Temperature-control dual-channel bound-state metasurface for dynamic display application

Abstract

The invention discloses a dynamic display application-oriented temperature-control dual-channel bound-state metasurface, which comprises a dielectric substrate and a metal array structure arranged on the upper surface of the dielectric substrate, the metal array structure comprises a gold pattern layer arranged in an array, a plurality of vanadium dioxide pattern layers are embedded in the gold pattern layer, and the vanadium dioxide pattern layers are arranged on the upper surface of the dielectric substrate. The geometrical shape of the gold pattern layer is one or more of a rectangle, a cross, a square split ring and a disc with a hole, and the geometrical shape of the vanadium dioxide pattern layer is one of a rectangular block, an ellipse and a circle. According to the temperature control dual-channel bound-state metasurface for the dynamic display application, the BIC and the Q-BIC correspond to a high transmission spectrum and a low transmission spectrum, the conductivity of the vanadium dioxide is changed through external temperature excitation, the reversible phase change process of the vanadium dioxide from a medium phase to a metal phase is achieved, dynamic adjustability of the BIC and the Q-BIC is achieved, and the application range of the temperature control dual-channel bound-state metasurface is widened. Temperature regulation and control are achieved by applying DC bias current through the FPGA, and therefore diversified dynamic display is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of electromagnetic metamaterials, and in particular to a temperature-controlled dual-channel bound-state metasurface for dynamic display applications. Background Art

[0002] Electromagnetic metamaterials (Metamaterials) refer to equivalent homogeneous composite materials that have physical properties that exceed those of natural materials. Ordinary materials are composed of molecules or atoms. Compared with ordinary materials, metamaterials are composed of artificially designed resonant units. They are artificially designed periodic structures that can exhibit electromagnetic properties that natural media do not have, such as negative refraction, inverse Cherenkov radiation, inverse Doppler effect, perfect lens, invisibility cloak, etc.

[0003] Theoretically, by designing different structures, the sum can be made to any value. Its principle is to design a unit structure to simulate the molecules in ordinary materials, and then arrange this unit structure in a specific way. The resonance generated between the units can change the state of the incident wave, so the material as a whole can show some strange electromagnetic properties, even some electromagnetic properties that natural materials do not have. This is also the origin of the name of "super" structure materials.

[0004] Metasurfaces are the two-dimensional counterparts of metamaterials, with a thickness that is negligible relative to the wavelength of the surrounding space. Compared with metamaterials, metasurfaces do not require complex three-dimensional manufacturing technology and have less loss, making them a hot topic of research.

[0005] Vanadium dioxide (VO2) is a thermally controlled phase change material. Driven by external thermal excitation, it can achieve phase change from dielectric phase to metallic phase. During the phase change, the conductivity changes by 5 orders of magnitude, and the phase change rate is extremely fast, only tens of femtoseconds. The phase transition temperature of vanadium dioxide is 355K. When the temperature is higher than the phase transition temperature, VO2 will change from insulating state to metallic state, accompanied by a sharp increase in conductivity. The composite design of patterned VO2 combined with artificial microstructure can adjust the resonant mode of the microstructure under terahertz wave by controlling the conductivity of VO2, thereby realizing the amplitude and phase regulation of terahertz wave.

[0006] The continuum bound state (BIC) is a special optical bound state. Although its frequency is included in the continuous spectrum range and coexists with the radiation wave, it still remains in a completely closed state and the energy is completely bound in the continuous spectrum. Therefore, the continuum bound state can be considered as a resonant state with no leakage and infinite quality factor.

[0007] There are two main methods to realize optical BIC. One is radiation suppression induced by the symmetry incompatibility principle, and the other is accidental decoupling from the radiation continuum due to the continuous adjustable system parameters. In practical applications, the former is widely used in realizing bound states in the continuum domain. This type of optical BIC is also called symmetry-protected BIC. When the symmetry of the system is broken, radiation leakage occurs. The symmetry-protected BIC leakage is quasi-BIC (Q-BIC), which is a resonant state with a finite quality factor. Compared with other resonant states in the continuous spectrum, the high quality factor of BIC makes it have broad application prospects in the fields of optics and photonics, and has great significance for the development of practical devices.

