Electromagnetically Induced Transparency Metamaterials 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.

Dielectric‐Based Electromagnetically Induced Transparency Metamaterial in the Microwave Band

AbstractAn electromagnetically induced transparency metamaterial (EITM) based on dielectric resonators is presented in this paper, which consists of a cut wire (CW) and ten dielectric columns. Destructive interference between the CW, which is a branch of the microstrip line, and the dielectric resonators causes the EIT phenomenon. The simulation results show that the dielectric‐based EITM designed can obtain a transmission peak of 0.938 at 2.17 GHz, and the two‐oscillator model is utilized to verify the effectiveness of the structure. In addition, samples of the dielectric‐based EITM are also fabricated and the effectiveness of the metamaterial is experimentally verified. The proposed metamaterial has several advantages, including high efficiency, low loss, a simple structure, and ease of manufacture, which has good prospects for application in the fields of electromagnetic switches, sensors, and nonlinear metamaterials.

Tunable Electromagnetically Induced Transparency in a Metal-Perovskite Hybrid Metamaterial and Its Sensing Performance

A metal-perovskite hybrid metamaterial, comprising a gold cross and two gold arcs, is proposed. An electromagnetically induced transparency (EIT) based on bright–bright coupling model leads to a transparent window at 0.75 THz. A multipole scattering theory indicates that the EIT effect is generated by the destructive interference between the electric dipole and the toroidal dipole. By tuning the conductivity of perovskite, the EIT effect is dynamically controlled and shows the modulation depth of 34% at 0.75 THz. Moreover, the theoretical results calculated by the two-particle model are in good agreement with the simulated results. The group delay of the proposed EIT metamaterial can also be dynamically tuned and the maximum value of group delay is 3.53 ps. The sensitivity of the proposed EIT metamaterial is 0.182 THz/RIU. Compared with other sensors, our EIT metamaterial shows excellent sensitivity in the terahertz band. Our work provides a novel method for tunable EIT metamaterials and shows a great practical application value of modulators, slow light devices, and sensors.

Terahertz Electromagnetically Induced Transparency with Electric-Field-Coupled Inductor-Capacitor Resonators on LCP Substrate

Electromagnetically induced transparency (EIT) metamaterials (MTMs) based on the bright-dark mode theory have gained great interest in slow light, sensing, and energy storage in recent years. Typically, various split ring resonators with magnetic response have been proposed as dark resonators in EIT MTMs. Here, we have employed a cut-wire (CW) and two electric-field-coupled inductor-capacitor (ELC) resonators with a pure electrical response on a liquid crystal polymer (LCP) substrate with a low loss tangent to fulfill the EIT effect in the terahertz (THz) region. The former works as the bright mode, and the latter functions as the dark mode. The EIT phenomenon results from the destructive interference between these two modes, which can be verified by numerical simulation and near field distribution. In addition, a Lorentz oscillator model was studied to quantitatively analyze the relationship between the coupling strength and the coupling distance. As a demonstration, an EIT MTM device with 5000 units was fabricated and characterized, which showed a transmission window with a peak value of 0.75 at 0.414 THz. This work may inspire new multifunctional EIT MTMs, especially the flexible applications at THz frequencies.

Polarization manipulation associated with electromagnetically induced transparency based on metamaterials

The polarization of electromagnetic waves is a key feature in modern optics and information science research fields. How to effectively control the polarization state of electromagnetic waves in electromagnetically induced transparency (EIT) is still a challenge. Herein, the EIT behavior associated with transmissive linear-to-circular (LTC) polarization conversion is theoretically proposed in the terahertz (THz) regime by employing a metamaterial. Four asymmetric H-shaped resonators are arranged in a cross-shaped arrangement on the metamaterial. It has numerically demonstrated that the electric and magnetic resonances are mutually coupled, leading to the famous EIT phenomenon. Because of the strong dispersion properties and high transmission dominated by the EIT behavior and the anisotropy of metamaterial, the transmissive LTC polarization conversion is conspicuously realized while the x- and y-polarized waves are incidents. Furthermore, two new transparent windows are located in 1.396–1.654 THz and 1.258–1.721THz, which are higher than 0.9 can be gained from 1.409 (1.323) THz to 1.467 (1.594) THz, and the relative bandwidths are 4.0% and 18.6%, respectively. Moreover, the values of the maximum group delay and group index under the x- and y-polarized waves respectively reach 504 ps, 122 ps, and 18861, 4575, displaying a slow-light effect. In addition, the LTC polarization conversion is well obtained at 1.685 THz, where the transmission coefficient highly reaches 0.605. Based on the Stokes parameters, the corresponding ellipticity η, the band of the maximum 3 dB axial ratio, and the polarization azimuth ψ respectively are 0.961, 2.1%, and −42.5°. It is worth noting that not only the thickness of the reported metamaterial is subwavelength, but also the proposed structure with low loss is great transparency for the electromagnetic waves. Surpassing conventional EIT metamaterials and polarization converters, the proposed structure synchronously equipped with those two characteristics has numerous potential applications in the integration to the existing terahertz devices, future polarization controls, and the antenna fields.

