EIT-like Metamaterial Research Articles

Electrically switchable metamaterial analogue to electromagnetically induced transparency

In this paper, we propose an active electromagnetically induced transparency-like (EIT-like) metamaterial to investigate the electrically switchable behaviors. The EIT-like metamaterial is constructed by a “bright” comb-line resonator side-coupled with a “dark” split-ring resonator. The “bright” and “dark” resonators are individually or simultaneously soldered with PIN diodes. The diodes are connected with DC voltage sources through conducting wires. By adjusting the bias voltage within the range of 0.0–1.2 V, the resistance of PIN diode can be changed from 9000 to 1 Ω, thereby dynamically modulating the EIT-like spectrum. Both simulation and experiment results indicate that this active configuration can generate remarkable multi-band amplitude modulations on the EIT-like spectrum, and a significant modulation depth of up to 18.3 dB was achieved on the tested transmission through the metamaterial. Moreover, the transformation of transparency-to-absorption and slow light on-to-off switching actions are also obtained via electric biasing the proposed sample. These findings resulted from the EIT-like mechanism, which may promote the development of actively controlled photonic devices.

A high Q-factor metamaterial sensor based on electromagnetically induced transparency-like

This paper proposes an electromagnetically induced transparency-like (EIT-like) metamaterial with a high-quality factor (143.54), which is composed of a square ring resonator (SRR) and a cross-shaped resonator (CR). The designed metamaterial generates a sharp transparency peak at 15.79 GHz. The electric field distributions reveal that appearance of the transparency window results from the coupling between bright mode and dark mode. Moreover, analysis of the surface current distributions verifies that the EIT-like effect is induced by the destructive interference of the electric dipoles . Furthermore, the metamaterial is equated to a circuit model, which provides a better fit to the simulated transmission spectrum. These theories fully explain the generation mechanism of the EIT-like phenomenon. In addition, the EIT-like metamaterial is able to detect the dielectric constant of the target analyte (glucose solution), and the sensing performance is evaluated. The results demonstrate that the sensitivity (S) is 4.80 GHz R−1IU−1 and the figure of merit (FOM) reaches 43.71. The proposed EIT-like metamaterial shows prominent sensing abilities, consequently it has potential applications in environmental monitoring, biological and chemical measurements.

Electromagnetically induced transparency based on spoof localized surface plasmons

A pair of resonators are used to realize multiple electromagnetically induced transparency-like (EIT-like) transmission peaks operating in the microwave band, with the bright and dark modes being symmetric double-ellipsoids and spoof localized surface plasmons. The simulation and test results reveal that the EIT-like metamaterial may generate three transparent EIT-like transmission peaks in the 9~12 GHz frequency range. Following that, we propose a plasmonically induced transparency refractive index sensor that operates in the IR range. The group delay in this sensor has broad applicability in diverse surface sensing based on EIT-like metamaterials.

Strong coupling of plasmonic bright and dark modes with two eigenmodes of a photonic crystal cavity.

Dark modes represent a class of forbidden transitions or transitions with weak dipole moments between energy states. Due to their low transition probability, it is difficult to realize their interaction with light, let alone achieve the strong interaction of the modes with the photons in a cavity. However, by mutual coupling with a bright mode, the strong interaction of dark modes with photons is possible. This type of mediated interaction is widely investigated in the metamaterials community and is known under the term electromagnetically induced transparency (EIT). Here, we report strong coupling between a plasmonic dark mode of an EIT-like metamaterial with the photons of a 1D photonic crystal cavity in the terahertz frequency range. The coupling between the dark mode and the cavity photons is mediated by a plasmonic bright mode, which is proven by the observation of a frequency splitting which depends on the strength of the inductive interaction between the plasmon bright and dark modes of the EIT-like metamaterial. In addition, since the plasmonic dark mode strongly couples with the cavity dark mode, we observes four polariton modes. The frequency splitting by interaction of the four modes (plasmonic bright and dark mode and the two eigenmodes of the photonic cavity) can be reproduced in the framework of a model of four coupled harmonic oscillators.

