Electromagnetically Induced Transparency Structure Research Articles

Terahertz metal-graphene hybrid metamaterial for active manipulation of electromagnetically induced transparency

The dynamic tuning of terahertz (THz) electromagnetically induced transparency (EIT) offers significant potential in rapidly changing THz regulation fields, such as the next generation wireless communication, switching, and sensing. In this work, we demonstrate a THz EIT metamaterial by combining a circular and a rectangular split-ring resonator (CSRR and RSRR) based on the bright-bright mode coupling. The introduction of graphene into the EIT structure enables active tuning, and reveals two distinct regulation mechanisms in the metal-graphene hybrid EIT metamaterial: 1. the internal coupling effect diminishes with the increase of the Fermi level in the CSRR-graphene integration; 2. the surface electric field undergoes redistribution in the RSRR-graphene integration. These two dynamic regulation mechanisms are well confirmed by the simulated electric field distribution. As a result, the transmittance within the EIT window of the hybrid metamaterial can be precisely modulated, exhibiting a significant modulation depth of >85%. Notably, the integration with graphene in the RSRR allows for simultaneous modulation of resonances on either side of the EIT peaks, which expands more THz modulation channels. This work enriches the design and implementation methods for active THz EIT and shows potential applications in THz dynamic application scenarios.

Linear Polarization Conversion Based on Symmetry‐Breaking in an Electromagnetically Induced Transparency Structure

AbstractTraditional polarization converters suffer from drawbacks such as significant thickness and high losses, which limit their practical applications. This study introduces a novel metamaterial structure that combines electromagnetically induced transparency (EIT) with linear polarization conversion to overcome these limitations. By harnessing the properties of EIT, this structure achieves low‐loss polarization conversion. The mechanism behind this is the generation of an EIT effect through the coupling of the light and dark modes. Additionally, this study focuses on introducing a slight vertical polarization symmetry disruption and inducing the excitation of small components within the dipole of the EIT structure to achieve close‐to‐complete cross‐polarization conversion. The effect of asymmetry on the polarization conversion rate is also explored. This study offers an innovative approach to designing low‐loss polarization converters utilizing EIT technology.

Thermally controllable electromagnetically induced transparency in a coupled terahertz metamaterial

We investigate the thermally controllable electromagnetically induced transparency (EIT) effect in a planar terahertz (THz) metamaterial configuration comprising metallic semi-circular split ring resonators (MSCSRR) integrated with indium antimonide (InSb). In transmission configuration, a transparency window is observed by placing a horizontal cut wire (HCW) in close proximity to the MSCSRR. It develops by frequency detuning and strong near-field coupling between both the bright resonators. The transparency window is found to be controllable with temperature along with the structural parameters of the unit cell. The blue shift of 0.028 THz is observed when the temperature increases from 260 K to 320 K. Moreover, the group delay of the designed EIT structure can also dynamically tune by varying temperature of InSb. The shift from 3.19 ps to 1.98 ps is observed when the temperature increases from 260 K to 320 K. We used a coupled harmonic oscillator model to thoroughly understand the coupling between resonators and interpret the transparency effect. Our findings can be closely predicted from the model. The present study can be significant for the development of active and controllable terahertz photonic components such as slow light systems, buffers, etc.

Interplay of polarizations in a cascade EIT system in the presence of vortex coupling light in 87Rb atomic vapor medium

We investigate both experimentally and theoretically the cascade electromagnetically induced transparency (EIT) in configuration in 87Rb atomic vapor medium in the presence of vortex coupling Laguerre Gaussian (LG) light. We demonstrated Doppler free double resonance EIT structure in cascade configuration and observed transmission spectra for and polarized probe and coupling lights. We demonstrate that the double resonance structure can be identified by two photon transition probabilities and it is found to be and . By considering coupling LG light, several polarization combinations are taken into account, and their effects on amplifying and diminishing the EIT resonances are demonstrated experimentally. In order to understand the polarization effects of vortex coupling light on EIT spectrum in a degenerate multilevel atomic system, a theoretical model is developed by considering a simplified double hut level structure. Semi-classical density matrix analysis is used to understand the dynamics and also to establish the enhancement and reduction of EIT peak height with coupling light polarizations. The impact of two photon transition probabilities, polarization combinations and relative orientations of probe and coupling lights in degenerate multilevel atomic systems leads to modification of EIT resonances significantly. We establish quantitative agreement between our theory and experimental results.

