Graphene Metamaterials Research Articles

A triple plasmon-induced transparency terahertz sensor based on graphene metamaterials

A metamaterial-based terahertz sensor design is presented in this paper. The metamaterial unit structure comprises a graphene cross and three sets of graphene strips, which collectively achieve a triple plasmon-induced transparency (PIT) in both polarization directions. The theoretical results based on the Lorentz resonance theoretical model are in good agreement with finite difference time domain (FDTD) simulations. The sensor is polarization-independent and changes in the angle of incidence between 0° and 10° have a negligible impact on the sensing performance. Furthermore, the sensor exhibits a notable slow-light effect, with a maximum sensitivity of 1.65 THz/RIU and a FOM value of 4.74/RIU for the triple PIT, which is superior to that of comparable devices.

Dynamic tunable triple-band terahertz perfect absorber based on graphene metamaterial

This work developed a graphene-based perfect absorber with dynamic tuning capabilities. This absorber consists of a metal substrate, a layer of graphene square rings, a layer of graphene disks, and two layers of SiO2 dielectric sandwiched between them. Simulation results demonstrate absorption peaks at 1.23 THz, 4.2 THz, and 6.38 THz, with respective absorption rates of 99.9 %, 99.8 %, and 98.3 %. By analyzing the distributions of the electric field and surface current at the central frequencies of the three absorption peaks, the excitation mechanism of each absorption peak was discussed. It was found that by adjusting graphene's chemical potential, the absorption spectrum can be actively controlled. Furthermore, the absorber is insensitive to polarization and can sustain the stability of the absorption spectrum within an incident angle range of 0∼35°. This work has the potential to advance the research of multi-band terahertz absorbers, dynamically tunable devices, and other graphene-based photonic devices.

Polarization-desensitization dynamically adjustable quintuple plasmon-induced transparency multi-frequency modulator based on graphene metamaterial

The monolayer metamaterial that consists of graphene arrangement squares and four L-shaped graphene blocks is designed to achieve quintuple plasmon-induced transparency (quintuple-PIT). First, the accuracy of the results has been validated through finite difference time domain simulations and coupled mode theory, which show good agreement. Second, a quadruple-frequency asynchronous switch with amplitude modulation degree (AMD) values of 94.7%, 91.1%, 96.6%, and 77.4% and a sextuple-frequency synchronous switch with AMD values of 95.0%, 96.8%, 88.0%, 93.3%, 58.6%, and 71.5% have been proposed by dynamic control, respectively. It is worth noting that the number of PIT windows in the transmission curve can be freely adjusted from a quintuple-PIT to single-PIT mode by manipulating the Fermi level states of different parts of the structure. Finally, further investigations have demonstrated that the proposed structure exhibits excellent slow-light properties and is insensitive to polarized light, which indicates that the metamaterial structure possesses good stability and anti-interference capabilities under various polarization conditions. The metamaterial and results provide valuable insights and ideas for the design of optoelectronic devices.

Optimized graphene metamaterial for dual plasmon-induced transparency in terahertz band with multifunctional applications

Abstract This paper proposes a patterned graphene periodic metamaterial structure, optimized using an improved genetic algorithm to adjust the position and size of each graphene strip, thereby achieving dual plasmon-induced transparency (PIT) effects in the terahertz band, resulting in extraordinary multifunctionality. The finite difference time domain method is employed to obtain the transmission spectrum, and coupled mode theory is used for theoretical analysis and verification of the dual-PIT effect. The structure exhibits multifunctionality: when used as a photoelectric switch, it achieves a modulation depth of up to 99.04% with an insertion loss as low as 0.16 dB by tuning the Fermi level. Additionally, the structure demonstrates excellent sensing performance, with a maximum sensitivity and figure of merit reaching 0.84 THz/RIU and 88.55, respectively. Furthermore, the slow light performance of the structure is investigated, showing a group delay of up to 0.5 picoseconds.

A 2 to 4 Graphene Metamaterial Decoder and Tetrahydrofuran Detection

A 2 to 4 Graphene Metamaterial Decoder and Tetrahydrofuran Detection

Triple plasmon induced transparency based on multilayer graphene metamaterials

In this study, a novel multilayer terahertz metamaterial with four graphene sub-structures is designed to achieve dynamically tunable triple plasmon-induced transparency (PIT) due to interference among bright-bright modes. Coupled mode theory (CMT) and finite-difference time-domain (FDTD) simulations show a high degree of consistency in their results. Interestingly, enhanced transmission dips are observed when various graphene structures couple with the two longitudinal graphene strips at the bottom layer. Based on the dynamic modulation characteristics of graphene, the metamaterial demonstrates seven-band optical switching capabilities, achieving modulation depths (MD) of 94.6%, 88.1%, 90.8%, 90.8%, 90.4%, 86.6%, and 87.5%. Additionally, the proposed graphene metamaterial also shows excellent slow-light effects, with a group index reaching up to 1034. This proposed terahertz metamaterial holds significant theoretical implications for the development of dynamically integrated terahertz optoelectronic devices.

