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Our group is composed of people interested and enthusiastic about light, photons, and small devices. Currently, we study and utilize three-dimensionally confined nanoparticles such as colloidal quantum dots (QD) and plasmonic nanoparticles (NP). These materials harvest strong near-field interaction with light, and have opened new directions in nanophotonic devices and integration, as well as various applications in biomedicine and nanotechnology. In addition, we also pursue device integration in micro-scale utilizing optical MEMS technology. Our current research directions are:

Quantum dot nanophotonics

QD Waveguides
Nano Letters 2006, Optics Letters 2007, Nanoscale Research Letters 2007
QD Photodetectors
Optics Express 2007, Applied Physics Letters 2010
Plasmonic-enhanced QD photodetection
CLEO/QELS 2010, Applied Physics Letters 2011
Silicon quantum dots
Optics Express 2010, Applied Physics Letters 2011, Optics Express 2012

Quantum dots have unique optical and electrical properties that arise from the very small size of the particles, resulting in quantization of electron-hole energy levels in the particle. This leads to their various properties that are far superior to the corresponding materials in bulk form, such as high quantum efficiency, size-dependent tunable emission, and high sensitivity. In addition, they have flexible surface chemistry that can be modified for various self-assembly fabrication, which provides a powerful route to integrated fabrication on a wide range of substrates. We have demonstrated sub-diffraction limit QD waveguides that exploits near-field coupling between QDs, nanogap QD photodetectors with high sensitivity and spatial resolution, QD photodetectors and photodiodes using electrostatic layer-by-layer self-assembly. We have investigated explored integrating plasmonic nanoparticles with QD photodetectors to enhance their efficiency at specific spectral regions. Recently, we started to explore fabrication of Si QDs and photonic devices based on these materials.Along a different application direction, we have also studied using optically-excited quantum dots to stimulate cells and neurons.

At our spare time, we enjoy turning our research into fun stuff. For example, the logo on the uppper-left corner is the red fluorescence of CdSe QDs patterned using self-assembly fabrication process.

Nanostructure-enhanced laser tweezers

Nanostructure-Enhanced Laser Tweezers
Optics Letters 2007, JSTQE 2007, JSTQE 2009
DNA Concentration
Optics Express 2008
Sub-micron Particle Trapping and Oblong Particle Alignment
Optics Express 2010
Ovarian Cancer Cell Nuclei Trapping Video
Optics Express 2010
Plasmonic Micro-fluidic Mixer
Applied Physics Letters 2008
Assembly of Nanowires and CNTs
Optics Express 2008

Optical manipulation of particles has broad applications in nanoscience, biological study, and biomedicine. Conventional optical tweezers require high optical intensity to achieve sufficient force due to low efficiency in direct conversion from optical energy to mechanical energy. The challenge becomes more severe as the particle size decreases to sub-micron regime. We explore the enhanced field from plasmonic or periodic dielectric nanostructures to increase the trapping efficiency and functionality of optical tweezers. Using these approaches, we have demonstrated efficient trapping and rotation of micro- and nano-particles, nanowires, cells and nuclei with low optical intensity. In addition, trapping and concentration of DNA, micro-fluidic mixing, and scalable assembly of nanoparticles have also been achieved using the platform.

Micro-instrunmentation by optical MEMS

Our current focus is on developing a scanning micro-mirror with an adjustable focal length for endoscope applications. Gastrointestinal (GI) cancers, as a group, are amongst the highest cause of mortality. To cure or, better still, prevent cancer, early diagnosis, detection and treatment is essential. A miniaturized scanner integrated with the distal end of an endoscope and advanced optical imaging technologies such as optical conherence tomography and confocal fluorescence endomicroscopy allows imaging of the GI system with high controlability. A MEMS scanning micro-mirror is an outstanding candidate technology for such an application. With active focus tracking capability, it allows high-resolution 3-D imaging to be achieved with the endoscope system, which can significantly improve our currently limited ability for detecting early and pre-cancers.