Triple plasmon-induced transparency and optical switch desensitized to polarized light based on a mono-layer metamaterial

SRR inspired inversion symmetry-shaped left-handed metamaterial with a high effective medium ratio for ASR and WLAN applications

This study developed a metamaterial-inspired split-ring resonator (SRR) based inversion symmetry-shaped structure for airport surveillance radar and local area wireless network applications. The proposed device exhibited suitability for S- and C-band applications, featuring distinct resonance peaks at 2.8 and 4.9 GHz, respectively. The two-layer double negative metamaterial unit cell comprises a copper-based resonator, patch, and a low-loss substrate material known as Rogers RT5800 with a thickness of 1.575 mm. The 8 × 8 mm2 structure unit cell was identified with an effective medium ratio (EMR) of 13.4 at the resonance peak of 2.8 GHz. With the alteration of the metamaterial unit cell structure, the electric field, surface current distribution, magnetic field, and design evolution were observed, analysed, and investigated in this study. Meanwhile, the retrieved data from the reflection and transmission coefficients from CST Microwave Studio were validated using the Ansys High-Frequency Structure Simulator (HFSS) software. A Vector Network Analyzer (VNA) further measured the numerical results. Based on the findings, the proposed novel double negative metamaterial device is suitable for radar communication and satellite applications, especially airport surveillance radar (ASR) and wireless local area network (WLAN), due to its high EMR at the desired resonance frequency.

Development of double-layer metamaterial with high effective medium ratio values for S- and C-band applications

This study introduces a compact double negative metamaterial (DNM) composed of three split rings connected slab resonator (TSRCSR) based double-layer design with a high 13.9 EMR (effective medium ratio) value. A double-layer patch is introduced to achieve the novel double negative properties, including negative behaviours of effective medium parameters, including refractive index, permittivity, and permeability with a high effective medium ratio for the miniaturised size of the introduced unconventional material that is highly suitable for microwave S and C band covering applications. The popular low-loss Rogers RT5880 (thickness 1.575 mm) substrate and copper resonator materials are utilized to develop the metamaterial unit cell that offers triple resonance between frequencies from 1 to 8 GHz. Therefore, the proposed metamaterial exhibits resonance peaks at 2.75, 5.2, and 6.3 GHz, suitable for radar, communication satellite, and long-distance telecommunication applications, respectively. The commercially available simulator known as Computer Simulation Technology (CST) is adopted to develop and simulate the 8 × 8 mm2 metamaterial design. The simulation results of the introduced TSRCSR design structure were verified by adopting the Ansys High-Frequency Structure Simulator (HFSS). Furthermore, it was then proved with the help of equivalent circuit model findings gained from the Advanced Design Structure (ADS) software. On the other hand, the analytical results were further validated by measuring the TSRCSR design utilizing a Vector Network Analyzer (VNA). These analyses become one of the novelties of this work, where the compact TSRCSR metamaterial successfully gained small discrepancies in transmission coefficient values when compared to both analytical and measurement results. The proposed metamaterial is highly suggested for communication devices for its extensive effective characteristics and compactness.

Logic operation and all-optical switch characteristics of graphene surface plasmons

Terahertz logic gates play a crucial role in optical signal processing and THz digitization. In this paper, we propose a design strategy for graphene-based metamaterial THz all-optical logic gate devices based on the induced transparency effect of surface isolated. Theoretically, we realize Boolean operations by coupling of a hexagonal graphene resonant cavity with dual embedded rotatable ellipses. Based on the coupled mode theory, the elliptical rotation angle of the resonator is an important factor affecting the PIT phenomenon. We control the logic input by adjusting the rotation angles of the two embedded ellipses. The analysis results show that: under the incidence of y-polarized light, the ellipse deflection angle of 0° represents the input signal '0', and the ellipse deflection angle of 30° represents the input signal '1'. Through numerical simulation, the structure realizes two logical operations of NAND and AND. Under the incidence of x-polarized light, the ellipse deflection angle of 0° represents the input signal '0', and the ellipse deflection angle of 90° represents the input signal '1'. Through numerical simulation, the structure realizes three logical operations of NAND, XNOR and OR. Finally, we analyze the performance of the logic gates by extinction ratio. The extinction ratio of the logic gate is up to 10.38 dB when performing OR Boolean operations. Numerically simulated all-optical logic gates can be key components of optical processing and telecommunication equipment.

