Research Project
GaN Photonic Crystals
Advances in III-nitride processing have led to the formation of air-gap distributed Bragg reflectors (DBRs), freestanding photonic crystal (PC) membrane nanocavities, and high-quality low-threshold microdisk lasers. The unique control over the selective removal of embedded materials is obtained by the photo-electro-chemical (PEC) wet-etching technique. This selective wet etching can allow the larger index contrast between the air and the remaining material for higher index contrast in the DBRs, and therefore achievement of higher reflectivity with fewer mirror layers as well as good optical confinement for strong spatial coupling between optical modes and the embedded PC nanostructures. GaN microcavity light-emitting diodes, vertical-cavity surface emitting lasers utilizing air-gap nitride DBR reflectors, and hybrid three-dimensional active PC nanostructures are of specific interests.
Coupled Waveguide-resonator Systems
The search for the ability to arbitrarily tailor the propagation of light has recently led to many researches on integrated optical systems based on two types of building blocks, waveguides and resonators, which facilitates the novel optoelectronics as well as the fundamental study of physical phenomena based on coherent wave interactions, such as electromagnetically induced transparency and strong photon coupling. In particular, I am interested in a dispersive phase response of optical waveguide-resonator systems, where two Whispering-Gallery-Modes (WGMs) of microcavity couple to the single mode of a tapered, accessing optical fiber. The observed phase responses are shown to stem from the coherent interference between light waves coupled to each doublet WGMs. The resulting group delay becomes either positive or negative near the high-Q (~100000) WGMs. These phenomena arise in the all-optical and linear regime, and therefore will be useful for controlling single photon transfer and studying the phase-sensitive dynamics of quantum-dot-cavity coupled systems.
Laser Photon Statistics
A deeper insight into the onset of lasing in the high beta regimes can be found from the study of laser photon statistics based on the Hanbury-Brown Twiss measurement.