Inverse engineering of electromagnetically induced transparency in terahertz metamaterial via deep learning

In this paper, we apply the deep learning network to the inverse engineering of electromagnetically induced transparency (EIT) in terahertz metamaterial. We take three specific points of the EIT spectrum with six inputs (each specific point has two physical values with frequency and amplitude) into the deep learning model to predict and inversely design the geometrical parameters of EIT metamaterials. We propose this algorithm for the general inverse design of EIT metamaterials, and we demonstrate that our method is functional by taking one example structure. Our deep learning model exhibits a mean square error of 0.0085 in the training set and 0.014 in the test set. We believe that this finding will open a new approach for designing geometrical parameters of EIT metamaterials, and it has great potential to enlarge the applications of the THz EIT metamaterial.

Terahertz Polarization Conversion in an Electromagnetically Induced Transparency (EIT)‐Like Metamaterial

AbstractIn this paper, a unique metamaterial (MM) design incorporating both electromagnetically induced transparency (EIT) effect and polarization conversion is proposed. It consists of a cut‐wire as a bright resonator and a side coupled split‐ring resonator (SRR) as a dark resonator, on the one hand, the dark resonator can be excited by the bright resonator via the magnetic near‐field coupling, thereby contributing to a strong cross‐polarization conversion. On the other hand, the destructive interference between the sub‐radiant (dark) SRR and the super‐radiant (bright) cut‐wire results in an EIT effect. Benefiting from the destructive interference between the radiative and dark elements in the EIT MM, radiation loss is greatly suppressed and nearly perfect cross‐polarization conversion with high transmission and low‐loss is realized. In addition, the importance of symmetry is demonstrated by the phenomenon of polarization conversion and EIT effects disappearing when an identical cut‐wire is placed on the other side of the SRR. The proposed MM design provides a new way to address the loss problem in MM polarization devices. More importantly, this design principle of taking advantage of one area to solve the challenges in others may inspire new high‐performance multifunctional MM designs.

Actively tunable THz filter based on an electromagnetically induced transparency analog hybridized with a MEMS metamaterial

Electromagnetically induced transparency (EIT) analogs in classical oscillator systems have been investigated due to their potential in optical applications such as nonlinear devices and the slow-light field. Metamaterials are good candidates that utilize EIT-like effects to regulate optical light. Here, an actively reconfigurable EIT metamaterial for controlling THz waves, which consists of a movable bar and a fixed wire pair, is numerically and experimentally proposed. By changing the distance between the bar and wire pair through microelectromechanical system (MEMS) technology, the metamaterial can controllably regulate the EIT behavior to manipulate the waves around 1.832 THz, serving as a dynamic filter. A high transmittance modulation rate of 38.8% is obtained by applying a drive voltage to the MEMS actuator. The dispersion properties and polarization of the metamaterial are also investigated. Since this filter is readily miniaturized and integrated by taking advantage of MEMS, it is expected to significantly promote the development of THz-related practical applications such as THz biological detection and THz communications.

Electromagnetically induced transparency metamaterial with strong toroidal dipole response

This paper designs a planar electromagnetically induced transparency (EIT) metamaterial, which comprises an asymmetric ellipse split resonance ring (AESRR) and cut wire (CW). The proposed EIT metamaterial works in the wide range of incident angles and has polarization-sensitive at two transmission dips. The frequency of transparency peak is 10.67 GHz and maintains a high quality-factor (180.84). By calculating the multipole’s radiated power, it can be found that the toroidal dipole response is enhanced, while the electric dipole response is suppressed at the transparency peak. Interestingly, this paper firstly uses the radiated power of electric dipole to elucidate the polarization sensitivity in two minimal transmissions. Meanwhile, the coupling mechanism of the EIT metamaterial is analyzed by the two-oscillator model and equivalent circuit.

