflection effect is as shown in Figure 5 .

[0049] In order to verify the coverage capability of the programmable metasurface in the upper half space, the coding sequences applied by the AB layers are changed respectively to traverse all possible situations, the beam deflection angles under different coding sequence combinations are calculated, and the azimuth and elevation angles of all beam deflections of the programmable metasurface are plotted in the form of polar coordinates. Figure 6 Calculation results show that the programmable metasurface can achieve beam coverage within an elevation angle of less than 27° and an azimuth angle of almost 360°.

Claims

1. A programmable metasurface for terahertz beam steering based on modular addition operation, characterized in that: The programmable metasurface comprises a first quartz substrate, a second quartz substrate, a first metal structure grown on the first quartz substrate, a second metal structure grown on the second quartz substrate, and a liquid crystal material sealed between the first and second metal structures. The programmable metasurface adopts a cross-structure, wherein the first metal structure comprises a first linear array comprising 32 elements arranged along the y-axis, and the second metal structure comprises a second linear array comprising 32 elements arranged along the x-axis. The first and second linear arrays are selectively loaded with a threshold voltage or no voltage, and the differential voltage applied to the programmable metasurface drives the liquid crystal molecules to redirect, causing the refractive index of the liquid crystal to change. The unit coding value of the programmable metasurface is equal to the result of adding the corresponding first and second linear array coding values ​​modulo each other. The first metal structure is a disc, and is connected to other discs in the same column by metal wires to achieve column control. The second metal structure is rectangular.

2. A method for preparing a programmable metasurface for realizing terahertz beam steering based on modular addition operation as claimed in claim 1, characterized in that: The invention comprises the following steps: (1) substrate pretreatment: cleaning the first quartz substrate and the second quartz substrate; (2) spin coating photoresist: spin coating the photoresist LOR10B and AZ1500 on the surfaces of the first quartz substrate and the second quartz substrate and drying them; (3) photolithography: forming a geometric structure on the photoresist layer by exposure and development, and developing with a positive photoresist developer after exposure; (4) metal sputtering deposition and stripping: using a magnetron sputtering instrument, sputtering and depositing a metal film on the first quartz substrate and the second quartz substrate after the operation in step (3), and placing the sputtered samples in an organic solution for stripping; (5) making a liquid crystal box and pouring liquid crystal: using copper foil tape and conductive silver glue to lead the electrodes of the first metal structure to the back side, using Mylar film as a spacer layer, placing the processed first metal structure and the second metal structure face to face, and using AB glue to package them into a box and then pouring liquid crystal, and finally using an aluminum wire welding machine to complete the electrical connection between the device and the PCB board by wire bonding.

3. The control circuit of a programmable metasurface for implementing terahertz beam steering based on modular addition operation as claimed in claim 1, characterized in that: An FPGA program capable of controlling the output voltages of 64 ports was written, and DuPont cables were used to connect the FPGA output ports to the input ports of the 64-channel amplifier circuit. The bias voltages applied to the first and second linear arrays were respectively changed using the FPGA program to achieve independent coding control of the upper and lower perpendicular array units.

4. The method for testing a programmable metasurface for implementing terahertz beam steering based on modular addition operation according to claim 1, wherein: The method comprises the following steps: fixing the programmable metasurface at the center of a rotating table of a terahertz time-domain spectroscopy system so that the programmable metasurface is located at the intersection of optical paths of a terahertz transceiver module; changing the coding sequence applied to the programmable metasurface by a control circuit, and finally measuring the spatial beam distribution of the programmable metasurface under different coding sequences.

5. The beam steering method of a programmable metasurface for implementing terahertz beam steering based on modular addition operation as claimed in claim 1, characterized in that: There is a Fourier change relationship between the electric field distribution E and the far-field radiation F on the programmable metasurface. Let u = sinθcosφ, v = sinθsinφ, θ and φ are the elevation angle and azimuth angle in any direction, respectively. By controlling the electric field distribution in the x- and y-axis directions, full coverage of the beam in the uv space can be achieved. The electric field phase response of each unit of the programmable metasurface corresponds to the sum of the row and column phases. Therefore, the coding state of the unit corresponds to the modular addition of the row and column coding, which can be expressed as: Among them, S1 and S2 are the coding matrices along the x and y axes, respectively, and A0 is the amplitude; E(S1) and E(S2) represent the electric field distribution of the metasurface when loaded with the S1 and S2 coding matrices, respectively, and F(u,v), F(u,0), and F(0,v) represent the far-field radiation of the metasurface in the uv coordinate; therefore, the beam deflection control of the u and v axes can be achieved separately by controlling two orthogonal coding sequences separately; the modular addition operation of the two coding sequences forms a two-dimensional phase distribution on the programmable metasurface. When a plane wave is incident vertically, the reflected light beam can be deflected along any azimuth angle in the half space.

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