Dual-band electromagnetically induced transparent metamaterial with slow light effect and energy storage

The realization of electromagnetically induced transparency (EIT) on metamaterials has special properties, such as strong slow-light, frequency-selection and so on, which have allowed EIT to be widely used in the fields of slow-light, optical storages and filters. In this paper, a metamaterial with two pairs of split ring resonators and one cut-wire is designed to achieve dual-band EIT effect at 0.5–2.14 GHz and 0.4–2.10 GHz with independently tunable bandwidths of 1.64 GHz and 2.7 GHz, respectively. The coupled Lorentz model is adopted to principally study the coupling characteristics between dark and bright modes. It is shown that the coupling strength between the dark and bright modes could be modulated by the coupling distance, which make the dual-band transparent window could be independently modulated by only changing the coupling distance between the bright and dark mode. The group delay and energy storage are also simulated by setting the Gaussian pulse signal passing through the EIT structure. The results show that the group delay of the designed EIT structure is 16.9 times that of the same thickness of dielectric material. The manufactured metamaterial is tested in a microwave anechoic chamber. The experimental and theoretical results are well consistent. These results could be beneficial for the development of EIT research toward some up-and-coming novel slow-light, optical storage, sensor and optical filter applications.

Theoretical proposal of electromagnetically induced transparency with a transmissive polarization conversion based on metamaterials

The polarization of electromagnetic waves is a key feature in the research areas of modern optics and information science. How to efficiently convert the polarization directions of the EM waves remains to be a challenge in electromagnetically induced transparency (EIT). Here, we theoretically propose a double-layer metamaterial with four symmetric H-shaped resonators, which can achieve the EIT phenomenon and transmissive linear polarization conversion (LPC). The EIT effect is acquired depending on the destructive interference between the electric and magnetic resonances. It is demonstrated that electromagnetic coupling is realized by reducing the structural symmetry of the rotated H-shaped resonators. Furthermore, the value of the maximum transmission coefficient reaches up to 0.900 at 14.202 GHz. The values of the transmission dips are 0.094 at 9.913 GHz and 0.176 at 16.101 GHz, respectively. Moreover, a broad transparency window that is higher than 0.8 can be gained spanning from 11.913 GHz to 15.289 GHz, and the relative bandwidth is 24.8%. Meanwhile, the momentous capability of the LPC is also observed. The transmissive cross-polarization conversion is well observed at 9.913 GHz and 16.101 GHz, where the polarization conversion ratios respectively are 90.2% and 91.8%. In the transparent window, a slow-light effect is highlighted. The values of the maximum group delay and group index respectively approach 91 ns and 1925. The FDTD simulation had been employed to further verify the effectiveness of group delay. In particular, the surface current distributions of the H-shaped resonators are employed to explain the mechanisms of the EIT effect and the transmissive LPC. Surpassing the general EIT structures and polarization converters, the proposed metamaterial is synchronously equipped with the EIT behavior and LPC by one same structure, which has numerous potential applications in communication and antenna technologies.

Tunable ultranarrow-band metamaterial perfect absorber based on electromagnetically induced transparency structure

A tunable ultranarrow-band metamaterial perfect absorber (MPA) based on electromagnetically induced transparency (EIT) is demonstrated theoretically and experimentally. An EIT structure (EITS) with a full width at half-maximum (FWHM) of 0.12 nm is first studied, then the transmission peak is converted into an absorption peak by adding an Ag substrate beneath the EITS. After optimization for the structure and parameters, an ultranarrow-band MPA with a FWHM of 0.52 nm is obtained. Theoretical results show the ultranarrow-band absorption spectra of the proposed MPA can be tuned by rotating the incident angle. Moreover, the MPA exhibits obvious spectral shift as the refractive index of the surrounding medium increases. Finally, a MPA sample is fabricated to verify the theoretical results, and the measured spectra are consistent with the theoretical ones.

Electromagnetically induced transparency metamaterial with polarization independence and multi-transmission windows.