Graphene metamaterial (GMM) based dual mode, tunable, and broadband THz absorber with triple circular split ring structure

In this study we investigated a novel approach to designing a graphene metamaterial (GMM) based terahertz (THz) absorber with dual-mode functionality, tunability, and broadband absorption capabilities. The study leverages the unique properties of graphene, a material known for its exceptional electronic and optical characteristics, combined with metamaterials to achieve efficient THz absorption. Here we performed extensive simulation on four different types of configurations and found the optimized structure has the highest bandwidth of 3.8 THz and absorption over 90 %. The absorber is designed to operate in two distinct modes, enhancing its versatility for different applications in the THz spectrum. Moreover, the tunability of the absorber is a significant feature, allowing for dynamic adjustment of the absorption frequency, which is crucial for applications in THz imaging, sensing, and communication systems. The broadband nature of the absorber ensures effective performance over a wide range of frequencies, addressing the need for flexible and high-performance devices in emerging THz technologies. This work represents a significant advancement in the field of THz metamaterials, with potential implications for the development of next-generation THz devices.

Plasmon-Induced Transparency-Based Dual-Polarization Multifunctional Graphene Metamaterial

Plasmon-Induced Transparency-Based Dual-Polarization Multifunctional Graphene Metamaterial

Multi-frequency and multi-functional optical switch based on dual plasmon-induced transparency

Research into multi-frequency and multi-functional optical switches for complex applications is pioneering territory. By employing a single-layer structure comprising three distinct graphene strips, we successfully created a dual-PIT effect through the destructive interference among two bright modes and a dark mode. The numerical simulations were corroborated by coupled mode theory, reflecting a high degree of consistency between the theory and the simulations. Remarkably, the modulation of the Fermi level in graphene metamaterials through gate voltage enabled the realization of asynchronous optical switches capable of operating at six, five, four, and three frequencies. Notably, the six-frequency switch exhibited an impressive modulation depth of 88.54% and an insertion loss of just 0.15 dB, highlighting its superior performance. This study lays a solid foundation for future multi-frequency and multi-functional optical switch designs, offering significant implications and practical applications.

Parametric Interactions of Waves in Terahertz Devices Based on Graphene Metamaterials

Parametric Interactions of Waves in Terahertz Devices Based on Graphene Metamaterials

Tunable triple plasmon-induced transparency in E-type graphene metamaterials

Enhancing light-matter interaction is crucial for boosting the performance of nanophotonic devices, which can be achieved via plasmon-induced transparency (PIT). This study introduces what we believe to be a novel E-type metamaterial structure crafted from a single graphene layer. The structure, comprising a longitudinal graphene ribbon and three horizontal graphene strips, leverages destructive interference at terahertz frequencies to manifest triple plasmon-induced transparency (triple-PIT). Through a comparison of simulations using the finite difference time domain (FDTD) method and theoretical coupled-mode calculations, we elucidate the physical mechanism behind triple-PIT. Our analysis shows that the PIT effect arises from the interplay between two single-PITs phenomena, further explored through field distribution studies. Additionally, we investigate the impact of varying Fermi levels and carrier mobility on the transmission spectrum, achieving amplitude modulation in photoelectric switches of 85.5%, 99.2%, and 93.8% at a carrier mobility of 2 m2/(V·s). Moreover, we explore the relationship between Fermi levels and carrier mobility concerning the slow light effect, discovering a potential group index of up to 1021 for the structure. These insights underscore the significant potential of this graphene-based metamaterial structure in enhancing optical switches, modulators, and slow light devices.

Ultra wideband absorption absorber based on Dirac semimetallic and graphene metamaterials

This paper proposes an ultra-broadband absorber operating in the terahertz band, utilizing the surface plasmon resonance characteristics of micron-scale structured Dirac semimetals and single-layer graphene and the bound-state electromagnetic coupling effect in the continuum domain. The performance of the absorber was verified by finite difference method simulation. Its average absorption rate reached 92 % in the range of 38.64–227.76 THz. Where 43.44–50.4 THz, 62.48–72.96 THz, 85.68–87.12 THz and 192.24–195.36 THz band with an average absorption rate of 99 %. The study also explored the Fermi level and relaxation time of graphene and found that the absorber has good physical tunability. The absorber has a structural symmetry, independent of the polarization. Compared with previous designs, the absorber designed in this paper has a simple structure, is easy to adjust, is insensitive to large angles, and has extensive application potential in solar energy, photoelectric detection, sensors and other fields.

