Teun-Teun Kim

Metamaterials with classical analogues of electromagnetically induced transparency open new avenues in photonics for realizing smaller, more efficient slow light devices without quantum approaches. However, most of the metamaterial-based slow light devices are passive, which limits their practical applications. Here, by combining diatomic metamaterials with a gated single-layer graphene, we demonstrate that the group delay of terahertz light can be dynamically controlled under a small gate volta

Active control of polarization states of electromagnetic waves is highly desirable because of its diverse applications in information processing, telecommunications, and spectroscopy. However, despite the recent advances using artificial materials, most active polarization control schemes require optical stimuli necessitating complex optical setups. We experimentally demonstrate an alternative-direct electrical tuning of the polarization state of terahertz waves. Combining a chiral metamaterial

Abstract Exceptional points (EPs), also known as non‐Hermitian degeneracies, have been observed in parity‐time symmetric metasurfaces as parity‐time symmetry breaking points. However, the parity‐time symmetry condition puts constraints on the metasurface parameter space, excluding the full examination of unique properties that stem from an EP. Here, we thus design a general non‐Hermitian metasurface with a unit cell containing two orthogonally oriented split‐ring resonators (SRRs) with overlappi

Non-Hermitian degeneracies, also known as exceptional points (EPs), have been the focus of much attention due to their singular eigenvalue surface structure. Nevertheless, as pertaining to a non-Hermitian metasurface platform, the reduction of an eigenspace dimensionality at the EP has been investigated mostly in a passive repetitive manner. Here, we propose an electrical and spectral way of resolving chiral EPs and clarifying the consequences of chiral mode collapsing of a non-Hermitian gated g

A two-dimensional photonic crystal asymmetric Mach-Zehnder filter (AMZF) based on the self-collimation effect is studied by numerical simulations and experimental measurements in microwave region. A self-collimated beam is effectively controlled by employing line-defect beam splitters and mirrors. The measured transmission spectra at the two output ports of the AMZF sinusoidally oscillate with the phase difference of pi in the self-collimation frequency range. Position of the transmission peaks

Anisotropic materials with chirality or birefringence can be used to manipulate the polarization states of electromagnetic waves. However, the comparatively low anisotropy of natural materials hinders the miniaturization of optical components and devices at terahertz frequencies. In this study, we experimentally demonstrate that the relative phase retardation of a THz wave can be electrically controlled by integrating patterned mono- and bilayer graphene onto an otherwise isotropic metasurface.

Progressive Alzheimer's disease is correlated with the oligomerization and fibrillization of the amyloid beta (Aβ) protein. We identify the fibrillization stage of the Aβ protein through label-free near-field THz conductance measurements in a buffer solution. Frequency-dependent conductance was obtained by measuring the differential transmittance of the time-domain spectroscopy in the THz range with a molar concentration of monomer, oligomer, and fibrillar forms of the Aβ protein. Conductance at

The polarization of light can be rotated in materials with an absence of molecular or structural mirror symmetry. While this rotating ability is normally rather weak in naturally occurring chiral materials, artificial chiral metamaterials have demonstrated extraordinary rotational ability by engineering intra-molecular couplings. However, while in general, chiral metamaterials can exhibit strong rotatory power at or around resonances, they convert linearly polarized waves into elliptically polar

Subwavelength terahertz (THz) imaging methods are highly desirable for biochemical sensing as well as materials sciences, yet sensitive spectral fingerprinting is still challenging in the frequency domain due to weak light-matter interactions. Here, we demonstrate subwavelength THz resonance imaging (STRING) that overcomes this limitation to achieve ultrasensitive molecular fingerprinting. STRING combines individual ring-shaped coaxial single resonators with near-field spectroscopy, yielding con

We experimentally confirm that the antireflection structures effectively minimize unnecessary reflections of self-collimated microwave beams at the interfaces of a two-dimensional photonic crystal, which is composed of cylindrical alumina rods. Optimized design parameters for the antireflection structures are obtained from the one-dimensional antireflection coating theory and the finite-difference time-domain simulations. Measured transmittance through the photonic crystal samples with and witho

We propose a ring-type Fabry-Pérot filter (RFPF) based on the self-collimation effect in photonic crystals. The transmission characteristics of self-collimated beams are experimentally measured in this structure and compared with the results obtained with the simulations. Bending and splitting mechanisms of light beams by the line defects introduced into the RFPF are used to control the self-collimated beam. Antireflection structures are also employed at the input and output photonic crystal int

The color change of photonic crystals (PCs) has been widely studied due to their beauty and anti-counterfeiting applications. Herein, we demonstrated security codes based on chiral PCs that cannot be easily mimicked and are quite different from the conventional technology used currently. The chiral PCs can be made by self-assembly and the structural colors change based on the polarization of the light in the transmission mode. These color changes are easily detected in real-time and are useful i

The prime example of a two-dimensional photonic crystal featuring Dirac cones is based on the honeycomb lattice. Colloidal self-assembly can produce a two-dimensional colloidal structure over a large area but is limited to hexagonal-close-packed structures. Therefore, it has been challenging to fabricate honeycomb monolayers by colloidal self-assembly. Here, we fabricate a dielectric honeycomb lattice in a large area by template-assisted self-assembly and analyze its photonic structure. Although

We demonstrate an electrically controllable light-matter interaction in a gate-controlled active graphene metamaterial, which shows an electrically controlled memory effect as well as the modulation of terahertz waves in the extreme subwavelength-scale.