A tunable electromagnetically induced transparent metamaterial and its tuning method and application

Abstract

The present invention discloses a tunable electromagnetically induced transparent metamaterial and its tuning method and application, which belong to the field of terahertz metamaterial technology. The tunable electromagnetically induced transparent (EIT) metamaterial is arranged in order from top to bottom: a vanadium dioxide film, a dielectric layer, a grating layer and a reflective layer. The EIT-like effect is generated by the guided mode resonant coupling between the grating and the dielectric layer, avoiding the complex structure of the metasurface used in the past. The metamaterial achieves flexible adjustment of the EIT-like peak (63%-98%) and the slow light effect in the EIT-like window (group delay 1.87ps-2.86ps) by externally stimulating the change in the conductivity of vanadium dioxide (45000S / m-200S / m). It has the advantages of simple structure, easy processing, and easy operation of the tuning method.

Description

Technical Field

[0001] The present invention relates to the technical field of terahertz metamaterials, and in particular to a tunable electromagnetically induced transparent metamaterial, a tuning method thereof, and an application thereof. Background Art

[0002] Terahertz waves generally range from 0.1 to 10 THz. Their exceptional properties have broad applications in medical testing, imaging, communications, and sensing. These applications require highly responsive devices, but natural materials with high responsiveness in the terahertz band are limited. Since John Pendry proposed the concept of metamaterials, their development has been rapid. Particularly in the terahertz band, metamaterials exhibit superior electromagnetic response compared to natural materials.

[0003] Electromagnetically induced transparency (EIT) is a quantum interference effect that typically occurs in atomic three-level systems. When this effect occurs, a sharp transparency window is created across a broad absorption spectrum. This phenomenon is often accompanied by a significant change in the dispersion properties of the medium, resulting in a slowing of the speed of light. This gives EIT enormous potential for applications in slow light, optical sensing, and filtering. However, the complex and demanding experimental conditions required, such as ultra-low temperatures and high vacuum, limit its widespread practical application.

[0004] In recent years, researchers have proposed an electromagnetically induced transparency (EIT-like) effect based on metamaterials. By designing the metamaterial's microstructure to achieve an EIT-like effect, independent of complex atomic systems, this approach overcomes EIT's reliance on demanding experimental conditions such as ultra-low temperatures and high vacuum, enabling similar optical phenomena to be realized at room temperature and pressure.

[0005] Due to practical needs, tunable EIT-like effects have become a major research topic. However, the EIT-like effect is highly dependent on the geometric dimensions of metamaterials. Once fabricated, metamaterials are fixed in size, failing to meet the tunability requirements of practical applications. This significantly limits the practical application of EIT-like phenomena. VO2 is a material that exhibits an insulator-metal phase transition. Under external conditions (such as heating, electric fields, or light), it can rapidly and reversibly transform from an insulating phase to a metallic phase. Its conductivity can vary widely, ranging from 200 S / m to 200,000 S / m, and the phase transition exhibits an extremely short response time (sub-picoseconds). This makes VO2 an ideal material for tunable EIT-like phenomena. However, most current VO2-based tunable metamaterials utilize metasurface structures to achieve EIT-like effects. However, the fabrication of metasurface structures is challenging and places extremely stringent demands on machining precision. Minor manufacturing errors can lead to significant performance differences, complicating practical applications. Summary of the Invention

[0006] The purpose of the present invention is to provide a tunable electromagnetically induced transparent metamaterial and its tuning method and application, which can realize flexible adjustment of the EIT-like peak and the slow light effect in the EIT-like window through external excitation, and has the advantages of simple structure, easy processing and easy operation of the tuning method.

[0007] To achieve the above objectives, the present invention provides a tunable electromagnetically induced transparent metamaterial, which includes a vanadium dioxide film, a dielectric layer, a grating layer and a reflective layer arranged in sequence from top to bottom. The guided mode coupling between the grating and the dielectric layer produces an EIT-like effect, and the reflective layer is a terahertz shielding layer.

[0008] Preferably, the thickness of the vanadium dioxide film is 0.2 μm to 0.3 μm.

[0009] Preferably, the dielectric layer is a Topas material layer, the thickness of the dielectric layer is 16 μm to 18 μm, and the relative dielectric constant is 2.35.

