We demonstrate a classical analogue of electromagnetically induced transparency (EIT) in a highly flexible planar terahertz metamaterial (MM) comprised of three-gap split ring resonators. The keys to achieve EIT in this system are the frequency detuning and hybridization processes between two bright modes coexisting in the same unit cell as opposed to bright-dark modes. We present experimental verification of two-bright mode coupling for a terahertz EIT-MM in the context of numerical results and theoretical analysis based on a coupled Lorentz oscillator model. In addition, a hybrid variation of the EIT-MM is proposed and implemented numerically in order to dynamically tune the EIT window by incorporating photosensitive silicon pads in the split gap region of the resonators. As a result, this hybrid MM enables the potential active optical control of a transition from the on-state (EIT mode) to the off-state (dipole mode). PACS numbers: 81.05.Xj, 78.67.PtMetamaterials (MMs) offer versatile and remarkableways to manipulate electromagnetic waves for extraordianary applications such as sub-diffraction focusing 1 , sensing 2,3 , electro-magnetic cloaking 4 , near-perfect absorption 5,6 , etc. In recent years, the concept of electromagnetically induced transparency (EIT) has attracted significant interest due to its potential applications in sensing, controllable delay lines, optical buffers, slow light devices and nonlinear effects 7-10 . EIT is a quantum phenomenon that arises from the destructive interference between different excitation pathways in a three level atomic system, making an initially opaque medium transparent to a probe laser beam 11,12 . However, practical applications of EIT are limited by severe experimental conditions such as high intensity lasers and cryogenic temperatures. The emergence of MMs as classical analogues of EIT have paved the way for the development of new applications such as sensing, THz modulators and slow light metadevices for operation at room temperature.The generation of an EIT analogue in MMs is achieved by two different approaches: (i) bright-dark mode coupling and (ii) bright-bright mode coupling. The first approach typically involves a bright mode resonator coupled to the incident wave directly which is highly radiative and exhibits a low Q-factor. By contrast, the dark mode resonator is characterized by a high Q-factor, and could not be excited by the incident wave directly. However, this dark mode is activated by the bright mode resonator via near-field coupling. In such systems, the necessary condition to achieve EIT is to couple the bright and quasidark resonances at the same resonance frequency with each possessing contrasting linewidths [13][14][15][16][17][18][19][20] .The second approach based on the frequency detuning and hybridization of two bright modes placed in a close proximity of one another has been rarely reported in literature. Such reported works for bright-bright mode coupling in the terahertz frequency regime is very limited 21-24 . In one example, the a...
Bound states in the continuum (BICs) are widely studied for their ability to confine light, produce sharp resonances for sensing applications and serve as avenues for lasing action with topological characteristics. Primarily, the formation of BICs in periodic photonic band gap structures are driven by symmetry incompatibility; structural manipulation or variation of incidence angle from incoming light. In this work, we report two modalities for driving the formation of BICs in terahertz metasurfaces. At normal incidence, we experimentally confirm polarization driven symmetry-protected BICs by the variation of the linear polarization state of light. In addition, we demonstrate through strong coupling of two radiative modes the formation of capacitively-driven Freidrich-Wintgen BICs, exotic modes which occur in off-Γ points not accessible by symmetry-protected BICs. The capacitance-mediated strong coupling at 0° polarization is verified to have a normalized coupling strength ratio of 4.17% obtained by the Jaynes-Cummings model. Furthermore, when the polarization angle is varied from 0° to 90° (0° ≤ ϕ < 90°), the Freidrich-Wintgen BIC is modulated until it is completely switched off at 90°.
High-speed electrical switching of Ge 2 Sb 2 Te 5 (GST) remains a challenging task due to the large impedance mismatch between the low-conductivity amorphous state and the highconductivity crystalline state. In this letter, we demonstrate an effective doping scheme using nickel to reduce the resistivity contrast between the amorphous and crystalline states by nearly three orders of magnitude. Most importantly, our results show that doping produces the desired electrical performance without adversely affecting the film's optical properties. The nickel doping level is approximately 2% and the lattice structure remains nearly unchanged when compared with undoped-GST. The refractive indices at amorphous and crystalline states were obtained using ellipsometry which echoes the results from XRD. The material's thermal transport properties are measured using time-domain thermoreflectance (TDTR), showing no change upon doping. The advantages of this doping system will open up new opportunities for designing electrically reconfigurable high speed optical elements in the near-infrared spectrum.
The large impedance mismatch between the highly resistive amorphous state and the highly conductive crystalline state of Ge2Sb2Te5 is an impediment for the realization of high-speed electrically switched optical devices. In this paper, we demonstrate that tungsten doping can reduce this resistivity contrast and also results in a lower amorphous state resistivity. Additionally, it lowers the contact resistance, improves the optical contrast, and extends the face-centered-cubic state up to 350 °C, with a minimal impact on thermal conductivity.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.