MIT Reports to the President 1999–2000
The Research Laboratory of Electronics (RLE), founded in 1946, is the Institute’s first interdisciplinary research laboratory. Today it is the largest such laboratory at MIT in terms of faculty and student participation. RLE grew out of the wartime MIT Radiation Laboratory and was formed to bring together physicists and electrical engineers to work on problems in electromagnetic radiation, circuits, and specialized vacuum tubes. Over the years, RLE’s research interests have branched in many directions and have led to the creation of additional laboratories. Research within RLE is conducted by approximately 40 faculty members who are affiliated with the Departments of Electrical Engineering and Computer Science, Physics, Chemistry, Materials Science and Engineering, Aeronautics and Astronautics, and Linguistics. During the past year, approximately 250 graduate students and 60 undergraduates pursued research within RLE. The research is supported primarily by the Department of Defense (DoD) agencies; the Department of Energy (DOE); the National Science Foundation (NSF); the National Institutes of Health (NIH); and the National Aeronautics and Space Administration (NASA). In addition, numerous projects are funded through industry and private foundations. RLE research is widely varied and consists of two major thrust areas and several smaller focus areas. One thrust is centered on electronics and optics; the other is centered on language, speech, hearing, and sensory communication.
Detailed information about RLE research in the calendar year 1999 can be found in the RLE Progress Report No. 142. The report can be accessed electronically at http://rleweb.mit.edu/Publications/prog.htm.We summarize here research highlights during the past year.
Professor Leslie Kolodziejski is working on the design and fabrication of photonic bandgap structures. Theoretical analysis indicates that a six-fold enhancement in the emission of light should be possible, and this has been realized experimentally. The results represent an advance in the crucial problem of efficiently coupling light into photonic and optoelectronic integrated circuits.
Professor Henry Smith is carrying out research in the NanoStructures Laboratory on a wide variety of nanostructure techniques and devices. The research encompasses innovations in electron-beam and x-ray lithography, and the creation of optical devices for communications and nanostructures for information storage. Among the recent accomplishments is the development of a technique called zone-plate-array lithography, which simplifies ultraviolet and x-ray lithography, making it more accessible to academic researchers and small companies.
Professor James Fujimoto is continuing to develop optical coherence tomography, a technique for optical imaging of biological tissue that he developed in 1990, which is finding increasing applications in medical imaging. The technique is currently being applied to arterial imaging for cancer detection and surgical guidance, and to ophthalmology. During the past year he improved the resolution by a factor of close to ten, down to approximately 1 micrometer. With Professors Herman Haus and Erich Ippen, he has generated optical pulses less than 5.5 femtoseconds long at a wavelength of 800 nanometers, and 15-femtosecond pulses at the telecommunications wavelength of 1300 nanometers.
Professor Hermann Haus is working on a variety of problems important to optical communication: solitons, fiber-optical chip coupling, and timing jitter in mode-locked lasers. He has demonstrated that solitons can be stabilized against dispersive effects that have so far impeded their use for optical communications. Using computer simulations, he has achieved high efficiency in the coupling of modes between optical waveguides of very different dimensions. In addition, he has demonstrated experimentally and theoretically the limits on timing jitter of actively mode-locked fiber lasers, helping to make these devices practical for applications that require extremely accurate time delays.
Professor Erich Ippen is continuing research on ultrafast optics and fiber optics. He has developed two new fiber laser sources of short pulses, in addition to the femtosecond source developed with Professor Fujimoto, which is described above. One fiber laser is suitable for multi-gigahertz repetition-rate communications and optical signal processing; the other is intended for ultra-broadband wavelength-division-multiplexed networks.
Professor Qing Hu is continuing research on the physics and applications of millimeter-wave and terahertz devices. He has recently developed an on-chip submillimeter-wave transceiver.
Professor John Joannopoulos is continuing work on the theory of photonic band-gap structures as part of a theoretical-experimental collaboration with Professors Kolodziejski, Ippen, and Smith.