In this paper, an electromagnetically induced transparency (EIT) metamaterial with the performances of polarization independence and multi-transmission windows is proposed. First, we design an EIT with a single transmission window, which is composed of an H-shaped structure and two split-ring resonators (SRRs). Then, by sequentially rotating the unit by 90°, a new EIT structure with rotational symmetry is obtained. The results show that the new EIT structure has the characteristics of polarization independence and multiple transmission windows, and each transmission window has a high maximum transmittance and group index. The first transmission window has a maximum group index of 88.9 and 98.9% maximum transmission. The maximum group indices of the second and third transmission windows are 117.9 and 215.3, and the peak transmissions are 89.9% and 97.4%, respectively. The multiple transmission windows with polarization independence widen the application scope of the proposed EIT metamaterial and are suitable for high-performance slow-wave devices with the above two requirements.

Dual-band asymmetric transmission based on electromagnetically induced transparency (EIT) effect in a microstrip transmission line

A dual-band asymmetric transmission device based on the nonlinear electromagnetically induced transparency (EIT) effect is presented in this paper. The device structure is composed of two P-type branches and two split ring resonators (SRRs). Dual-band EIT effect is induced based on the destructive interferences between scattering fields of the SRRs and branches in a microstrip transmission line system. Moreover, nonlinear varactor diodes and the asymmetric absorption resistor are added to EIT structure based on microstrip line couplings, which results in the asymmetric transmission property. The 10 dB and 7.5 dB transmission light contrasts at the frequencies of 0.85 GHz and 0.95 GHz with the input power of − 3 dBm are demonstrated experimentally. Such low-loss, broadband and high-contrast asymmetric transmission device results from the EIT mechanism, which possesses narrower, sharper and higher transmittance features. Such results will be very beneficial for new nonlinear electromagnetic devices.

Terahertz polarization-independent electromagnetically-induced transparency structures

Two simple polarization-independent electromagnetically-induced transparency (EIT) metamaterials are numerically and experimentally demonstrated at the terahertz region. The first structure is composed of two metal concentric rings on a substrate, while the second one is composed of one metal ring with a cross in it. The bright–bright coupling behavior appears in the two symmetric polarization-independent EIT structures while it is generally observed in asymmetrically structures. In addition, the large group index is extracted to verify the slow-light effect of the two EIT structures. These simple EIT structures may have potential applications in certain areas, including sensing, slow-light and filtering devices.

Terahertz broadband filter and electromagnetically induced transparency structure with complementary metasurface

A broadband terahertz metamaterial filter and its complementary metasurface-electromagnetically induced transparency structure are designed, fabricated and demonstrated. The proposed terahertz broadband filter is a single-layer metal-dielectric metamaterial structure, which is easier to fabricate and control compared with the multi-layer metal-dielectric structures reported before. The 3 dB relative bandwidth of the filter is 27% with the center frequency of 0.405 THz. By changing the metal pattern of the filter into a complementary structure, a polarization independent electromagnetically induced transparency (EIT) structure is formed with the transmission peak appearing at 0.3 THz between the two dips at 0.27 THz and 0.42 THz. The filter and EIT samples have the same dimension in the unit cell, and could be fabricated from the same mask but using different polar photoresist during the photolithographic process. The transmission spectra and physical mechanism of the two complementary structures are investigated based on the superposition theory, surface currents and field distributions. The encouraging results afforded by the filter and the EIT structure could find their applications in broadband terahertz communication systems, terahertz sensors and other emerging THz technologies.

Design of Broad Stopband Filters Based on Multilayer Electromagnetically Induced Transparency Metamaterial Structures.

Broad stopband filters are proposed, based on multilayer electromagnetically induced transparency (EIT) metamaterial structures. The single EIT metamaterial consists of a U-shaped resonator and a strip on a polyimide substrate. The EIT-like spectral feature is firstly utilized to achieve stopband filters by properly coupling two layers of EIT structure. Influences of different rotation angles on the transmission properties of the two-layer EIT structure are investigated. It is found the wider low-transmission band can be obtained for the Transverse Magnetic (TM) polarization when the two EIT metal structures are vertical to each other. Furthermore, the bandwidth of the stopband can be controlled by increasing layers of the EIT structures with the proper architectural design. The design using a coupling effect of multi EIT-like resonances in the metamaterial would provide a new method for broad stopband filters in highly integrated optical circuits.

