Analogue Of Electromagnetically-induced Transparency Research Articles

Active Control of Electromagnetically Induced Transparency Analogy in Spoof Surface Plasmon Polariton Waveguide

Metamaterial analogues of electromagnetically induced transparency (EIT) enable a unique avenue to endow a coupled resonator system with quantum interference behavior, exhibiting remarkable properties in slow-wave and highly sensitive sensing. In particular, tunable and ultracompact-chip-integrated EIT-like effects reveal fantastic application prospects in plasmonic circuits and networks. Here, we demonstrate an electrically tuned on-chip EIT analogue by means of dynamic EIT modules side-coupled to ultrathin corrugated metallic strips supporting spoof surface plasmon polaritons (SSPPs). By embedding PIN diodes into the subradiant mode, on-to-off control of the destructive coupling between the radiative and subradiant modes results in dynamic chip-scale EIT-like behavior under the change of the bias voltage, allowing for an electrically tunable group delay of the surface waves. The physical mechanism of the active modulation is elucidated with the coupled mode theory. In addition, the cascaded capacity performed by installing multiple EIT modules with an interval of equivalent wavelength are also characterized on a planar plasmonic waveguide. The proposed system will pave a versatile route toward dynamic control in chip-scale functional devices.

Analogue of electromagnetically induced transparency in square slotted silicon metasurfaces supporting bound states in the continuum.

In this work, a silicon metasurface designed to support electromagnetically induced transparency (EIT) based on quasi-bound states in the continuum (qBIC) is proposed and theoretically demonstrated in the near-infrared spectrum. The metasurface consists of a periodic array of square slot rings etched in a silicon layer. The interruption of the slot rings by a silicon bridge breaks the symmetry of the structure producing qBIC stemming from symmetry-protected states, as rigorously demonstrated by a group theory analysis. One of the qBIC is found to behave as a resonance-trapped mode in the perturbed metasurface, which obtains very high quality factor values at certain dimensions of the silicon bridge. Thanks to the interaction of the sharp qBIC resonances with a broadband bright background mode, sharp high-transmittance peaks are observed within a low-transmittance spectral window, thus producing a photonic analogue of EIT. Moreover, the resonator possesses a simple bulk geometry with channels that facilitate the use in biosensing. The sensitivity of the resonant qBIC on the refractive index of the surrounding material is calculated in the context of refractometric sensing. The sharp EIT-effect of the proposed metasurface, along with the associated strong energy confinement may find direct use in emerging applications based on strong light-matter interactions, such as non-linear devices, lasing, biological sensors, optical trapping, and optical communications.

Analogue of electromagnetically-induced transparency with ultra-narrow bandwidth in a silicon terahertz metasurface

Achieving an ultra-narrow bandwidth analogue of electromagnetically induced transparency (EIT) in bright–bright mode coupling metasurface requires a large contrast of the Q factor and small wavelength detuning between the two coupled modes. Here, by coupling a toroidal dipole (TD) high-Q Fano resonance and a low-Q magnetic dipole (MD) mode, we numerically demonstrated a high Q factor analogue of EIT on an all-silicon metasurface in the terahertz regime. The Q factor of Fano resonance and consequent EIT can be easily adjusted by the spacing between the air holes. By adjusting the radii of the air holes, the thickness of the silicon wafer, or the lattice constant of the metasurface, EIT-like response exhibiting a very high group refractive index and a large group delay was achieved. The proposed EIT metasurface is easy to fabricate and has potential applications in the fields of narrowband filtering and slow-light based devices.

Analogue of Electromagnetically Induced Transparency Based on Bright–Bright Mode Coupling Between Spoof Electric Localized Surface Plasmon and Electric Dipole

We report a novel type of electromagnetically induced transparency (EIT) analogue based on metamaterials (MMs) with hybrid structures, in which spiral and cut-wire structures serve as bright-mode resonators with the spoof electric localized surface plasmons and electric dipole resonance. With the simulations and experiments, the EIT analogue generated by the frequency detuning and hybridization between the resonators is verified. The simulated surface charge density and electric and magnetic field distributions, together with the theoretical analysis based on the Lorentz oscillator model, reveal the principle of the EIT analogue. Moreover, the transmission window of the MM demonstrates linear dependence on the refractive index’s change of surrounding media, showing the potential as a tool for environmental detection.