Analog of electromagnetically induced transparency from electric dipole and quadrupole excitation with a Reuleaux triangle split-ring resonator

We simulate, measure, and analyze an electromagnetically induced transparency-like (EIT-like) metamaterial with a unit cell composed of a Reuleaux triangle split-ring resonator (RT-SRR) and a Y-type strip (YS). The transparency peak of the EIT-like metamaterial is located at 12.54 GHz, and the transmission coefficient is 91%. The electric field distributions indicate that the RT-SRR plays the role of the bright mode, and the YS plays the role of the dark mode. The coupling between the bright and dark modes leads to the EIT-like phenomenon. The surface current distributions and the calculated results for the radiated power of the electric multipoles are used to analyze the physical mechanism behind the transparency peak, which can be understood in terms of the electric dipole interacting with the electric quadrupole. As the polarization angle increases, the transmission coefficient of the transparency peak decreases, indicating polarization sensitivity. When the YS is rotated around the center and the RT-SRR is kept fixed, the EIT-like phenomenon appears and disappears. Therefore, the proposed metamaterial has potential applications in detectors and switches. The experimental results are well-matched with the simulation results.

Surface-enhanced Raman scattering from an electromagnetic induced transparency substrate for the determination of hepatocellular carcinoma.

Surface-enhanced Raman scattering (SERS) is a powerful analytical method that is especially suitable for the detection of protein molecules. Detection sensitivity of SERS is directly related to the enhancement factor of the substrate, which is dependent on the strength of a local surface electric field generated by surface plasmonic resonance from substrate. In this study, an electromagnetic induced transparency like (EIT-like) metamaterial was used as the SERS substrate. The corresponding plasmonic resonance structure not only produces stronger optical near field but also reduces the spectral line broadening due to radiation damping. This is very beneficial for SERS process, which is strongly dependent on electric field intensity, to improve the sensitivity of SERS detection. Compared with the single resonance mode substrate, the enhancement factor for SERS with the double-mode substrate was increased by an order of magnitude. The obtained EIT-like substrate was used as a SERS-active substrate to detect Lens culinaris agglutinin (LCA)-reactive fraction of AFP (AFP-L3), a hepatocellular carcinoma (HCC)-specific maker. Experimental results are in good agreement with the clinical diagnosis, which demonstrates the potential application of metamaterials in the SERS-based diagnosis and biosensing.

Dynamically Tunable Electromagnetically Induced Transparency-Like Effect in Terahertz Metamaterial Based on Graphene Cross Structures

A simple and multi-layer metamaterial made of graphene to realize excellent manipulation of EIT-like effect is proposed. The unit cell consists of four layers: Substrate 1, Cross 1, Substrate 2 and Cross 2, which can obtain tunable EIT-like effect by adjusting the Fermi level of graphene. The surface current distributions of four different views clearly explain the underlying physical mechanism. A three-level Λ-type system is employed to describe the coupling process between Cross 1 and 2. The calculated transmission spectra based on two-particle model have great agreement with the simulated transmission spectra. In addition, the effects of geometrical parameters on EIT-like effect are discussed and wideband EIT-like effect with high transmission can be obtained by adjusting the lengths of Cross 1 and 2. Also, the polarization-insensitive character of EIT-like metamaterial is confirmed by the transmission spectra under different polarization angles. The maximum of group delay (25.48 ps) is far greater than the group delay of previously reported EIT-like metamaterials. Our study provides a novel way for the development of slow-light devices and modulators.

Research on analogue of electromagnetically induced transparency effect based on asymmetric structure all-dielectric metamaterial

