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.
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.
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.
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.
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.
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.
In this paper, an electromagnetically induced transparency metamaterial simultaneously coupled with the incident electric and magnetic fields is designed and presented theoretically, whereas its reconfigurability, slow-wave effect, low-loss, and polarization insensitivity are analyzed and discussed principally. Based on the tunable solid-state plasma, there is a transmission peak with a 92.06% transmission at 0.544 THz in State 1 and a transmission peak with a 92.84% transmission at 0.7535 THz in State 2, thus achieving a frequency shift of 0.2085 THz. The maximum group delay, group index, and delay-bandwidth product in State 1 or 2, which are 723.7 ps or 494.7 ps, 1024.1 or 700.1, and 48.5 or 36.1, respectively, and the excellent slow-wave effects are discussed. In addition, the low-loss and polarization insensitivity are realized by rotating the split-ring resonators 180° and twisting the planar structure 90°. Considering the unique features of the designed metamaterial, it can be extensively applied to slow-light devices, communication, sensors, and nonlinear devices.