| Home | Research | Publications | People | Meetings | Links |
The information carrying capacity of optical fibers has been growing exponentially since the advent of fiber optical networks. Commercially deployed systems, which started at ~ 45 Mb/s around 1980, can now carry ~ 3 Tb/s in a single fiber, with state-of-the-art research experiments demonstrating capacities of ~ 10 Tb/s. Much of the capacity improvement in the last decade came from the implementation of dense wavelength division multiplexing (DWDM) and the increase in the per channel data rate. Although the demonstrated total capacity is impressive, it is still far from the physical limits of optical fibers.
Our work in fiber optic communications involves both numerical modeling and experiments. With significant help from the fiber optic industry, we have completed the establishment of a state-of-the-art 600-km fiber testbed. Our current efforts in this area include the study of various modulation formats and nonlinearity management techniques for long haul optical communications and new techniques for fiber optic access networks.
Flexible Fiber Optic Endoscope. Optical endoscopes have played a major role in medical diagnostic and minimally invasive surgery by making it possible to visualize tissue at remote internal sites. There are two general classes of optical endoscope used: rigid and flexible. Rigid instruments include the laparoscope and the anthroscope; flexible fiber-optical devices include instruments such as bronchoscope, gastroscope, and colonoscope. Rigid designs permit the use of glass lens and rods, and offers significant improvement in image qualities over fiber-optic-based flexible devices. The intrinsic difference between an image formed by lens (rigid devices) and that formed by a coherent fiber bundle (flexible devices) lies in the fact that a lens system transports an entire optical wavefront while a coherent fiber bundle (i.e., the input and output fibers are spatially correlated) transports real image pixel by pixel. In this regard, the coherent fiber bundle serves simply as a pixelated light guide and actually transports the image incoherently. Although this technology provides an adequate view, there still exists significant graininess resulting from the pixelation by individual fiber. In our current research, we are exploring new concepts and devices that would significantly improve the performance of existing flexible endoscopes.
Deep Imaging in Scattering Biological Tissue. The Holy Grail for biomedical optics is to create a device that provides non-invasive diagnostic capability through imaging, providing chemically specific, or ‘functional’ information about biological tissue. This goal, often described as ‘optical biopsy’, inevitably requires image acquisition through significant depths of biological tissues. Its realization, however, presents a major scientific challenge since tissue is extremely heterogeneous and the strong scattering of the various tissue components have historically restricted optical imaging to thin histological tissue sections or to superficial tissues.
Laser scanning multiphoton microscopy (MPM) has greatly improved the penetration depth of optical imaging and proven to be well suited for a variety of imaging applications deep within intact or semi-intact tissues. Nonetheless, MPM has so far been restricted to less than 1 mm in depth in brain tissues, which is only about a quarter of the ~ 4 mm cortex thickness of human. We are currently developing new concepts and techniques for imaging deep into scattering biological specimens.
One of the most satisfying things about research is creating new ideas, inventing new instruments, and finding new applications. We view optics as a valuable tool for a wide range of research and engineering fields. Our research in optical instrumentation focuses on real-world applications and dynamically evolves around the research area of the group. Our current efforts are devoted to the manipulation of light fields, with applications targeting both biomedical imaging and optical networking.
September 15, 2004