Abstract Metamaterials are a class of non-natural materials with special properties, the microstructure of which does not exist in nature. By artificially designing the structure of such materials, they can acquire electromagnetic properties that conventional materials in nature do not have. Electromagnetically induced transparency refers to the process of quantum interference effect between atomic energy levels in microscopic systems, which makes an energy-transmitting window appear in the original energy-absorbing region, simply put, a medium strongly absorbs a certain frequency of the light beam, and when another light beam is applied, the absorption of the first light beam by the medium will be greatly reduced or no longer absorbed. This phenomenon is called electromagnetically induced transparency, or EIT for short. In this paper, we combine the graphene material with the EIT structure to improve the manipulability of the EIT structure and obtain a controllable EIT structure based on the multi-mode coupled EIT extension.
Abstract Metamaterials are a class of non-natural materials with special properties, the microstructure of which does not exist in nature. By artificially designing the structure of such materials, they can acquire electromagnetic properties that conventional materials in nature do not have. Electromagnetically induced transparency refers to the process of quantum interference effect between atomic energy levels in microscopic systems, which makes an energy-transmitting window appear in the original energy-absorbing region, simply put, a medium strongly absorbs a certain frequency of the light beam, and when another light beam is applied, the absorption of the first light beam by the medium will be greatly reduced or no longer absorbed. This phenomenon is called electromagnetically induced transparency, or EIT for short. In this paper, we combine the graphene material with the EIT structure to improve the manipulability of the EIT structure and obtain a controllable EIT structure based on the multi-mode coupled EIT extension.
Abstract Electromagnetically induced transparency (EIT) stems from a quantum system, where an opaque atomic medium appears the narrow transparent state within a wide absorption area. This phenomenon can be achieved by quantum interference of pumping light and detecting light at different energy levels of transitions. In the generation process of EIT effect, in addition to transparent state, the atomic medium is usually accompanied with a strong dispersion effect, which will bright about a significant reduction of light velocity, thus realizing many important applications, such as slow light propagations. Although the EIT effect has many important applications, its application scenarios are greatly limited due to the fact that EIT realization usually requires specific and complicated conditions, such as refrigeration temperature, high intensity laser, etc. Recently, the analogue of EIT effect in metamaterial has attracted increasing attentions due to its advantages such as controllable room temperature and large operating bandwidth. Metamaterial analogue of EIT effect has become a new research focus. In this article, we review current research progresses on EIT metamaterials. Firstly, we describe the theoretical models for analyzing EIT metamaterials, including the mechanical oscillator model and the equivalent circuit model. Then, we describe the simulations, designs and experiments of passive EIT metamaterials with fixed structures and active EIT metamaterials with tunable elements. Furthermore, the applications of EIT metamaterials in the areas of slow lights, sensings, absorptions and other fields are also reviewed. Finally, the possible directions and key issues of future EIT metamaterial researches are prospected.
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(Q) 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 Q value (Q ≈ 8616) and the high transmission (T = 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.
Metamaterials, or artificial materials with optical properties not known for natural materials, have recently been used to demonstrate unusual optical phenomena, such as negative refraction, perfect lenses, subwavelength components, and electromagnetic invisibility cloaks. Most of the metamaterials designed to date are periodic structures containing a single resonating element in each unit cell, such as a split-ring resonator (SRR), a cutwire, or a slab-wire pair [1]. In this contribution, we demonstrate that a metamaterial with two coupled SRRs can exhibit an effect reminiscent of electromagnetically induced transparency (EIT), a coherent process normally observed in three-level atomic media [2]. Due to this process, a small transparency window with low absorption appears in the spectral response of the metamaterial. Simultaneously, extremely steep normal dispersion is observed in the transparency window, which is useful for slow-light applications.
Electromagnetically induced transparency is an optical phenomenon that is characterized by the elimination of the effect of a medium on a propagating beam of electromagnetic radiation in a specific frequency band. In this study, EIT was investigated at a proposed metamaterial with the dimensions milimeter and in the area of frequency of GHz. The computation results indicated that EIT with high transmission rate and high Q factor occurs in certain frequencies by breaking the symmetry in this structure. The sensitivity studies showed that the use of silver in the structure increases the quality factor so significantly that this quantity reaches 338 for gold and copper, while it reaches 677 for silver. In addition, By reducing the temperature, the transmission rate in the structure increases and reaches acceptable degree 98%. This structure can be an appropriate option for slow light usages, and it can be utilized for light amplification in microwave structures.
Abstract Based on graphene, an ultra-broadband electromagnetically induced transparency (EIT) window with dynamic tunability is realized in theory. Through altering the Fermi level of graphene that can be regulated by the external voltage, the EIT window and the EIT effect, especially the slow-wave effect, can be easily adjusted. Moreover, the bandwidth of the EIT window can be changed by the incidence angle, achieving the transformation from broadband to narrowband. At the same time, by discussing the polarization state and loss index, the characteristics of polarization insensitivity and low loss are proved. Additionally, the influences of other parameters are discussed, such as the relaxation time of graphene and coupling distance. These unique features enable the designed EIT metamaterial to be masterly applied to optical switches, optical modulators, and slow-light devices.
We theoretically investigate dynamical control of light slowing within the induced transparent window, e.g., in near-infrared frequencies, in electromagnetically induced transparent (EIT) metamaterials loaded by low-lossy graphene. Coupling with graphene enables distinctive optical responses of the "bright" and "dark" resonators in EIT metamaterials, rendering a switching of the transparent window and a modulation on light dispersion. Optical performance of the transparent window manifests continuous tuning as the graphene doping level changes. We show that the active modulation on optical properties of the transparent window enabled by low-lossy graphene is distinctive either by passively adjusting the interspacing between the building blocks of EIT metamaterials, or active tuning by high-lossy graphene. Furthermore, we report that the group refractive index can be in situ tuned dynamically over a broad range, e.g., ∼2 orders for near-infrared frequencies, together with absorption maintained at a level similar to that of the unloaded structure. Our study offers new possibilities towards chip-scale devices, such as active optical switching, filtering, and data storing.