Dissertation Proposal Defense – Chun Hao Lin
Dr. Vladimir Tsukruk, Advisor, MSE
Prof. Zhiqun Lin, MSE
Prof. Wenshan Cai, MSE/ECE
Prof. Qin Dong, MSE
Prof. Eric Vogel, MSE
"Controlling light-matter interactions via manipulation of optical gain and loss in local-assemblies of colloidal quantum dots"
The goal of this research is to control light-matter interactions in three levels of hierarchical robust photonic systems: individual and assembled nanostructures, individual local assemblies and coupled local assemblies. Specifically, controlled optical properties of individual nanostructures such as emission/absorption peak position and photoluminescence intensity will be investigated via the selection of materials and dimensions. In addition, spatial arrangements of assembled nanostructures will be examined to see the effect on the degree of light amplification/attenuation and real refractive index which are important variables for the design of novel photonic systems that obey parity-time symmetry. Finally, manipulation of optical activity of local assemblies including cavity modes, emission output and mode splitting will be investigated by altering coupling strength between assemblies, localized gain/loss contrast and arrangement of engineered defects.
Conventionally, two types of materials have been used to fabricate common photonic systems: inorganic and organic systems. The inorganic system typically relies on the epitaxially-grown inorganic materials where lattice mismatch between different layers greatly limits the selection of materials and substrates. On the other hand, the organic system typically utilizes organic dyes as emitters whose photoluminescence intensity decreases significantly under strong optical pumping, known as photobleaching effect. It would be of great interest to develop new type of material that can mitigate all the issues encountered in these conventional systems by providing tunable optical properties, solution processability and stable lasing output. In this research, quantum dots are used as the optically active component due to their tunable emission and absorption properties that arise from the confinement of exciton within nanoscale quantum dots. In addition, they are solution- processable via the unique combination of organic ligands and inorganic cores, leading to improved material processing. Core/shell and ligand engineering will be adopted to develop high quality assembled quantum dot solids with superior lasing properties such as tunable gain/loss values, low lasing thresholds and stable lasing output. Microscale and nanoscale deposition and microfabrication techniques will be used to further arrange quantum dots into local assemblies. In addition, physical and non-physical method are proposed to manipulate the optical gain/loss values in localized region to achieve the exceptional point.
The design and fabrication principles proposed in this work will help guide the development of miniaturized photonic system with highly tunable optical properties, tunable mode activity and unprecedented optical phenomena such as unidirectional invisibility, unidirectional reflection/directional optical manipulation, coherent perfect absorbers and highly directional output.