Analytical investigation of unidirectional reflectionless phenomenon near the exceptional points in graphene plasmonic system

We propose a two-dimensional array made of a double-layer of vertically separated graphene nanoribbons. The transfer matrix method and coupled mode theory are utilized to quantitatively depict the transfer properties of the system. We present a way to calculate the radiative and the intrinsic loss factors, combined with finite-difference time-domain simulation, conducting the complete analytical analysis of the unidirectional reflectionless phenomenon. By adjusting the Fermi energy and the vertical distance between two graphene nanoribbons, the plasmonic resonances are successfully excited, and the unique phenomena can be realized at the exceptional points. Our research presents the potential in the field of optics and innovative technologies to create advanced optical devices that operate in the mid-infrared range, such as terahertz antennas and reflectors.

THz broadband and dual-channel perfect absorbers based on patterned graphene and vanadium dioxide metamaterials

This paper proposes a novel and perfect absorber based on patterned graphene and vanadium dioxide hybrid metamaterial, which can not only achieve wide-band perfect absorption and dual-channel absorption in the terahertz band, but also realize their conversion by adjusting the temperature to control the metallic or insulating phase of VO₂. Firstly, the absorption spectrum of the proposed structure is analyzed without graphene, where the absorption can reach as high as 100% at one frequency point (f = 5.956 THz) when VO₂ is in the metal phase. What merits attention is that the addition of graphene above the structure enhances the almost 100% absorption from one frequency point (f = 5.956 THz) to a wide frequency band, in which the broadband width records 1.683 THz. Secondly, when VO₂ is the insulating phase, the absorption of the metamaterial structure with graphene outperforms better, and two high absorption peaks are formed, logging 100% and 90.7% at f₃ = 5.545 THz and f₄ = 7.684 THz, respectively. Lastly, the adjustment of the Fermi level of graphene from 0.8 eV to 1.1 eV incurs an obvious blueshift of the absorption spectra, where an asynchronous optical switch can be achieved at fK₁ = 5.782 THz and fK₂ = 6.898 THz. Besides, the absorber exhibits polarization sensitivity at f₃ = 5.545 THz, and polarization insensitivity at f₄ = 7.684 THz with the shift in the polarization angle of incident light from 0° to 90°. Accordingly, this paper gives insights into the new method that increases the high absorption width, as well as the great potential in the multifunctional modulator.

Multiband tunable exciton-induced transparencies: Exploiting both strong and intermediate coupling in a nanocube-hexagonal-nanoplate heterodimer J-aggregates hybrid

Understanding and mastering the light-light and light-matter interactions in coupled structures have become significant subjects, as they provide versatile tools for manipulating light in both classical and quantum regimes. Mimicking quantum interference effects in pure photonic nanostructures, from weak Fano dip to intense electromagnetically induced transparency, usually requires strong asymmetries in complex geometries and larger interactions between resonances, i.e., in the intermediate coupling regime. Here, we numerically demonstrate a simple and chemically feasible plasmonic nanocube-hexagonal-nanoplate heterodimer with a strong, tunable self-induced transparency window created by the intermediate coupling between the near-degenerate dark and bright hybridized modes. Further assisted by the strong coupling introduced by the J-aggregate excitons covering the heterodimer, three evident exciton-induced transparency windows were observed. These multiband transparencies in a single-particle-level subwavelength configuration, could on one hand enrich the toolbox of multi-frequency light filtering, slowing and switching beyond the diffraction limit, and on the other hand, work as a fundamental testbed for investigating multiscale light-matter interactions at the nanoscale.

Multiple plasmon-induced transparency based on black phosphorus and graphene for high-sensitivity refractive index sensing

A hybrid bilayer black phosphorus (BP) and graphene structure with high sensitivity is proposed for obtaining plasmon-induced transparency (PIT). By means of surface plasmon resonance in the rectangular-ring BP structure and ribbon graphene structure, a PIT effect with high refractive index sensitivity is achieved, and the surface plasmon hybridization between graphene and anisotropic BP is analyzed theoretically. Meanwhile, the PIT effect is quantitatively described using the coupled oscillator model and the strong coherent coupling phenomena are analyzed by adjusting the coupling distance between BP and graphene, the Fermi level of graphene, and the crystal orientation of BP, respectively. The simulation results show that the refractive index sensitivity S = 7.343 THz/RIU has been achieved. More importantly, this is the first report of tunable PIT effects that can produce up to quintuple PIT windows by using the BP and graphene hybrid structure. The high refractive index sensitivity of the quintuple PIT system for each peak is 3.467 THz/RIU, 3.467 THz/RIU, 3.600 THz/RIU, 4.267 THz/RIU, 4.733 THz/RIU and 6.133 THz/RIU, respectively, which can be used for multiple refractive index sensing function.

