A digital light-controlled coded THz reflectarray based on PB phase

Abstract

The application discloses a digital light-controlled coded THz reflection array based on PB phase, and belongs to the field of electromagnetic wave front control, and aims at solving the problem that the independent control of each array element of the THz coded reflection array by the electric control means is hindered in the prior art; in the application, the reflection array is formed by the periodic arrangement of composite microstructure array elements in a two-dimensional plane; the composite microstructure array element comprises a substrate, a metal microstructure and a VO2 microstructure; the metal microstructure comprises a rectangular metal structure and a metal ring, the rectangular metal structure is provided with a circular hole, and the metal ring is located in the circular hole; the VO2 microstructure comprises left VO2 microstructure and right VO2 microstructure which are nested between the metal ring and the circular hole, and the included angles between the symmetry axes of the x-y plane and the x axis are +45° and -45° respectively; the composite microstructure array element of the application controls the THz wave based on the PB phase, the amplitudes in two states are completely the same in the working frequency band, the phase difference is always 180°, and the THz wave can be stably and widely controlled.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic wavefront modulation, and particularly to a digitally controlled coded THz reflector array based on PB phase. Background Technology

[0002] A metasurface is a planar array composed of subwavelength microstructure elements arranged periodically on a two-dimensional plane. By encoding these microstructure elements with different phase responses, programmable control of the electromagnetic wavefront can be achieved. By designing artificial microstructures in conjunction with electronic components or tunable materials such as transistors and phase-change materials, and using external physical stimuli to adjust the electronic components or tunable materials, the phase of the array elements can be controlled, enabling the coded metasurface to achieve dynamic beam control.

[0003] Terahertz waves refer to electromagnetic waves with frequencies ranging from 0.1 to 10 THz. Due to their abundant spectrum resources, large bandwidth, and anti-interference capabilities, they are highly suitable for applications such as high-capacity high-speed wireless communication and super-resolution radar imaging. However, for terahertz coded reflector arrays, electronically controlled coding requires a complex feeding system. Limited by micro-nano technology and the wavelength of terahertz waves, it is difficult to fabricate terahertz coded reflector arrays with subwavelength microstructures. Furthermore, the complex feeding system can induce severe parasitic interference, significantly hindering the independent control of each element of the terahertz coded reflector array through electronic means.

[0004] Vanadium dioxide (VO2), as a phase change material, can undergo a phase transition from a dielectric phase to a metallic phase under various external driving forces, including light, heat, and electricity. For VO2 thin films grown on different substrates, the conductivity variation range in the terahertz band is 3 to 5 orders of magnitude, with a phase transition rate of only tens of femtoseconds. At 300K, it is approximately in an insulating state. When the temperature exceeds the phase transition temperature of 355K, VO2 will undergo a transition from an insulating state to a metallic state, accompanied by a sharp increase in conductivity. The composite design of patterned VO2 combined with artificial microstructures can adjust the resonance mode of the microstructure under terahertz waves by controlling the conductivity of VO2, thereby achieving terahertz wave modulation. Therefore, to solve the power supply problem, it is possible to consider combining the phase change characteristics of vanadium dioxide and using its optical control instead of electrical control to achieve digital coding control. Summary of the Invention

[0005] To address the problems existing in the background technology, the present invention provides a digitally controlled coded THz reflector array based on PB phase, with the aim of designing a digitally controlled coded reflector array that is easy to fabricate, has low loss, large bandwidth, and can operate in the terahertz band with beam reconstruction capability.

[0006] The present invention provides the following technical solution to solve the above-mentioned technical problems:

[0007] A digitally controlled coded THz reflector array based on PB phase, characterized in that the reflector array is composed of composite microstructure elements arranged periodically in a two-dimensional plane;

[0008] The composite microstructure array element includes a metal microstructure and a VO2 microstructure disposed on a substrate;

[0009] The metal microstructure includes a rectangular metal structure and a metal ring. The rectangular metal structure is disposed at one end of the substrate and has a through hole. The metal ring is disposed at one end of the substrate and is located inside the through hole.

[0010] The VO2 microstructure includes a left VO2 microstructure and a right VO2 microstructure nested between a metal ring and the inner wall of a circular hole. The left VO2 microstructure and the right VO2 microstructure are fan-shaped structures with identical size and shape, and their axes of symmetry in the xy plane make angles of +45° and -45° with the x-axis, respectively.

[0011] The reflector array has no metal base plate.

[0012] Furthermore, the substrate is either quartz or sapphire.

