The Research Laboratory of Electronics (RLE), the Institute's oldest interdisciplinary research laboratory, was founded in 1946 as the natural evolution of the wartime MIT Radiation Laboratory. Initially, RLE was formed to bring together interests in physics and electrical engineering to work on problems in electromagnetic radiation, circuits, and specialized vacuum tubes. Over the years, RLE's research interests have branched out in many directions, and in fact several of these interests have precipitated the formation of additional laboratories. Research within RLE is conducted by approximately 55 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 200 graduate students and 75 undergraduates have worked on research projects within RLE. Major support is derived from the Joint Services Electronics Program (JSEP) of the Army, Navy, and Air Force; other Defense Department 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, many research projects are funded through industry and private foundations. Although RLE has a very heterogeneous character, its organization is composed of two major thrusts and several smaller focus areas. One major thrust is centered on electronics and optics, and the other is centered on language, speech, and hearing. Each of the smaller focus areas often has substantial overlap with other research in RLE.
In the following remarks, several research highlights from 1995 are briefly mentioned. The interested reader can obtain further information from RLE Progress Report No. 138, which describes research activities during calendar year 1995.
Professor Jesús del Alamo has been studying pseudomorphic high-electron mobility transistors. Special attention is paid to the electrostatic interaction of the device's source with its gate, which degrades the device's gate-to-drain breakdown voltage. These studies have led to new insight into the design and characterization of these devices, which permit high-voltage operation. Professor Clifton Fonstad has developed a unique process to fabricate complex monolithic optoelectronic integrated circuits. These circuits combine integrated light-emitting diodes and photodetectors with high-performance VLSI-density gallium arsenide electronic circuitry available from commercial sources. This new technology is being applied to components in fiber communications systems and infrared focal plane arrays, and raises the possibility of a portable digital ophthalmoscope.
Professor Marc Kastner continues to focus his research on the production of single-electron transistors that can operate at liquid nitrogen (or higher) temperatures using silicon. Operation of these transistors has already been achieved at temperatures of up to 20 K using conventional lithography. Considerably higher temperatures are expected with fine-line lithography and improved device design. Professor Patrick Lee has studied the behavior of two quantum dots connected in series. Additional charge to this structure can reside in either one of the two dots, resulting in a rich, resonant structure. He has found that transmission of current through the double quantum dots displays peaks as a function of gate voltage, and that the height of these peaks depends on temperature in a power law manner. A new x-ray mask alignment system called interferometric broadband imaging has been developed by Professor Henry Smith. Using this technique, mean misalignments as small as one-tenth of a nanometer can be reliably detected. He has also developed new techniques for spatial phase-locked electron-beam lithography on a global fiducial grid. This will enable commercial ULSI technology to move into the sub-100-nanometer domain, which will be needed in the 21st century.
Professor James Fujimoto has developed new technology for in vitro optical imaging of human tissue. A new, high-resolution fast acquisition imaging instrument has been developed, which will be important for a variety of medical fields such as cardiology, urology, and gastroenterology. In these fields, the visualization of microscopic tissue morphology plays a role in the diagnosis and intervention of disease. Professor Hermann Haus has made substantial improvements to fiber-ring lasers that operate at the 1.54 micron wavelength. Having previously shown that the timing jitter can be attributed fully to fundamental quantum noise, he has demonstrated the lowest amplitude noise and timing jitter ever observed in a mode-locked laser. Professor Qing Hu has built a micromachined millimeter-wave superconducting receiver and an uncooled bolometric detector. Both achieved performance that was comparable to the best sensors by using conventional waveguide technology. Professor Erich Ippen has developed a high-power femtosecond fiber laser that is attracting interest for applications in communication systems and in scientific instrumentation. It has already been patented and licensed for commercial use. He has also developed a new method to study ultrafast dynamics in semiconductor laser diodes, in addition to demonstrating all-optical wavelength shifting of picosecond pulse signals in semiconductor quantum well waveguides. This will be important for wavelength division multiplexed networks.
Professor Robert Birgeneau has been using x-ray diffraction techniques to study silicon surfaces miscut from the (111) orientation, up to 8 degrees towards the (112) orientation. This has revealed dynamical changes in the surface morphology that are reversible, and which can be controlled by the direction of current flow through the crystal. The ability to manipulate the morphology of silicon surfaces on a mesoscopic scale is directly relevant to silicon device fabrication.