[0008] In the existing technology, most imaging metasurfaces still find it difficult to achieve dynamic display of images. Once the structure of the metasurface is determined, it can only correspond to static images and cannot be controlled in real time as required, which greatly limits the application of bound-state metasurfaces. Summary of the invention

[0009] The purpose of the present invention is to provide a temperature-controlled dual-channel bound-state metasurface for dynamic display applications, which utilizes the phase change conversion characteristics of vanadium dioxide from a dielectric phase to a metallic phase as the temperature changes, and uses FPGA to individually control each unit of the array structure, thereby realizing the dynamic display of any two-dimensional image.

[0010] To achieve the above-mentioned purpose, the present invention provides a temperature-controlled dual-channel bound-state metasurface for dynamic display applications, comprising a dielectric substrate and a metal array structure arranged on the upper surface of the dielectric substrate, the metal array structure comprising a gold pattern layer arranged in an array, a plurality of vanadium dioxide pattern layers embedded on the gold pattern layer, the geometric shape of the gold pattern layer is one or more of a rectangle, a cross, a square open ring and a disk with holes, and the geometric shape of the vanadium dioxide pattern layer is one of a rectangular block, an ellipse and a circle.

[0011] Preferably, the geometric shape of the gold pattern layer is a square open ring, and the vanadium dioxide pattern layer is respectively embedded at the center point of the lower side length of the gold pattern layer and a position d to the right of the center line of the upper side length, and the width of the vanadium dioxide is g, where d is an asymmetry factor.

[0012] Preferably, the vanadium dioxide pattern layer is a phase change material, and its relative dielectric constant is expressed by the Drude model, that is:

[0013]

[0014] Among them, ε ∞ is the metal dielectric constant at infinite frequency, γ = 5.75 × 10 13rad / s, σ is the conductivity of vanadium dioxide, ω is the angular frequency of the electromagnetic wave, and the plasma frequency

[0015] σ0=3×10 3 Ω -1 cm -1 ,ω p (σ0)=1.4×10 15 S / m;

[0016] By changing the conductivity of the vanadium dioxide pattern layer through external temperature excitation, a reversible phase change process of the vanadium dioxide pattern layer from the dielectric phase to the metallic phase is realized, which is used for the dynamic adjustment of the continuous domain bound state and the quasi-continuous domain bound state. The external temperature is regulated by applying a DC bias current through FPGA.

[0017] Preferably, the output of the DC bias current is adjusted by setting the FPGA program, thereby achieving dynamic display, specifically:

[0018] When the FPGA outputs a small current, the vanadium dioxide is in an insulating state, the periodic array is an asymmetric structure, and the metasurface excites the quasi-continuous domain bound state, and the display effect is a dark spot.

[0019] When the FPGA outputs a large current, the vanadium dioxide is in a metallic state, the periodic array is a symmetrical structure, the metasurface excites the continuous domain bound state, and the display effect is a bright spot.

[0020] Preferably, the dielectric substrate is made of polyimide, and its composite dielectric constant ε P =2.93+0.044i.

[0021] Preferably, the conductivity of the gold pattern layer is 4.56×10 7 S / m.

[0022] To achieve the above objectives, the present invention also provides an application of a temperature-controlled dual-channel bound-state metasurface in dynamic display imaging.

[0023] Preferably, the method comprises the following steps:

[0024] S1. Design the geometric shape and spatial distribution of the metal array structure to form a bound state metasurface;

[0025] S2, controlling the voltage bias corresponding to the FPGA output, the vanadium dioxide pattern layer undergoes phase change as the degree changes, forming symmetrical units and asymmetrical units;

[0026] S3. Electromagnetic wave incident light irradiates the bound state metasurface, exciting BIC and D-BIC. The transmission spectrum corresponds to the output dark state and bright state, realizing dynamic display.

[0027] Preferably, the incident electromagnetic wave light is one of linearly polarized light, left-handed polarized light and right-handed polarized light.

[0028] Therefore, the present invention adopts the above-mentioned temperature-controlled dual-channel bound-state metasurface for dynamic display applications, and the beneficial effects are as follows:

[0029] The present invention arranges the basic units of bound state metasurface into a periodic two-dimensional array, and utilizes the phase change property of vanadium dioxide pattern layer under temperature change to break the symmetry of the square structure, thereby causing mode leakage. The BIC mode of the metasurface is converted into the D-BIC mode, thereby realizing the transition from the dark state to the bright state of the transmission spectrum, and finally realizing the dynamic display of the image, solving the problem of single imaging of traditional metasurfaces and expanding the application prospects of bound state metasurfaces.

