전자기파 세기 조절이 가능한 유도 투과 현상을 보이는 메타물질 연구

Abstract

Over the past years, the classical analog of the electromagnetically-induced transparency (EIT) phenomenon (hereafter, I refer to it an EIT-like phenomena), has attracted great research attention due to its many applications in slow-light phenomenon, low-loss metamaterials (MMs), nonlinear enhancements, quantum optics, and sensors. The EIT is a phenomenon generally induced by a laser, which is based on the destructive interference between atomic energy levels. This phenomenon requires special conditions such as a cryogenic laser. In recent years, however, the use of MMs does not need special equipments, and makes it possible for the EIT-like effect to be implemented above the room temperature. The phenomena are obtained by a broken structural symmetry or by a near-field subwavelength-scale coupling. The latter origin of EIT can be interpreted by the near-field coupling between a radiative bright resonator that couples strongly with the incident light, and a dark resonator that couples weakly with light. However, the EIT-like behavior also occurs without the dark-mode excitation, which is described by the interference between bright modes. In addition, the EIT-like effect, based on the phase coupling, can be switched by adjusting the incident angle. First of all, I propose a simple scheme based on the phase coupling between two different snake-shape resonators (SRs) to construct the EIT-like spectral response at microwave frequencies. It was found that two SRs in the MM were activated in bright modes, and the coupling between two bright modes induced the EIT-like effect. Furthermore, I confirmed that the EIT-like feature could be controlled by adjusting the geometric parameters of MM. The main advantage of this approach is that the bright-mode coupling strength is entirely improved by the bar-length symmetry. I have also shown that a high group index can be achieved because the coupling between the two bright modes leads to a high-dispersion transparency. I also investigated the EIT-like effect at microwave frequencies using the structure of cut-wire resonator/ring resonator. This induced transmission caused an asymmetrical transmission at 5.69 GHz due to the trap-and-radiation mode that occurs in the transmission dip. I have successfully implemented the EIT-like effect in the bilayer structure through the bright-bright mode coupling. This MM exhibited the dependence on the incident angle. I also used a flexible substrate to elucidate the bending effect and confirmed that the transmission was manipulated by the bending parameters, which resulted in an adjustable EIT-like effect. In particular, the additional transmission peak and the broadband transmission were observed in the bent state. In this way, the transmission switching and the wide-band transmission were controlled by the bending parameters of structure, depending on the incident angle. My approach provides significant advances in tuning the electromagnetic responses, which are useful for the potential switching sensors.