Polarization-insensitive tunable electromagnetic induction transparent metamaterial structure

Abstract

The invention discloses a polarization-insensitive tunable electromagnetically-induced transparent metamaterial structure, which comprises a dielectric substrate; the metamaterial unit structures are periodically arranged on the dielectric substrate; each metamaterial unit structure comprises a graphene disc located in the center and a graphene hole groove in the periphery, and the graphene hole groove is annular and surrounds the graphene disc; the diameter D1 of the graphene disc and the diameter D2 of the graphene hole groove meet D2gt; d1; the period P of the metamaterial unit structure meets Pgt; d2. According to the invention, dynamic regulation and control of electromagnetically induced transparency are realized. The structure not only enhances the response of the material to electromagnetic waves, but also realizes an all-around EIT-like effect, is insensitive to a polarization state and an incident angle, and provides a new view angle for the practical application of the EIT effect.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metamaterials, and particularly relates to a polarization-insensitive tunable electromagnetic induced transparency metamaterial structure. BACKGROUND

[0002] The electromagnetic induced transparency (EIT) phenomenon, which is initially discovered in a three-level atomic system, is caused by a coherent process of mutual transition of electrons on different paths. This phenomenon can make an originally opaque medium transparent in a specific frequency band, forming a transparent window. Although the EIT effect has important application potential, its application is limited by high experimental conditions, such as a large-scale high-power laser system and a low-temperature environment. The EIT-like effect in metamaterials provides a new way to overcome these limitations. Since Zhang et al. first proposed the EIT-like effect of a metal silver metamaterial in the terahertz wave band in 2008, this field has become a research hotspot.

[0003] The fixed structure and material of the traditional metamaterial limit its ability to adjust the EIT-like effect. In order to overcome this limitation, the introduction of materials such as graphene provides new possibilities for dynamic adjustment. Graphene, as a material with high electron mobility and excellent conductivity, can be externally excited by voltage regulation and the like. For example, the electronic properties can be dynamically changed, and the interaction characteristics with electromagnetic waves can be changed, thereby realizing dynamic adjustment of the EIT-like effect.

[0004] In previous studies, graphene metamaterials can realize the EIT-like effect that is usually only exhibited in a specific polarization direction of electromagnetic waves. There are few documents on how to use structural symmetry to realize the EIT-like effect that is not sensitive to the polarization direction of electromagnetic waves. SUMMARY

[0005] The purpose of the present application is to provide a polarization-insensitive tunable electromagnetic induced transparency metamaterial structure to realize dynamic regulation of the electromagnetic induced transparency (EIT) phenomenon.

[0006] To achieve the above purpose, the present application adopts the following technical solutions:

[0007] A polarization-insensitive tunable electromagnetic induced transparency metamaterial structure comprises:

[0008] a dielectric substrate;

[0009] a metamaterial unit structure periodically arranged on the dielectric substrate;

[0010] The metamaterial unit structure comprises a graphene disc at the center and a graphene hole slot at the periphery, and the graphene hole slot is annular and surrounds the graphene disc.

[0011] The diameter D1 of the graphene disc and the diameter D2 of the graphene slot satisfy D2>D1.

[0012] The period P of the metamaterial unit structure satisfies P>D2.

[0013] Preferably, the dielectric substrate is SiO2, with a dielectric constant of 3.9 and a thickness of 1 μm.

[0014] Preferably, the period P=5 μm, the diameter D1 of the graphene disc is 2 μm, and the diameter D2 of the graphene slot is 4.7 μm.

[0015] Preferably, the structure further comprises an ionic gel layer and a metal gate electrode; the ionic gel layer covers the graphene disc and the graphene slot, and has a dielectric constant of 1.82 and a thickness of 0.2 μm; the metal gate electrode is located on the upper surface of the ionic gel layer and directly contacts the ionic gel layer.

[0016] Preferably, the Fermi energy level E F The dynamic regulation of the electromagnetic induced transparency window is realized.

