A temperature-controlled dual-channel bound-state metasurface for dynamic display applications

Abstract

The present invention discloses a temperature-controlled dual-channel bound-state metasurface for dynamic display applications, comprising a dielectric substrate and a metal array structure disposed on the upper surface of the dielectric substrate. The metal array structure comprises an array of gold pattern layers, on which a plurality of vanadium dioxide pattern layers are embedded. The gold pattern layers have a geometric shape of one or more of a rectangle, a cross, a square open ring, and a circular disk with holes, and the vanadium dioxide pattern layers have a geometric shape of one or more of a rectangular block, an ellipse, and a circle. The present invention employs the aforementioned temperature-controlled dual-channel bound-state metasurface for dynamic display applications. BIC and Q-BIC correspond to high and low transmission spectra. External temperature excitation changes the conductivity of vanadium dioxide, achieving a reversible phase transition from a dielectric phase to a metallic phase, enabling dynamic adjustment of the BIC and Q-BIC. Temperature control is achieved by applying a DC bias current via an FPGA, thereby enabling diverse dynamic displays.

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) are homogeneous composite materials with inherent physical properties exceeding those of natural materials. Unlike ordinary materials, which are composed of molecules or atoms, metamaterials are composed of artificially designed resonant units. These periodic structures exhibit electromagnetic properties not found in natural media, such as negative refraction, inverse Cherenkov radiation, inverse Doppler effect, perfect lenses, and invisibility cloaks.

[0003] Theoretically, by designing different structures, the sum can be made to any value. The 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. As a result, the material as a whole can exhibit some unique electromagnetic properties, even some electromagnetic properties that are not possessed by natural substances. This is the origin of the name "super" structure material.

[0004] Metasurfaces are the two-dimensional counterparts of metamaterials, with thickness negligible relative to the wavelength of the surrounding space. Compared to metamaterials, metasurfaces do not require complex three-dimensional manufacturing techniques and exhibit lower losses, making them a hot topic of research.

[0005] Vanadium dioxide (VO2) is a thermally controlled phase change material that, driven by external thermal stimulation, can achieve a phase transition from a dielectric phase to a metallic phase. During the phase transition, the electrical conductivity undergoes a dramatic change of five orders of magnitude, and the phase transition 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 transform from an insulating state to a metallic state, accompanied by a sharp increase in electrical conductivity. The composite design of patterned VO2 combined with artificial microstructures can adjust the resonant mode of the microstructure under terahertz waves by controlling the electrical conductivity of VO2, thereby achieving amplitude and phase control of terahertz waves.

[0006] A continuum bound state (BIC) is a special type of optical bound state. Although its frequency lies within the continuum spectrum and coexists with the radiated wave, it remains completely closed, with its energy completely confined within the continuum. Therefore, a BIC can be considered a resonant state with no leakage and infinite quality factor.

[0007] There are two main approaches to achieving optical BICs: one is based on symmetry-incompatibility-induced radiation suppression, and the other is the unintended decoupling of the radiation continuum due to continuously adjustable system parameters. In practical applications, the former is widely used to achieve bound states in the continuum domain. This type of optical BIC is also called a symmetry-protected BIC. When the symmetry of the system is broken, radiation leaks. The leakage of the symmetry-protected BIC is a quasi-BIC (Q-BIC), a resonant state with a finite quality factor. Compared with other resonant states in the continuum spectrum, the high quality factor of BICs makes them have broad application prospects in the fields of optics and photonics, and is of great significance for the development of practical devices.

[0008] In existing technologies, 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. This utilizes the phase transition characteristics of vanadium dioxide from a dielectric phase to a metallic phase as the temperature changes, and uses an 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 objectives, 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 disposed on the upper surface of the dielectric substrate. The metal array structure includes an array of gold pattern layers, on which a plurality of vanadium dioxide pattern layers are embedded. The geometric shape of the gold pattern layers is one or more of a rectangle, a cross, a square open ring, and a circular disk with a hole, and the geometric shape of the vanadium dioxide pattern layers 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 the 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 transition process of the vanadium dioxide pattern layer from the dielectric phase to the metallic phase is realized, which is used for dynamic adjustment of the continuous domain bound state and the quasi-continuous domain bound state. Among them, the external temperature is controlled 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 a quasi-continuous domain bound state, which is displayed as 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, and the metasurface excites a continuous domain bound state, displaying a bright spot effect.

[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 is irradiated onto 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 the bound-state metasurface into a periodic two-dimensional array, and utilizes the phase change property of the vanadium dioxide pattern layer under temperature change to break the symmetry of the square structure, thereby causing the mode to leak. 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 ultimately realizing the dynamic display of the image, solving the problem of the 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 This is a schematic structural diagram of an embodiment of a temperature-controlled dual-channel bound-state metasurface for dynamic display applications according to the present invention;

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

[0033] Figure 3 This 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 This is a circular polarization response diagram of a temperature-controlled dual-channel bound-state metasurface embodiment for dynamic display applications of the present invention, where (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 σ of vanadium dioxide is 2×10 5 Circular polarization response of bound-state metasurface at S / m;

[0035] Figure 5 This 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 6This is a two-dimensional arrangement diagram of a metasurface with 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 an embodiment of a temperature-controlled dual-channel bound-state metasurface for dynamic display applications of the present invention;

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

[0039] Figure 9 This 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 with reference to the accompanying drawings and embodiments.

[0041] Unless otherwise defined, technical or scientific terms used in the present invention shall have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs.