Polarization-controlled and symmetry-dependent multiple plasmon-induced transparency in graphene-based metasurfaces

In this paper, we theoretically and numerically demonstrate a polarization-controlled and symmetry-dependent multiple plasmon-induced transparency (PIT) in a graphene-based metasurface. The unit cell of metasurface is composed of two reversely placed U-shaped graphene nanostructures and a rectangular graphene ring stacking on a dielectric substrate. By adjusting the polarization of incident light, the number of transparency windows can be actively modulated between 1 and 2 when the nanostructure keeps a geometrical symmetry with respect to the x-axis. Especially, when the rectangular graphene ring has a displacement along the y-direction, the number of transparency windows can be arbitrarily switched between 2 and 3. The operation mechanism behind the phenomena can be attributed to the near-field coupling and electromagnetic interaction between the bright modes excited in the unit of graphene resonators. Moreover, the electromagnetic simulations obtained by finite-difference time-domain (FDTD) method agree well with the theoretical results based on the coupled modes theory (CMT). In addition, as applications of the designed nanostructure, we also study the modulation degrees of amplitude, insertion loss and group index of transmission spectra for different Fermi energies, which demonstrates an excellent synchronous switch functionality and slow light effect at multiple frequencies. Our designed metasurface may have potential applications in mid-infrared optoelectronic devices, such as optical switches, modulators, and slow-light devices, etc.

Dual-Channel Mid-Infrared Toroidal Metasurfaces for Wavefront Modulation and Imaging Applications

In this paper, we propose a dual-channel mid-infrared toroidal metasurface that consists of split equilateral triangular rings. The electromagnetic responses are analyzed by the finite-difference-time-domain (FDTD) method and temporal coupled-mode theory (TCMT). The results show that one channel of the metasurface is insensitive to the polarization angle of the incident light and temperature, while the other channel is sensitive. The reflectance and resonance wavelength can be manipulated by the polarization angle and temperature independently. Based on such a mechanism, we propose metasurfaces for two-bit programmable imaging and thermal imaging. The metasurfaces are believed to have potential applications in information processing and thermal radiation manipulation.

Multifunctional Plasmon-Induced Transparency Devices Based on Hybrid Metamaterial-Waveguide Systems

In this paper, we design a multifunctional micro-nano device with a hybrid metamaterial-waveguide system, which leads to a triple plasmon-induced transparency (PIT). The formation mechanisms of the three transparent peaks have their own unique characteristics. First, PIT-I can be switched into the BIC (Friedrich-Wintge bound state in continuum), and the quality factors (Q-factors) of the transparency window of PIT-I are increased during the process. Second, PIT-II comes from near-field coupling between two bright modes. Third, PIT-III is generated by the near-field coupling between a low-Q broadband bright mode and a high-Q narrowband guide mode, which also has a high-Q transparent window due to the guide mode. The triple-PIT described above can be dynamically tuned by the gate voltage of the graphene, particularly for the dynamic tuning of the Q values of PIT-I and PIT-III. Based on the high Q value of the transparent window, our proposed structure can be used for highly sensitive refractive index sensors or devices with prominent slow light effects.

Double Narrowband Induced Perfect Absorption Photonic Sensor Based on Graphene-Dielectric-Gold Hybrid Metamaterial

Double narrowband induced perfect absorption in the terahertz region is achieved in a graphene-dielectric-gold hybrid metamaterial, whose physical mechanism is analyzed using the coupled-mode theory (CMT), which agreed well with the finite-difference time-domain (FDTD) simulation. This study found that the Fermi level of graphene can be adjusted to improve the absorptivity when the refractive index (RI) n_d of the chosen dielectric cannot achieve a good absorption effect. In addition, the blue shift of absorption spectrum can be used in the design of dual-frequency electro-optical switches, of which the modulation degree of amplitude (MDA) can reach as high as 94.05% and 93.41%, indicating that this is a very promising electro-optical switch. Most significantly, the RI sensing performance is investigated, which shows an ultra-high absorption sensitivity S_A = 4.4°/RIU, wavelength sensitivity S_λ = 9.8°/RIU, and phase shift sensitivity S_φ = 2691°/RIU. At last, an interesting finding is that the two peaks (R1 and R2) of plasmon-induced absorption (PIA) show different polarization characteristics (insensitive or sensitive) to the incident light angle; this polarization-sensitive is particularly important for the PIT/PIA-based optical polarizers. Undoubtedly, this paper is of great significance to the research and design of terahertz photonic devices and sensors.

