Hybrid Metal-graphene Metamaterials Research Articles

Terahertz hybrid metal-graphene metamaterials with tunable dual-band electromagnetically induced transparency

The electromagnetically induced transparency (EIT) effects in metamaterials have been widely studied due to their broad application prospects in the field of optical communications. Previous researchers focused mainly on the regulation of a single EIT effect. Here we proposed a structure containing two pairs of asymmetric C-shaped double-split ring resonators (DSRRs) placed on the two sides of cut wire (CW), and we studied the EIT effect of the structure. Furthermore, in order to tune the EIT peak, two graphene strips are placed on the two pairs of DSRRs. Simulation results show that, the EIT peak can be modulated by adjusting the Fermi level of the graphene strips and the modulation depths as high as 83 % and 87 % can be realized. Besides, slow light phenomenon accompanied by the EIT effect in the structure was investigated. Simulation results implied that, double group delays of 4.4 ps and 3.4 ps can be achieved in the design, and the delays can be adjusted by changing the graphene Fermi level. The physical mechanism of the tunable metamaterial was analyzed in terms of the three-oscillator model.

Actively tunable and switchable electromagnetically induced transparency in hybrid metal-graphene metamaterials

Active control of the electromagnetically induced transparency (EIT) is highly desirable for advanced terahertz (THz) device applications. Currently, the EIT peak positions in the graphene-based metamaterials have been actively controlled by tailoring Fermi energy of graphene via electric doping. However, there is still a considerable challenge to realize active strength modulation of the EIT peak without frequency shifting. Here, a hybrid metal-graphene structure, consisting of the metal-based EIT metamaterial and patterning graphenes, is proposed at the THz frequencies. Through changing Fermi energy of graphene, the EIT peak strength can exhibit both active modulation and on-to-off switch without frequency shifting. Moreover, theoretical model and field distributions discover that the active response can be attributed to the increasing damping rate of the dark mode caused by the controllable conductivity of graphene. In addition, the controllable group delay is also achieved for the slow light applications. Therefore, this work provides the possibility for designing compact slow light devices in the information processing and telecommunication applications.

Fano-Resonance in Hybrid Metal-Graphene Metamaterial and Its Application as Mid-Infrared Plasmonic Sensor.

Fano resonances in nanostructures have attracted widespread research interests in the past few years for their potential applications in sensing, switching and nonlinear optics. In this paper, a mid-infrared Fano resonance in a hybrid metal-graphene metamaterial is studied. The hybrid metamaterial consists of a metallic grid enclosing with graphene nanodisks. The Fano resonance arises from the coupling of graphene and metallic plasmonic resonances and it is sharper than plasmonic resonances in pure graphene nanostructures. The resonance strength can be enhanced by increasing the number of graphene layers. The proposed metamaterial can be employed as a high-performance mid-infrared plasmonic sensor with an unprecedented sensitivity of about 7.93 μm/RIU and figure of merit (FOM) of about 158.7.

Tunable THz Graphene Filter Based on Cross-In-Square-Shaped Resonators Metasurface

The tunable terahertz (THz) Fano-resonant filter based on hybrid metal-graphene metamaterial was proposed. The optical parameters of metasurface with unit cell in the form of a cross-shaped graphene sheet in the center of a square gold ring were simulated by the finite element method using a surface conductivity model of a graphene monolayer. The narrowband modulation of the transmission by varying the Fermi level of the graphene and the position of graphene cross inside the metal ring was demonstrated. Simulation results were well explained theoretically using a three-coupled oscillator model. The proposed device can be used as a narrowband filter in wireless THz communication systems and sensing applications.

Active control of electromagnetically induced transparency based on terahertz hybrid metal-graphene metamaterials for slow light applications

Recently, the dynamically controlled electromagnetically induced transparency (EIT) metamaterials have been widely used in the slow light effect field to enhance the light-matter interactions and nonlinear effects, which has aroused the great attraction of many researchers. The emergence of two-dimensional materials has pushed this research to a new research hot again. Therefore, a terahertz hybrid metal-graphene metamaterial, consisting of a bi-layer metallic EIT metamaterial, an unpatterned monolayer graphene, and an encapsulated ion-gel layer, was proposed to actively control the EIT resonance. In this structure, the transparency peak of the bi-layer metallic EIT metamaterial can realize on-to-off switch through shifting the Fermi energy of graphene covering onto the dark mode resonators. Theoretical analysis and surface current distributions reveal that the active modulation can be attributed to the increasing damping rate of the dark mode caused by the actively controllable conductivity of the graphene. In addition, the active control of the group delay in the hybrid metamaterial is also demonstrated for the slow-light applications. Therefore, this work provides an alternative way to design compact slow-light devices for future terahertz wireless communications.

Dynamically Tunable Plasmon-Induced Transparency Based on Radiative–Radiative-Coupling in a Terahertz Metal–Graphene Metamaterial

New technologies and materials with superior characteristics impel great development of functional devices in the terahertz field. The dynamically tunable plasmon-induced transparency (PIT) based on radiative–radiative-coupling in terahertz hybrid metal–graphene metamaterial is numerically investigated in this paper. For the active manipulation of the PIT device, the single-layer graphene is integrated into the proposed structure consisting of the split-ring-resonator (SRR) and the closed-ring-resonator (CRR). Dynamically adjusting Fermi energy in graphene leads to modulation of the PIT window, allowing for the active control of the group delay. From the simulated electrical field distributions and effective circuit model to analyze, the transmission spectrum modulation can be attributed to the altering in the energy loss of the dark mode resonator through the conduction effect of the graphene layer. Our work offers theoretical references for the development of slow light terahertz devices in the future.