Analog of multiple electromagnetically induced transparency using double-layered metasurfaces

We reported an analog of electromagnetically induced transparency (A-EIT) featured by double transparent peaks in the spectrum. The A-EIT is realized by double-layered metasurface which consists of spoof localized surface plasmons (S-LSP) and cut-wire (CW)-square rings (SR) hybrid. Electric and magnetic S-LSP are excited as bright and dark modes respectively then couple with resonant modes of CW and SR simultaneously to achieve multiple A-EIT. Two bright modes of the electric S-LSP and SR are excited by external electric field directly that produce a bright-bright mode A-EIT. Moreover, the magnetic S-LSP, which cannot be excited by external field directly, is excited through near field coupling from CW, inducing another bright-dark mode A-EIT. Theoretical analysis with corresponding experiment in microwave band are introduced for better insights into physical essence of the double-peaks A-EIT.

Polarization-Independent Terahertz Tunable Analog of Electromagnetically Induced Transparency

The analogs of electromagnetically induced transparency (EIT) based on the concept of metamaterials (MMs) bring the primitive quantum phenomena into the scope of classical optics. However, most of the previous designs are anisotropic. Here, in this letter, a tunable isotropic classical analog of EIT is studied based on the wide-angle MM with a layer of vanadium dioxide underneath it. The tunable conductivity of vanadium dioxide is the key point to realize the dynamic modulation of EIT. The numerical calculation tells that the transmission peak of EIT can be tuned from 66% to 12% when the conductivity of vanadium dioxide is changed from 10 to $2000\;\Omega ^{-1}$ cm−1. Furthermore, such design possesses a nearly insensitive characteristic of transmission on polarization and incident angle. Although the simple planar structure presented here is a specific design to manipulate EIT-like phenomenon in terahertz MMs, it can be easily scaled to other electromagnetic spectra. This letter could provide one possible way for the plasmonic filter and sensing application.

Autler-Townes Splitting and Acoustically Induced Transparency Based on Love Waves Interacting with a Pillared Metasurface

Autler-Townes Splitting (ATS) and Electromagnetically Induced Transparency (EIT) are similar phenomena but distinct in nature. They have been widely discussed and distinguished by employing the Akaike information criterion (AIC). However, such work is lacking in acoustic system. In this work, the interaction of Love waves with two-line pillared meta-surface is numerically investigated by Finite Element Method. Acoustic analogue of ATS, Fabry-Perot resonance and cavity modes are first demonstrated in two lines of identical pillars by varying the distance between the pillar lines. By detuning the radius of one line of pillars, Fabry-Perot resonance along with two different pillar resonances give rise to the acoustic analogue of EIT (AIT) when the distance between the pillar lines is a multiple of half wavelength. ATS and AIT formula models are used to fit the transmission spectra, showing good agreements with numerical results. The quality of the fit models is quantitatively evaluated by resorting to the AIC. We show that theoretical and analytical discrimination between ATS and AIT are methodologically complementary. These results should have important consequences for potential acoustic applications such as wave control, designing of meta-materials and bio-sensors.

Active control of photo-induced electromagnetically induced transparency in terahertz region

The characteristic of an all-optical electromagnetically induced transparency (EIT) analogue generated on GaAs substrate in terahertz (THz) region has been investigated. By increasing power of pump laser, a phenomena of EIT analogue emerged. It was found that the resonance frequency as well as the time delay can be dynamic tuned by controlling the power of pump laser, which displayed a blue shift by increasing the conductivity. Furthermore, the coupled Lorentz oscillator model has been used to analyze the physical mechanism of photo-generated EIT analogue as well. This approach may provide a reference for the design of the rapid tuning device.

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.

Acoustic analogue of electromagnetically induced transparency and Autler–Townes splitting in pillared metasurfaces

Electromagnetically induced transparency (EIT) and Autler–Townes splitting (ATS) originating from multilevel atomic systems have similar transparency windows in transmission spectra which causes confusion when discriminating between them, despite the difference in their physical mechanisms. Indeed, Fano interference is involved in EIT but not in ATS. There has been significant interest in the classic analogues of EIT and ATS in recent years, such as in photonics, plasmonics, optomechanics; however, the acoustic analogue of ATS has been rarely studied. In this work, we propose to investigate these phenomena in a pillared metasurface consisting of two lines of pillars on top of a thin plate. The existence of Fabry–Pérot resonance and the intrinsic resonances of the two lines of pillars act as a three-level atomic system that gives rise to the acoustic analogue of EIT and ATS. Since the frequency of Fabry–Pérot resonance can be tuned by controlling the distance between the two lines, the underlying physics, whether Fano interference is involved or not, is quite clear in order to discriminate between them. The realizations of EIT and ATS are put forward to control elastic waves for potential applications such as sensing, imaging, filtering.