[0030] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a structural schematic diagram of an embodiment of a temperature-controlled dual-channel bound-state metasurface for dynamic display applications of the present invention;

[0032] Figure 2 It is a flow chart of an embodiment of a temperature-controlled dual-channel bound-state metasurface dynamic display imaging for dynamic display applications of the present invention;

[0033] Figure 3 is a linear polarization response diagram of a temperature-controlled dual-channel bound-state metasurface embodiment for dynamic display applications of the present invention, wherein (a) is the conductivity σ of vanadium dioxide is 2×10 2 The linear polarization response of the bound state metasurface at S / m. (b) is the conductivity σ of vanadium dioxide is 2×10 5 Linear polarization response of bound-state metasurface at S / m;

[0034] Figure 4 is a circular polarization response diagram of a temperature-controlled dual-channel bound-state metasurface embodiment for dynamic display applications of the present invention, wherein (a) is the conductivity σ of vanadium dioxide is 2×10 2 The circular polarization response of the bound state metasurface at S / m. (b) is the conductivity of vanadium dioxide σ is 2×10 5 Circular polarization response of bound-state metasurface at S / m;

[0035] Figure 5 It is a two-dimensional arrangement diagram of the unit structure of an embodiment of a temperature-controlled dual-channel bound-state metasurface for dynamic display applications of the present invention;

[0036] Figure 6It is a two-dimensional arrangement diagram of a metasurface of a specific image "H" in an embodiment of a temperature-controlled dual-channel bound-state metasurface for dynamic display applications of the present invention;

[0037] Figure 7 It is a basic unit structure shape of various metal arrays of a temperature-controlled dual-channel bound-state metasurface embodiment for dynamic display applications of the present invention;

[0038] Figure 8 It is a dynamic display diagram under linear polarization response of a temperature-controlled dual-channel bound-state metasurface embodiment for dynamic display applications of the present invention;

[0039] Fig. 9 It is a dynamic display diagram under circular polarization response of an embodiment of a temperature-controlled dual-channel bound-state metasurface for dynamic display applications of the present invention, wherein (a) is a dynamic display diagram under left-handed circular polarization response, and (b) is a dynamic display diagram under right-handed circular polarization response. DETAILED DESCRIPTION

[0040] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0041] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0042] Embodiment 1

[0043] A temperature-controlled dual-channel bound-state metasurface for dynamic display applications includes a gold pattern layer with a square ring geometry and a vanadium dioxide pattern layer embedded in the gold pattern layer. The temperature-change characteristics of the vanadium dioxide pattern layer (phase change material) are used to achieve structural symmetry and asymmetry switching. The center of the coordinate axis is the center of the gold pattern layer, the z axis is the rotation axis parallel to the structure, and the schematic diagram of the structure of the xy plane of the metasurface is as follows: Figure 1 As shown. The metal array structure is covered on a dielectric substrate, the side length of the dielectric substrate is P, the side length of the gold pattern layer is L, and the width is w. The phase change material vanadium dioxide pattern layer is respectively embedded at the center point of the lower side length of the gold pattern layer and the position of the upper side length from the center line to the right of the distance d, and the width of the embedded vanadium dioxide is g, and the distance d is also called the asymmetry factor. In addition, the thickness of the dielectric substrate is h, and the thickness of the gold pattern layer and the vanadium dioxide pattern layer are both t.

[0044] In the simulation process, the finite element analysis software is used to simulate the designed metasurface structure. The frequency domain solver is used in the simulation process. The boundary conditions in the x and y directions are unit cell, and the boundary condition in the z direction is open (add space). The material of the dielectric substrate is polyimide, and its composite dielectric constant εP =2.93+0.044i, the conductivity of the gold pattern layer is 4.56×10 7 S / m, the relative dielectric constant of the phase change material vanadium dioxide is expressed by the Drude model, that is:

[0045]

[0046] Among them, ε ∞ is the metal dielectric constant at infinite frequency, which is 12; γ = 5.75 × 10 13 rad / s; σ is the conductivity of vanadium dioxide material; ω is the angular frequency of electromagnetic wave, which is the independent variable; plasma frequency σ0=3×10 5 Ω -1 cm -1 ,ω p (σ0)=1.4×10 15 S / m.

