Research
We are developing medical imaging techniques using special light beams such as Airy beams. Airy beam Optical Coherence Tomography (OCT) technology has the potential to enhance the depth of field and penetration in samples for non-invasive imaging in ophthalmic applications. In ultrahigh resolution AB-OCT, maintaining sensitivity for deep-field imaging is a critical issue. Using phase and intensity modulations, we are developing new ultrahigh resolution OCT imaging systems that surpass the limits of current optical imaging technology. Another biomedical imaging project we are working with is fluorescence mediated tomography (FMT) based on the heterodyne method and the development of site-specific fluorescent peptides. The proposed FMT technique is an in vivo biomedical imaging technique that can provide quantitative and molecular imaging of fluorescent probes in small animals. The system is to be used for simultaneous imaging of fusion probes of tumor-targeting radiolabeled and fluorescent peptides by optical and other modalities.
The wavelength of light is a degree of freedom that can be used to carry information for telecommunication and quantum information. The development of cost effective and integrated devices has allowed dense wavelength division multiplex (DWDM) to be widely used in telecommunication. However, DWDM has approached its capacity limit. Further development of spatial division multiplexing (SDM) based on spatial separation of light beam has also reached its capacity limit since all fundamental parameters in orthogonal dimensions from a conventional light wave have already been used for carrying the optical information. Twisted light offers a new degree of freedom to boost optical and quantum information. It is based on unbounded sets of OAM eigen-states with different topological charges that are mutually orthogonal to each other and each OAM state can carry independent optical information without crosstalk. We are developing various OAM states for the applications in tele- and quantum communications.
We are working on several material systems using second harmonic generation (SHG). Polar alignment in organic crystals is a potential nonlinear optical (NLO) material that can create high SHG. Since the dipole cancellation is avoided, the nonlinear coefficients can be enhanced at certain configuration according to the symmetry of the crystal and the polarization of light waves. The huge SHG is achieved with defined orientation of the crystal to allow the phase matching.
Wide-bandgap semiconductors have shown great potential for ultraviolet (UV) detection. During the past decade, wide-bandgap III-V GaN and AlGaN photodetectors have been extensively studied and show high photoresponsivity. However, these devices suffer from the problem of persistent photoconductivity due to deep level defects, grain boundaries and surface states in the material. As a wide-bandgap II-VI semiconductor, ZnO is a potential candidate material for UV detectors. Previous UV detectors based on ZnO showed either relatively low photoresponsivity or lacked the capability of visible rejection. In our current work new metal-semiconductor-metal and s-I-n ZnO UV detectors have been realized. The mechanism of carrier generation and recombination has been studied to explain the observed photoresponse.
The development of nanoporous carbon is significant for energy storage and transport based on reversible hydrogen storage. To increase the hydrogen storage capacity, metalloid atoms such as boron are proposed to dope into activated carbon. Boron atoms serve as strong sites to increase the capability of hydrogen adsorption. It is very important that boron and carbon form a chemical bond, so that the boron doped nanoporous carbon matrix is a stable structure. We study chemical bonds by using microscopic FTIR for nanoporous materials. Boron doped nanoporous carbon is an excellent example for the studies.