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.

An electromagnetic modulator based on electrically controllable metamaterial analogue to electromagnetically induced transparency

Electromagnetically induced transparency (EIT) is a promising technology for the enhancement of light-matter interactions, and recent demonstrations of the EIT analogue realized in artificial micro-structured medium have remarkably reduced the extreme requirement for experimental observation of EIT spectrum. In this paper, we propose to electrically control the EIT-like spectrum in a metamaterial as an electromagnetic modulator. A diode acting as a tunable resistor is loaded in the gap of paired wires to inductively tune the magnetic resonance, which induces remarkable modulation on the EIT-like spectrum through the metamaterial sample. The experimental measurements confirmed that the prediction of electromagnetic modulation in three narrow bands on the EIT-like spectrum, and a modulation contrast of up to 31 dB was achieved on the transmission through the metamaterial. Our results may facilitate the study on active/dynamical technology in translational metamaterials, which connect extraordinary manipulations on the flow of light in metamaterials, e.g., the exotic EIT, and practical applications in industry.

Active control of electromagnetically induced transparency with dual dark mode excitation pathways using MEMS based tri-atomic metamolecules

We report experimental results of the active switching of electromagnetically induced transparency (EIT) analogue by controlling the dark mode excitation pathways in a microelectromechanical system based tri-atomic metamolecule, operating in the terahertz spectral region. The tri-atomic metamolecule consists of two bright cut wire resonators (CWRs) on either side of the dark split ring resonators (SRRs). Each of the CWRs can independently excite the dark inductive-capacitive resonance mode of the SRRs through inductive coupling, and this allows for the dual pathways of dark mode excitation. The CWRs are made movable along the out-of-plane direction and electrically isolated to achieve selective reconfiguration. Hence, by controlling the physical position of these CWRs, the excitation pathways can be actively reconfigured. This enables the strong excitation of EIT analogue at 0.65 THz, only when one of the pathways is made accessible. Moreover, the transparency peak is completely modulated when both pathways are made either inaccessible or equally accessible. The proposed approach of realizing independent control of constituent resonators in a multi-resonator coupled system, enables the realization of efficient slow light devices and tunable high-Q resonators in terahertz spectral region.

Frequency-agile electromagnetically induced transparency analogue in terahertz metamaterials.

Recently reported active metamaterial analogues of electromagnetically induced transparency (EIT) are promising in developing novel optical components, such as active slow light devices. However, most of the previous works have focused on manipulating the EIT resonance strength at a fixed characteristic frequency and, therefore, realized on-to-off switching responses. To further extend the functionalities of the EIT effect, here we present a frequency tunable EIT analogue in the terahertz regime by integrating photoactive silicon into the metamaterial unit cell. A tuning range from 0.82 to 0.74 THz for the EIT resonance frequency is experimentally observed by optical pump-terahertz probe measurements, allowing a frequency tunable group delay of the terahertz pulses. This straightforward approach delivers frequency agility of the EIT resonance and may enable novel ultrafast tunable devices for integrated plasmonic circuits.

Plasmonic analog of electromagnetically-induced transparency of asymmetrical slots waveguide

In this paper, electromagnetically-induced transparency (EIT) phenomena have been investigated numerically in the plasmonic waveguides composed of unsymmetrical slot shaped metal–insulator–metal (MIM) structures. By the transmission line theory and Fabry–Perot model, the formation and evolution mechanisms of plasmon-induced transparency were exactly analyzed. The analysis showed that the peak of EIT-like transmission could be changed easily according to certain rules by adjusting the geometrical parameters of the slot structures, including the coupling distances and slot depths. We can find a new method to design nanoscale optical switch, devices in optical storage and optical computing.