Professor Anantha Chandrakasan has demonstrated that embedding power supply control circuits into variable-load digital signal processing computation systems can significantly reduce energy consumption. The supply voltage and clock frequency are lowered during reduced computational workload periods. This can reduce power by more than a factor of five in some applications, when contrasted with conventional fixed-voltage systems. In addition, signal statistics can be exploited in order to further reduce power consumption in a variety of digital filter structures. A new low-bandwidth protocol for battery-operated multimedia terminals in a network environment has optimized the partitioning of computation between high-power remote servers and low-power portable systems. Professor Srinivas Devadas has provided several compiler optimizations that improve the quality and performance of embedded control software in mixed hardware-software systems. These results are helpful in exploring the architectural design space of digital signal processing systems. Professor John Wyatt, working with Dr. Joseph Rizzo of the Massachusetts Eye & Ear Infirmary and Harvard Medical School, has been working on the development of a microelectronic retinal implant device to restore useful vision to patients blinded by diseases of the outer retina (specifically, retinitis pigmentosa and macular degeneration). They have completed a large biocompatibility study in which five materials were placed in a rabbit's eye for one year, while the health of the retina and the eye was monitored. No damage to the eye was found from using these materials. In addition, a major in vitro study of the response of rabbit retinal ganglion cells to minute electrical stimulation was completed. This study will be essential to further development of the prosthetic device.
Dr. Joseph Perkell has consolidated evidence from several projects that support a new theoretical overview of speech production. In this view, phonemic information is transmitted by the actions of neuromuscular synergisms, which are organized to achieve articulatory and acoustic goals. Acoustic goals are achieved through the use of an internal model of the relations between the articulatory commands and sound output. Auditory feedback is used to acquire and maintain the model, and to enable situation-dependent adjustments in several parameters that influence clarity and intelligibility. Dr. Stefanie Shattuck-Hufnagel has shown that intonational phrase structure influences the placement of pitch accents on different syllables within a word. She has demonstrated that word-initial vowels are more likely to be produced with glottalization (a rapid decrease of fundamental frequency) when they occur at the onset of a new intonational phrase or at a pitch accent. These results have been facilitated by the use of a large new prosodically labeled speech database. Professor Kenneth Stevens has studied the variability in speech sounds and words, depending on the speaker and on the context in which the sound or word is produced. Through an acoustic analysis of vowels, the range of characteristics that occur in the pattern of vocal-fold vibration among male and female speakers has revealed different attributes. This is important for the improved synthesis of female voices by computers.
Mr. Nathaniel Durlach has been studying human perception and sensory motor performance in the context of human-machine interfaces for teleoperators and virtual environments. Multimodal interactions have been characterized and modeled, and a theory of adaptation to altered perceptual cues associated with the use of such interfaces has been completed. Dr. Kenneth Salisbury, in collaboration with Dr. Mandayam Srinivasan, has developed new touch perception algorithms that enable robots to deduce contact conditions from simple force-sensing fingertips. Work continues on a new force-controllable multifinger hand and on planning algorithms that enable the hand to continuously reorient objects held in its fingertips. Dr. David Zeltzer has developed a new prototype virtual environment system for training the officer of the deck on a submarine. In this way, naval officers can learn this difficult task in a virtual environment, without the need to involve actual submarines in difficult docking situations.
Dr. Donald Eddington and Mr. Joseph Tierney have developed a new sound processing system for use with cochlear implants. Qualitative assessment of this new system has been positive, and subjects have reported that the range of sounds (in loudness and pitch) is much greater with the new processor, and that their ability to understand speech is significantly improved. Professor Dennis Freeman has developed a computer microvision system that can measure nanometer motions of micrometer-sized targets. This system combines stroboscopic illumination with video microscopy in order to acquire sequences of stop-action images. Motions are determined directly from the video images using algorithms originally conceived for robot vision. This approach has been extended to the design and fabrication of microelectromechanical systems, which now allows frequency response in three dimensions to be accurately characterized.
Professor Wolfgang Ketterle has demonstrated the production of a Bose-Einstein condensate. He has shown that if sodium atoms are cooled below a critical temperature, they behave as a coherent matter wave. Work continues on splitting a condensate into two coherent halves that can then be made to interfere within the range of the de Broglie wavelength. This work will demonstrate the feasibility of an atom laser that could be used as a source of coherent matter waves. These atom sources are likely to replace conventional atomic beams in demanding applications such as atom interferometry, precision measurements, future atomic clocks, matter-wave microscopy, and the creation of microscopic structures by direct-write lithography. Professor Daniel Kleppner has developed a new form of spectroscopy to investigate the connections between quantum and classical mechanics, including the problem of quantum chaos. Professor David Pritchard has demonstrated that his new separated-beam atom interferometer is approximately as sensitive to rotations as commercially available laser gyroscopes. This work is promising for compact and ultraprecise gyroscopes.
