EIT-like Window Research Articles

Tunable multifunctional terahertz metamaterial device based on metal-dielectric-vanadium dioxide

The Electromagnetically Induced Transparency (EIT) effect in terahertz (THz) metamaterial devices has garnered extensive attention owing to its distinctive advantages in the slow light devices and quantum communication. However, the application of EIT has been constrained by the limitation to a single transparent window and the fixed intensity of the electromagnetic response at the transmission peak after fabrication. To achieve a dual-frequency EIT effect and enable active tunability, this paper presents a tunable multifunction THz metamaterial device based on vanadium dioxide (VO2). The transition of VO2 from the insulator to the metal allows for the active control of EIT and multi-band absorption switching in the THz range. When VO2 is in its dielectric state, two EIT-like windows could be observed with a maximum value of 86.9 % and 71.7 % of the transmission amplitude, respectively. By adjusting the temperature of the VO2, a modulation depth of up to 99 % can be achieved, enabling active control of the EIT-like effect. In addition, active adjustment of group delay of up to 5.47 ps was demonstrated. When VO2 is in the metallic state, the device serves as a tunable multiband absorber, capable of achieving perfect absorption and modulation amplitude of up to 92 %. The results indicated that the presented devices hold significant value for research in the THz range, particularly for applications related to switching and slow light devices. Therefore, the tunable multifunctional THz metamaterial device is of great significance for THz technology.

Analogy of polarization-independent, multi-band and tunable electromagnetically induced transparency with high sensitivity based on simple circular ring resonators and vanadium dioxide film

An analogy of polarization-independent, multi-band and tunable electromagnetically induced transparency (EIT) effect is proposed based on simple combination of circular ring resonators and vanadium dioxide film. The EIT-like effect is generated by bright-bright coupling resulting from adjacent ring resonators. High sensitivity up to 1.60 THz/RIU to the environmental refractive index is achieved utilizing the transparency peak. Accompanying with the EIT-like effect, the multi-band slow light phenomenon is obtained around the transparency windows. In addition, by inducing the insulator-metallic transition of the vanadium dioxide layer, the EIT-like curves can be actively manipulated while the multiple modulation is realized without refabricating the structure. Particularly, due to structural symmetry, the EIT-like windows keep unchanged and maintain noticeable with various polarization angles. The proposed structure has potential applications such as terahertz sensors, slow-light devices and modulators.

Constant frequency reconfigurable terahertz metasurface based on tunable electromagnetically induced transparency-like approach

A terahertz constant frequency reconfigurable metasurface based on tunable electromagnetically induced transparency (EIT)-like property was designed, whose transparency window frequency did not vary with Fermi energy. This structure was composed of two single-layer graphene resonators, namely, left double big rings and right double small rings. An evident transparency window (EIT-like phenomenon) was caused by the near-field coupling between bright modes of the two resonators in the transmission spectrum, in which amplitude over 80% was acquired at 1.98 THz. By individually reconfiguring the Fermi energy of each resonator, the EIT-like effects, transparency window amplitude, modulation speed and group delay could be actively controlled while the frequency of EIT-like window remained constant. Significantly, the transparency window was fully modulated without changing the frequency, and the maximum modulation depth reached 78%. Furthermore, the modulation speed also increased because the total graphene area A was effectively reduced in the proposed structure. Compared with other metasurface structures, the modulation properties of the proposed structure showed higher performance while the EIT-like window frequency remained static. This research provides an alternative method for developing constant frequency reconfigurable modulation terahertz devices (such as optical switches and modulators), as well as a potential approach for miniaturization of terahertz devices.

Active and selective manipulation of dual transparency windows in hybrid graphene-vanadium dioxide metamaterial

Active and selective manipulation of dual–spectral electromagnetically induced transparency (EIT) metamaterial constructed by three graphene strips and vanadium dioxide (VO2) layer is proposed and demonstrated numerically. Simulation results illustrate that the dual-spectral EIT-like effect are induced by adjacent graphene strips acted as bright and bright mode and excited opposite-phase electric field distributions. One or two of EIT-like windows can be modulated by selectively varying graphene strip’s Fermi energy. Meanwhile, the Fermi energies of three graphene strips are varying simultaneously, the position of dual transparency windows as a whole obviously exhibit blue shift. Moreover, the amplitude of dual–spectral EIT windows can be simultaneously manipulated while frequency remain rough constant during the phase transition process of VO2. The physical mechanism underneath the phenomenon of actively and selectively tunable EIT, which is revealed by theoretically calculated results based on the classical three-oscillator model, can be attributed to the variation of resonance frequency, coupling coefficient and losses of the resonators caused by varying Fermi energy of graphene strips and conductivity of VO2.