[0017] Preferably, the Fermi energy level adjustment range is 0.4 eV to 0.7 eV.

[0018] Preferably, the Fermi energy level adjustment mode is one or a combination of the following: an applied voltage, an applied electric field, and chemical doping.

[0019] Preferably, when E F When the Fermi energy level E F increases from 0.4 eV to 0.7 eV, the center frequency of the transparency window moves from 4.68 THz to 6.16 THz, and the transmission peak intensity increases with the increase of E

[0020] Preferably, when the incident angle is less than 60°, the transmission peak intensity of the polarization-insensitive tunable electromagnetic induced transparency metamaterial structure is maintained at more than 80%.

[0021] Preferably, the polarization-insensitive tunable electromagnetic induced transparency metamaterial structure is not sensitive to the polarization state of linearly polarized light (0°-90° polarization angle) and left / right circularly polarized light (LCP / RCP).

[0022] Preferably, the electromagnetic induced transparency effect is generated by the coupling of two bright modes of the graphene disc and the annular slot.

[0023] Preferably, when E F =0.5 eV, a transparency window with a transmittance of ≥93.5% is formed at 5.21 THz, and the transmission valleys on both sides are located at 4.73 THz and 5.69 THz.

[0024] The application further provides a method for regulating the polarization-insensitive tunable electromagnetic induced transparency metamaterial structure.

[0025] The method for regulating the polarization-insensitive tunable electromagnetic induced transparency metamaterial structure comprises the following steps:

[0026] Adjusting the graphene Fermi energy E F to control the transparent window frequency;

[0027] Increasing the graphene hole slot diameter D2 to move the transparent window to a low frequency;

[0028] Increasing the graphene disc diameter D1 to move the transparent window to a high frequency.

[0029] The application further provides a refractive index sensor.

[0030] The refractive index sensor comprises the polarization-insensitive tunable electromagnetic induced transparency metamaterial structure.

[0031] When the environmental refractive index changes in the range of 1.0-1.3, the transparent window frequency is linearly red-shifted;

[0032] The sensitivity is characterized by the frequency shift caused by the refractive index change.

[0033] The application further provides a slow light device.

[0034] The slow light device comprises the polarization-insensitive tunable electromagnetic induced transparency metamaterial structure.

[0035] A positive group delay is generated near the transparent window frequency;

[0036] The group delay size is controlled by adjusting the Fermi energy.

[0037] Beneficial effects: The application provides a polarization-insensitive tunable electromagnetic induced transparency metamaterial structure, which is based on disc graphene and hole slot graphene and realizes dynamic regulation of electromagnetic induced transparency. The structure not only enhances the response of the material to electromagnetic waves, but also realizes all-around EIT-like effect, which is insensitive to the polarization state and the incident angle, thereby providing a new perspective for the practical application of EIT effect. Through the symmetric structure design of the graphene metamaterial, the application successfully realizes the EIT-like effect which is insensitive to the polarization state and the incident angle of electromagnetic waves. This is an important improvement on the traditional EIT-like effect. Through electric field analysis, the application also analyzes the interaction between the bright mode and the bright mode to reveal the physical mechanism of the EIT-like effect. In addition, the application analyzes the influence of the change of the graphene metamaterial structure and the potential application in the refractive index detector and the slow light device. The application provides a new perspective and method for the wide application of EIT-like effect in practical application. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 Schematic diagram of the unit structure of the polarization-insensitive tunable electromagnetically induced transparency (EIT) metamaterial of the present application, wherein (a) is a perspective view and (b) is a top view, showing the symmetrical arrangement of the central graphene disk (D1 = 2 μm) and the peripheral annular hole (D2 = 4.7 μm);