Professor Abraham Bers has been studying the interaction of ionospheric ions with electrostatic waves in the upper auroral atmosphere. This study is being conducted in order to understand rocket observations which show thermal ionospheric oxygen and hydrogen ions are accelerated to gravitational escape energies by intense lower hybrid waves. These waves were found to be spatially localized to narrow regions that are perpendicular to the geomagnetic field. Professor Bruno Coppi has developed several techniques to study the physics of high-temperature plasmas. These include the degradation of energy confinement by ion temperature gradient-driven modes, the isotropic effect on plasma confinement time, the existence of impurity-driven modes that are localized at the plasma edge, and the time-dependent path to ignition in magnetically confined plasmas.
Professor Jacqueline Hewitt is carrying out time-delay measurements in gravitational lens systems, thereby providing a measurement of linear distance in a high redshift system. This provides cosmographic information that constrains the values of the Hubble constant, the deceleration parameter, and the cosmological constant--all of which are parameters of the standard cosmological model. Dr. Philip Rosenkranz has studied techniques for the interpretation of measured, or simulated, microwave radiometer data in order to infer parameters describing the state of the atmosphere. These results indicate soundings comparable in accuracy and superior in timeliness to low or earth-orbit microwave instruments can be obtained.
Professor Gregory Wornell has developed new multiscale models for fractal point processes. These are applied to the problems of modeling and managing data traffic in packet-switch communication networks. He has also introduced new methods to efficiently exploit transmit diversity through large antenna arrays and wireless communication systems, such as cellular, personal communication, and broadcasting systems.
Professor Jae Lim and his group have contributed to the design of the Grand Alliance's digital high-definition television system. This system has been judged to meet or exceed all test requirements, and is expected to serve as the basis for the United States' high-definition television standard for terrestrial broadcasting. Professor William Schreiber has completed the development of a new advanced television system for terrestrial broadcasting. The most important performance factors of the system are the efficient use of over-the-air spectrum, support for less expensive receivers for less demanding applications, and the existence of a practical transition scenario from the current terrestrial broadcast system. In addition, this system has been shown to operate successfully in the presence of strong analog channel impairments.
Professor Jin Au Kong has developed new techniques for the interpretation of remote sensing data, has modeled microstrip integrated circuits, and has developed new precision navigation instrument landing systems.
Professor Jeffrey Shapiro has completed the study of the role of local oscillator optimization in quadrature noise squeezing. These techniques have been used in conjunction with his earlier research on Raman noise in fiber four-wave mixing in order to predict a new Raman squeezing regime. Dr. Ngai Chuen Wong has fabricated periodically poled lithium niobate as a versatile nonlinear optical material that can be phase-matched over a broad wavelength range. This will be applicable to widely tunable sources in nonlinear optics as well as optical amplifiers and frequency shifters in optical communication.
Dr. Mark Hollis is developing a new technology for DNA sequence determination that offers the potential for much lower cost and higher throughput than conventional techniques based on gel electrophoresis. His approach exploits the natural base-pairing property of DNA by attaching short, single-stranded DNA fragments (probes) of known sequences to specific sites on a microelectronic chip. Single-stranded DNA fragments (targets) of unknown sequence are then washed across the chip. The target DNA binds or hybridizes strongly to probes that contain the Watson-Crick complement, and much less strongly to other probes. Specialized circuitry on the chip detects and reports the sites that contain hybridized DNA, thus enabling the base sequence of the target DNA to be derived by using a novel algorithm.
Professor Donald Troxel is developing tools and infrastructure to enable virtual and physical prototyping of advanced microsystems. For example, a remote microscope was developed that allows users to operate and view an actual microscope located at a distant microfabrication facility. In this way, semiconductor processing facilities can be shared by many users in a cost-effective way.
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: (1) maintaining our high standards for recruitment procedures that include sending job postings to minority colleges and organizations; (2) 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 (3) being committed to finding new techniques to more effectively identify women and minority candidates and to being more open to suggestions in this area. During the past year, fifteen searches were conducted, resulting in the hiring of three females and one African American male.
MIT Reports to the President 1995-96