Professor John Wyatt is continuing research on a microchip retinal implant. This device stimulates the retina electrically through microelectrodes placed directly on it. The ultimate goal is to develop a prosthetic device for patients who are blind from retinitis pigmentosa or macular degeneration. During the past year, a series of surgeries were carried out on six blind volunteers. Every patient reported some sort of visual response to the electrical stimulation.
Professor Kenneth Stevens is studying models of human speech production at the acoustic and articulatory levels, with the goal of extending the models to disordered speech. He is also developing models of the process by which human listeners extract word sequences from running speech. In addition to unraveling the fundamental processes of speech production, the research has application to the development of machines for speech recognition.
Dr. Joseph Perkell continues to study strategies for speech motor control, how they are influenced by properties of the production mechanism, and the role of self-hearing. He has found evidence to support the hypothesis that speech movements are programmed to achieve auditory or acoustic goals.
Dr. Stefanie Shattuck-Hufnagel is studying speech production at the phonological level. The goals include analyzing the planning that leads to production of sound segments and the processes of prosodic planning. New studies of error correction have clarified a longstanding puzzle in the modeling of sound production, and are expected to have a significant impact on cognitive modeling of speech production planning.
Research Scientist Dr. Andrew Oxenham is continuing research on auditory perception and cognition, with a particular focus on the nature of the changes in auditory waveforms as they are processed in the cochlea. The research has implications for computational auditory scene analysis and may ultimately benefit groups working on models of the human auditory periphery.
Professor Dennis Freeman has improved the imaging of sound-induced motions of sensory cells in the inner ear so that the motion can be viewed from arbitrary perspectives, similar to tomographic reconstruction of MRI images, but at a micrometer scale. He has also developed a new type of optical microscopy–synthetic aperture microscopy–in which the target is illuminated by 10 to 100 computer-controlled laser beams. The goal is to produce giga-pixel images using a mega-pixel camera, and to achieve major increases in working distances, depth-of-focus, and field of view.
Professor William Peake is studying the relationships between animals’ life styles and the structure and function of their ears. A study of 37 cat species has shown that the middle ear’s frequency response tends to shift toward lower frequencies with increasing animal size. The results demonstrate a structural basis for a variation in sensory capability.
Professor Wolfgang Ketterle is continuing to explore the properties of atomic Bose-Einstein condensates. During the past year, he demonstrated the superfluidity of the condensate by observing a critical velocity for dissipation when a macroscopic body–a "laser knife"–moved through the condensate. He also observed a critical velocity for microscopic impurities–a wave of atoms in a different hyperfine state that propagated through the condensate. In other experiments he demonstrated that the condensate could serve as a matter-wave amplifier in an experiment that constitutes the first realization of an active matter-wave interferometer.
Professor David Pritchard has extended his studies of decoherence in elementary quantum systems by demonstrating the loss of coherence in entangled atomic systems that are spatially separated by more than a million times the size of an atom. Decoherence is a crucial issue for quantum communications and for all scenarios in quantum computing. In a separate series of experiments, he is continuing to develop techniques to advance the resolution of mass spectroscopy toward the goal of 10-12.
Professors Thomas Greytak and Daniel Kleppner are continuing their studies of Bose-Einstein condensation in atomic hydrogen and the optical properties of ultracold hydrogen. The condensation dynamics of hydrogen, which are different from other gases, are being studied, and atomic interactions are being investigated through their effect on optical excitation.
Professor Seth Lloyd is working on quantum information processing, including quantum computing, and quantum control. With Professor Jeffrey Shapiro and Drs. Ngai-Chuen Wong and Selim Shahriar, he has developed a design for a quantum communications network for linking quantum computers. He has continued work on implementing quantum computation algorithms using nuclear magnetic resonance. He has worked with a group in Delft that has demonstrated a superconducting quantum bit.