Multi-channel switch and sensing applications based on multilayered annular graphene metamaterials at terahertz frequency

In this study, a novel silica-graphene–silica periodic graphene structure consisting of six graphene semi-rings is proposed. The structure is based on a three-layer graphene metamaterial with a semicircular ring that achieves a tunable double plasmon-induced transparency (PIT) effect. In the proposed structure, the double-PIT window can be switched simultaneously at multiple frequencies through the dynamic tunability of graphene. Besides, the sensitivities of the refractive index for the PIT windows are investigated with the maximum values of 1.42 THz RIU−1 and 1.09 THz RIU−1, respectively, indicating the structure’s performance as a terahertz sensor. Overall, it shows the potential of PIT effect in graphene metamaterials in controlling electromagnetic field responses. It has made positive contributions to the development of terahertz technology and related fields.

Tunable band-stop fiber filter based on laser-induced graphene metamaterial in THz frequency

As an important device in the application of terahertz (THz) technology, a THz filter has broad application prospects in the fields of THz communication, imaging, and sensing. In this paper, a THz filter based on grating structure laser-induced graphene (LIG)/ side polishing terahertz fiber composite structure is proposed. In the experiment, we achieved the maximum Q factor of 23.83 at the central resonant frequency of 0.715 THz. By modifying the grating structure, a tunable operational span of 269 GHz was achieved, along with a tunable range of 21 GHz through laser stimulation. In testing, we found that LIG materials prepared with circular filling are more sensitive to relatively high-power pump lasers, while LIG samples prepared with line filling exhibit better linear response to laser power. Furthermore, the compact and highly integrated nature of the device suggests its broad potential utility in the realm of THz frequency selection.

Design of optically pumped ultrahigh-performance terahertz sensors based on graphene metamaterials

The surface conductivity of graphene can be precisely adjusted to approach the sigma-near-zero (SNZ) point by manipulating the quasi-Fermi level via optical pumping. This capability holds great promise for advanced graphene metamaterials-based terahertz (THz) sensors. In this study, we present a rational approach for designing two distinct types of patterned graphene THz sensors, each tailored to specific requirements regarding the quasi-Fermi level, resonance frequency, and Q-factor. The first sensor type operates in transmission mode and is well-suited for analytes with refractive indices ranging from 1 to 2. With a fixed analyte thickness of 40 nm, it achieves a frequency sensitivity of 1.036 THz/RIU, a Q-factor between 230 and 360, and a figure of merit (FOM) ranging from 51/RIU to 74/RIU. The second sensor type operates in reflection mode and is optimized for detecting biomolecules with refractive indices between 1.5 and 1.7. It exhibits a significant frequency shift of approximately 0.16 THz and a reflectance variation as high as 0.941 when the bio-analyte thickness is 100 nm. Numerical simulations of the sensing performances confirm the potential of these designed sensors for applications in detecting thin dielectric films and biosensing.

Strongly coupled quasi bound states in the continuum stimulated by Bloch surface wave in the non-subwavelength metamaterials

Bound states in the continuum (BICs) are unique in their ability to maintain high quality factor (Q factor) within non-Hermitian platforms that have open scattering channels. Simultaneously, Bloch surface waves (BSWs), guided modes with photonic bands positioned below the light line, confine optical energy on device surfaces. Although BICs and BSWs are generally located on opposite sides of the light line without intersecting, we put forward a novel concept that these two phenomena could be interconnected through a non-subwavelength structure. Specifically, BSWs in a graphene metamaterial can stimulate a strongly coupled quasi-BIC by mode coupling, reminiscent of the Friedrich-Wintgen BIC (FW BIC) that has sparked our interest. We delve into the intricate generation mechanism of this coupled quasi-BIC, uncovering that within metamaterials comprising two-dimensional (2D) grating structures, BSWs remarkably enhance the Q factor of few-diffraction-order (FDO) resonances. Another intriguing discovery is that altering the number of bilayers allows the coupled quasi-BIC to manifest after the photonic bands go over an exceptional point. Advancing further, we expand the 2D grating concept to a 3D square block structure, demonstrating that the coupled quasi-BIC associated with the BIC of 0th-order diffraction, can substantially improve the Q factor. The insights gained from these manipulations have practical implications for high-Q metadevices, paving the way for BIC-based sensor, filter, and absorber research.