[0039] Figure 2 Transmission spectrum comparison of the graphene metamaterial, wherein the disk curve: single disk structure (D1 = 2 μm), transmission valley at 5.69 THz; hole curve: single hole structure (D2 = 4.7 μm), transmission valley at 4.76 THz; EIT curve: mixed structure of disk and hole, transmission peak (≥ 93.5%) at 5.21 THz, transmission valleys on both sides at 4.73 THz and 5.69 THz;

[0040] Figure 3 Electric field distribution corresponding to the EIT transmission spectrum of the mixed structure, wherein (a) left transmission valley (4.73 THz): electric field concentrated at both ends of the hole, dipole resonance; (b) transparent window (5.21 THz): disk and hole are excited simultaneously, forming a quadrupole field distribution; (c) right transmission valley (5.69 THz): electric field concentrated at both ends of the disk, dipole resonance;

[0041] Figure 4 Graphene Fermi energy (E F = 0.4-0.7 eV) control effect on the EIT transmission spectrum, showing that the transmission peak frequency moves from 4.68 THz (E F = 0.4 eV) to 6.16 THz (E F = 0.7 eV);

[0042] Figure 5 Transmission spectrum of the graphene metamaterial under different incident conditions; wherein (a) influence of different incident angles; (b) influence of left-handed circularly polarized light (LCP) and right-handed circularly polarized light (RCP);

[0043] Figure 6 Performance characterization of the graphene metamaterial under polarization control; wherein (a) transmission spectrum of the EIT-like effect under different polarization angles (0°-45°), showing that the transmission curve is not sensitive to the change of the polarization angle; (b) electromagnetic field distribution corresponding to the left transmission valley (4.73 THz) when the polarization angle is 45°, showing the dipole resonance characteristics at both ends of the hole structure.

[0044] Figure 7For when the Fermi level Ef=0.5eV, the regulation characteristics of the transmission spectrum line are changed by changing the geometry of the metamaterial alone; wherein (a) the hole slot diameter; (b) the disc diameter;

[0045] Figure 8 For the application of graphene metamaterial in refractive index sensing, wherein: (a) the transmission spectrum under different environmental refractive indexes (1.0-1.3), showing that the transparent window frequency linearly red shifts with the increase of the refractive index; (b) the function relationship between the transparent window resonance frequency and the sensitivity with the change of the refractive index, and the sensitivity is characterized by the frequency shift amount Δf / refractive index change Δn;

[0046] Figure 9 For the phase and group delay characteristics of graphene metamaterial at a Fermi level of 0.5eV, wherein: (a) the phase change curve of the transmitted light, showing that there is significant phase dispersion near the transparent window; (b) the corresponding group delay τg spectrum, showing a positive group delay of 1.2ps at the transparent window of 5.21THz, indicating a slow light effect. DETAILED DESCRIPTION

[0047] The application will be further explained below with reference to the accompanying drawings.

[0048] As shown in Figure 1 , a polarization-insensitive tunable electromagnetic induced transparency metamaterial structure of the application comprises:

[0049] a dielectric substrate;

[0050] a metamaterial unit structure periodically arranged on the dielectric substrate;

[0051] The metamaterial unit structure comprises a graphene disc at the center and a graphene hole slot at the periphery, and the graphene hole slot is annular and surrounds the graphene disc.

[0052] The graphene disc diameter D1 and the graphene hole slot diameter D2 satisfy D2>D1.

[0053] The period P of the metamaterial unit structure satisfies P>D2.

[0054] The dielectric substrate is SiO2, the dielectric constant of which is 3.9, and the thickness is 1μm.

[0055] The period P is 5μm, the graphene disc diameter D1 is 2μm, and the graphene hole slot diameter D2 is 4.7μm.