[0013] Furthermore, in the metal microstructure, the metal is one of gold, silver, copper, or aluminum.

[0014] Furthermore, the phase modulation structure is an M*N type array composed of multiple modulation units, where M and N are positive integers; and M>3, N>3.

[0015] In the composite microstructure array elements, the radius of the metal ring and the orientation and size of the VO2 microstructure affect the operating frequency band and efficiency of the reflection array.

[0016] When only one of the two VO2 regions in the composite microstructure array element is in a metallic state, the reflected wave will undergo polarization conversion. Conversely, when only the other region's VO2 is in a metallic state, the reflected wave will also undergo polarization conversion. The conversion efficiencies of the two are exactly the same, with a phase difference of 180°.

[0017] The composite microstructure is placed at the bottom of the substrate, serving not only as a modulation structure but also as a reflective substrate. The digital optical control end and the terahertz wave transceiver end are respectively placed on both sides of the reflective array, avoiding spatial conflicts between the control end and the transceiver end, while not affecting the beam modulation behavior of the coded reflective array on the array surface.

[0018] The reflection array projects a laser digitized pattern onto a designated area based on a digital micromirror device (DMD). It then digitally and independently controls the VO2 phase transition in each area using optical control, thereby enabling the composite microstructure array elements to modulate terahertz waves.

[0019] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0020] (1) The present invention uses a light-controlled method to avoid the problems of difficult fabrication and large insertion loss caused by the complex power supply system under the electric control method.

[0021] (2) The composite microstructure array element designed in this invention modulates the terahertz wave based on the PB phase. Within the working frequency band, the amplitude is exactly the same in the two states, and the phase difference is always 180°, which can stably modulate the terahertz wave in a wideband.

[0022] (3) The composite microstructure of the present invention is placed at the bottom of the substrate, serving not only as a modulation structure but also as a reflective substrate. The digital optical control end and the terahertz wave transceiver end are respectively placed on both sides of the reflective array, avoiding spatial conflicts between the control end and the transceiver end, and at the same time not affecting the beam modulation behavior of the coded reflective array on the array surface.

[0023] (4) This invention uses DMD to realize the digital projection of laser, so that the reflective array has the ability to control the light of terahertz waves in a coded manner.

[0024] (5) This invention can work in a normal temperature and pressure environment, and is easy to manufacture and use, and has great application potential and prospects. Attached Figure Description

[0025] Figure 1 A schematic diagram of a digitally controlled optically encoded THz reflector array based on PB phase;

[0026] Figure 2 This is a three-dimensional schematic diagram of the modulation unit of the device in the embodiment;

[0027] Figure 3 The diagram shows the current distribution on the upper surface of the composite microstructure under different states of the array elements.

[0028] Figure 4 The electric field distribution of the array elements on the composite microstructure under different states is shown.

[0029] Figure 5 The amplitude and phase response diagrams of the composite microstructure of the array elements under different states are shown.

[0030] In the figure: 1-metal microstructure, 2-VO2 microstructure, 3-substrate, 4-laser projection surface, 101-metal ring, 102-rectangular metal structure, 201-left VO2 microstructure, 202-right VO2 microstructure. Detailed Implementation

[0031] To make the technical means, features and effects of the present invention easier to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings.

[0032] like Figures 1-5 As shown, the present invention provides the following technical solution:

[0033] A digitally controlled optically encoded THz reflector array based on PB phase combines VO2 with an optimized metamaterial containing a metal ring. By utilizing the phase transition properties of VO2 and the metamaterial's ability to control electromagnetic waves, the phase transition region of the phase transition material VO2 is precisely controlled through an external digital laser pattern, thereby achieving the desired phase distribution and corresponding functions.

[0034] Therefore, this invention is a digitally controlled coded THz reflector array based on PB phase, which is formed by periodically arranging composite microstructure elements in a two-dimensional plane. The composite microstructure elements are composed of a substrate, a metal microstructure, and a VO2 microstructure. The metal microstructure includes a metal ring and a rectangular metal structure with a circular hole in the middle. The VO2 microstructure includes two fan-shaped regions that are symmetrical about the y-axis, with their axes of symmetry in the xy plane making angles of +45° and -45° with the x-axis, respectively, and are nested between the metal ring and the rectangular metal structure with a circular hole in the middle.

[0035] Furthermore, the substrate is either quartz or sapphire.

[0036] Furthermore, in the metal microstructure, the metal is one of gold, silver, copper, or aluminum.

[0037] Furthermore, the phase modulation structure is an M*N type array composed of multiple modulation units, where M and N are positive integers; and M>3, N>3.