[0047] When the conductivity of vanadium dioxide is in a metallic state, the structure has high symmetry in the z direction. When electromagnetic wave incident light is incident along the z axis, the symmetry-protected BIC will be excited. At this time, all the energy in the metasurface is bound, and the BIC in the spectrum appears as a dark state. When the temperature of vanadium dioxide changes and the phase changes to an insulating state, the symmetry of the system is broken, resulting in radiation leakage, and the symmetry-protected BIC leaks into Q-BIC.

[0048] Figure 3 It shows that when the conductivity of VO2 increases from 2×10 2 S / m (insulating state) changes to 2×10 5 When S / m (metallic state), the bound-state metasurface switches from Q-BIC to BIC, and the incident light is linearly polarized.

[0049] Figure 4 It shows that when the incident light is circularly polarized light, left-handed circularly polarized light and right-handed circularly polarized light will undergo BIC to Q-BIC conversion near 460μm and 400μm, respectively. The temperature can be controlled by setting different excitation voltages, and temperature-controlled dual-channel imaging can be achieved in the 460μm and 400μm bands.

[0050] exist Figure 5A two-dimensional arrangement diagram of a unit structure that can be used for dynamic display applications is shown in the figure. The dynamic display process of the image is demonstrated. The electromagnetic wave is incident along the z-axis, and the FPGA applies electrical excitation to control the phase change process of vanadium dioxide, thereby manipulating the conversion between the metasurface BIC and Q-BIC, and finally realizing image display. In addition, data can be transmitted on the computer terminal at any time according to the use requirements. According to the 0 / 1 level value of different FPGA development boards corresponding to the low level and high level, the high and low DC bias outputs of the FPGA are changed to realize the real-time switching of the bound state metasurface unit BIC and Q-BIC, that is, to complete the dynamic display. Figure 6 A specific two-dimensional arrangement diagram shaped like "H" is shown. When a high-level excitation is applied to the "H" part, it behaves in a metallic state, while the rest of the part is applied with a low-level excitation and behaves in an insulating state.

[0051] exist Figure 7 The basic unit structures of several bound state metasurfaces with different geometric shapes are provided. The geometric shapes of the metal array structures here are rectangular bars, crosses, rectangular blocks, circular disks with holes, and square open rings. They all belong to symmetry-protected bound state metasurfaces, where the gray part is vanadium dioxide and the black part is gold. By introducing structured vanadium dioxide into these metasurfaces to construct metasurface arrays, the establishment and breaking of structural symmetry are manipulated to achieve switching between BIC and Q-BIC. In practical applications, under the premise of ensuring that the metasurface is a symmetry-protected bound state metasurface, the unit structure and spatial distribution of the metal array are not limited to the above-mentioned ones, and can be further changed and optimized according to specific requirements.

[0052] Embodiment 2

[0053] like Figure 2 As shown, a dynamic display imaging of a temperature-controlled dual-channel bound-state metasurface for dynamic display applications includes the following steps:

[0054] S1. According to the design requirements, the geometric shape and spatial distribution of the metal array structure are designed to form a bound state metasurface;

[0055] S2. According to the imaging requirements, the voltage bias corresponding to the FPGA output is controlled, and the vanadium dioxide pattern layer undergoes phase change as the degree changes, forming symmetrical units and asymmetrical units;

[0056] S3. Electromagnetic wave incident light irradiates the bound state metasurface, exciting BIC and D-BIC. The transmission spectrum corresponds to the output dark state and bright state, realizing dynamic display.

[0057] like Figure 8 As shown in the figure, an imaging example of a 16×16 bound state metasurface array is shown. The two-dimensional arrangement of the metasurface is similar to Figure 6The operating frequency range is 0.6THz-0.8THz, and the unit structure is as follows Figure 1 As shown, the metal array structure is covered on a dielectric substrate, the side length of the substrate is P = 270μm, the side length of the gold ring is L = 240μm, the width is w = 28μm, and the phase change material vanadium dioxide is embedded in the center point of the lower side of the gold ring and the position d = 70μm away from the center line of the upper side. The width of the embedded vanadium dioxide is g = 10μm, the thickness of the substrate is h = 20μm, and the thickness of gold and vanadium dioxide is t = 0.2μm. The incident electromagnetic wave light is one of linear polarized light, left-handed polarized light and right-handed polarized light. When linear polarized light is incident, the conductivity of vanadium dioxide is changed by temperature control to achieve Figure 6 The designed image display. At the same time, when circularly polarized light is incident, the desired image display can also be achieved. Fig. 9 (a) shows the image display effect when left-handed polarized light is incident. Fig. 9 (b) shows the image display effect when right-handed polarized light is incident.