Electromagnetically Induced Transparency Analogue by Self‐Complementary Terahertz Meta‐Atom

In the past years, many researchers have tried to realize the electromagnetically induced transparency (EIT) phenomena from the metamaterial arrays for the attractable applications such as slow light devices, novel optical communication systems, and nonlinear optical devices. Most of metamaterial enabled EIT analogues reported so far are based on the destructive interference between the bright and dark meta‐atoms. Whether they are located on the same plane or off the plane, EIT‐like properties can be achieved only by breaking the symmetry between the bright and dark meta‐atoms. In this study, a novel self‐complimentary terahertz meta‐atom is developed by combining cut‐wire resonators and its pseudo‐complimentary pattern within a single meta‐atom. From the measurement results, it is verified that the proposed meta‐atom can exhibit EIT‐like phenomenon within a single unit cell by controlling the focus of the electric field induced by the incident terahertz waves within the self‐complimentary meta‐atom cell as predicted by the numerical simulation as well as by the theoretical forced oscillation model.

Experimental distinction of Autler-Townes splitting from electromagnetically induced transparency using coupled mechanical oscillators system.

Here we experimentally demonstrated the electromagnetically induced transparency (EIT) and Autler-Townes splitting (ATS) effects in mechanical coupled pendulums. The analogue of EIT and ATS has been studied in mechanical systems and the intrinsic physics between these two phenomena are also been discussed. Exploiting the Akaike Information Criterion, we discern the ATS effect from EIT effect in our experimental results.

Oscillator Model Analysis for Slow Light in Bright-Dark-Dark Waveguide Systems

The tunable wideband slow-light based on plasmonic analogue of electromagnetically induced transparency (EIT) in bright-dark-dark mode waveguide systems is investigated in this letter. A three-oscillator model is established to characterize optical responses and slow-light effects in the waveguide systems. The main dependent factors of slow-light effects based on plasmonic analogue of EIT, namely, the cavity-cavity separation and media environment of resonators, are numerically and theoretically discussed in this letter. We find that both the group index and the bandwidth of the slow light in the bright-dark-dark waveguide structures show better performance than those in the normal bright-dark ones. These results suggest that the contradiction between the large group index and the wideband slow light in the bright-dark mode waveguide system can be weakened. At the same time, tunable wideband slow-light effects are also achieved. Our researches may have an application in optical slow-light devices.

Experimental study of the band-pass filter and slow-wave effect in a MDM channel based on a magnetic plasmonic analogue of EIT

In connection with an analogue of electromagnetically-induced transparency (EIT), this paper studied experimentally the tunable band-pass filter and tunable slow-wave effect of MDM (μ-negative materials/double positive materials/μ-negative materials) magnetic plasmonic channel. The results of simulations and experiments show that an evident electromagnetically-induced transparency phenomenon appears in this channel with double-side resonators, which can be used to realize simultaneous the band-pass filter and the slow-wave effect. The band-pass filter’s center frequency is founded to be determined by the size of the side resonator, the resonator direction and the effective permeability of μ-negative (MNG) metamaterials. The bandwidth can be adjusted by detuning of the two resonator frequencies, the band size of the band-pass filter depends on the number of the resonators, Thus, the band-pass filter characteristics of the MDM waveguide can be tuned by changing the resonator parameters, the resonator direction and the effective permeability of the MNG materials. Moreover, the MDM structure can also be utilized to obtain a tunable slow-wave effect (such as an adjustable frequency, a slow-down factor, and even a muti-band slow wave) based on EIT. The experimental results are in good agreement with the simulation results.

Perfect absorbers for electromagnetic wave, based on metamaterials

Metamaterials (MMs), which are not existing in nature, but artificially-engineered materials for controlling electromagnetic wave. MMs have attracted more and more research attentions, since they have shown greatly novel properties such as left-handed behavior, negative refractive index, classical analog of electromagnetically-induced transparency, and extraordinary transmission. Among MMs, MM perfect absorbers (MMPAs), which are useful to enhance the efficiency in capturing solar energy and applied to various application areas, have been rapidly developed. In general, the structure of MMPAs is very simple, which consist of three layers: patterned conductor layer, which is used for minimizing the reflection by impedance matching, dielectric layer and continuous conductor layer for blocking the transmission. In addition, the unit-cell size of general MM absorbers is only 1/3−1/5 of the working wavelength of incident electromagnetic wave. Nevertheless, the properties of general MMPAs are in problems of the absorption only at specific frequency, the narrow absorption band, the polarization sensitivity and so on. In this review paper, the introduction of recent researches in the field of MMPAs operating in different frequency ranges is presented. Moreover, the researches on the improved electromagnetic properties are discussed, which comprise multi-band, broadband, tunable, polarization-insensitive, and wide-incident-angle MMPAs. The perspectives and the future works for the further investigations and the various real applications of MMPAs are also presented.