[0010] Preferably, the height of the grating layer is 80 μm to 84 μm, the width is 41 μm to 45 μm, the gap width of the grating is 47 μm to 49 μm, and the grating gap material is air.

[0011] Preferably, the grating layer is made of silver and is prepared by photolithography.

[0012] Preferably, the reflective layer is a metallic silver layer that is not transparent to terahertz waves, and the thickness of the reflective layer is 4 μm-6 μm.

[0013] The tuning method of the tunable electromagnetically induced transparent metamaterial comprises the following steps:

[0014] S1. Applying external excitations such as electricity, magnetism, light, or temperature to the metamaterial to change the conductivity of the vanadium dioxide film;

[0015] S2. The terahertz wave signal is input from the end of the vanadium dioxide film. The terahertz wave signal is output from the end of the vanadium dioxide film under the action of the reflective layer. By changing the conductivity of the vanadium dioxide film, the EIT-like reflection peak of the metamaterial is continuously adjusted.

[0016] Preferably, in the S2, when the conductivity of vanadium dioxide is adjusted from 45,000 S / m to 200 S / m, the amplitude change of the EIT-like peak increases from 63% to 98%.

[0017] Preferably, in the S2, when the conductivity of vanadium dioxide is adjusted from 45000 S / m to 200 S / m, the group delay increases from 1.87 ps to 2.86 ps.

[0018] The above-mentioned tunable electromagnetically induced transparent metamaterial is used in tunable terahertz modulators and slow light devices.

[0019] The advantages and positive effects of the tunable electromagnetically induced transparent metamaterial and its tuning method and application described in the present invention are:

[0020] 1. The metamaterial described in the present invention utilizes a vanadium dioxide medium-grating hybrid to achieve a quasi-electromagnetic induced transparency function in the terahertz band. The metamaterial has a simple structure, a simple and easy preparation method, and the quality stability of the metamaterial is easy to control.

[0021] 2. The metamaterial of the present invention changes the conductivity of the vanadium dioxide film under external stimulation, thereby achieving continuous adjustment of the EIT-like peak.

[0022] 3. The metamaterial described in this invention can effectively increase group delay in an electromagnetically induced transparency window, thereby achieving a slow-light effect. By varying the conductivity of vanadium dioxide, the slow-light effect in the EIT-like window can be flexibly adjusted.

[0023] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A schematic diagram of a three-dimensional structure of a metamaterial according to an embodiment of the present invention;

[0025] Figure 2 A front view of a metamaterial structure according to an embodiment of the present invention;

[0026] Figure 3 is the reflectivity of the metamaterial of this embodiment at different terahertz frequencies and different vanadium dioxide film conductivities when the electromagnetic wave is vertically incident;

[0027] Figure 4 The phase spectrum of the metamaterial of this embodiment at different terahertz frequencies and different vanadium dioxide film conductivities when the electromagnetic wave is vertically incident;

[0028] Figure 5 is the group delay of the metamaterial of this embodiment at different terahertz frequencies and different vanadium dioxide film conductivities when the electromagnetic wave is vertically incident.

[0029] Reference numerals

[0030] 1. Vanadium dioxide thin film; 2. Dielectric layer; 3. Grating layer; 4. Reflective layer. DETAILED DESCRIPTION

[0031] In the description of the present invention, it should be noted that the terms "upper", "lower", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, or the orientations or positional relationships in which the inventive product is usually placed when in use. These are only for the convenience of describing the present invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations on the present invention. In the description of the present invention, it should also be noted that, unless otherwise expressly specified and limited, the terms "setting", "installation" and "connection" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be a communication between the internal parts of two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0032] In this application, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs. In the event of any inconsistency, the meaning described in this specification or the meaning derived from the contents recorded in this specification shall prevail. In addition, the terms used herein are only for the purpose of describing the embodiments of this application and are not intended to limit this application. In order to accurately describe the technical content in this application and to accurately understand the present invention, the following explanations or definitions are given for the terms used in this specification before describing the specific embodiments:

[0033] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0034] Example

[0035] like Figure 1 、 Figure 2 A tunable, electromagnetically induced transparent metamaterial is shown. The metamaterial consists of a vanadium dioxide film 1, a dielectric layer 2, a grating layer 3, and a reflective layer 4, arranged from top to bottom. The guided mode coupling between the grating layer 3 and the dielectric layer 2 produces an EIT-like effect. The reflective layer 4 acts as a terahertz shielding layer, preventing terahertz radiation from penetrating and reflecting it instead.