[0058] Therefore, the present invention adopts the above-mentioned temperature-controlled dual-channel bound-state metasurface for dynamic display applications, utilizes the phase change conversion characteristics of vanadium dioxide from the dielectric phase to the metallic phase as the temperature changes, and uses FPGA to individually control each unit of the array structure, thereby realizing the dynamic display of any two-dimensional image.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A temperature-controlled dual-channel bound-state metasurface for dynamic display applications, characterized in that: The invention comprises a dielectric substrate and a metal array structure arranged on the upper surface of the dielectric substrate, wherein the metal array structure comprises a gold pattern layer arranged in an array, and a plurality of vanadium dioxide pattern layers are embedded on the gold pattern layer, wherein the geometric shape of the gold pattern layer is one or more of a rectangle, a cross, a square open ring and a circular disk with holes, and the geometric shape of the vanadium dioxide pattern layer is one of a rectangular block, an ellipse and a circle.

2. The temperature-controlled dual-channel bound-state metasurface for dynamic display applications according to claim 1, characterized in that: The geometric shape of the gold pattern layer is a square open ring, and the vanadium dioxide pattern layer is respectively embedded at the center point of the lower side length of the gold pattern layer and the position at a distance d to the right of the center line of the upper side length. The width of the vanadium dioxide is g, where d is an asymmetry factor.

3. The temperature-controlled dual-channel bound-state metasurface for dynamic display applications according to claim 2, characterized in that: The vanadium dioxide pattern layer is a phase change material, and its relative dielectric constant is expressed by the Drude model, that is: Among them, ε ∞ is the metal dielectric constant at infinite frequency, γ = 5.75 × 10 13 rad / s, σ is the conductivity of vanadium dioxide, ω is the angular frequency of the electromagnetic wave, and the plasma frequency σ0=3×10 3 Oh -1 cm -1 Oh, oh p (σ0)=1.4×10 15 S / m; By changing the conductivity of the vanadium dioxide pattern layer through external temperature excitation, a reversible phase change process of the vanadium dioxide pattern layer from the dielectric phase to the metallic phase is realized, which is used for the dynamic adjustment of the continuous domain bound state and the quasi-continuous domain bound state. The external temperature is regulated by applying a DC bias current through FPGA.

4. The temperature-controlled dual-channel bound-state metasurface for dynamic display applications according to claim 3, characterized in that: By setting the FPGA program and adjusting the output of the DC bias current, dynamic display can be achieved. Specifically: When the FPGA outputs a low level, the vanadium dioxide is in an insulating state, the periodic array is an asymmetric structure, and the metasurface excites the quasi-continuous domain bound state, and the display effect is a dark spot. When the FPGA outputs a high level, vanadium dioxide is in a metallic state, the periodic array is a symmetrical structure, the metasurface excites the continuous domain bound state, and the display effect is a bright spot.

5. The temperature-controlled dual-channel bound-state metasurface for dynamic display applications according to claim 1, characterized in that: The dielectric substrate is made of polyimide, and its composite dielectric constant ε P =2.93+0.044i.

6. The temperature-controlled dual-channel bound-state metasurface for dynamic display applications according to claim 1, characterized in that: The conductivity of the gold pattern layer is 4.56×10 7 S / m.

7. An application of the temperature-controlled dual-channel bound-state metasurface for dynamic display applications as described in claims 1-6 in dynamic display imaging.

8. The use according to claim 7, characterized in that: The following steps are involved: S1. Design the geometric shape and spatial distribution of the metal array structure to form a bound state metasurface; S2, controlling the voltage bias corresponding to the FPGA output, the vanadium dioxide pattern layer undergoes phase change as the degree changes, forming symmetrical units and asymmetrical units; S3. Electromagnetic wave incident light irradiates the bound state metasurface, exciting BIC and D-BIC. The transmission spectrum corresponds to the output dark state and bright state, realizing dynamic display.

9. The use according to claim 8, characterized in that: The electromagnetic wave incident light is one of linearly polarized light, left-handed polarized light and right-handed polarized light.

Images