[0042] Example 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 within the gold pattern layer. The temperature-dependent properties of the vanadium dioxide pattern layer (a phase-change material) are exploited to achieve structural symmetry and asymmetry. The center of the coordinate axis is the center of the gold pattern layer, and the z-axis is the rotation axis parallel to the structure. A schematic diagram of the metasurface's xy plane structure is shown below. Figure 1 As shown in Figure 1, the metal array structure is overlaid on a dielectric substrate with a side length of P. The gold pattern layer has a side length of L and a width of w. The vanadium dioxide pattern layer, a phase-change material, is embedded at the center of the lower side of the gold pattern layer and at a distance d to the right of the centerline of the upper side. The width of the embedded vanadium dioxide is g, and distance d is also known as the asymmetry factor. Furthermore, the dielectric substrate has a thickness of h, and both the gold pattern layer and the vanadium dioxide pattern layer have a thickness of t.

[0044] During the simulation process, the designed metasurface structure was simulated and calculated using finite element analysis software. The frequency domain solver was used, and the boundary conditions in the x and y directions were unit cells, and the boundary condition in the z direction was open (add space). The dielectric substrate is made of 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 phase change material vanadium dioxide is expressed by the Drude model, that is:

[0045]

[0046] Among them, ε ∞ is the dielectric constant of the metal 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 exhibits high symmetry in the z-direction. Incident electromagnetic light along the z-axis excites symmetry-protected BICs. At this point, all energy within the metasurface is confined, and the BICs appear dark in the spectrum. However, when the temperature of the vanadium dioxide changes, transforming it into an insulating state, the system's symmetry is broken, leading to radiation leakage and the symmetry-protected BICs becoming Q-BICs.

[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, left-handed circularly polarized light and right-handed circularly polarized light will undergo BIC to Q-BIC conversion near 460μm and 400μm, respectively. By setting different excitation voltages, the temperature can be controlled, and temperature-controlled dual-channel imaging can be achieved in the 460μm and 400μm bands.

[0050] exist Figure 5A two-dimensional unit structure layout for dynamic display applications is presented in [1]. The dynamic display process of an image is demonstrated. Electromagnetic waves are incident along the z-axis, and the FPGA applies electrical excitation to control the phase transition of vanadium dioxide, thereby manipulating the transition between the metasurface BIC and Q-BIC, ultimately achieving image display. Furthermore, data can be transmitted to a computer terminal at any time according to usage needs. By changing the FPGA's high and low DC bias outputs, corresponding to low and high levels based on the 0 / 1 levels of different FPGA development boards, real-time switching between the bound-state metasurface unit BIC and Q-BIC is achieved, thus completing 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 in this paper. The geometric shapes of the metal array structures here are rectangular bars, crosses, rectangular blocks, circular disks with holes, and square open rings. They are all symmetry-protected bound-state metasurfaces, with the gray part being vanadium dioxide and the black part being gold. By introducing structured vanadium dioxide into these metasurfaces, metasurface arrays are constructed, and the establishment and breaking of structural symmetry are manipulated to achieve switching between BIC and Q-BIC. In practical applications, the unit structure and spatial distribution of the metal array are not limited to the above-mentioned ones, provided that the metasurface is a symmetry-protected bound-state metasurface, and can be further modified and optimized according to specific requirements.

[0052] Example 2

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

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

[0055] S2. According to the imaging requirements, the FPGA outputs the corresponding voltage bias, 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 is irradiated onto 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, it shows an imaging example of a 16×16 bound state metasurface array. 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 to the right of 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 linearly polarized light, left-handed polarized light and right-handed polarized light. When linearly polarized light is incident, the conductivity of vanadium dioxide is changed by temperature control to achieve Figure 6 The designed image is displayed. At the same time, when circularly polarized light is incident, the desired image display can also be achieved. Figure 9 (a) shows the image display effect when left-handed polarized light is incident. Figure 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 dielectric phase to 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 solutions of the present invention rather than to limit the same. 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 solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A temperature-controlled dual-channel bound-state metasurface for dynamic display applications, characterized by: The invention comprises a dielectric substrate and a metal array structure disposed on the upper surface of the dielectric substrate, wherein the metal array structure comprises a gold pattern layer arranged in an array, wherein 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; By setting the FPGA program and adjusting the output of the DC bias current, the phase transition temperature of the vanadium dioxide is controlled to achieve dynamic display. Specifically: 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 a quasi-continuous domain bound state, which is displayed as a dark spot. When the FPGA outputs a large current, the vanadium dioxide is in a metallic state, the periodic array is a symmetrical structure, and the metasurface excites a continuous domain bound state, displaying a bright spot effect.

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: ； in, is the metal dielectric constant at infinite frequency, is the ratio of the scattering rate to the collision frequency, rad / s, is the electrical conductivity of vanadium dioxide, is the angular frequency of the electromagnetic wave, the plasma frequency , , rad / s, is the reference conductivity, is the plasma frequency of the reference conductivity; By changing the conductivity of the vanadium dioxide pattern layer through external temperature excitation, a reversible phase transition process of the vanadium dioxide pattern layer from the dielectric phase to the metallic phase is realized, which is used for dynamic adjustment of the continuous domain bound state and the quasi-continuous domain bound state. Among them, the external temperature is controlled by applying a DC bias current through FPGA.

4. 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 is .

5. 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 S / m.

6. A method for realizing dynamic display imaging using a temperature-controlled dual-channel bound-state metasurface for dynamic display applications according to any one of claims 1 to 5, 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, causing the vanadium dioxide pattern layer to undergo a phase change as the temperature changes, forming symmetrical units and asymmetrical units; S3. Electromagnetic wave incident light is irradiated onto the bound state metasurface, exciting BIC and Q-BIC. The transmission spectrum corresponds to the output dark state and bright state, realizing dynamic display.

7. The method according to claim 6, characterized in that: The incident electromagnetic wave light is one of linearly polarized light, left-handed polarized light and right-handed polarized light.

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