A terahertz metamaterial device implementing eit-like and broadband absorption dual functional conversion

Abstract

The application discloses a terahertz metamaterial device realizing EIT-like and broadband absorption dual-function conversion, and belongs to the technical field of terahertz application.The device is composed of three layers of structures, from top to bottom, a resonator layer 1 of a top layer, a medium layer 2 in the middle and a substrate layer 3 at the bottom, and the three layers of structures are closely combined to form a structure period, and one structure period P is 80.The resonator layer 1 of the top layer is combined by three resonators, which are a cross structure resonator structure 1, four strip-shaped short arm resonator structures 2 and four T-shaped resonator structures 3.The device utilizes the phase change characteristic of vanadium dioxide to realize the dynamic conversion between EIT-like and broadband absorption, when the vanadium dioxide is in an insulating state, the device can realize the EIT-like effect, and when the vanadium dioxide is in a metallic state, the device can realize the broadband absorption function.The device integrates the EIT-like and broadband absorption functions into one device, is beneficial to the integration of equipment, and can be applied to broadband wave absorbers, slow light devices, optical switch devices, modulators and other optical equipment.

Description

Technical Field

[0001] This invention relates to the field of terahertz application technology, specifically to a terahertz metamaterial device that achieves dual-function conversion of EIT-like and broadband absorption, which can be used in optical devices such as broadband absorbers, slow-light devices, optical switches, and modulators. Background Technology

[0002] Terahertz (THz) waves refer to electromagnetic waves with frequencies ranging from 0.1 THz to 10 THz and wavelengths ranging from 0.03 mm to 3 mm. Due to their various favorable electromagnetic properties, they are widely used in fields such as biomedicine, food safety, and safety detection. Metamaterials (MMS) are specially designed artificially synthesized structures with unique electromagnetic properties such as negative conductivity and negative dielectric constant. By artificially adjusting the unit structure and size parameters of metamaterials, different electromagnetic responses can be generated. Currently, researchers have used terahertz metamaterial devices to achieve beam modulation, broadband absorption, polarization conversion, and electromagnetically induced transparency.

[0003] Electromagnetically induced transparency (EIT) is a nonlinear quantum interference effect occurring in a three-level atomic system, causing transparent windows to appear in the spectral absorption region of an originally opaque medium, accompanied by a "slow light effect." This has significant application value in fields such as optical storage and slow-light devices. Simulating the EIT phenomenon using metamaterials is called Electromagnetically Induced Transparency-Like (EIT-like), which reduces the stringent experimental conditions of traditional EIT and broadens the research and application of EIT effects. Broadband terahertz absorbers, as important terahertz functional devices, are widely used in electromagnetic stealth and terahertz imaging due to their excellent absorption characteristics.

[0004] In early research, the fixed structural dimensions of terahertz metamaterials limited their properties, severely restricting their development. To address this challenge, researchers have begun incorporating active materials, such as graphene and vanadium dioxide (VO2), into metamaterials. Among these, VO2 exhibits advantages such as fast response speed and deep modulation, showing promising application prospects in terahertz metamaterial functional devices. VO2 is an excellent phase change material, and its conductivity can be dynamically adjusted by changing the temperature. When the temperature exceeds 340 K (approximately 68 °C), VO2 exhibits strong metallic properties; conversely, it exhibits insulating properties at room temperature. By applying stimuli such as light or temperature, a reversible phase transition from an insulating state to a metallic state can be achieved.

[0005] However, most current results only demonstrate one function, and devices with two or more functions have been proposed. Therefore, designing devices with two or more functions is essential. This will significantly improve the performance of terahertz metamaterial devices to meet diverse application requirements and integration needs. Summary of the Invention

[0006] In view of the problems existing in the terahertz metamaterial devices described above, the present invention provides a terahertz metamaterial device that realizes dual-function conversion of EIT-like and broadband absorption, which solves the key problems existing in the background technology of terahertz metamaterial devices such as non-tunability, inability to perform function conversion, and unfavorable integration of terahertz metamaterial devices.

[0007] This invention provides a terahertz metamaterial device that achieves dual-function conversion between EIT-like and broadband absorption. The terahertz metamaterial device consists of a three-layer structure, from top to bottom: a top resonator layer, an intermediate dielectric layer, and a substrate layer. The surface of the top resonator layer is the front side of the terahertz metamaterial device that achieves dual-function conversion between EIT-like and broadband absorption.

[0008] Preferably, the thickness of the substrate layer is 0.2 mm. Both the length and width are 80 The substrate layer is made of VO2 material, and the relative permittivity of VO2 can be calculated using the Drude model.

[0009] (1)

[0010] in, =12 is the high-frequency dielectric constant; =5.75 10 13 rad / s is the collision angular frequency; the plasma frequency is related to the conductivity of VO2. The plasma frequency at that location can be approximated by... express, =3 10 5 S / m, =1.4 10 S / m.