[0038] In the composite microstructure array elements, the radius of the metal ring and the orientation and size of the VO2 microstructure affect the operating frequency band and efficiency of the reflection array.

[0039] When only one of the two VO2 regions in the composite microstructure array element is in a metallic state, the reflected wave will undergo polarization conversion. Conversely, when only the other region's VO2 is in a metallic state, the reflected wave will also undergo polarization conversion. The conversion efficiencies of the two are exactly the same, with a phase difference of 180°.

[0040] The composite microstructure is placed at the bottom of the substrate, serving not only as a modulation structure but also as a reflective substrate. The digital optical control end and the terahertz wave transceiver end are respectively placed on both sides of the reflective array, avoiding spatial conflicts between the control end and the transceiver end, while not affecting the beam modulation behavior of the coded reflective array on the array surface.

[0041] The reflection array projects a laser digitized pattern onto a designated area based on a digital micromirror device (DMD). It then digitally and independently controls the VO2 phase transition in each area using optical control, thereby enabling the composite microstructure array elements to modulate terahertz waves.

[0042] To enable those skilled in the art to better understand the principles of the present invention, further explanation is provided below in conjunction with the accompanying drawings:

[0043] The PB-phase-based digitally controlled coded THz reflector array of this invention is a composite array structure that cleverly and effectively combines the phase-change material VO2 with a metallic microstructure. This design utilizes the PB phase principle, ensuring that the amplitudes of the two states are equal and at a high level, and that the phase difference between the two states remains at 180° within the operating frequency band, enabling broadband modulation of THz waves. The composite microstructure, nested with VO2 microstructures, is placed at the bottom of the substrate, serving not only as a modulation structure but also as a metallic reflector. The digitally controlled optical control terminal is located at the bottom to drive the VO2 phase transition, while the terahertz wave transceiver is located on the other side, avoiding spatial conflicts between the control and transceiver terminals. Furthermore, to achieve digitally controlled optical actuation, a spatial light modulator projects a digital laser pattern onto a designated area, digitally and independently controlling the designated VO2 phase transition region on each array element to generate a phase transition, thus achieving modulation of the terahertz wave response by the composite microstructure array elements. Simulation calculations demonstrate that this is a dynamic THz modulation device with significant development potential and practical value.

[0044] like Figure 1 and Figure 2As shown, the reflective array element in this invention includes a metal microstructure 1, a VO2 microstructure 2, and a substrate 3. The metal microstructure 1 includes a metal ring 101 and a rectangular metal structure 102 with a circular hole inside, with the VO2 microstructure 2 embedded between them. The VO2 microstructure 2 contains two fan-shaped regions symmetrical about the y-axis, where the left VO2 microstructure is 201 and the right VO2 microstructure is 202, and their symmetry axes in the xy-plane make angles of +45° and -45° with the x-axis, respectively. The substrate of the composite microstructure element is made of quartz with a thickness of 200 μm and a side length of 650 μm; the metal material is gold, and the thickness of both VO2 and gold is 300 nm; the inner radius of the metal ring is 140 μm, and the linewidth is 60 μm; the radius of the circular hole in the rectangular metal microstructure is 280 μm, the linewidth of VO2 is 80 μm, and the corresponding central angle is 30°.

[0045] When vanadium oxide is in a dielectric state, its conductivity is approximately 30 S / m, and it functions equivalent to a dielectric in the terahertz band. When irradiated by a laser, VO2 reaches the phase transition threshold, and as it transitions from an insulating state to a metallic state, its conductivity increases to approximately 3 × 10^6. 5 S / m. Here, we define: when the VO2 microstructure 201 on the left side of the reflective array element is irradiated by laser and becomes metallic, while the VO2 microstructure 202 on the right side is in a dielectric state, it is encoded as "0"; when the VO2 microstructure 202 on the right side of the reflective array element is irradiated by laser and becomes metallic, while the VO2 microstructure 202 on the left side is in a dielectric state, it is encoded as "1".

