Bumki Min

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.

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

Periodically driven systems are ubiquitously found in both classical and quantum regimes. In the field of photonics, these Floquet systems have begun to provide insight into how time periodicity can extend the concept of spatially periodic photonic crystals and metamaterials to the time domain. However, despite the necessity arising from the presence of nonreciprocal coupling between states in a photonic Floquet medium, a unified non-Hermitian band structure description remains elusive. We exper

A controllable and reversible transition between parametric and Raman oscillations in an ultrahigh-Q silica toroidal microcavity is experimentally demonstrated and theoretically analyzed. By direct change of cavity loading and indirect adjustment of frequency detuning, parametric and/or Raman oscillation can be accessed selectively without modification of cavity geometry in a toroidal microcavity with a large enough aspect ratio. Based on an effective cavity gain theory, this transition is analy

A perturbation theoretic approach is proposed as an efficient characterization tool for a tapered fiber coupled ultrahigh-quality factor $(Q)$ toroidal microcavity with a small inverse aspect ratio. The Helmholtz equation with an assumption of quasi-TE/TM modes in local toroidal coordinates is solved via a power series expansion in terms of the inverse aspect ratio and the expanded eigenmode solutions are further manipulated iteratively to generate various characteristic metrics of the ultrahigh

Photonic crystals have revolutionized the field of optics with their unique dispersion and energy band gap engineering capabilities, such as the demonstration of extreme group and phase velocities, topologically protected photonic edge states, and control of spontaneous emission of photons. Time-variant media have also shown distinct functionalities, including nonreciprocal propagation, frequency conversion, and amplification of light. However, spatiotemporal modulation has mostly been studied a

Abstract Terahertz radiation and its nonlinear optical manipulation may possess potential for a variety of applications in next‐generation electronics and optics. Pioneering studies have shown that the nonlinearity of carrier drift in semiconductors and graphene can be utilized for nonlinear optical processes at terahertz frequencies. However, because of the symmetric response of carriers to the terahertz field direction, most experiments have confirmed only the presence of odd‐order nonlinear p