[0011] Preferably, the thickness of the intermediate dielectric layer is 34. Both the length and width are 80 The intermediate dielectric layer is made of polymethacrylamide (PMI), and its relative permittivity is... It is 1.1.

[0012] Preferably, the top resonator layer is a patterned structure composed of three resonators: structure 1, composed of a cross-shaped resonator; structure 2, composed of four strip-shaped short-arm resonators; and structure 3, composed of four T-shaped resonators. The four strip-shaped short-arm resonators are located within the four quadrants of the cross-shaped resonator, and one end of each strip-shaped short-arm resonator is connected to one arm of the cross-shaped resonator. Thus, structure 1 and structure 2 together constitute a windmill-shaped resonator. The four T-shaped resonators are located in the four arm extension directions of the cross-shaped resonator. Each T-shaped resonator includes a vertical strip and a horizontal strip, with the vertical strip positioned in the gap formed by one arm of the cross-shaped resonator and the corresponding strip-shaped short-arm resonator. Based on the material, the three types of resonators can be divided into two categories. The first category is the windmill-shaped resonator composed of structures 1 and 2, made of gold with a conductivity of 3.56 × 10⁻⁶. 7 The second type is structure 3, which uses VO2 as its material.

[0013] Preferably, the lengths of both the horizontal and vertical bars of structure 1 are L1=52. Width W1 is 6 The length L2 of the short arm of structure 2 is 23. The width is also W1=6 The length L3 of the vertical strip of structure 3 is 29 mm. The width is W2=2 The length of the horizontal bar L4 is 28. The width is W1=6 The top resonator layer is composed of structures 1, 2 and 3.

[0014] Preferably, the structural period P of the terahertz metamaterial device that realizes dual-function conversion of EIT-like and broadband absorption is 80. The terahertz metamaterial device is an array formed by splicing together multiple structural periods.

[0015] The beneficial effects of the terahertz metamaterial device that achieves dual-function conversion of EIT-like and broadband absorption described above are as follows: (1) EIT-like effect can be achieved when VO2 is in an insulating state; (2) Broadband absorption can be achieved when VO2 is in a metallic state; (3) Reversible changes in VO2 can be achieved by applying excitations such as light and temperature, so that the two functions can be switched and used in one device; (4) It can be used as an optical device such as a broadband absorber, a slow light device, an optical switch, and a modulator. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structural period of a terahertz metamaterial device that realizes dual-function conversion of EIT-like and broadband absorption, provided by the present invention.

[0017] Figure 2 This is a front view of a terahertz metamaterial device that realizes dual-function conversion of EIT-like and broadband absorption, provided by the present invention, and a schematic diagram of the structures 1, 2, and 3 and the windmill model resonator.

[0018] Figure 3 This is an array diagram formed by splicing multiple structural periods of a terahertz metamaterial device that realizes dual-function conversion of EIT-like and broadband absorption, as provided by the present invention.

[0019] Figure 4 This is an EIT-like transmission curve of a terahertz metamaterial device that achieves dual-function conversion of EIT-like and broadband absorption, provided by the present invention.

[0020] Figure 5 This is the group delay curve of a terahertz metamaterial device that realizes dual-function conversion of EIT-like and broadband absorption, provided by the present invention.

[0021] Figure 6 This is a graph showing the transmittance of a terahertz metamaterial device that achieves dual-function conversion of EIT-like and broadband absorption as a function of VO2 conductivity, provided by the present invention.

[0022] Figure 7 This is a broadband absorption curve of a terahertz metamaterial device that achieves dual-function conversion of EIT-like and broadband absorption, provided by the present invention.

[0023] Figure 8 This is an impedance matching diagram of a terahertz metamaterial device that achieves dual-function conversion of EIT-like and broadband absorption, provided by the present invention, when VO2 is in the metallic state.

[0024] Figure Labels

[0025] 1. Top resonator layer; 2. Intermediate dielectric layer; 3. Substrate layer. Detailed Implementation

