Abstract Electromagnetically induced transparency (EIT), characterised by strong dispersion and a narrow transparency window, holds great potential for developing slow light devices in communications. However, in the GHz regime, achieving a simple EIT structure with high group delay and tunability remains challenging. This paper reports an asymmetric plasma waveguide capable of producing EIT analogues, as demonstrated by finite element method simulations and a two-oscillator model (TOM). The asymmetric plasma waveguide consists of a plasma–dielectric–plasma structure with non-uniformly sized teeth. The results indicate that the EIT analogue is attributed to detuning induced by the difference in tooth size. Specifically, the detuning creates an interference band, which governs the interaction between two bright modes (i.e. resonance modes in the two teeth). The TOM aligns excellently with numerical simulations. Notably, unlike previous works, the TOM is also analysed from a fundamental energy perspective. The operating frequency can be easily tuned by adjusting plasma frequencies. The maximum group delay can reach 8.5 ns. Our study advances the understanding of the EIT phenomenon in slot waveguides with asymmetric resonators and may offer a new platform for developing actively tunable microwave slow-light devices.
Abstract Electromagnetically induced transparency (EIT), characterised by strong dispersion and a narrow transparency window, holds great potential for developing slow light devices in communications. However, in the GHz regime, achieving a simple EIT structure with high group delay and tunability remains challenging. This paper reports an asymmetric plasma waveguide capable of producing EIT analogues, as demonstrated by finite element method simulations and a two-oscillator model (TOM). The asymmetric plasma waveguide consists of a plasma–dielectric–plasma structure with non-uniformly sized teeth. The results indicate that the EIT analogue is attributed to detuning induced by the difference in tooth size. Specifically, the detuning creates an interference band, which governs the interaction between two bright modes (i.e. resonance modes in the two teeth). The TOM aligns excellently with numerical simulations. Notably, unlike previous works, the TOM is also analysed from a fundamental energy perspective. The operating frequency can be easily tuned by adjusting plasma frequencies. The maximum group delay can reach 8.5 ns. Our study advances the understanding of the EIT phenomenon in slot waveguides with asymmetric resonators and may offer a new platform for developing actively tunable microwave slow-light devices.
Abstract 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.
The tunable wideband slow-light based on plasmonic analogue of electromagnetically induced transparency (EIT) in bright-dark-dark mode waveguide systems is investigated in this letter. A three-oscillator model is established to characterize optical responses and slow-light effects in the waveguide systems. The main dependent factors of slow-light effects based on plasmonic analogue of EIT, namely, the cavity-cavity separation and media environment of resonators, are numerically and theoretically discussed in this letter. We find that both the group index and the bandwidth of the slow light in the bright-dark-dark waveguide structures show better performance than those in the normal bright-dark ones. These results suggest that the contradiction between the large group index and the wideband slow light in the bright-dark mode waveguide system can be weakened. At the same time, tunable wideband slow-light effects are also achieved. Our researches may have an application in optical slow-light devices.
Based on solid-state plasma (SSP), an electromagnetically induced transparent (EIT) metamaterial is proposed. Simulations illustrate that the given metamaterial has the characteristics of adjustment, polarization insensitivity, and low dissipation. Because SSP can be coordinated in state I, the ideal transmittance frequency band can cover 8.0335–9.02531 GHz (a narrow band). If the regulatory status is switched to state II, that frequency region will alter to 9.7982–12.9275 GHz (a broad band). As SSP can be switched back and forth between states I and II under actual demand, the tailored EIT metamaterial can be achieved. The maximum group delays of state I and state II are 0.9437 ns and 0.5546 ns, respectively, and the maximum group refractive indices are 526.60 and 300.45, respectively, which conforms to its slow light characteristic. Regardless of how the polarization angle changes, the two transmission valleys of state I are at 7.9172 GHz and 10.4446 GHz, and the transmission peak is situated at 8.2091 GHz, and those values of state II are 9.3777 GHz, 13.9600 GHz, and 10.1920 GHz, respectively, which proves that the obtained EIT is polarization independent and also has a low dissipation factor. Such an EIT metamaterial has excellent properties in sensing, communication, slow light, and other fields.
Slow light technique has significant potential applications in many contemporary photonic device developments for integrated all-optical circuit, such as buffers, regenerators, switches and interferometers. In this paper, we present an efficient coupling mechanism of an electromagnetically induced transparency like (EIT-like) effect in an all-dielectric nano-metamaterial. This EIT-like effect is generated by destructive interference between a radiative Fabry-Perot (FP) mode and a dark waveguide (WG) mode, which is based on a combined structure of a dielectric grating and multilayer films. The dark WG mode is excited by guided mode of dielectric grating instead of radiative FP mode. In analogy to the molecular transition process, the FP mode, guided mode and WG mode are denoted by excited states of |1〉, |2〉 and |3〉. The two coupling pathways of the EIT-like effect in our metamaterial are |0〉 → |1〉 and |0〉 → |2〉 → |3〉 → |1〉, where |0〉 is the ground state. The simulated resonant wavelength of WG mode is consistent with theoretical result. We further confirm this EIT-like effect through a two-oscillator coupling analysis. We achieve a group refractive index of 913.6 by adjusting these two modes coupling of the EIT-like effect, which is useful for developing slow light device. This work provides a valuable solution to realize electromagnetically induced transparency in all-dielectric nanomaterial.
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.