Polarization-insensitive electromagnetically-induced transparency in planar metamaterial based on coupling of ring and zigzag spiral resonators

A planar metamaterial (MM) mimicking electromagnetically-induced transparency (EIT) effect is demonstrated numerically and experimentally in the microwave region. The structure of MM is a periodicity of ring and zigzag spiral resonators, in which each resonator can be excited directly by the external field. By matching the characteristic resonance frequencies of two resonators, the coupling of two bright modes appears, leading to an EIT effect with a transparency peak at 4.86 GHz. Although the geometry of the structure is not perfectly symmetric, the proposed electromagnetically-induced transparency metamaterial (EIT-MM) is insensitive to the polarization of incoming wave. Furthermore, the EIT-MM exhibits a strong dispersion behavior, which leads to a high group index of 2785 and a group delay of 0.83 ns. Our work might be useful to potential applications using EIT-MM such as modulators, filters and sensors.

Structure-based tunable metamaterials for electromagnetically induced transparency windows in low terahertz frequency

The electromagnetically induced transparency (EIT) metamaterials with active or passive modulation have been extensively studied and applied in slow-light devices, light on-off, and light storage. However, the preparation complexity and characterization difficulties of the EIT metamaterials limit their optoelectronic applications. Here, we have employed a structure-based tunable design to fulfill the passive modulation of EIT metamaterial. We propose a simple but effective EIT structural model composed of a cutting wire and two circular split rings. Through theoretical analysis and computational simulation, it is found that the localized surface plasma and the inductive-capacitive resonance mode coincidently contribute to the EIT effect, giving rise to a narrow transparency window. Moreover, the amplitude of the transparency peak gradually decreases at the same resonance frequency with the increment of the lateral distance between the wire and split ring, while it decreases proportionally with the increment of the radius of the split ring. Interestingly, when the radius continues to increase, the asymmetry of the EIT window aggravates and the second EIT broad transparency window appears, indicating the existence of another intriguing coupling mechanism. Our work unveils a simple and practical modulation strategy for EIT-based multifunctional optical devices and shed light on its potential application on the optical devices.

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.

Staggered H-shaped metamaterial based on electromagnetically induced transparency effect and its refractive index sensing performance

In this work, we report numerical research concerning a planar electromagnetically induced transparency (EIT) terahertz metamaterial capable of exhibiting refractive index sensing with high sensitivity. The unit cell of the proposed EIT metamaterial is consisted by metal cut wires with staggered H-shaped arrangement, and can display a sharply narrow transmission transparency peak at 2.653 THz with high quality-factor (Q-factor) valued 48.3. Through analysis of the extracted surface current distributions on metallic structures, it is confirmed that the EIT-like resonance results from the destructive interference of the electric quadrupole excited by the strong radiation of electric dipole. Furthermore, the EIT-like effect shows highly sensitive response to the refractive index of the covered layer. When it covered by 3μm-thickness analyte layer, the EIT metamaterial can yield a sensitivity of 0.2695 THz/refractive index unit (RIU) and a figure of merit (FOM) of 5.39. Meanwhile, it is also found that the sensitivity S is inversely proportional to the dielectric constant of the substrate material, and effective sensing capability maintains when the coverage thickness within 15μm. The proposed EIT metamaterial design provides great potential application for refractive index sensing performance.

Dual-band polarization convertor based on electromagnetically induced transparency (EIT) effect in all-dielectric metamaterial.

In this study, electromagnetically induced transparency (EIT) effect in all-dielectric metamaterial for dual-band linear-to-circular (LTC) polarization conversion is demonstrated numerically and experimentally. The unit cell is composed of three ceramic blocks with different sizes. Due to the anisotropy of metamaterial and polarization dependence of subsequent EIT effects, transmission spectra for x- and y-polarized incident waves are realized to induce LTC polarization conversion. It is numerically demonstrated that a linearly polarized incident wave is transformed to a nearly perfect circularly polarized wave at around 6.24 and 6.38 GHz. The corresponding ellipticity and transmittivity are about 0.96, 0.6 and 0.94, 0.37, respectively. A metamaterial sample is fabricated and its transmission spectra are measured. The measured results are nearly equal to the simulated results. This LTC polarization convertor, with low loss and ultra thinness, may expand the application of EIT metamaterials, and it can be extended to terahertz up to optical bands. Such a design may find potential applications in microwave wave plates and metamaterial antennas, or other electromagnetic control devices.

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.

Realization of switchable EIT metamaterial by exploiting fluidity of liquid metal.