The electromagnetically induced transparency (EIT), which is a result of destructive interference between different excitation paths in a three-energy-level atomic medium, makes opaque probe light transparent over a range of frequencies. As this EIT effect is usually accompanied with strong dispersion, it has potential applications such as slow light propagation, optical buffering, nonlinear optics, optical sensing, etc. However, for conventional quantum EIT effect which requires stable gas lasers and low temperature environment, the implementation of EIT in chip-scale applications is severely hampered by the scathing experimental requirements. Recently, the EIT-like effect in metamaterials, which are constructed by designing the artificial subwavelength functional elements and arranging the spatial sequences, attracts tremendous attention because of its advantages, such as room temperature manipulability, large bandwidth, and small sizes. In addition, the high-quality factor(<i>Q</i>) value obtained by EIT-like effect has great significance in designing the metamaterial-based devices. In this paper, we design an EIT-like metamaterial with such a structure. The unit cell of the proposed metamaterial is constructed by two asymmetric silicon blocks embedded on a silicon dioxide substrate. Meanwhile, we analyze its optical properties and EIT-like effects by using three-dimension (3D) FDTD method. Based on the coupled Lorentz model, the EIT-like effect of the designed metamaterial is investigated. Then, by employing the electric field distribution on the surface of the metamaterial, and combining with the three-level atomic system, the mechanism of the EIT-like effect is analyzed in detail. We find that the EIT-like effect in the proposed metamaterial has high <i>Q</i> value (<i>Q</i> ≈ 8616) and the high transmission (<i>T</i> = 96%). By changing the length of the silicon block to destroy the asymmetry of the metamaterial structure, an active tuning EIT-like effect is realized. Furthermore, the metamaterial structure has the advantages of low loss, easy preparation, and active-controllability. This study represents an innovative approach to designing the EIT-like metamaterial, which is expected to be useful for designing active tunable slow-light devices and highly sensitive optical sensors.

A theoretical proposal for the tunable electromagnetically induced transparency with superior properties based on the solid-state plasma

Based on the solid-state plasma (SSP), a metamaterial analog of electromagnetically induced transparency (EIT-like) with superior properties is theoretically proposed, including tunability, a large group index, and delay-bandwidth product (DBP), polarization independence, and low-loss. By exciting different specific parts of the SSP, the EIT-like peak frequency switches from 8.518 GHz with 90.92% transmissivity in state I to 11.26 GHz with 93.76% transmissivity in state II, i.e. a 2.742 GHz shift. Meanwhile, the metamaterial has 0.679 ns or 1.314 ns group delay, 453 or 876.1 group index, and 0.422 or 1 DBP in state I or III. Additionally, the transmission curves are the same under the circular polarization waves or linear polarization waves at any angle. The low-loss feature is likewise demonstrated. Therefore, the EIT-like metamaterial has superior properties for related applications, especially in slow light, sensing, switching, and communication.

Dynamically tunable dual-band electromagnetically induced transparency-like in terahertz metamaterial

A dynamically tunable dual-band electromagnetically induced transparency-like (EIT-like) metamaterial in terahertz region is proposed. The EIT-like metamaterial consists of a left metal strip (LMS), a right metal strip (RMS) and an asymmetric two-gap rectangular split resonator (ARSR) based on vanadium dioxide film (VO2). Two transparency windows can be observed and the maxima of transmission amplitude are 92.5% and 90.5%, respectively. The surface current distributions can well explain the physical mechanism of the dual-band EIT-like effect. In addition, the influence of structure parameters on dual-band EIT-like effect is also be discussed. The four-level tripod (FLT) system, which is make up of a Λ-system and a control state, can validate the numerical results and explain the mechanism of the dual-band EIT-like effect better. The theoretically fitted transmission spectra are in good agreement with the simulated spectra for different conductivity of VO2. By tuning the conductivity of VO2, dual-band EIT-like effect and slow light effect can be dynamically controlled without the shift of frequency. In addition, the EIT-like metamaterial with low loss can be proved by the effective medium theory. Therefore, our dual-band EIT-like metamaterial is very promising for making multiple-band terahertz functional and slow light devices.

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.

Planar metamaterial analogue of electromagnetically induced transparency for a miniature refractive index sensor

A planar metamaterial of analogue of Electromagnetically Induced Transparency (EIT-like) is theoretically and experimentally investigated. The EIT-like metamaterial unit cell, whose electrical size is only 0.2λ0, consists of a split ring resonator (SRR) and a folded-line pair resonator (FLPR). For the TM wave incidence, a sharp transmitted peak with high quality factor can be observed. The EIT-like metamaterial is fabricated and measured. Good agreement is obtained between the simulation and measurement results. A miniature refractive index sensor based on the proposed metamaterial is simulated and exhibits high sensitivity and Figure of Merit (FOM).

