Wonki Min

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 Although recent progress in metasurfaces has shown great promise for applications, optical properties in metasurfaces are typically fixed by their structural geometry and dimensions. Here, an electrically controllable amplitude of anomalously‐refracted waves in a hybrid graphene/metasurface system are experimentally demonstrated, which consists of an artificially constructed two‐dimensional metallic apertures array and naturally occurring two‐dimensional carbon atoms (graphene) in the s

Cascaded Raman Stokes lasing in an ultrahigh-Q silica microsphere resonator coupled to a tapered fiber is demonstrated and analyzed. With less than 900 microW of pump power near 980 nm, five cascaded Stokes lasing lines are generated. In addition, a threshold power of 56.4 microW for the first-order Stokes lasing is achieved. The Stokes lasing lines exhibit distinct characteristics depending on their order, as predicted by theoretical analysis.

Memory metamaterials are artificial media that sustain transformed electromagnetic properties without persistent external stimuli. Previous memory metamaterials were realized with phase-change materials, such as vanadium dioxide or chalcogenide glasses, which exhibit memory behaviour with respect to electrically/optically induced thermal stimuli. However, they require a thermally isolated environment for longer retention or strong optical pump for phase-change. Here we demonstrate electrically p

Metamaterials, artificially constructed structures that mimic lattices in natural materials, have made numerous contributions to the development of unconventional optical devices. With an increasing demand for more diverse functionalities, terahertz (THz) metamaterials are also expanding their domain, from the realm of mere passive devices to the broader area where functionalized active THz devices are particularly required. A brief review on THz metamaterials is given with a focus on research c

Lasing from an erbium-doped high-$Q$ silica toroidal microcavity coupled to a tapered optical fiber is demonstrated and analyzed. Average erbium ion concentrations were in the range $0.009\text{--}0.09\phantom{\rule{0.3em}{0ex}}\mathrm{at.}\phantom{\rule{0.2em}{0ex}}%$, and a threshold power as low as $4.5\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{W}$ and an output lasing power as high as $39.4\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{W}$ are obtained from toroidal cavities with

Chemically synthesized nanocrystal, CdSe∕ZnS (core/shell), quantum dots are coated on the surface of an ultrahigh-Q toroidal microcavity and the lasing is observed at room and liquid nitrogen temperature by pulsed excitation of quantum dots, either through tapered fiber or free space. Use of a tapered fiber coupling substantially lowered the threshold energy when compared with the case of free space excitation. The reason for the threshold reduction is attributed to the efficient delivery of pum

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

Abstract The spin Hall effect of light (SHEL) refers to a transverse and spin‐dependent shift of light in real space at an optical interface. Previous studies of enhancing the SHEL have involved extremely low efficiency, and achieving a large SHEL and high efficiency simultaneously has never been reported. Here, an approach using anisotropic impedance mismatching to attain a large SHEL with near‐unity efficiency in the microwave spectrum is proposed. A wire medium that has a near‐unity transmiss