Professor Abraham Bers is studying heating and current drives in magnetic confinement, ion energization in space plasmas, and intense laser-plasma interactions in inertial fusion experiments. He has analyzed the intense fields produced in inhomogeneous waveguide plasmas, and has applied the results to explain the creation of energetic oxygen and hydrogen ions in the lower magnetosphere.
Dr. Linda Sugiyama, working with Professor Bruno Coppi, has developed time-dependent numerical models for confined high-temperature plasmas. During the past year, she has found that several categories of large-scale plasma instabilities can have significantly different loss rates that are not included in usual theoretical analyses. The results can be destabilizing, but they can also be stabilizing.
Professor David Staelin has developed a new noise estimation algorithm for data from unknown sources that yields estimates of the signal order and noise variance. The results are potentially useful for data analysis in science, engineering, medicine, finance, and manufacturing. In the area of atmospheric sensing, he has developed a new method for estimating instantaneous precipitation rates from passive microwave satellites observing in and near the opaque bands of oxygen and water vapor. The results agree well with radar data, but have the important advantage of offering full global coverage over land and sea.
Dr. Phillip Rosenkranz is carrying out research on the inversion of microwave radiometer measurements made from satellites or aircraft to obtain profiles of temperature and moisture in the atmosphere. The method has revealed stratospheric temperature waves and sea-state effects from surface emission and reflection data from the NOAA-15 satellite.
Professor Gregory Wornell is working on fundamental principles and algorithms for wireless and broadband communication, and multimedia signal processing. He has developed promising new classes of space-time coding techniques that have potential for dramatically increasing the capacity of wireless links without requiring additional power or bandwidth, and have low computational complexity. He has developed a suite of new interference suppression algorithms for wireless communications. He has also developed a new generation of digital earmarking technology, which is a compelling candidate for next-generation systems for copyright notification and enforcement.
Professor Jae Lim is addressing the need to broadcast high-definition television at resolutions higher than those permitted by the current standard. He is investigating several methods to transmit video at these higher resolutions, and is studying new video compression methods that use preprocessing techniques.
Professor Jin Au Kong is working in the areas of electromagnetic wave theory and applications. During the past year, he has developed techniques of inverse scattering for data interpretation of active spaceborne imaging radar and passive airborne radiometric experiments for the remote sensing of the earth and its oceans.
Professor Jeffrey Shapiro, serving as principal investigator, has assembled a team to work on quantum information theory under a grant from the Department of Defense’s Multidisciplinary Research Program of the University Research Initiative (MURI). The team includes Professors Seth Lloyd, Peter Hagelstein, and Madhu Sudan; Drs. Selim Shahriar and Ngai-Chuen Wong; and collaborators at Northwestern University and the Air Force Research Laboratory at Hanscom Field.
Working with Dr. Ngai-Chuen Wong, Professor Shapiro has developed an optical parametric amplifier concept for an ultrabright source of photon-entangled photon pairs. The technique is intended for use in quantum information processes, and represents a million-fold increase in brightness over previous sources.
Professor Donald Troxel has developed a remotely operated microelectromechanical system (MEMS) station, in collaboration with Professor Dennis Freeman. He has also developed a new tool for determining the reliability of very large system integration (VLSI) design.
RLE has worked and will continue working to increase the number of women and minorities in career positions in the laboratory, in the context of the limited pool of qualified technical applicants and the unique qualifications of RLE's sponsored research staff. Specific measures will include: maintaining our high standards for recruitment procedures that include sending job postings to minority colleges and organizations; working closely with the RLE faculty/staff supervisor at the beginning of each search to identify ways of recruiting minority and women candidates for the new position; and being committed to finding new techniques to identify more effectively women and minority candidates. During the past year, due to limited turnover in RLE’s research staff, success in affirmative action for research staff has been limited. Nevertheless, of the three research staff appointments made this year, one was made to a woman.
More information about the Research Laboratory of Electronics can be found at http://rleweb.mit.edu/.
Daniel Kleppner
MIT Reports to the President 1999–2000