A terahertz metamaterial based on electromagnetically induced transparency effect and its sensing performance

Abstract We present a terahertz metamaterial based on electromagnetically induced transparency (EIT), of which the unit cell is made up of the coupled “bright” circular split-ring resonator (CSRR) and “dark” square split-ring resonator (SSRR) with practically equal resonance frequency. With the strong coupling of bright mode and dark mode, a sharply narrow transparency peak is observed at terahertz region. Then, the influences of the physical parameters on EIT-like effect are simulated and analyzed by the electromagnetic simulation software CST. Furthermore it is numerically demonstrated that the EIT-like metamaterial is a promising candidate for sensing with refractive index sensitivity of 96.2 GHz/RIU, which means that the transmission peak of the sensor shifts 96.2 GHz per unit change of refractive index of the surrounding medium. Finally, transmission responses of the sensor based on EIT-like effect are investigated by terahertz time-domain spectroscopy, showing a good perception capability consistent with the simulation results. With the property of high refractive index sensitivity, the metamaterial can play an important role in terahertz sensing and detection technology.

Broadband tunable electromagnetically induced transparency analogue metamaterials based on graphene in terahertz band

Most of the actively controlled electromagnetically induced transparency analogue (EIT-like) metamaterials were implemented with narrowband modulations. In this paper, a broadband tunable EIT-like metamaterial based on graphene in the terahertz band is presented. It consists of a cut wire as the bright resonator and two couples of H-shaped resonators in mirror symmetry as the dark resonators. A broadband tunable property of transmission amplitude is realized by changing the Fermi level of graphene. Furthermore, the geometries of the metamaterial structure are optimized to achieve the ideal curve through the simulation. Such EIT-like metamaterials proposed here are promising candidates for designing active wide-band slow-light devices, wide-band terahertz active filters, and wide-band terahertz modulators.

A polarization independent electromagnetically induced transparency-like metamaterial with large group delay and delay-bandwidth product

In this study, a classical analogue of electromagnetically induced transparency (EIT) that is completely independent of the polarization direction of the incident waves is numerically and experimentally demonstrated. The unit cell of the employed planar symmetric metamaterial structure consists of one square ring resonator and four split ring resonators (SRRs). Two different designs are implemented in order to achieve a narrow-band and wide-band EIT-like response. In the unit cell design, a square ring resonator is shown to serve as a bright resonator, whereas the SRRs behave as a quasi-dark resonator, for the narrow-band (0.55 GHz full-width at half-maximum bandwidth around 5 GHz) and wide-band (1.35 GHz full-width at half-maximum bandwidth around 5.7 GHz) EIT-like metamaterials. The observed EIT-like transmission phenomenon is theoretically explained by a coupled-oscillator model. Within the transmission window, steep changes of the phase result in high group delays and the delay-bandwidth products reach 0.45 for the wide-band EIT-like metamaterial. Furthermore, it has been demonstrated that the bandwidth and group delay of the EIT-like band can be controlled by changing the incidence angle of electromagnetic waves. These features enable the proposed metamaterials to achieve potential applications in filtering, switching, data storing, and sensing.

Tunable grapheme amplitude based broadband electromagnetically-induced-transparency-like metamaterial

Metamaterials, composed of subwavelength resonators, have extraordinary electromagnetic properties which rely on the sizes and shapes of the resonance structures rather than their compositions. Recently, achieving electromagnetically induced transparency (EIT) in metamaterial system, also called electromagnetically-induced-transparency-like (EIT-like) analogue, has attracted intense attention. Many studies of EIT-like metamaterials have been reported at microwave, terahertz, and optical frequencies numerically and experimentally. However, most of the EIT-like metamaterials can only control the transmission window by changing the structure size of the metamaterial which restricts the practical applications of the EIT-like metamaterial. Therefore, a broadband tunable EIT-like metamaterials based on graphene in terahertz band is presented in this paper, which consists of a cut-wire as the bright resonator and two couples of H-shaped resonators in mirror symmetry as the dark resonators. The transmissivity of the metamaterial structure is simulated by the software CST Microwave Studio. And the simulation results show that the transmission window of this structure is in a frequency range from 1.05 THz to 1.46 THz, which is attributed to the interference between the plasmon resonance of wire resonators and the LC resonance of H-shaped resonators. In addition, increasing the number of dark mode resonators leads to an increase in transmission window bandwidth. Furthermore, a broadband tunable property of transmission amplitude is realized by changing the Fermi level of graphene. When the graphene Fermi level gradually increases from 0 eV to 1.5 eV, the transmission amplitude of the transmission window gradually decreases from 87% to 20%, which realizes the broadband tunability of transmission window. At the same time, the distribution of the electric field at a central frequency of 1.26 THz is simulated to analyse the transmission mechanism. Finally, the EIT metamaterial samples are prepared and the transmission curves of the samples are tested by terahertz time-domain spectroscopy. Such an EIT-like metamaterial not only realizes the broadband EIT property but also realizes the characteristic of the tunable amplitude of the transmission window, which has potential applications in designing the active slow-light devices, terahertz active filtering and terahertz modulator.