Electromagnetically Induced Transparency-Like Terahertz Graphene Metamaterial With Tunable Carrier Mobility

In this work, a graphene-based planar terahertz electromagnetically induced transparency-like (EIT-like) metamaterial, composed of two horizontally symmetric mono-layer graphene micro-ring resonators (MRR) and a vertical mono-layer graphene micro-strip resonator (MSR), has been proposed. The transparent window was observed in the y polarization direction. By changing the carrier mobility of the graphene, the transparent window could be opened and closed while the position of the EIT-like window remained unchanged. The physical mechanism of the EIT-like effect was explained by the distribution of the electric field on E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>z</i></sub> and the three-level <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Lambda $ </tex-math></inline-formula> -type system. The theoretical fitting results based on the Lorentz oscillator model and the S-parameter inversion method were consistent with the numerical simulation results. In addition, the performance of the metamaterial for detecting the refractive index of the surrounding medium was analyzed. Numerical simulation showed that when the FOM exceeded 8.0, the sensitivity was 1.6 THz/RIU. Finally, as the graphene carrier mobility increased, the group delay of the device increased. The delay time reached 1.49 ps, and the group index was as high as 400. The proposed design provides a feasible method for the development of optical switches, biochemical molecular detection, and slow light equipment.

Theoretical design of a reconfigurable broadband integrated metamaterial terahertz device.

An actively reconfigurable broadband terahertz (THz) metamaterial functional device based on the phase-change material vanadium dioxide (VO2) and two-dimensional graphene material is theoretically proposed and demonstrated. The device has excellent tolerance under oblique incidence. When the VO2 is in the metallic state, and the Fermi energy of graphene is fixed at 0.1 eV, the designed device acts as a broadband THz absorber in the transverse magnetic (TM) polarization mode. The absorptance bandwidth exceeds 0.55 THz with a complete absorption intensity of more than 90%. In this state, the absorber operates as a broadband modulator with the total modulation depth exceeding 91.5% as the continually decreased conductivity of VO2 from 200000 S/m to 10 S/m. In the transverse electric (TE) polarization process, the structure behaves as a dual-band absorber with two perfect absorption peaks. When the conductivity of VO2 is changed, the tunable absorber can also be regarded as an absorptance modulator, with a maximum modulation intensity of 92.1%. Alternatively, when VO2 behaves as an insulator at room temperature in the TE polarization mode, a strong broadband electromagnetically induced transparency (EIT) window is obtained, with a bandwidth exceeding 0.42 THz in the transmittance spectrum. By varying the Fermi energy of graphene from 0 to 0.9 eV, the EIT-like window or broadband transmission spectrum (in TM mode) can be switched. The results indicate that the device can also be operated as a modulator in the transmission mode. The impedance matching theory is used, and electric field distributions are analyzed to quantify the physical mechanism. An advantage of the manipulation of the polarization angle is that the modulation performance of the proposed multi-functional THz device can be regulated after fabricated.

Realizations of Electromagnetically Induced Transparency Effect in Microwave Frequency Based on Metamaterials

A novel electromagnetically induced transparency (EIT) effect analogue based on metamaterials is proposed, which is composed of metal-based H shaped cut wires (MH) and parallel cut wires (MPW) on F4BM substrate. Distinct EIT-like window can be observed under irradiation of plane wave with y polarised direction through the coupling of bright element MH and dark element MPW. In addition, relative position of MH and MPW can influence the EIT-like effect which can be validated by experimental test and expressed by damping rate of bright mode and coupling coefficient of bright-dark mode on the basis of two particles mode. The work exhibits guiding function in EIT designs and realizations.