Dynamically Tunable and Multifunctional Polarization Beam Splitters Based on Graphene Metasurfaces

Based on coupled-mode theory (CMT) and the finite-difference time-domain (FDTD) approach, we propose a graphene metasurface-based and multifunctional polarization beam splitter that is dynamically tunable. The structure, comprising two graphene strips at the top and bottom and four triangular graphene blocks in the center layer, can achieve triple plasma-induced transparency (PIT). In a single polarization state, the computational results reveal that synchronous or asynchronous six-mode electro-optical switching modulation may be performed by modifying the Fermi levels of graphene, with a maximum modulation degree of amplitude (MDA) of 97.6% at 5.148 THz. In addition, by varying the polarization angle, a polarization-sensitive, tunable polarization beam splitter (PBS) with an extinction ratio and insertion loss of 19.6 dB and 0.35 dB at 6.143 THz, respectively, and a frequency modulation degree of 25.2% was realized. Combining PIT with polarization sensitivity provides a viable platform and concept for developing graphene metasurface-based multifunctional and tunable polarization devices.

Unified model for plasmon-induced transparency with direct and indirect coupling in borophene-integrated metamaterials

We propose, both numerically and theoretically, a uniform model to investigate the plasmonically induced transparency effect in plasmonic metamaterial consisting of dual-layer spatially separated borophene nanoribbons array. The dynamic transfer properties of light between two borophene resonators can be effectively described by the proposed model, with which we can distinguish and connect the direct and indirect coupling schemes in the metamaterial system. By adjusting the electron density and separation of two borophene ribbons, the proposed metamaterials enable a narrow band in the near-infrared region to reach high transmission. It provides a new, to the best of our knowledge, platform for optoelectronic integrated high-performance devices in the communication band.

Investigation of bound states in the continuum in dual-band perfect absorbers

Enhancing the light-matter interaction of two-dimensional materials in the visible and near-infrared regions is highly required in optical devices. In this paper, the optical bound states in the continuum (BICs) that can enhance the interaction between light and matter are observed in the grating-graphene-Bragg mirror structure. The system can generate a dual-band perfect absorption spectrum contributed by guided-mode resonance (GMR) and Tamm plasmon polarition (TPP) modes. The optical switch can also be obtained by switching the TE-TM wave. The dual-band absorption response is analyzed by numerical simulation and coupled-mode theory (CMT), with the dates of each approach displaying consistency. Research shows that the GMR mode can be turned into the Fabry-Pérot BICs through the transverse resonance principle (TRP). The band structures and field distributions of the proposed loss system can further explain the BIC mechanism. Both static (grating pitch P) and dynamic parameters (incident angle θ) can be modulated to generate the Fabry-Pérot BICs. Moreover, we explained the reason why the strong coupling between the GMR and TPPs modes does not produce the Friedrich-Wintgen BIC. Taken together, the proposed structure can not only be applied to dual-band perfect absorbers and optical switches but also provides guidance for the realization of Fabry-Pérot BICs in lossy systems.

Terahertz multimode modulator based on tunable triple-plasmon-induced transparency in monolayer graphene metamaterials

A simple monolayer graphene metamaterial based on silicon/silica substrates is proposed, and typical triple-plasmon-induced transparency (PIT) is realized in the terahertz band. The physical mechanism is analyzed by coupled mode theory (CMT), and the results of CMT agree well with the finite-difference time-domain simulation. A multimode electro-optical switch can be designed by dynamic tuning, and the modulation degrees of its resonant frequencies are 84.0%, 87.3%, 83.0%, 88.1%, and 76.7%. In addition, triple-PIT gradually degenerates into dual-PIT with a decrease in the length of one bright mode. Interestingly, the group index can reach 770 at Ef=0.8eV, which shows that it can be designed as a slow light device with extraordinary ability. Therefore, the results of this paper are of great significance to the research and design of electro-optical switches and slow light devices in the terahertz band.