Tunable polarization-nonsensitive electromagnetically induced transparency in Dirac semimetal metamaterial at terahertz frequencies

Tunable polarization-nonsensitive electromagnetically induced transparency (EIT) based on Dirac semimetal films (DSF) at terahertz frequencies is numerically studied in this paper. We first numerically investigate the EIT effect in a DSF-based terahertz metamaterial structure comprising a DSF strip and two DSF L-shaped resonators. To achieve the polarization-nonsensitive EIT effect, we introduce one vertical strip and two more L-shaped resonators to the above structure. The transmission spectra of the new structure show strong polarization-nonsensitive characteristic because of the fourfold symmetry. By analyzing the surface currents and electric field distribution at the resonant frequencies, we demonstrate that an EIT effect arises from the bright–bright mode coupling. Moreover, the polarization-nonsensitive EIT structure exhibits a blue shift with the increase in the Fermi energy of the DSF without having to re-optimize its geometrical parameters. Our study opens a new path for developing terahertz devices such as terahertz switches.

Electrical Manipulation of Electromagnetically Induced Transparency for Slow Light Purpose Based on Metal-Graphene Hybrid Metamaterial

A terahertz metamaterial is presented and numerically investigated to achieve tunable electromagnetically induced transparency (EIT) for slow light. The unit cell consists of cut-wire pairs and U-shaped ring resonators with graphene strips placed between the metal film and the SiO2/Si substrate. Through bright-dark mode coupling, the radiative resonance induced by the U-shaped ring is suppressed, and then the typical EIT effect is realized. The transparency window and the accompanied group delay can be electrically manipulated with different Fermi energy of the graphene. By analyzing the surface distribution, the underlying tuning mechanism of this hybrid metamaterial is investigated in detail. Moreover, the transparency peak decreases slightly with the increasing strip width of the graphene layer but completely vanishes as the strip width exceeds the length of the covered U-shaped ring. The influence of the critical index of graphene quality, i.e., carrier mobility on the EIT effect, is considered. The results of this study may provide valuable guidance in designing and analyzing tunable EIT structures based on a metal-graphene hybrid structure for slow light purposes.

ELECTROMAGNETICALLY INDUCED ABSORPTION IN METAMATERIALS IN THE INFRARED FREQUENCY

In this paper, the author studies, through numerical simulation, the classical analog of the electromagnetically induced absorption/re∞ection (EIA) in a planar metamaterial structure in the near infrared spectral region. The structure is designed by transforming an electromagnetically induced transparency (EIT) structure into an EIA structure using Babinet's principle. The structure exhibits a coupling between a bright mode (a complementary ring resonator (CRR)) and a dark mode (pair of parallel straight slits) imprinted on a glass substrate. A narrow absorption window, induced in a wide transparent window, is achieved by the structure and the strength of coupling is tuned by the degree of breaking symmetry and relative displacement of the two mode elements. Electromagnetically induced transparency (EIT) is a quantum mechanical phenomenon in which an absorption is transformed into a transparency, and this is associated with strong dispersion that reduces the group velocity (1{3). This phenomena has many potential applications in signal processing, optical flltering and sensing technologies (4{7). The classical analog of the EIT has been achieved and reported by many researchers using a planar metamaterial structures that are generally composed of two metallic elements imprinted on a dielectric substrate. The two elements are metallic resonators that act either as two bright modes or a bright and dark mode. A bright mode element couples strongly with the incident excitation fleld while the dark element does not couple with the incident fleld but couples with the magnetic fleld induced by the bright element. Several EIT metamaterial structures have been employed and reported in the microwave, terahertz and optical frequency regions (8{14). In this paper, we propose a new EIT structure that achieves a more pronounced narrow transparency window sandwiched between two absorption bands compared with a similar structure proposed in (14). Also compared with (14), the structure proposed here is independent of the polarization orientation with respect to the bright mode element. Then we transform this structure into an EIA structure using Babinet's principle (15,16), where a narrow absorption/re∞ection window is sandwiched between two transparency bands. The structures proposed here may be used as obscurant particles that allow the passage of a speciflc window/windows of the electromagnetic spectrum and obscure the neighboring frequencies, for this reason the transmission spectrum will be discussed and addressed for the potential obscurant applications. Although the orientational average response of the structure is what matters, it is of good beneflt to get the behavior in a given orientation. The EIT structure is composed of a metallic ring resonator (RR) which acts as a bright mode and a pair of metallic rods that act as a dark mode. Here we overlap the RR wide antenna resonance and the narrow line width quadrupole rod resonance, which in turn produces the EIT-like efiect. The structure is transformed into an EIA structure by replacing the metallic RR and the pair of rods resonator with complementary ring resonator (CRR) and