[0036] The thickness t of the vanadium dioxide thin film 1 is 0.2 μm.

[0037] The dielectric layer 2 is a Topas material layer, the thickness h1 of the dielectric layer 2 is 17 μm, and the relative dielectric constant is 2.35.

[0038] The height h2 of the grating layer 3 is 82 μm, the grating period p is 90 μm, the gap width w of the grating is 47 μm, and the grating gap material is air.

[0039] The material of the grating layer 3 is silver, and the grating layer 3 is prepared by a photolithography process.

[0040] The metal layer is a metallic silver layer that is not transparent to terahertz waves, and has a thickness h3 of 5 μm.

[0041] The metamaterial structure of the present invention only requires the metal grating to be processed by a photolithography process. The preparation method is simple and easy to operate, and is easier to control and implement.

[0042] The EIT-like effect of metal gratings originates from the coupling between the grating and the guided modes of dielectric layer 2. The resulting resonance is typically simple and direct. Metal grating structures not only offer a simpler structure and processing, but also, due to their single coupling mechanism, require less precision during manufacturing, and errors have a minimal impact on performance, further reducing the complexity of practical applications.

[0043] The tuning method of the tunable electromagnetically induced transparent metamaterial comprises the following steps:

[0044] S1, applying external stimulation (electricity, magnetism, light or temperature) to the metamaterial to change the conductivity of the vanadium dioxide film 1;

[0045] S2. A terahertz wave signal is input from the end of the vanadium dioxide film 1. The terahertz wave signal is output from the end of the vanadium dioxide film 1 under the action of the reflective layer 4. By changing the conductivity of the vanadium dioxide film 1, the EIT-like reflection peak of the metamaterial is continuously adjusted.

[0046] like Figure 1 As shown in the figure, the incident electromagnetic wave vector k is assumed to be along the z-axis, the electric field component E is assumed to be along the y-axis, and the magnetic field component H is assumed to be along the x-axis. Finite element simulations were performed using periodic boundary conditions in the x and y directions and a Floquet port in the z direction. The simulations revealed the metamaterial's reflection spectrum in the terahertz band.

[0047] Figure 3 The reflectivity of the metamaterial of this embodiment at different terahertz frequencies and different vanadium dioxide film conductivity levels when the electromagnetic wave is perpendicularly incident. The results show that as the VO2 conductivity decreases, the EIT-like peak of the reflection window gradually increases. When the VO2 conductivity decreases from 45,000 S / m to 200 S / m, the reflectivity at 5.50 THz increases from 0.63 to 0.98, achieving dynamic modulation of the EIT-like window.

[0048] Define modulation depth ΔR / R0=(R0–R p ) / R0, where R0 represents the reflectivity of VO2 with a conductivity of 200S / m, R pThe VO2 conductivity is 45,000 S / m, the reflectivity is 35.7%, and the modulation depth of the peak amplitude is 35.7%. This provides potential applications for the metamaterial of the present invention in the fields of THz imaging and communications.

[0049] EIT-like spectra are basically related to steep dispersion, which leads to a decrease in the group velocity of light propagation. The EIT-like spectral profile shows that there are abnormal changes in strong phase dispersion near the sharp transparent window. A significant feature of the EIT-like response in atomic systems is the slow light effect. In a strongly dispersive system, the group velocity v g It can be expressed as

[0050]

[0051] The effective group index This equation shows that The strong dispersion response of can induce a large group index to suppress the group velocity. Therefore, a group deceleration effect is generated. The performance of the group deceleration effect can be characterized by the following relationship

[0052]

[0053] Among them, v g is the group velocity, τ g is the group delay, c is the speed of light in vacuum, L is the thickness of the structure, represents the phase dispersion response of the resonant spectrum, and ω is the angular frequency of the field.