Triple plasmon-induced transparency and dynamically tunable electro-optics switch based on a multilayer patterned graphene metamaterial

A terahertz-band metamaterial composed of multilayer patterned graphene is proposed and triple plasmon-induced transparency is excited by coupling three bright modes with one dark mode. The Lorentz curve calculated by the coupled-mode theory agrees well with the finite-difference time-domain results. Dynamic tuning is investigated by changing the Fermi level. Multimode electro-optics switching can be designed and achieved, and the amplitude modulations of four resonance frequencies are 94.3%, 92.8%, 90.7%, and 93%, respectively, which can realize the design of synchronous and asynchronous electro-optics switches. It is hoped that these results can provide theoretical support and guidance for the future design and application of photonic and optoelectronic devices.

Quadruple plasmon-induced transparency of polarization desensitization caused by the Boltzmann function

This study proposes a graphene metamaterial desensitized to the polarized angle to produce tunable quadruple plasmon-induced transparency (PIT). As a tool employed to explain the PIT, n-order coupled mode theory (CMT) is deduced for the first time and closely agrees with finite-difference time-domain (FDTD) simulations according to the quadruple PIT results in the case of n = 5. Additionally, the response of the proposed structure to the angle of polarized light is investigated. As a result, the Boltzmann function satisfied by the response of graphene strips to the polarization direction of incident light is proposed for the first time. Its property of polarization desensitization can be attributed to structural centrosymmetry, and conjugated variety which the Boltzmann functions result in. Therefore, a quintuple-mode modulation based on simultaneous electro-optical switch is realized by tuning Fermi levels within graphene. Its modulation degrees of amplitude and dephasing times are obtained. Given that the slow-light property is an important application of PIT, the n-order group index is thereby obtained. Hence, not only do the insights gained into polarization-desensitization structure provide new ideas for the design of novel optoelectronic devices, but also the results from the n-order CMT offer new research progress and references in theory.

Three-band perfect absorber with high refractive index sensing based on an active tunable Dirac semimetal

In this paper, we designed a three-band narrowband perfect absorber based on bulk Dirac semi-metallic (BDS) metamaterials. The absorber consists of a hollow Dirac semi-metallic layer above, a gold layer below and a photonic crystal slab (PCS) in the middle. The study found that the terahertz wave absorber achieved three perfect absorption rates of more than 95% in the range of 1 to 2.4 THz. The minimum bandwidth (FWHM) is 0.02 THz, and the maximum quality factor (Q) is 106. A reasonable explanation of high absorption can be obtained by impedance matching, electric dipole and other principles. The absorption spectra of the two polarizations show different responses at different incident angles. In addition, we also obtained the influence of the structural parameters of the upper layer of the metamaterial on the absorption performance. We defined the refractive index sensitivity (S) with a maximum sensitivity of 0.1525 THz RIU^-1 and a highest quality factor (FOM) of 4.26 in the refractive index range of 1 to 1.8. The maximum adjustable range is 0.06 THz in the Fermi energy range of 60 to 140 meV. Because of its excellent characteristics, our absorber will have good development prospects in the fields of optical switching, biochemical imaging, and space detection.

Ultra-wideband and wide-angle perfect solar energy absorber based on Ti nanorings surface plasmon resonance

Solar energy absorption is a very important field in photonics. The successful development of an efficient, wide-band solar absorber is an extremely powerful driver in this field. We propose an ultra-wideband (UWB) solar energy absorber composed of a Ti ring and SiO2-Si3N4-Ti thin films. In the range of 300-4000 nm, the wide band has an absorption efficiency of more than 90% and can reach 3683 nm, and it has four absorption peaks with a high absorptivity. Moreover, the weighted average absorption efficiency of the solar absorber under AM 1.5 is maintained above 97.03%, which indicates it has great potential for use in the field of solar energy absorption. Moreover, we proved that the polarization is insensitive by analyzing the absorption characteristics at arbitrary polarization angles. For both the transverse electric (TE) and transverse magnetic (TM) modes, the UWB absorption is maintained at more than 90% in the wide incidence angle range of 60°. The UWB solar energy absorber has great potential for use in a variety of applications, such as converting solar light and heat into electricity for public use and reducing the side effects of coal-fired power generation. It can also be used in information detection and infrared thermal imaging owing to its UWB characteristics.