[0056] In some preferred embodiments, an ionic gel layer and a metal gate electrode are further included; the ionic gel layer covers the graphene disc and the graphene hole slot, the dielectric constant of the ionic gel layer is 1.82, and the thickness is 0.2 μm; the metal gate electrode is located on the upper surface of the ionic gel layer and directly contacts the ionic gel layer. An external voltage is applied through the metal gate electrode, and the Fermi energy level of graphene is regulated by the double-layer effect of the ionic gel layer: when a positive voltage is applied, anions in the ionic gel gather at the graphene interface, increasing the electron concentration and moving the Fermi energy level upward; when a negative voltage is applied, the gathering of cations increases the hole concentration, and the Fermi energy level moves downward. The size of the voltage directly controls the adjustment range of the Fermi energy level, achieving continuous regulation in the range of 0.4-0.7 eV.

[0057] The Fermi energy level E F of the graphene is adjusted. The dynamic regulation of the electromagnetic induced transparency window is achieved.

[0058] The adjustment range of the Fermi energy level is 0.4 eV to 0.7 eV.

[0059] The adjustment mode of the Fermi energy level is one or more combinations of an external voltage, an external electric field, and chemical doping.

[0060] When E F = 0.5 eV, a transparent window with a transmittance of ≥ 93.5% is formed at 5.21 THz, and the transmission valleys on both sides are located at 4.73 THz and 5.69 THz. F The transparent window center frequency moves from 4.68 THz to 6.16 THz as E

[0061] When the incident angle is less than 60°, the transmission peak intensity of the polarization-insensitive tunable electromagnetic induced transparency metamaterial structure remains above 80%.

[0062] The polarization-insensitive tunable electromagnetic induced transparency metamaterial structure is insensitive to the polarization state of linearly polarized light (0°-90° polarization angle) and left / right circularly polarized light (LCP / RCP).

[0063] The electromagnetic induced transparency effect is generated by the coupling of the two bright modes of the graphene disc and the ring-shaped hole slot.

[0064] When E F = 0.5 eV, a transparent window with a transmittance of ≥ 93.5% is formed at 5.21 THz, and the transmission valleys on both sides are located at 4.73 THz and 5.69 THz.

[0065] The present application provides a regulation method for the polarization-insensitive tunable electromagnetic induced transparency metamaterial structure.

[0066] A regulation method for the polarization-insensitive tunable electromagnetic induced transparency metamaterial structure, comprising:

[0067] Adjusting the Fermi energy level E FTo control the frequency of the transparent window;

[0068] Increasing the diameter D2 of the graphene slot moves the transparent window to lower frequencies;

[0069] Increasing the diameter D1 of the graphene disc moves the transparent window to higher frequencies.

[0070] The present application uses the Finite-Difference Time-Domain (FDTD) method to perform simulation calculations. Periodic boundary conditions are used in both the x and y directions to simulate the periodic arrangement of the metamaterial samples in the experiment. The electromagnetic wave is normally incident (the direction of electromagnetic wave transmission is along the negative z-axis direction). In the infrared to terahertz wave band, the surface conductivity of graphene σ(ω) can be approximately described by the Drude model where ω represents the angular frequency, E F represents the Fermi energy level of graphene, e represents the electronic charge, represents the reduced Planck constant, and τ represents the electron-phonon relaxation time. The relaxation time is equal to μ is the electronic mobility of graphene. v f = 10 6 m / s represents the Fermi velocity. The Fermi energy level can be adjusted by one or more combinations of an applied voltage, an applied electric field, chemical doping, etc.

[0071] It is well known that the generation of EIT-like effects is usually caused by two cases: 1) the bright mode has a strong response to the incident electromagnetic wave, while the dark mode cannot be coupled with the incident wave or has a weak coupling response. When the bright mode and the dark mode destructively interfere, an EIT-like effect occurs. 2) The EIT effect is generated by the joint action of two bright modes with different frequencies. The present application adopts the second case. Figure 2 The transmission spectra of single graphene disc structure, slot structure, and mixed disc-slot structure are shown. Due to electric field resonance, the single graphene disc exhibits a clear transmission valley at 5.69 THz, and the single graphene slot exhibits a clear transmission valley at 4.76 THz. This means that both structures with specific geometric parameters have resonance modes, i.e. bright modes. Figure 2 The EIT transmission spectrum generated by the mixed disc-slot structure is shown. When the two structures are mixed, the metamaterial is simultaneously excited by the electric field, and we observe that the EIT transparent window appears as a transmission peak between the two transmission valleys. The transmission rate at 5.21 THz exceeds 93.5%, and the two transmission valleys are located at 4.73 THz and 5.69 THz. This phenomenon confirms that the EIT effect is caused by the synergistic coupling of double bright modes.

