MIT
Reports to the President 1994-95
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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