Novel manipulation techniques for the propagation of electromagnetic waves based on metamaterials can only be performed in narrow operating bands, and this drawback is a major challenge for developing metamaterial-based practical applications. We demonstrate that the scattering of metamaterials can be switched and that their operating band can be tuned by introducing liquid metal in the design of functional metamaterials. The proposed liquid metal-based metamaterial is composed of a copper wire pair and a tiny pipe filled with a liquid metal, namely eutectic gallium-indium. The interference of the sharp magnetic resonance of the copper wire pair and the broad dipolar mode of the liquid metal rod lead to an electromagnetically induced transparency (EIT)-like spectrum. We experimentally demonstrate that this EIT-like behavior can be switched on or off by exploiting the fluidity of the liquid metal, which is useful for multi-frequency modulators. These findings will hopefully promote the development of fluid matter-based metamaterials for extending the operating band of novel electromagnetic functions.

Comparison of Electromagnetically Induced Transparency Performance in Metallic and All-Dielectric Metamaterials

Analogs of Electromagnetically Induced Transparency (EIT) in metamaterial have undoubtedly become a research hotspot in recent years. In this paper, we summarized some of the literature on EIT published to date and compared their performance. Then, we designed two kinds of metamaterials using aluminum and silicon. Both have the similar glasses-shaped structure of a periodic lattice with one bar resonator and two split ring resonators. We analyzed and compared the EIT performance in the near infrared waveband of these two metamaterials. The metallic EIT metamaterials with large radiation loss and ohmic heat loss have a smaller Q-factor than the dielectric counterpart with less energy loss, while having a higher sensitivity toward the ambient refractive index. The Q-factor of our designed aluminum metamaterial and silicon metamaterial are 10.06 and 412.6, respectively. Their sensitivities are 1642.97 nm/RIU and 433.05 nm/RIU, respectively, which are higher than most of their counterparts in the same waveband in the other literature. For the application of slow light, the dielectric metamaterials with higher Q-factor are far superior to the metallic metamaterials in the same waveband and comparable propagation distance. The group index of the aluminum metamaterial is 42.9, and the group delay is 0.01 ps in the near infrared waveband. For the silicon metamaterial, the group index is approximately 1907.1, and the group delay is 0.89 ps within the transmission window in the near infrared waveband; these values are both higher than most counterparts in the same waveband in other literature. The EIT metamaterials that we designed have excellent performance, and to the best of our knowledge, this paper presents the first detailed comparison of EIT metamaterials made of dielectric and metal with similar structure; this paper may have certain instructive meaning for further research on metamaterial analogues of EIT in the future.

Polarization-insensitive electromagnetically induced transparency based on ultra-thin coupling planar metamaterials

Polarization-insensitive electromagnetically induced transparency (EIT) based on ultra-thin coupling planar metamaterials has been numerically demonstrated. The height (h) of ultra-thin coupling planar metamaterials can reach to 1/94 λ, which is the thinnest height so far. Such ultra-thin EIT metamaterials can reduce the cost of production. When the angles of the incident electromagnetic wave are changed, the EIT metamaterials show polarization-insensitive characteristics. When the height of the EIT metamaterials gradually increases, the group index gradually decreases and the transmission peak value and h/λ gradually increase. All of above characteristics make the ultra-thin coupling EIT have potential application in slow light devices. In addition, using the coupling of the top and below layer has proposed a way to obtain ultra-thin metamaterials in the microwave region.

Polarization-Independent Plasmon-Induced Transparency in a Symmetric Metamaterial

We propose a novel mechanism for generating electromagnetically induced transparency (EIT) in a symmetric metamaterial. The proposed metamaterial consists of double nanorod pairs, perpendicular to each other in the form of a 2-by-2 matrix. This metamaterial shows a polarization-independent EIT-like effect without breaking its symmetry. Since conventional plasmonic EIT metamaterials induce transparency in the transparent window through the coupling between the localized surface plasmon resonance modes, most of existing structures have asymmetric geometry. This limitation means the EIT-like effect can occur only under a particular linearly polarized incident light. The proposed structure, however, has a simple geometry and polarization independence, so it has the potential to be used in high sensitivity sensors and to slow light in the visible spectral range.

Mode coupling in terahertz metamaterials using sub-radiative and super-radiative resonators

We theoretically and experimentally explored the electromagnetically induced transparency (EIT) mode-coupling in terahertz (THz) metamaterial resonators, in which a dipole resonator with a super-radiative mode is coupled to an inductance-capacitance resonator with a sub-radiative mode. The interference between these two resonators depends on the relative spacing between them, resulting in a tunable transparency window in the absorption spectrum. Mode coupling was experimentally demonstrated for three spacing dependent EIT metamaterials. Transmittance of the transparency windows could be either enhanced or suppressed, producing different spectral linewidths. These spacing dependent mode-coupling metamaterials provide alternative ways to create THz devices, such as filters, absorbers, modulators, sensors, and slow-light devices.