[0054] like Figure 4 The phase spectra of the metamaterial of this embodiment at different terahertz frequencies and different conductivity of vanadium dioxide film 1 when the electromagnetic wave is incident vertically are shown. The results show that the phase changes with the increase of VO2 conductivity. The slope of the phase dispersion curve is steepest at the EIT-like resonance of 5.50 THz. Therefore, the time delay can be calculated based on the phase dispersion. Based on formulas (1)-(3), the group delay and group index can be evaluated based on the abrupt phase dispersion of the EIT-like resonance. Strong dispersion is a significant feature of the EIT-like response. The slow light effect is closely related to the group index, which can be generated by a very steep normal phase dispersion.

[0055] Figure 5 The group delay of this embodiment's metamaterial at different terahertz frequencies and different vanadium dioxide film conductivity levels when the electromagnetic wave is perpendicularly incident is shown in Figure 1. The results show that when the VO2 conductivity is 200 S / m, a larger group delay is achieved around the reflection peak, indicating potential applications in slow-light devices. As the conductivity increases, the group delay decreases, enabling flexible control of both group delay and the slowing effect.

[0056] The tunable electromagnetically induced transparent metamaterial described in this invention achieves dynamic modulation of an EIT-like effect by regulating the conductivity of VO2 through external stimulation. By adjusting the conductivity of VO2 from 45,000 S / m to 200 S / m, the amplitude of the EIT-like peak can be effectively controlled from 0.62 to 0.98, while simultaneously increasing the group delay from 1.87 ps to 2.86 ps. This modulation process occurs exclusively within the EIT window, with minimal variation in the reflection valley, demonstrating excellent tuning stability, thus achieving an actively tunable slow-light effect.

[0057] Therefore, the tunable electromagnetically induced transparent metamaterial and its tuning method and application described in the present invention can achieve flexible adjustment of the EIT-like peak and the slow light effect in the EIT-like window through external excitation, which has the advantages of simple structure and easy operation of the tuning method.

[0058] 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 tunable electromagnetically induced transparent metamaterial, characterized by: The metamaterial consists of a vanadium dioxide film, a dielectric layer, a grating layer, and a reflective layer arranged in sequence from top to bottom. The guided mode coupling between the grating and the dielectric layer produces an EIT-like effect. The reflective layer serves as a terahertz shielding layer. The dielectric layer is a Topas material layer with a thickness of 16 to 18 μm and a relative dielectric constant of 2.

35. The grating layer is prepared by a photolithography process; A tuning method for a tunable electromagnetically induced transparent metamaterial comprises the following steps: S1. Applying external excitations such as electricity, magnetism, light, or temperature to the metamaterial to change the conductivity of the vanadium dioxide film; S2. Inputting a terahertz wave signal from the vanadium dioxide film end, and outputting the terahertz wave signal from the vanadium dioxide film end under the action of the reflective layer, and realizing continuous adjustment of the EIT-like reflection peak of the metamaterial by changing the conductivity of the vanadium dioxide film; In the S2, when the conductivity of vanadium dioxide decreases from 45000 S / m to 200 S / m, the amplitude change of the EIT-like peak increases from 63% to 98%; In S2, when the conductivity of vanadium dioxide decreases from 45000 S / m to 200 S / m, the group delay increases from 1.87 ps to 2.86 ps; Tunable electromagnetically induced transparent metamaterials are used in tunable terahertz modulators and slow light devices.

2. The tunable electromagnetically induced transparent metamaterial according to claim 1, characterized in that: The thickness of the vanadium dioxide film is 0.2 μm to 0.3 μm.

3. The tunable electromagnetically induced transparent metamaterial according to claim 1, characterized in that: The height of the grating layer is 80 μm to 84 μm, the width is 41 μm to 45 μm, the gap width of the grating is 47 μm to 49 μm, and the grating gap material is air.

4. The tunable electromagnetically induced transparent metamaterial according to claim 1, characterized in that: The material of the grating layer is silver.

5. The tunable electromagnetically induced transparent metamaterial according to claim 1, characterized in that: The reflective layer is a metallic silver layer that is not transparent to terahertz waves, and the thickness of the reflective layer is 4 μm-6 μm.

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