Switchable dual ultra-broadband perfect absorber based on graphene and vanadium dioxide hybrid metamaterials

The phase transition property of vanadium dioxide (VO2) makes it an attractive field in temperature-controlled chips. In this paper, a microstructure based on a graphene disk and a ring-shaped VO2 hybrid metamaterial is proposed to achieve switchable dual ultra-broadband perfect absorption in the terahertz region, which is analyzed by the phase transition property of VO2 and the dynamic electrical regulation of graphene. When the graphene disk is not present, the absorption intensity can reach up to 97.07%. When the graphene disk is present and respectively interacts with the VO2 metallic and insulated phases, the results exhibit an ultra-broadband perfect absorption (>90%) from 1.620 THz to 4.533 THz and from 1.506 THz to 3.576 THz, respectively, where the bandwidths are as high as 2.913 THz and 2.070 THz, respectively. Adjusting the Fermi level of graphene and the VO2 conductivity allows the absorption intensity and bandwidth to be effectively controlled, where the fractional bandwidth from 81.46% to 94.69% and a high modulation depth of 95.09% can be achieved. These results suggest that dual ultra-broad perfect absorption can be dynamically switched within a single absorber and has various modulation means, which are expected to be developed in applying multifunctional modulators.

High sensitivity terahertz biomedical sensing with graphene metamaterial

Identification of biomedical molecules by terahertz (THz) sensing is a quite promising noninvasive technique. Here, we present a THz graphene metamaterial with plasmon-induced transparency (PIT) for high sensitivity biosensing. The strong PIT effect is generated by the destructive interference between the plasmon modes excited by two graphene strips. For testing different biomedical analytes, a distinct frequency shift at PIT resonance can be observed due to the effect of surrounding refractive index variation. The metamaterial scheme for noninvasive biomedical sensing can achieve the sensitivity as high as 2.6 THz/RIU. Particular, it can not only detect the phase of red blood cell infected by malaria but also the concentration of ethanol aqueous solution. The underlying mechanism is discussed for understanding the THz sensing operation.

Tunable High-Sensitivity Four-Frequency Refractive Index Sensor Based on Graphene Metamaterial.

As graphene-related technology advances, the benefits of graphene metamaterials become more apparent. In this study, a surface-isolated exciton-based absorber is built by running relevant simulations on graphene, which can achieve more than 98% perfect absorption at multiple frequencies in the MWIR (MediumWavelength Infra-Red (MWIR) band as compared to the typical absorber. The absorber consists of three layers: the bottom layer is gold, the middle layer is dielectric, and the top layer is patterned with graphene. Tunability was achieved by electrically altering graphene's Fermi energy, hence the position of the absorption peak. The influence of graphene's relaxation time on the sensor is discussed. Due to the symmetry of its structure, different angles of light source incidence have little effect on the absorption rate, leading to polarization insensitivity, especially for TE waves, and this absorber has polarization insensitivity at ultra-wide-angle degrees. The sensor is characterized by its tunability, polarisation insensitivity, and high sensitivity, with a sensitivity of up to 21.60 THz/refractive index unit (RIU). This paper demonstrates the feasibility of the multi-frequency sensor and provides a theoretical basis for the realization of the multi-frequency sensor. This makes it possible to apply it to high-sensitivity sensors.

Comparing the plasmon dispersion in graphene and MoS2 nanoribbons array under Electromagnetic excitation

Terahertz properties of different materials have been recently studied due to their wide applications in optoelectronics, industry, product inspection, and spectroscopy. Terahertz frequency applications are promising for the medical field as they are considered safe frequencies. Previous terahertz plasma response focused on 2D materials like graphene and transition metal dichalcogenides (TMDs) due to their favourable electronic properties, high electric conductivity, and their band gap characteristics, so they can be used in electronic devices. Some of these materials showed good biocompatibility so they can be used in biomedical applications. Since graphene has zero band gap, researchers are continuously exploring methods to increase its band gap to be used in electronics. Graphene heterostructures or metamaterials are ways to enhance graphene characteristics for specific applications. This work investigates the possibility of using MoS2 with graphene in THz applications. The plasmon dispersion for graphene and MoS2 nanoribbon array structure is compared. Both graphene and MoS2 behave differently in response to terahertz radiation due to their different band gaps. The results showed that MoS2 exhibits a plasmonic response in the THz region at high carrier concentrations. This opens up opportunities for MoS2 to be employed in THz sensors, both independently and in conjunction with graphene within heterostructures or metamaterials for power sources and detectors. These advancements hold significant potential for the future THz imaging and communication technologies.