Multiple electromagnetically induced transparency-like effects of a metal nanostructure induced by a graphene grating deposited on a gallium oxide substrate
The electromagnetically induced transparency (EIT)-like effect can be generated in the metamaterial system, but most metamaterial systems are composed of complex and elaborated components (nanostructures) that cannot be removed or replaced easily. In this paper, a graphene grating is used to interact with random metal nanostructures (i.e., individual and connecting nanostructures) to induce the EIT-like effect through two destructive interference excitation pathways. Except for the new induced EIT-like mode, the overall original optical patterns (the shape and intensity of the transmission spectrum) remain unchanged as compared with the single metal nanostructure. Furthermore, due to the optical properties of graphene, the induced EIT-like effect was blueshifted as the Fermi energy of graphene increased. By depositing the graphene grating and the metal nanostructures on a gallium oxide substrate, the EIT-like effect was redshifted as the temperature of the environment increased. Through this study, the EIT-like effect induced by the graphene grating with a random metal nanostructure system was demonstrated by using a simple geometric system; further, the mechanism is easy and can be introduced to many different metamaterial systems to generate the EIT-like effect without changing other optical properties of the original metamaterial system. As such, this opens the door to broader applications for optical communication networks.
The electromagnetically induced transparency (EIT)-like effect can be generated in the metamaterial system, but most metamaterial systems are composed of complex and elaborated components (nanostructures) that cannot be removed or replaced easily. In this paper, a graphene grating is used to interact with random metal nanostructures (i.e., individual and connecting nanostructures) to induce the EIT-like effect through two destructive interference excitation pathways. Except for the new induced EIT-like mode, the overall original optical patterns (the shape and intensity of the transmission spectrum) remain unchanged as compared with the single metal nanostructure. Furthermore, due to the optical properties of graphene, the induced EIT-like effect was blueshifted as the Fermi energy of graphene increased. By depositing the graphene grating and the metal nanostructures on a gallium oxide substrate, the EIT-like effect was redshifted as the temperature of the environment increased. Through this study, the EIT-like effect induced by the graphene grating with a random metal nanostructure system was demonstrated by using a simple geometric system; further, the mechanism is easy and can be introduced to many different metamaterial systems to generate the EIT-like effect without changing other optical properties of the original metamaterial system. As such, this opens the door to broader applications for optical communication networks.
Electromagnetically induced transparency-like (EIT-like) effect is a promising research area for applications of slow light, sensing and metamaterials. The EIT-like effect is generally formed by the destructive interference of bright-dark mode coupling and bright-bright mode coupling. There are seldom reports about EIT-like effect realized by the coupling of two dark modes. In this paper, we numerically and theoretically demonstrated that the EIT-like effect is achieved through dark-dark mode coupling of two waveguide resonances in a compound nanosystem with metal grating and multilayer structure. If we introduce |1⟩, |2⟩ and |3⟩ to represent the surface plasmon polaritons (SPPs) resonance, waveguide resonance in layer 2, and waveguide resonance in layer 4, the destructive interference occurs between two pathways of |0⟩→|1⟩→|2⟩ and |0⟩→|1⟩→|2⟩→|3⟩→|2⟩, where |0⟩ is the ground state without excitation. Our work will stimulate more studies on EIT-like effect with dark-dark mode coupling in other systems.
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.
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.
We propose a graphene metamaterial consisting of several layers of longitudinally separated graphene nanoribbon array embedded into gain-assisted medium, demonstrating electromagnetically induced transparency-like spectra. Combined with finite-difference time-domain simulations, the transfer matrix method and temporal coupled-mode theory are adopted to quantitatively describe its transmission characteristics. These transmission characteristics can be tuned by altering the gain level in medium layer and the Fermi energy level in graphene. Additionally, it is the incorporation between gain medium and graphene nanoribbons with optimized geometrical parameters and Fermi energy level that the destructive interference between high order graphene plasmonic modes can be obtained, suggesting drastic phase transition with giant group delay and ultra-high group index up to 180 ps and 104, respectively. Our results can achieve efficient slow light effects for better optical buffers and other nonlinear applications.
We investigate the plasmonic analog of electromagnetically induced transparency (EIT) using two adjacent graphene-based Fabry-Perot (F-P) resonators side coupling to a nanoribbon waveguide. By the coupling mode theory in time and F-P resonant model, the destructive interference from the coupling of the two F-P resonators results in the EIT-like optical response. The induced peak and width of the transparency window can be dynamically manipulated by varying the coupling distance of the two resonators, and the transparent window is easily shifted by tuning the resonator length or the chemical potential of the graphene nanoribbon. In order to verify the characteristics of slow light, the group index profile is analyzed at different coupling distances. The proposed graphene-based EIT-like system could open up new opportunities for potential applications in plasmonic slow light and optical information buffering devices.
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.