[0072] In order to better understand the physical meaning of the EIT effect, the present application plots the electric field distribution diagram of the z-axis component of the two transmission valleys and the transmission peak, as shown inFigure 3 The graphene disc and the hole slot can be strongly excited by the incident electromagnetic wave as a dipole antenna, and the excited dipole antennas can interact with each other. Figure 3 In (a), when the frequency is 4.76 THz, that is, the left dip, only the graphene hole slot is strongly excited by the electric field of the incident wave, and the central graphene disc is weakly excited, and the electric field is mainly distributed at both ends of the hole slot. Considering the periodic distribution of the structure, the electric field is between two periods at this time, which is similar to a dipole antenna, which will be used when discussing the polarization insensitivity. At the same time, in the Figure 3 In (c), when the frequency is 5.69 THz, that is, the left dip, only the graphene disc is strongly excited by the electric field of the incident wave. The electric field is mainly distributed at both ends of the graphene disc, and the hole slot is weakly excited, which is similar to a dipole antenna. Figure 3 (b) shows that, at 5.21 THz, that is, the center frequency of the projection window, when the plasmon resonance occurs, we observe that the graphene disc and the hole slot are excited at the same time. The two bright modes occur at the same time, thereby forming an EIT effect. The coupling between the two bright modes forms an electric field distribution similar to a quadrupole antenna, and the electric field is distributed on the disc and the hole slot at this time.

[0073] The controllability is one of the main advantages of the graphene metamaterial compared with the metal metamaterial. Figure 4 The transmission spectrum of the graphene metamaterial at different graphene Fermi levels is shown. It can be seen that, as the Fermi level E F From 0.4 eV to 0.7 eV, the EIT transmission peak moves to high frequency as a whole, the transmission rate of the EIT transmission valley decreases significantly, and the transmission peak frequency increases from 4.68 THz to 6.16 THz as EF increases. This behavior can be explained by the relationship between the resonance wavelength lambda and the width w of the graphene resonant cavity, and the fine structure constant alpha. The formula is Since the width of the graphene resonant cavity in the simulation is fixed, the increase of the Fermi level E F causes the wavelength to decrease and the frequency to increase, thereby verifying the simulation results. In addition, when the Fermi level is adjusted from 0.4 eV to 0.7 eV, the modulation similar to “on” and “off” or “1” and “0” can be realized, indicating that by adjusting the Fermi level, the on-off and modulation functions of light can be realized in multiple frequency bands, and the process is polarization insensitive.

[0074] The super material structure designed in the application can further discuss the angle and polarization insensitivity due to the symmetry of the disc and hole slot structure in the x-y plane. Figure 5(a) shows the transmission spectra at different incident angles. The results show that when the incident angle is less than 60°, the transmission window frequency and the transmission peak value change little, and the transmission peak intensity remains above 80%; when the incident angle is greater than 60°, the transmission peak intensity decreases rapidly. This shows that the super material structure studied has good angle insensitivity, and is expected to be used as an omnidirectional EIT-like device. Figure 5 (b) shows that when left circularly polarized light (LCP) and right circularly polarized light (RCP) are vertically incident on the surface of the graphene super material structure, the obtained transmission curves are completely coincident, indicating that the designed EIT-like device supports circularly polarized light. Therefore, the EIT-like effect can also be achieved under circularly polarized light conditions. This result has important significance for the design of high-performance optoelectronic switches and other applications based on the EIT-like effect.

