MIT Reports to the President 1994-95

Research Laboratory of Electronics

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 1994 are briefly mentioned. The interested reader can obtain further information from RLE Progress Report No. 137, which describes research activities during calendar year 1994.


Materials And Fabrication

Professor Jesús del Alamo continues his exploration of the physics of high-power millimeter-wave InAlAs/InGaAs double heterostructure field-effect transistors on InP. These designs are intended to exhibit both high speed and high power, which are difficult to achieve simultaneously. Recently, a new device model for these transistors has been completed, which helps to ensure first-time success in circuit designs that use these devices. Professor Leslie Kolodziejski is concentrating on the fabrication of photonic band-gap crystals, which can provide three-dimensional waveguides at integrated-circuit scales within semiconductors. These waveguides are designed to transmit ultrashort optical pulses at a wavelength of a few microns. The goal is 1.55 microns in order to correspond to optical fiber transmission.

Quantum-Effect Devices

In order to produce useful circuits, Professor Marc Kastner is concentrating on techniques to produce single-electron transistors that operate at or near room temperature. Recently, sample devices with island capacitances of a few ato-farads have been achieved, which are capable of operating in this temperature regime. Professor Henry Smith has utilized a combination of interferometric lithography, spatial phase-locked electron-beam lithography, x-ray lithography, and reactive ion etching to achieve optical filters for waveform-division multiplexing. These will be essential components in high-capacity, all-optical networks.

Optics And Devices

Recognizing that ultrahigh-bit-rate optical transmission requires high-bit-rate buffers and memories, Professor Hermann Haus has developed an optical fiber-loop memory that stores one gigabit of data. Further work at Lincoln Laboratory has increased this capacity to 50 gigabits. Professor James Fujimoto has further developed the technique of optical coherence tomography to diagnose and manage a variety of ophthalmic diseases, especially those of the retina. These techniques may be used for noninvasive "optical biopsy," eliminating the need to excisionally remove specimens. These techniques also suggest that coronary artery morphology can be diagnosed with significantly higher resolution than standard intraluminal ultrasound. Professor Qing Hu continues to develop electronic devices that operate above 100 gigahertz with response times less than 10 picoseconds. These devices exploit intersubband transitions in lateral and vertical quantum-well devices. Professor Hu has also developed new micromachining techniques for miniature horn antenna structures, which are fabricated using standard planar technology. These can be easily combined in a focal-plane array on a single wafer, and can provide significantly improved spatial resolution for many applications such as remote sensing.

Surfaces And Interfaces

Professor Robert Birgeneau is using x-ray and optical techniques to study instabilities in the step configuration of Si(111) driven by reconstructions or electromigration. These instabilities produce a rippling of the surface morphology for current that flows down steps on the surface, and will provide opportunities to understand the mechanisms of electromigration and sublimation, which are important in submicron devices. Professor John Joannopoulos has utilized scanning-tip microscopy to manipulate surface atoms on a Si(100) surface. Under appropriate conditions, the tip of the microscope can be used to flip dimers on the surface, thus suggesting the possibility of the silicon wafer serving as an ultrahigh-memory storage device approaching the limit of one bit of data per atom. Professor Simon Mochrie has studied the faceting kinetics of stepped Si(113) surfaces, which self-assemble into a remarkable mesoscopically grooved morphology. This can be used as a template for the creation of a mesoscopically and chemically heterogeneous substrate. These investigations demonstrate how the inherent constraints of self-assembly can be used to provide useful structures at very fine dimensions.

Circuits And Systems

Professor Jacob White has developed several fast algorithms for the three-dimensional extraction of inductance and capacitance, and hence the simulation of electronic packaging, interconnect lines, and microelectromechanical structures. In addition to the speed of these techniques, they also allow for general Green's functions so that the same algorithm can be used for static, full-wave, or layered media electromagnetic analysis. Professor Srinivas Devadas has produced computer aids for the design of embedded systems that contain both application-specific hardware and programmable processors. These techniques permit the minimization of code size for programmable digital signal processors and a variety of other embedded systems.


Speech Communication

Professor Kenneth Stevens has developed a variety of procedures to study the basic mechanisms of human speech production and perception, means to apply this understanding to speech recognition and speech synthesis, and the investigation of acoustic and articulatory manifestations of certain speech production disorders. Recently, new techniques have been developed to assess the presence of nasality in speech and a new model has been formulated to access words from continuous speech. These have led to a refined model of human lexical access. Dr. Joseph Perkell continues to study constraints and strategies in speech production. Recent data in this area suggests that speech motor programming is partially based on acoustic goals. The data supports a model in which hearing is mandatory in order to acquire speaking capability. But, as this basic competence is established, auditory input is used mainly to refine phonemic settings and to adjust to changes in speaking rate, pitch, and loudness, according to the acoustic environment.