[0046] When a y-polarized terahertz wave is incident perpendicularly, such as Figure 3 As shown, the surface current distributions of codes "0" and "1" are symmetrical about the y-axis, with similar current strengths but opposite directions, consistent with PB phase characteristics. Similarly, as... Figure 4 As shown, the electric field distributions of the codes "0" and "1" are also symmetrical about the y-axis. When a terahertz wave is irradiated perpendicularly in the form of a plane wave with y-polarization, the reflected wave undergoes polarization transformation and a certain phase shift due to the anisotropy of the coding state of the composite microstructure. Figure 5 The amplitude and phase responses of the array elements to terahertz waves in coded "0" and coded "1" states were calculated. Within the operating frequency band of 140-210 GHz, the reflection coefficients of our designed array elements in both coded "0" and coded "1" states are greater than 60%, reaching a maximum of 65%, with a bandwidth greater than 70 GHz. Furthermore, since our design is based on the PB phase principle, the reflection coefficients in coded "0" and coded "1" states are always equal, and the phase difference is always 180°, fully meeting the requirements of 1-bit binary encoding. Using this encoding theory, dynamic reconstruction of the reflected beam can be achieved by arranging the composite microstructure array elements in a two-dimensional plane according to a specific phase distribution.

[0047] like Figure 1 As shown, the terahertz digitally controlled optically coded reflection array is constructed by periodically arranging array elements in a two-dimensional plane. A y-polarized terahertz wave illuminates the front of the coded reflection array in the +z direction of the spatial coordinate system, while a laser beam, digitally projected by the DMD in the -z direction, illuminates the back of the array. On the laser projection surface 4, bright areas represent the laser-illuminated areas, and shadows represent the non-laser-illuminated areas. VO2 in the non-laser-illuminated areas does not reach the phase transition threshold, and its phase transition state remains unchanged; VO2 in the laser-illuminated areas undergoes a phase transition from a dielectric phase to a metallic phase. Therefore, by encoding the laser projection pattern in real time, we can manipulate the THz wavefront to achieve the desired function.

[0048] In summary, the PB-phase-based digital optically controlled coded THz reflector array is a highly promising and practical optically controlled real-time coded terahertz modulation device.

[0049] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A digitally controlled optically encoded THz reflector array based on PB phase, characterized in that, The reflection array is composed of composite microstructure elements arranged periodically in a two-dimensional plane; The composite microstructure array element includes a metal microstructure (1) and a VO2 microstructure (2) disposed on a substrate (3). The metal microstructure (1) includes a rectangular metal structure (102) and a metal ring (101). The rectangular metal structure (102) is disposed on the lower surface of the substrate (3) and a circular hole is provided through the rectangular metal structure. The metal ring (101) is disposed on the lower surface of the substrate (3) and the metal ring (101) is located inside the circular hole. The VO2 microstructure (2) includes a left VO2 microstructure (201) and a right VO2 microstructure (202) nested between the outer circle of the metal ring (101) and the inner circle of the circular hole. The left VO2 microstructure (201) and the right VO2 microstructure (202) are in contact with the outer circle of the metal ring (101) and the inner circle of the circular hole. The left VO2 microstructure (201) and the right VO2 microstructure (202) are fan-shaped structures with the same size and shape. The angle between the axis of symmetry of the left VO2 microstructure (201) in the xy plane and the x-axis is +45°, and the angle between the axis of symmetry of the right VO2 microstructure (202) in the xy plane and the x-axis is -45°. The reflector array has no other metal base plate.

2. The digitally controlled optically encoded THz reflector array based on PB phase according to claim 1, characterized in that, The substrate (3) is either quartz or sapphire.

3. The digitally controlled optically encoded THz reflector array based on PB phase according to claim 1, characterized in that, The rectangular metal structure and the metal ring (101) are made of one of gold, silver, copper or aluminum.

4. The digitally controlled optically encoded THz reflector array based on PB phase according to claim 1, characterized in that, The THz reflector array is an M*N type array composed of multiple modulation units, where M and N are positive integers; and M>3, N>3.

5. A digitally controlled optically encoded THz reflector array based on PB phase according to claim 1, characterized in that, When the left VO2 microstructure (201) is in a metallic state and the right VO2 microstructure (202) is in a dielectric state, the reflected wave will undergo polarization conversion and phase shift θ1; when the left VO2 microstructure (201) is in a dielectric state and the right VO2 microstructure (202) is in a metallic state, the reflected wave will undergo polarization conversion and phase shift θ2, and θ2-θ1=180°.

6. The digitally controlled optically encoded THz reflector array based on PB phase according to claim 1, characterized in that, The composite microstructure is located at the bottom of the substrate (3), and the digital optical control terminal and the terahertz wave transceiver terminal are respectively placed on both sides of the reflective array.

7. A digitally controlled optically encoded THz reflector array based on PB phase according to claim 1, characterized in that, The reflection array projects a laser digitized pattern onto a designated VO2 region based on a DMD, and digitally controls the VO2 in each region to generate a phase transition in a light-driven manner, thereby realizing the modulation of terahertz waves by the composite microstructure array elements.

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