Tailoring polarization of electromagnetically induced transparency based on non-centrosymmetric metasurfaces

In this manuscript, tailoring polarization of analogy of electromagnetically induced transparency (EIT-like) based on non-centrosymmetric metasurfaces has been numerically and experimentally demonstrated. The EIT-like metamaterial is composed of a rectangle ring and two cut wires. The rectangle ring and the cut wire are chosen as the bright mode and the quasi-dark mode, respectively. Under the incident electromagnetic wave excitation, a polarization insensitive EIT-like transmission window can be observed at specific polarization angles. Within the transmission window, the phase steeply changes, which leads to the large group index. Tailoring polarization of EIT-like metamaterial with large group index at specific polarization angles may have potential application in slow light devices.

Tunable electromagnetically induced transparency from a superconducting terahertz metamaterial

We demonstrate in this paper the tunable electromagnetically induced transparency (EIT) made from a superconducting (SC) niobium nitride (NbN) film induced by an intense terahertz (THz) field. As the variation of the incident THz field alters the intrinsic ohmic loss of the SC NbN film, the field-dependent transmittance is observed. To elaborate the role of the bright and dark modes, a hybrid coupling model is introduced to fit the experimental transmission spectra and extract the characteristic parameters of each mode. It is shown that the resonator for the bright mode is altered greatly due to strong direct coupling to the incident intense THz field, whereas the dark mode resonator has little interaction with the incident THz field via a weak near-filed coupling to the bright-mode resonator. This implies that we can partially control a mode or a part of metamaterial by introducing the intense THz field, which offers an effective manner to selectively control the electromagnetic property of the metamaterial. This work may bring many potential applications for the tunable EIT-like metamaterial.

Analog electromagnetically induced transparency for circularly polarized wave using three-dimensional chiral metamaterials.

In this paper, we theoretically and experimentally demonstrate a three-dimensional metamaterial that can motivate electromagnetic induced transparency (EIT) by using circular polarized wave as stimulations. The unit cell consists of a pair of metallic strips printed on both sides of the printed circuit board (PCB), where a conductive cylinder junction is used to connect the metal strips by drilling a hole inside the substrate. When a right circularly polarized wave is incident, destructive interference is excited between meta-atoms of the 3D structure, the transmission spectrum demonstrates a sharp transparency window. A coupled oscillator model and an electrical equivalent circuit model are applied to quantitatively and qualitatively analyze the coupling mechanism in the EIT-like metamaterial. Analysis in detail shows the EIT window's amplitude and frequency are modulated by changing the degree of symmetry breaking. The proposed metamaterial may achieve potential applications in developing chiral slow light devices.

Tunable Transmission-Line Metamaterials Mimicking Electromagnetically Induced Transparency

Tunable transmission-line (TL) metamaterials mimicking electromagnetically induced transparency (EIT) have been studied. Firstly, two types of tunable TL EIT-like metamaterial, based on the double split-ring resonator (DSRR) and single split-ring resonator (SSRR), were fabricated and their transmission properties carefully compared. The results showed that the transmittance maximum was almost invariable with shift of the transparency window for the tunable DSRR-based TL EIT-like metamaterial, but for the tunable SSRR-based TL EIT-like metamaterial, the transmittance maximum gradually diminished with shift of the transparency window toward the center of the absorption band. Moreover, the reason for these different transmission properties was explored, revealing that the reduction of the transmittance maximum of the transparency window for the tunable SSRR-based TL EIT-like metamaterial is mainly due to energy loss caused by the resistance of the loaded varactor diodes.