Dynamically tunable multi-resonance and polarization-insensitive electromagnetically induced transparency-like based on vanadium dioxide film

A dynamically tunable multi-resonance and polarization-insensitive electromagnetically induced transparency-like (EIT-like) metamaterial is proposed. The EIT-like structure consists of four cut-wire metals and a square metal frame. Two distinct transparency windows resulting from the near field coupling can be observed under x and y polarization directions, respectively. The physical mechanism of the proposed EIT-like metamaterial can be explained by the surface current distributions. The EIT-like effect can be adjusted by tuning the conductivity of vanadium dioxide (VO2). Meanwhile, a low-loss EIT-like metamaterial can be obtained, which can be proved by the effective medium theory. In addition, the EIT-like metamaterial shows polarization-insensitive characteristics for x and y polarized incidence. By varying the conductivity of VO2, the EIT-like windows and slow-light effect can be manipulated dynamically. These features can provide potential applications in terahertz modulators and slow-light terahertz devices.

Polarization-insensitive tunable multiple electromagnetically induced transparencies analogue in terahertz graphene metamaterial

A graphene-based metamaterial structure composed of multilayer graphene/dielectric stacking configuration is proposed, which achieves multiple analogue of electromagnetically induced transparencies (EIT) effect at terahertz frequencies. Using the phase-coupling scheme, a theoretical model is established to study the EIT-like effect of the proposed structure, and the theoretical calculations coincide well with the numerical simulated results. By varying the Fermi energy level of the graphene, the EIT-like windows can be dynamically tuned in a wide range of terahertz spectra. Particularly, since the symmetry of the structure, the EIT-like effect is polarization-insensitive and can be performed very well in a large incident angles, nearly 80° for both transverse electric and transverse magnetic waves. The proposed structure has potential applications in tunable terahertz chip-integrated optical devices, especially for dynamic multi-band filters, sensors, modulators and nonlinear devices.

Tunable multiple phase-coupled plasmon-induced transparencies in graphene metamaterials.

We demonstrate the existence of multiple electromagnetically induced transparencies (EIT)-like spectral responses in graphene metamaterials consisting of a series of self-assembled graphene Fabry-Pérot (FP) cavities. By exploiting the graphene plasmon resonances and phase-coupling effects, the transfer matrix model is established to theoretically predict the EIT-like responses, and the calculated results coincide well with numerical simulations. It is found that high-contrast (~90%) multiple EIT-like windows are observed over a broad range of mid-infrared. Additionally, these optical responses can be efficiently tuned by altering the Fermi level in graphene and the separations of FP cavities. The proposed scheme paves the way toward control of the multiple EIT-like responses, enabling exploration of the on-chip multifunctional electro-optic devices including multi-channel-selective filters, sensors, and modulators.

Achieving slow and fast light with high transmission by nanodiamond nitrogen-vacancy center coupling to photonic crystal cavity

Using a single diamond nitrogen-vacancy (NV) center embedded in a waveguide-coupled photonic crystal (PC) nanocavity and driven by a classical laser field, we investigate optical transmission and group delay characteristics of the hybrid system operating in the weak-coupling regime. It is found that double electromagnetically induced-transparency (EIT) transmission peaks and slow- and fast-light propagation inside the EIT-like windows can be realized with practical system parameters. The double-frequency transparency of the input light expands the frequency range of EIT and may improve the controllability of EIT in this composite PC-NV system. The present system also provides a way to achieve integrated photonic slow- and fast-light devices for applications requiring multiple EIT effect in a PC platform.

Interference of three multiwave mixings via electromagnetically induced transparency

We experimentally observe the interplay among coexisting multiwave-mixing (MWM) signals via multiple electromagnetically induced transparency (EIT) windows, including two ladder-type EIT windows and one V-type EIT-like window in a five-level atomic system of Rb85. In the presence of these EIT windows, one can control the interplay between these MWM signals easily by changing the frequency detuning. Meanwhile, we also report the spatial and temporal interferences with a femtosecond time scale among three coexisting MWM signals in two overlapped EIT windows.

Transmission-dispersion characteristics of waveguide-coupled photonic crystal two-mode nanocavity embedding three tunnel-coupled quantum dots

Using three tunnel-coupled quantum dots embedded in waveguide-coupled photonic crystal two-mode nanocavity, we investigate optical transmission-dispersion characteristics of the combined system. It is shown that multiple electromagnetically-induced-transparency (EIT) transmission peaks and strong normal/anomalous dispersion inside the EIT-like windows can be observed in the spectrum.