[0075] In the literature of super materials, the polarization usually changes from TE to TM, covering a range of 0° to 90°. In view of the symmetry of the super material structure designed in the present application, it is only necessary to study the transmission spectrum at a polarization angle of 0° to 45°. Figure 6 (a) shows the transmittance when the polarization angle is changed. It can be seen that the transmission spectrum hardly changes. It should be noted that at a polarization angle of 45°, the right dip, the disc size is unchanged, and the resonance frequency is stable. The left dip is caused by the electric dipole resonance between the periodic structures. For intuitive understanding, Figure 6 (b) gives the electromagnetic field distribution diagram at the left dip when the incident angle is 45°. Compared with Figure 3 a, the length of the dipole antenna resonance increases, but the resonance frequency changes little. Therefore, the super material structure designed in the present application exhibits excellent polarization insensitivity.

[0076] Figure 7 The Fermi energy level E f is 0.5 eV, the influence of the geometric parameters of the graphene structure on the EIT effect is given. From Figure 7 (a), it can be seen that as the diameter D1 of the graphene disc increases, the center frequency of the EIT transmission peak and the frequency of the right dip move to high frequency, and the frequency of the left dip remains unchanged. From Figure 7 (b), it can be seen that as the diameter D2 of the graphene hole slot increases, the center frequency of the EIT transmission peak and the frequency of the left dip move to low frequency, and the frequency of the right dip remains unchanged. Figure 7 In the slight change of the structure size in the middle, the EIT-like phenomenon appears, which provides a fault tolerance space for the preparation of related devices.

[0077] The slight change of the refractive index of the environment around the super material will cause the shift of the resonance peak of the EIT effect. From Figure 8It can be seen that the graphene metamaterial proposed by us has good sensing characteristics for different refractive indexes of external medium. With the increase of refractive index from 1.0 to 1.3, the transmission spectrum of the EIT effect moves obviously in the low frequency direction, almost keeps linear red shift, and can be used for the design of related sensors.

[0078] Based on this, the application further provides a refractive index sensor.

[0079] A refractive index sensor comprising the polarization-insensitive tunable electromagnetic induced transparency metamaterial structure;

[0080] When the environmental refractive index changes in the range of 1.0-1.3, the transparent window frequency linearly red shifts;

[0081] The sensitivity is characterized by the frequency shift amount caused by the refractive index change.

[0082] In addition, due to the dynamic adjustable characteristics of the transparent window, the slow light behavior can also be effectively controlled by changing the Fermi level. Here, the group delay of incident light is introduced to describe the slow light ability,

[0083]

[0084] Wherein And omega is the phase and angular frequency of light, respectively. Figure 9 The transmission phase shift of the graphene metamaterial under different Fermi levels and the calculated group delay are described respectively. It can be seen that strong phase dispersion occurs around the transparent window, which leads to obvious slow light phenomenon. The positive value of the group delay represents the slow light effect, and the negative group delay represents the fast light effect. There is a large positive group delay near the peak of the transparent window, which indicates that there is a slow light effect. This provides a new idea for the design of high-performance slow light devices in the future.

[0085] Based on this, the application further provides a slow light device.

[0086] A slow light device comprising the polarization-insensitive tunable electromagnetic induced transparency metamaterial structure;

[0087] A positive group delay is generated near the transparent window frequency;

[0088] The group delay size is controlled by adjusting the Fermi level.

[0089] The present invention proposes a graphene metamaterial-based structure for dynamically regulating the EIT-like effect. The structure consists of a graphene disk and a slot. Compared with metal metamaterials, this structure has the unique advantage of being able to dynamically adjust the EIT-like effect by adjusting the Fermi level. Compared with traditional graphene metamaterial structures, its notable feature is that due to the symmetry of the structure, it can achieve insensitivity to incident polarization. In addition, the inventors also studied the electric field mode of the metamaterial, analyzed the mechanism that produces the EIT-like effect, explored the transmission spectrum under different background refractive indices, and explored the slow-light effect existing in the transparent window. Therefore, the proposed disk-hole hybrid graphene metamaterial shows potential application prospects in the design of tunable slow-light devices, tunable sensors, and switches.

