Kyungmook Kwon

Efficient photon capturing with ordered three-dimensional nanowell arrays.

Unique light-matter interaction at nanophotonic regime can be harnessed for designing efficient photonic and optoelectronic devices such as solar cells, lasers, and photodetectors. In this work, periodic photon nanowells are fabricated with a low-cost and scalable approach, followed by systematic investigations of their photon capturing properties combining experiments and simulations. Intriguingly, it is found that a proper periodicity greatly facilitates photon capturing process in the nanowells, primarily owing to optical diffraction. Meanwhile, the nanoengineered morphology renders the nanostructures with a broad-band efficient light absorption. The findings in this work can be utilized to implement a new type of nanostructure-based solar cells. Also, the methodology applied in this work can be generalized to rational design of other types of efficient photon-harvesting devices.

Partially directional microdisk laser with two Rayleigh scatterers

We report a partially directional microdisk semiconductor laser with subwavelength-scale boundary perturbations for asymmetric backscattering of counterpropagating whispering gallery modes. Unlike the previous approaches based on optical bistability, the directionality and chirality of the laser modes can be fine-tuned and partially controlled by adjusting the dimension, shape, and relative positions of Rayleigh scatterers on the microdisk perimeter. The controlled directionality is investigated using numerical simulations and experiments for wavelength-scale microdisk resonators with an azimuthal mode number of 5.

In situ doping control and electrical transport investigation of single and arrayed CdS nanopillars

Highly aligned intrinsic and indium doped CdS nanopillar arrays were fabricated via a template assisted Solid Source Chemical Vapor Deposition method (SSCVD). The prepared nanopillar arrays were well aligned, dense and uniform in diameter and length. Their geometry can be well defined by the design of the templates. These unique properties make them promising candidates for future photonic and optoelectronic devices. The structure of the prepared nanopillars has been studied by high resolution transmission electron microscopy and their different growth orientation as compared to those grown in free space has been observed and interpreted by the template induced change of the liquid-solid interfacial energy and the surface tension at the edge of the circular interface. To investigate electrical property of CdS nanopillars, vertical nanopillar array devices and horizontal individual nanopillar field-effect transistors have been fabricated and characterized. The measurements showed that the location of the indium doping source significantly affected carrier concentration, conductivity and field-effect mobility of the prepared CdS nanopillars. Particularly, it was found that conductivity could be improved by 4 orders of magnitude and field-effect mobility could be enhanced up to 50 cm(2) V(-1) s(-1) via proper doping control. These results enable further applications of CdS nanopillars in nano-optoelectronic applications such as photodetection and photovoltaics in the future.

Fluorescence detection system with miniaturized integrating sphere

We report on the use of non-imaging reflectors to improve the collection efficiency of fluorescence detection systems. Half-sphere mirrors redirect the isotropic fluorescent emission toward the photodetector, and significantly enhance the fluorescence signal.

Hybrid integration of III-V semiconductor lasers on silicon waveguides using optofluidic microbubble manipulation.

Optofluidic manipulation mechanisms have been successfully applied to micro/nano-scale assembly and handling applications in biophysics, electronics, and photonics. Here, we extend the laser-based optofluidic microbubble manipulation technique to achieve hybrid integration of compound semiconductor microdisk lasers on the silicon photonic circuit platform. The microscale compound semiconductor block trapped on the microbubble surface can be precisely assembled on a desired position using photothermocapillary convective flows induced by focused laser beam illumination. Strong light absorption within the micro-scale compound semiconductor object allows real-time and on-demand microbubble generation. After the assembly process, we verify that electromagnetic radiation from the optically-pumped InGaAsP microdisk laser can be efficiently coupled to the single-mode silicon waveguide through vertical evanescent coupling. Our simple and accurate microbubble-based manipulation technique may provide a new pathway for realizing high precision fluidic assembly schemes for heterogeneously integrated photonic/electronic platforms as well as microelectromechanical systems.

Wavelength-Selective Optical Filters Based on Metal-Patch Cavities With Slot Waveguide Interfaces

We theoretically propose and investigate the resonant wavelength-selective optical filters based on the subwavelength metallo-dielectric nanopatch cavities and the metal slot waveguides. Using the temporal coupled-mode theory and three-dimensional finite-difference time-domain simulations, we analyze the optical coupling efficiencies and filtering characteristics, which are optimized by adjusting the waveguide-cavity distance to modify the decay rates from the cavity. The proposed optical filters can be extended to multiport channel-dropping filters while maintaining subwavelength-scale dimensions including the coupling regions.

Lasing in hybrid metal-Bragg nanocavities

We report room-temperature lasing from an optically pumped subwavelength-scale cylindrical InGaAsP pillar surrounded by circular Bragg reflectors on a metal substrate with a dielectric spacer layer. By taking advantage of wide in-plane photonic bandgaps and proper vertical antiresonances, three dielectric Bragg pairs produce a sufficient optical feedback capable of low threshold lasing from the fundamental TE011 mode. A large spontaneous emission coupling into the lasing mode is obtained from the cavity-enhanced Purcell effects and effective suppression of nonlasing modes.

Hydrothermal fabrication of patterned ZnO nanorod clusters using laser direct writing

We report on the hydrothermal synthesis of ZnO nanorod clusters by localized optical heating from the focused laser beam. The spatial distribution of the nanorods and their growth rate can be easily controlled.

Nano pillar array laser with a bottom metal plane

We report a photonic bandedge laser using subwavelength-scale pillars with a metal reflector plane bonded on the silicon substrate. Surface-emitting operation near the gamma point of the photonic band diagram is observed at 77 K.

Photothermal in-situ synthesis of localized tungsten oxide nanobeam structures

We demonstrate tungsten oxide semiconductor nanostructures fabricated by photothermal oxidation processes on the suspended metal nano-layer. The electrical conductivities of the nanobeam structures are measured against the temperature to validate their metal/semiconductor material properties.