[0026] This terahertz metamaterial device consists of a three-layer structure, from top to bottom: a top resonator layer, an intermediate dielectric layer, and a substrate layer, as shown below. Figure 1 As shown. The top resonator layer is a patterned structure composed of three resonators, represented as Structure 1, Structure 2, and Structure 3. The four strip-shaped short-arm resonators are located within the four quadrants of the cross-shaped resonator, with one end of each strip-shaped short-arm resonator connected to one arm of the cross-shaped resonator. Thus, Structure 1 and Structure 2 together form a windmill-shaped resonator. The four T-shaped resonators are located along the four arm extension directions of the cross-shaped resonator. Each T-shaped resonator includes a vertical strip and a horizontal strip, with the vertical strip positioned within the gap formed by one arm of the cross-shaped resonator and the corresponding strip-shaped short-arm resonator. The length of both the horizontal and vertical strips of Structure 1 is L1 = 52. Width W1=6 The length of the short arm of structure 2 is L2=23. The width is also W1=6 The vertical strip length L3 of structure 3 is 29 mm. The width is W2=2 The length of the horizontal bar is L4 = 28. The width is W1=6 The top resonator layer is composed of structures 1, 2, and 3. A windmill-shaped resonator made of gold and structure 3 made of VO2 material are combined to form a patterned top resonator layer. The surface of the top resonator layer is the front side of the terahertz metamaterial device that achieves EIT-like and broadband absorption dual-function conversion, as shown below. Figure 2 As shown. The thickness of the intermediate dielectric layer is 34. Both the length and width are 80 The material used is PMI. The thickness of the substrate layer is 0.2 mm. Both the length and width are 80 The material used is VO2. The three-layer structure is tightly bonded to form a structural cycle, and the value of P in one structural cycle is 80. The terahertz metamaterial device is an array formed by splicing together multiple structural periods, such as... Figure 3 As shown.

[0027] Example 1

[0028] This invention provides a method for realizing EIT-like functionality in a terahertz metamaterial device that achieves dual-function conversion of EIT-like and broadband absorption: when the conductivity of VO2 is =200 At this time, VO2 is in an insulating state, acting as a dielectric and not significantly reacting with or absorbing the incident wave. The incident wave is perpendicularly incident on the front side of the top resonator layer and resonates with the terahertz metamaterial device. In this state, the terahertz metamaterial device can achieve an EIT-like effect, producing a transparent window with a transmittance as high as 81.0% at 2.458 THz, such as... Figure 4 As shown by the solid line in the middle.

[0029] The basic working principle of the terahertz metamaterial device that achieves dual-function conversion of EIT-like and broadband absorption is as follows: When VO2 is in an insulating state, it has high transmittance and does not produce significant reflection or absorption of incident waves. Therefore, the top resonator layer, acting as a windmill resonator, plays a major role in generating the EIT-like effect. Currently, there are generally two ways to realize the EIT-like phenomenon: bright-mode coupling and dark-mode coupling. When an incident wave is incident on the metamaterial structure, the bright-mode resonator can be directly excited by the incident wave, while the dark-mode resonator cannot be directly excited by the incident wave but can be excited by the near-field coupling of the bright-mode resonator. The terahertz metamaterial device described in this invention achieves the EIT-like effect through bright-mode coupling. Structure 1, as a bright mode, will directly couple with the incident wave, generating a transmission peak at 2.608 THz, as shown below. Figure 4 As shown by the dashed line, structure 2, as a dark mode, cannot directly couple with the incident wave and therefore does not form a strong resonance, as... Figure 4 As shown by the dashed line, near-field coupling between bright and dark modes induces destructive interference in the electromagnetic field, resulting in a transparent window with 81.0% transmittance at 2.458 THz, achieving an EIT-like effect, such as... Figure 4 As shown by the solid line. Generally, the EIT-like effect slows down the propagation speed of electromagnetic waves, thus producing a "slow light effect," which can be represented by group delay (…). A visual description of the intensity of slow light. This can be achieved through... The group delay value is calculated, where It is angular frequency. It is the transmission phase. Based on the above... The calculation formula yields a maximum group delay of 0.691 ps for this terahertz metamaterial device, as shown in the group delay curve. Figure 5 As shown. The transmittance of the device can also be controlled by adjusting the conductivity of VO2, such as... Figure 6 As shown. When the conductivity is 200... At 2.458 THz, the transmittance is 81.0%, while when the VO2 conductivity is 200,000... At that time, the transmittance was only 0.7%, and the incident wave could hardly pass through the device. That is, as the conductivity of VO2 increases, the device gradually closes the EIT-like transparent window and begins to absorb the incident wave.

[0030] Example 2

[0031] This invention provides a method for achieving broadband absorption using a terahertz metamaterial device that realizes dual-function conversion of EIT-like and broadband absorption: when the conductivity of VO2 is =200000 When VO2 is in a metallic state, the incident wave is perpendicularly incident on the front side of the top resonator layer and resonates with the terahertz metamaterial device. At this time, the VO2 in the substrate acts as a reflective layer, and the structure 3 of the top resonator layer is also coupled with the incident wave. The terahertz metamaterial device can achieve broadband absorption, with an absorption rate exceeding 90% in the frequency range of 0.779 THz-2.596 THz and an absorption bandwidth of 1.817 THz. Figure 7 As shown.