[0090] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A polarization-insensitive tunable electromagnetically induced transparent metamaterial structure, characterized by: include: dielectric substrate; a metamaterial unit structure periodically arranged on the dielectric substrate; The metamaterial unit structure includes a graphene disk at the center and a graphene hole groove at the periphery, wherein the graphene hole groove is annular and surrounds the graphene disk; The graphene disc diameter D1 and the graphene pore diameter D2 satisfy D2>D1; The metamaterial unit structure period P satisfies P>D2.

2. The polarization-insensitive tunable electromagnetically induced transparent metamaterial structure according to claim 1, wherein: The dielectric substrate is SiO2, with a dielectric constant of 3.9 and a thickness of 1 μm; The period P=5 μm, the graphene disk diameter D1=2 μm, and the graphene pore diameter D2=4.7 μm.

3. The polarization-insensitive tunable electromagnetically induced transparent metamaterial structure according to claim 1, wherein: Also included is an ion gel layer and a metal gate electrode; The ion gel layer covers the graphene disk and the graphene pores, and the ion gel layer has a dielectric constant of 1.82 and a thickness of 0.2 μm; The metal gate electrode is located on the upper surface of the ion gel layer and is in direct contact with the ion gel layer.

4. The polarization-insensitive tunable electromagnetically induced transparent metamaterial structure according to any one of claims 1 to 3, characterized in that: By adjusting the Fermi level E of graphene F Realize dynamic control of electromagnetically induced transparent windows; The Fermi level adjustment range is 0.4eV to 0.7eV; The Fermi level is adjusted by one or more combinations of applied voltage, applied electric field, and chemical doping.

5. The polarization-insensitive tunable electromagnetically induced transparent metamaterial structure according to claim 4, characterized in that: When E F When the E increases from 0.4eV to 0.7eV, the center frequency of the transparent window shifts from 4.68THz to 6.16THz, and as E F increases with the increase of .

6. The polarization-insensitive tunable electromagnetically induced transparent metamaterial structure according to claim 1, wherein: When the incident angle is less than 60°, the transmission peak intensity remains above 80%; It is insensitive to the polarization state of linearly polarized light (0°-90° polarization angle) and left / right circularly polarized light (LCP / RCP).

7. The polarization-insensitive tunable electromagnetically induced transparent metamaterial structure according to claim 1, wherein: The electromagnetically induced transparency effect is generated by the coupling of two bright modes between the graphene disk and the annular aperture; In E F When =0.5eV, a transparent window with a transmittance ≥93.5% is formed at 5.21THz, and the transmission valleys on both sides are located at 4.73THz and 5.69THz.

8. A method for controlling the polarization-insensitive tunable electromagnetically induced transparent metamaterial structure according to any one of claims 1 to 7, characterized in that: include: Adjusting the graphene Fermi level E F To control the transparent window frequency; Increasing the graphene pore diameter D2 moves the transparent window toward lower frequencies; Increasing the graphene disk diameter D1 moves the transparent window toward higher frequencies.

9. A refractive index sensor, characterized in that: A polarization-insensitive tunable electromagnetically induced transparent metamaterial structure comprising any one of claims 1 to 7; When the ambient refractive index changes within the range of 1.0-1.3, the transparent window frequency linearly redshifts; Sensitivity is characterized by the amount of frequency shift caused by the change in refractive index.

10. A slow light device, characterized in that: A polarization-insensitive tunable electromagnetically induced transparent metamaterial structure comprising any one of claims 1 to 7; Generate positive group delay near the transparency window frequency; The group delay is controlled by adjusting the Fermi level.

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