Broadband Solar Absorber Based on Square Ring cross Arrays of ZnS

Solar energy is an inexhaustible clean energy. However, how to improve the absorption efficiency in the visible band is a long-term problem for researchers. Therefore, an electromagnetic wave absorber with an ultra-long absorption spectrum has been widely considered by researchers of optoelectronic materials. A kind of absorbing material based on ZnS material is presented in this paper. Our purpose is for the absorber to achieve a good and wide spectrum of visible light absorption performance. In the wide spectrum band (553.0 THz-793.0 THz) of the absorption spectrum, the average absorption rate of the absorber is above 94%. Using surface plasmon resonance (SPR) and gap surface plasmon mode, the metamaterial absorber was studied in visible light. In particular, the absorber is insensitive to both electric and magnetic absorption. The absorber can operate in complex electromagnetic environments and at high temperatures. This is because the absorber is made of refractory metals. Finally, we discuss and analyze the influence of the parameters regulating the absorber on the absorber absorption efficiency. We have tried to explain why the absorber can produce wideband absorption.

A Tunable “Ancient Coin”-Type Perfect Absorber with High Refractive Index Sensitivity and Good Angular Polarization Tolerance

In this paper, we design and present a graphene-based “ancient coin”-type dual-band perfect metamaterial absorber, which is composed of a silver layer, silicon dioxide layer, and a top “ancient coin” graphene layer. The absorption performance of the absorber is affected by the hollowed-out square in the center of the graphene layer and geometric parameters of the remaining nano disk. The optical properties of graphene can be changed by adjusting the voltage, to control the absorption performance of the absorber dynamically. In addition, the centrally symmetric pattern structure greatly eliminates the polarization angle dependence of our proposed absorber, and it exhibits good angular polarization tolerance. Furthermore, the proposed “ancient coin”-type absorber shows great application potential as a sensor or detector in biopharmaceutical, optical imaging, and other fields due to its strong tunability and high refractive index sensitivity.

Based on Ultrathin PEDOT:PSS/c-Ge Solar Cells Design and Their Photoelectric Performance

In recent years, nanostructures have improved the performance of solar cells and are regarded as the most promising microstructures. The optical properties of PEDOT:PSS/c-Ge hybrid solar cells (HSCs) based on the octagon germanium nanoparticles (O-GNPs) were numerically analyzed using the finite-difference time-domain (FDTD) method. The optimal structure of the hybrid solar cell is determined by changing the thickness of the organic layer and structural parameters of nanoparticles to enhance the optical absorption and eventually achieve high broadband absorption. By changing the structure parameter of O-GNPs, we studied its effect on solar cells. The optimization of geometric parameters is based on maximum absorption. The light absorption of our optimized HSCs is basically above 90% between 200 and 1500 nm. PEDOT:PSS is placed on top of O-GNPs to transmit the holes better, allowing O-GNPs to capture a lot of photons, to increase absorbance value properties in the AM1.5 solar spectral irradiated region. The transmittance is increased by adding poly-methyl methacrylate (PMMA). At the same time, the electrical characteristics of Ge solar cells were simulated by DEVICE, and short-circuit current (Jsc), open-circuit voltage (Voc), maximum power (Pmax), filling coefficient (FF) and photoelectric conversion efficiency (PCE) were obtained. According to the optimization results after adjusting the structural parameters, the maximum short-circuit current is 44.32 mA/cm2; PCE is 7.84 mW/cm2; FF is 69%. The results show that the O-GNPs have a good light trapping effect, and the structure design has great potential for the absorption of HSCs; it is believed that the conversion efficiency will be further improved through further research.

Broadband plasmon-induced transparency modulator in the terahertz band based on multilayer graphene metamaterials

In this study, multilayer graphene metamaterials comprising graphene blocks and graphene ribbon are proposed to realize dynamic plasmon-induced transparence (PIT). By changing the position between the graphene blocks, PIT phenomenon will occur in different terahertz bands. Furthermore, PIT with a transparent window width of 1 THz has been realized. In addition, the PIT shows redshifts or blueshifts or disappears altogether upon changing the Fermi level of graphene, and hence a frequency selector from 3.91 to 7.84 THz and an electro-optical switch can be realized. Surprisingly, the group index of this structure can be increased to 469. Compared with the complex and fixed structure of previous studies, our proposed structure is simple and can be dynamically adjusted according to demands, which makes it a valuable platform for ideas to inspire the design of novel electro-optic devices.