Sensory Communication

Professor Louis Braida continues his research on aids for the deaf. Recent studies have focused on the means to simulate the effect of sensorineural loss, where it has been shown that additive noise generally produces a realistic simulation of this loss. This has been demonstrated in audiological tests using simple stimuli. Dr. Kenneth Salisbury is focusing on the development of touch perception algorithms that will enable robots to deduce contact conditions from simple force-sensing fingertips. Using the PHANToM haptic interface, it is now possible to mechanically interact with virtual objects, permitting the perception of properties such as touch, shape, texture, and motion. Extensions of this technique are now underway using a new manual handle for human interaction.

Auditory Physiology

Dr. Donald Eddington continues to improve the performance of cochlear implant systems using a variety of techniques. These include a new sound processing system, which has led to considerable hearing improvement for subjects who can continually utilize this portable equipment. Steady improvements in this field have made cochlear implant systems by far the most successful artificial replacements of any sensory function. Dr. John Rosowski continues his studies of middle-ear function. He has produced the first measurements of the acoustic effects of the pars flaccida of the tympanic membrane, which can significantly reduce the low-frequency sensitivity of the ear.


Atomic, Molecular, And Optical Physics

Professor Shaoul Ezekiel has developed a fiber-optic scheme to detect a quench in a superconducting magnet. This is useful in environments that have been exposed to considerable magnetic and electrical noise, such as magnetic confinement fusion machines currently under development. Professor Daniel Kleppner has observed the important effect of periodic classical orbits on the quantum response of a system whose classical motion is chaotic. This will help to improve high-precision measurements of fundamental constants. Professor David Pritchard has developed a new single-ion cyclotron resonance mass spectrometer. This will help to improve the determination of atomic mass for approximately ten elements with an improved accuracy of more than an order of magnitude over the previous state of the art. These techniques will be essential ingredients in new procedures that will replace the current standard kilogram with an atomic-based standard, which is based on a precisely grown crystal of silicon. Professor Wolfgang Ketterle has combined laser cooling and evaporative cooling in a novel atom trap. The trap uses a combination of magnetic forces and far-off resonant light forces to achieve Bose-Einstein condensation. The resulting class of coherent atoms are likely to have applications in precision measurements, matter-wave microscopy, and the creation of microscopic structures by direct-write lithography.

Plasma Physics

Professor George Bekefi has designed a free-electron laser that has generated 60 MW of coherent radiation at 8.6 mm, which is the world's largest power at that wavelength. Current research is focused on the development of a new x-ray free-electron laser that is driven by a linear RF accelerator, which is the first demonstration of its kind.

Radio Astronomy

Dr. Philip Rosenkranz is studying the use of measured or simulated microwave radiometry data to infer parameters that describe the state of the atmosphere. These techniques provide a new means to characterize the behavior of storms, as well as the characterization of atmospheric radio transmission.

Digital Signal Processing

Professor Alan Oppenheim and Professor Gregory Wornell are developing several algorithms for: signal enhancement; active noise cancellation; the processing of speech, music, and underwater acoustic signals; advanced beam forming for radar and sonar systems; and signal coding and transmission. Several of these techniques utilize fractal-point processes as models, for which efficient nonlinear multiscale estimation and detection algorithms have been developed. An important application for these techniques is a new class of signal processing algorithms for wireless communication, which are increasingly needed.

Advanced Television And Signal Processing

Professor William Schreiber has completed the development of an advanced television system suitable for terrestrial broadcasting. This system provides efficient use of over-the-air spectrum, support for less expensive receivers for less demanding applications, and a practical transition scenario from the current television broadcast practice. The system features high resistance to analog channel impairments, self-optimization at each receiver (depending on signal quality and receiver performance), extended coverage as compared with conventional systems, and better quality when the signal-to-noise ratio is sufficiently high.


Professor Jin Au Kong continues to apply electromagnetic wave theory to a variety of applications, including remote sensing, synthetic aperture radar, microwave and millimeter-wave integrated circuits and interconnect, and the design of precision aircraft landing systems.

Optical Communications

Professor Jeffrey Shapiro and Dr. Ngai Chuen Wong have elucidated a hitherto unexpected Raman noise limit on the continuous-wave generation of squeezed-state light by fiber four-wave mixing. This further characterizes the ultimate noise limits for the use of squeezed-state light in fiber communications. Professor Shapiro has also developed a fast, multiresolution maximum-likelihood range imaging processing algorithm for laser radar data.

Electronics For Biological Analysis

Dr. Mark Hollis has developed a new technology for DNA sequence determination. This 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 origin are then washed across the chip. The target DNA binds or hybridizes strongly to probes that contain its Watson-Crick complement, and much less strongly to other probes. This technique promises to provide lower cost and higher throughput than conventional techniques based on gel electrophoresis.


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 the 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, due to limited turnover in RLE's research staff, success in affirmative action for research and support staff personnel has been limited. Of the three research staff appointments made this year, one was made to a woman.

Jonathan Allen

MIT Reports to the President 1994-95