Dynamically Tunable Resonant Strength in Electromagnetically Induced Transparency (EIT) Analogue by Hybrid Metal-Graphene Metamaterials

In this paper, a novel method to realize a dynamically tunable analogue of EIT for the resonance strength rather than the resonance frequency is proposed in the terahertz spectrum. The introduced method is composed of a metal EIT-like structure, in which a distinct EIT phenomenon resulting from the near field coupling between bright and dark mode resonators can be obtained, as well as an integrated monolayer graphene ribbon under the dark mode resonator that can continuously adjust the resonance strength of transparency peak by changing the Fermi level of the graphene. Comparing structures that need to be modulated individually for each unit cell of the metamaterials, the proposed modulation mechanism was convenient for achieving synchronous operations for all unit cells. This work demonstrates a new platform of modulating the EIT analogue and paves the way to design terahertz functional devices which meet the needs of optical networks and terahertz communications.

Electrically controllable plasmon induced reflectance in hybrid metamaterials

The tunable plasmon induced reflectance (PIR) effect has been numerically investigated and experimentally realized by hybrid metal-graphene metamaterials. The PIR effect is produced by two parallel strips of gold (Au) and controlled electrically by applying the gate voltage to the graphene layer. The PIR response is generated by the weak hybridization of two bright modes of the gold strips and tuned by changing the Fermi level (Ef) of the graphene. The total shift of 211.7 nm was achieved in the reflection peak by applying only 3 V. This concept of real time electrical tuning of PIR, with a modulation depth of ∼49% and a spectral contrast ratio of 66.6%, can be used for designing optical switches, optical modulators, and tunable sensors.

Active control of broadband plasmon-induced transparency in a terahertz hybrid metal-graphene metamaterial.

A hybrid metal–graphene metamaterial (MM) is reported to achieve active control of broadband plasmon-induced transparency (PIT) in the THz region. The unit cell consists of one cut wire (CW), four U-shaped resonators (USRs) and monolayer graphene sheets under the USRs. Via near-field coupling, broadband PIT can be produced through the interference between different modes. Based on different arrangements of graphene positions, not only can we achieve electrical switching of the amplitude of broadband PIT, but can also realize modulation of the bandwidth of the transparent window. Simultaneously, both the capability and region of slow light can be dynamically tunable. This work provides schemes to manipulate PIT with more degrees of freedom, which will find significant applications in multifunctional THz modulation.

Dynamically controllable plasmon induced transparency based on hybrid metal-graphene metamaterials

Novel hybrid metal-graphene metamaterials featuring dynamically controllable single, double and multiple plasmon induced transparency (PIT) windows are numerically explored in the terahertz (THz) regime. The designed plasmonic metamaterials composed of a strip and a ring with graphene integration generate a novel PIT window. Once the ring is divided into pairs of asymmetrical arcs, double PIT windows both with the spectral contrast ratio 100% are obtained, where one originates from the destructive interference between bright-dark modes, and the other is based on the interaction of bright-bright modes. Just because the double PIT windows are induced by two different mechanisms, the continuously controllable conductivity and damping of graphene are employed to appropriately interpret the high tunability in double transparency peaks at the resonant frequency, respectively. Moreover, multiple PIT windows can be achieved by introducing an additional bright mode to form the other bright-bright modes coupling. At the PIT transparent windows, the dispersions undergo tremendous modifications and the group delays reach up to 43 ps, 22 ps, and 25 ps, correspondingly. Our results suggest the existence of strong interaction between the monolayer graphene layer and metal-based resonant plasmonic metamaterials, which may hold widely applications in filters, modulators, switching, sensors and optical buffers.

Active modulation of electromagnetically induced transparency analogue in terahertz hybrid metal-graphene metamaterials

Metamaterial analogues of electromagnetically induced transparency (EIT) have been intensively studied and widely employed for slow light and enhanced nonlinear effects. In particular, the active modulation of the EIT analogue and well-controlled group delay in metamaterials have shown great prospects in optical communication networks. Here we integrate a monolayer graphene into metal-based terahertz (THz) metamaterials, and realize a complete modulation in the resonance strength of the EIT analogue via manipulating the Fermi level of graphene. The physical mechanism lies in the active tuning of the damping rate of the dark mode resonator through the recombination effect of the conductive graphene. This work presents a novel modulation strategy of the EIT analogue in the hybrid metamaterials, and paves the way towards designing very compact slow light devices to meet the future demand of ultrafast optical signal processing.

Independently tunable dual-band plasmonically induced transparency based on hybrid metal-graphene metamaterials at mid-infrared frequencies.

A tunable dual-band plasmonically induced transparency (PIT) device based on hybrid metal-graphene nanostructures is proposed theoretically and numerically at mid-infrared frequencies, which is composed of two kinds of gold dolmen-like structures with different sizes placed on separate graphene interdigitated finger sets respectively. The coupled Lorentz oscillator model is used to explain the physical mechanism of the PIT effect at multiple frequency domains. The finite-difference time-domain (FDTD) solutions are employed to simulate the characteristics of the hybrid metal-graphene dual-band PIT device. The simulated spectral locations of multiple transparency peaks are separately and dynamically modulated by varying the Fermi energy of corresponding graphene finger set, which is in good accordance with the theoretical analysis. Distinguished from the conventional metallic PIT devices, multiple PIT resonances in the hybrid metal-graphene PIT device are independently modulated by electrostatically changing bias voltages applied on corresponding graphene fingers, which can be widely applied in optical information processing as tunable sensors, switches, and filters.