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Our group is composed of people interested and enthusiastic about light, photons, optical devices and systems. We pursue new research discoveries in the broad fields of nanophotonics and biophotonics. Below are some of the research projects we have previously or are currently working on.

Nanostructure-enhanced laser tweezers (NELT)

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 photonic crystal 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. We have studied and verified that the cell viability is not compromised by the incident laser beam when operating the laser tweezers on a photonic crystal platform.
Efficient Patterned Trapping on 2D PhC platform
Sub-micron Particle Trapping and Oblong Particle Alignment
NELT on plasmonic platforms
DNA Concentration
Plasmonic Micro-fluidic Mixer
Assembly of Nanowires and CNTs

NELT-integrated MEMS for high-accuracy mass sensing

In this NSF-sponsored project, we integrate photonic crystal optical tweezers and microfluidic structures with MEMS resonators. By precisely trap and position the particles on the surface of the MEMS resonators, the mass of the particles can be measured and monitored with high accuracy and repeatability. The technology can be used for living cells and nanoparticles, for example, understanding how cell mass change under various cemo-mechanical stimuli and monitoring nanoparticle growth in nanofabrications. Its broader impacts include the fields of cell biology, tissue engineering, cancer and disease research, as well as nanotechnology.

Thin-film solar cell efficiency enhancemet by photonic crystal nanostructures

Quantum dot nanophotonics

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, nanogap QD photodetectors with high sensitivity and spatial resolution, plasmonic-enhanced QD photodetectectors with color selectivity, Si QDs with high photoluminescence quantum yield. We have also demonstrated photostimulation of cells and neurons through QDs with extremely low optical intensities.

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.
Flexible QD Photodetectors
Silicon Quantum Dots
QD Neuron Photostimulator
Plasmonic-enhanced QD Photodetection
Nanoscale QD Photodetectors
QD Waveguides

Micro-instrumentation by optical MEMS

We have developed a scanning micro-mirror with an adjustable focal length for endoscope applications. 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 gastrointestinal (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.