[0032] When VO2 is in a metallic state, the terahertz metamaterial device is equivalent to a broadband absorber, and the absorption rate can be calculated using the following formula: Where R represents reflectivity and T represents transmittance. Since the metallic VO2 in the substrate acts as a reflective layer, and the structure thickness is greater than the skin depth, the transmittance T can be ignored. This can be understood as the metallic VO2 in the substrate acting as a reflective layer preventing electromagnetic waves from passing through the metamaterial, thus resulting in zero transmittance. Therefore, the formula can be simplified to... Calculations show that the terahertz metamaterial device achieves an absorption rate exceeding 90% in the frequency range of 0.779 THz to 2.596 THz, with an absorption bandwidth of 1.817 THz, making it suitable for use as a broadband absorber. Besides bandwidth, relative absorption bandwidth is a crucial evaluation metric for terahertz metamaterial absorbers, which can be determined using the formula... The relative absorption bandwidth was calculated, where It is 0.779THz. It is 2.596THz, specifically as follows Figure 7 As shown, the relative absorption bandwidth of the device is calculated to be 103.3%.

[0033] To explain the principle behind its high absorption rate, impedance matching theory is introduced. The relationship between absorption rate and relative impedance is expressed as follows:

[0034] (2)

[0035] (3)

[0036] in, , and S represents the effective impedance and free space impedance of the terahertz metamaterial absorber, respectively. 11 and S 21 These are the parameters for reflection and transmission. When the real part of the relative impedance is closer to 1 and the imaginary part is closer to 0, the impedance of the absorber will match the space impedance, resulting in a high absorption effect. The impedance matching diagram is shown below. Figure 8 As shown, it is clear that the real part of the relative impedance of this structure is close to 1 in the range of 0.779THz-2.596THz, as... Figure 8 As shown by the solid line, the imaginary part is close to 0, as... Figure 8 As shown by the dashed line, this indicates that the device approximately achieves impedance matching, resulting in an absorption rate greater than 90%. However, after 2.596 THz, both the real and imaginary parts of the impedance gradually deviate from 1 and 0, and the impedance matching degree between the free space and the absorber gradually decreases. Therefore, the absorption rate decreases and cannot achieve the high absorption rate of greater than 90%.

[0037] In summary, the terahertz metamaterial device provided by this invention, which achieves dual-function switching between EIT-like and broadband absorption, utilizes the phase transition characteristics of VO2 to realize dynamic switching between broadband absorption and EIT-like, which is beneficial to promoting the integration of terahertz metamaterial devices and can be applied to optical devices such as broadband absorbers, slow-light devices, optical switches, and modulators.

Claims

1. A terahertz metamaterial device that achieves dual-function conversion of EIT-like and broadband absorption, characterized in that, The device is composed of periodically arranged resonant units, each of which has a patterned resonant layer, an intermediate dielectric layer and a substrate layer from top to bottom. The patterned resonant layer is a patterned structure composed of three resonators: structure 1, composed of a cross-shaped resonator; structure 2, composed of four short-arm strip resonators; and structure 3, composed of four T-shaped resonators. Structures 1 and 2 can be combined to form a windmill-shaped resonator. The four short-arm strip resonators are located within the four quadrants of the cross-shaped resonator, and one end of each short-arm strip resonator is connected to one arm of the cross-shaped resonator. Thus, structures 1 and 2 together constitute a windmill-shaped resonator. The four T-shaped resonators are located in the four arm extension directions of the cross-shaped resonator. Each T-shaped resonator includes a vertical strip and a horizontal strip. The vertical strip is located in the gap formed by one arm of the cross-shaped resonator and the corresponding short-arm strip resonator. The windmill-shaped resonator is made of gold, and structure 3 and the substrate are made of vanadium dioxide.

2. The terahertz metamaterial device for realizing dual-function conversion of EIT-like and broadband absorption according to claim 1, characterized in that, The period P of the resonant unit is 80 μm, and the device is composed of the resonant unit arranged periodically in a plane; the substrate layer has a thickness of 0.2 μm and a length and width of 80 μm. The thickness of the intermediate dielectric layer is 34 μm; the lengths of the horizontal and vertical strips of structure 1 are both L1=52. Width is W1=6 The length of the short arm of structure 2 is L2=23. The width is also W1=6 The length of the vertical strip in structure 3 is L3=29. The width is W2=2 The length of the horizontal bar is L4=28. The width is W1=6 .

3. A terahertz metamaterial device for realizing dual-function conversion of EIT-like and broadband absorption according to claim 1, characterized in that, The material of the intermediate dielectric layer is polymethacrylimide (PMI).

4. The terahertz metamaterial device according to claim 1, which realizes dual-function switching between EIT-like and broadband absorption, utilizes the phase transition characteristics of VO2 to achieve dynamic switching between EIT-like and broadband absorption. When VO2 is in an insulating state, the device can realize the EIT-like effect; when VO2 is in a metallic state, the device can realize the broadband absorption function.

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