MMPA, Based on Electromagnetically-Induced Transparency
Interests in asymmetric metamaterials (MMs) are increasing due to the existence of fascinating phenomena, such as high-quality-factor Fano resonance, analog of electromagnetically-induced transparency (EIT), slow light and chirality. However, there have b
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MMPA, Based on Electromagnetically-Induced Transparency
Abstract Interests in asymmetric metamaterials (MMs) are increasing due to the existence of fascinating phenomena, such as high-quality-factor Fano resonance, analog of electromagnetically-induced transparency (EIT), slow light and chirality. However, there have been few researches studying the application of them to MM perfect absorbers. In this chapter, we discuss about the exploitation of EIT effect and the asymmetric resonators in achieving MM perfect absorbers. By considering the phase coupling between resonators, the EIT can be transformed into the electromagnetically-induced absorption, giving rise to an ultra-narrow and high quality-factor absorption. In addition, breaking the symmetry of resonators can induce multi-resonance that is suitable for developing multi-band or broadband absorption.
4.1
Introduction
Basically, electromagnetically-induced transparency (EIT) is a quantum phenomenon caused by the interference between different excitation sources that makes a medium transparent to the incident electromagnetic (EM) wave [1–3]. Unfortunately, the quantum EIT phenomenon requires rigorous conditions which are normally achievable only in laboratories. Recently, EIT has been mimicked and easily achieved under normal conditions, but classically by using MMs [4–15]. Therefore, real applications in various devices, such as sensors [16–18] and slow-light devices [19, 20], come to be more realistic and can be accomplished in the near future. So far, two preferential approaches have been used to produce the EIT in MMs (EIT-MMs). The first type is called as bright-bright coupling, where both resonances can be directly excited by the incident EM wave. Exploiting this coupling, Fedotov et al. demonstrated a typical EIT-MM with a high quality factor in the microwave range [21]. By breaking the symmetry of MM structure, which consists of two split-ring resonators (SRRs), anti-symmetric currents were generated and © Springer Science+Business Media Singapore 2016 Y.P. Lee et al., Metamaterials for Perfect Absorption, Springer Series in Materials Science 236, DOI 10.1007/978-981-10-0105-5_4
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4 MMPA, Based on Electromagnetically-Induced Transparency
emitted fields which interfere destructively. Consequently, the incident EM wave propagated without loss, leading to a narrow transmission region in the spectrum. The second type is referred as bright-dark coupling, where only one resonance can be excited by the EM field and the other is stimulated by the near-field coupling of the initial resonance [4, 13, 22, 23]. Therefore, the former and the latter resonances are termed bright and dark modes, respectively. Although dark modes often exhibit higher quality factor of resonance than bright modes, both bright-bright coupling and bright-dark coupling can induce a highly dispersive transparency. The EM properties of EIT-MMs were described by a common model, the so-called coupled Lorentz-oscillator model [4, 6]. However, only the absorption property was quantitativ
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