Federico Capasso is the
Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior
Research Fellow at Harvard University, which he joined in 2003 after
a 26-year career at Bell Labs where he rose from postdoc to Vice President
of Physical Research. He holds a doctorate in Physics from the University
of Rome, Italy (1973) and an honorary doctorate in Electronic Engineering
from the University of Bologna (2003).
Capassos research has cut across several disciplines, bridging
basic and applied physics and engineering. These include photonics,
laser physics and nonlinear optics, electronics, nanotechnology, mesoscopic
physics, and most recently MEMS applied to basic studies of quantum
electrodynamics and its applications to nanomechanics. A unifying theme
of his research has been the quantum design and study of artificial
materials, nanostructures and new devices with man-made electronic and
optical properties, an approach that Capasso pioneered and dubbed bandstructure
engineering. These structures were grown by thin-film deposition techniques
such as Molecular Beam Epitaxy (MBE), pioneered by Al Cho. An excellent
example of this research is his invention and first demonstration in
1994 with Jerome Faist, Al Cho and other collaborators at Bell Laboratories
of the Quantum Cascade (QC) laser, a fundamentally new light source
whose emission wavelength can be designed to cover the entire spectrum
from the mid-infrared to the THz region by tailoring the active region
layer thickness. QC lasers are now commercially available and have wide
ranging applications to molecular spectroscopy, chemical sensing and
trace gas analysis (such as atmospheric chemistry, combustion diagnostics,
breath analyzers in medicine, pollution monitoring and industrial process
control, homeland security) and optical wireless.
Among Capassos other important contributions to photonics one
should mention multilayer low-noise avalanche photodiodes with artificially
enhanced ratio of ionization coefficients and the concept of the solid-state
photomultiplier, new photoconductors based on the different tunneling
rates of electrons and holes (effective mass filtering) and the demonstration
of a new class of giant optical nonlinearities in the mid-infrared,
associated with intraband transitions, that have found applications
in the modelocking of QC lasers.
In recent years Capassos photonics research has branched off to
new microlasers based on concepts of chaos and on photonic crystals.
His group and Douglas Stones at Yale demonstrated deformed (noncircular)
whispering gallery microlasers, capable of supporting chaotic rays,
which led to a major enhancement of their optical power through the
use of bow-tie modes. This year Capassos group and
Oskar Paynters groups at Caltech demonstrated the first electrically
pumped photonic crystal semiconductor microlaser.
Capassos contributions to high-speed electronic devices such as
heterostructure transistors and related investigations of electronic
transport have also had a major impact. In the early eighties he and
his collaborators initiated a new line of research on graded bandgap
semiconductors which led them to the direct demonstration that quasi
electric fields in these materials, a concept pioneered by Nobel
Prize winner Herbert Kroemer, can impart electron velocities in excess
of 2x107 cm/s, and to the first realization of Kroemers graded-gap
base transistor concept. This device, in its Silicon Germanium implementation,
is now commercial and has found many applications in electronics such
as lightwave communication systems.
Capasso then moved on to the investigation of resonant tunneling (RT)
in heterostructures and to its exploitation in novel devices. He proposed
and first demonstrated RT bipolar transistors, pioneering their use
in a new class of circuits with greatly reduced number of components
per function. This opened up a new direction of research in quantum
devices and related circuit architectures, which continues to be actively
pursued world-wide and broadly applied to materials ranging from semiconductors
to carbon nanotubes and other molecular structures.
Capassos current research activity also focuses on the investigation
of quantum electrodynamical phenomena such as the Casimir effect, i.e.
the attractive force between uncharged metallic surfaces, which is the
manifestation of quantum mechanical vacuum fluctuations, and its dependence
on the boundary conditions of the electromagnetic fields. The goal is
to tailor vacuum fluctuations and to investigate nanomechanical devices
based on the Casimir effect. For this new line of research Capasso is
using MEMS technology and has demonstrated new actuators and nonlinear
oscillators based on the Casimir effect, which have been widely cited.
He is the author of over 300 articles and coeditor of six volumes. He
holds over 45 US patents. Capasso has been widely honored for his work.
He is a member of the National Academy of Sciences, the National Academy
of Engineering, the American Academy of Arts and Sciences and an Honorary
Member of The Franklin Institute. His awards include the American Physical
Society Arthur Schawlow Prize for Laser Science, the Wetherill Medal
of the Franklin Institute, the Optical Society of America Wood Prize,
the Rank Prize in Optoelectronics (UK), the IEEE David Sarnoff Award
in Electronics, the IEEE LEOS W. Streifer Award, the Duddell Medal of
the Institute of Physics (UK), the Materials Research Society Medal,
the Willis Lamb Medal for Laser Physics and Quantum Optics, the Vinci
of Excellence Prize (France), the Welker Memorial Medal (Germany),
the International Symposium on Compound Semiconductor Award, the New
York Academy of Sciences Award, the Newcomb Cleveland Prize of AAAS,
the NASA Group Achievement Award, the Bell Labs Distinguished Member
of Technical Staff and the Bell Labs Fellow Award. He is a Fellow of
IEEE, the American Physical Society, the Optical Society of America,
SPIE and the American Association for the Advancement of Science.
I am very grateful for these honors (the IEEE Edison Medal and
the American Physical Society Schawlow Prize in Laser Science). I was
fortunate to join Bell Labs at the dawn of a new Golden Age in materials
science and solid-state physics, made possible by the advent of Molecular
Beam Epitaxy. MBE enabled the synthesis of semiconductor designer
materials in which the electrical and optical properties can be tailored
at will for new device applications and for the observation of new physics.
When I realized this tremendous potential shortly after coming to Bell
Labs in the early eighties, I all of a sudden felt like a kid in the
candy store! Almost anything is possible, I thought, the possibilities
are limitless! I can have fun for the rest of my life! And indeed the
impact of heterostructure materials on science and technology has been
remarkable, ranging form basic physics discoveries like the fractional
quantum Hall effect and an extremely rich variety of new quantum phenomena
to a host of useful devices that are widely used in fields such as communications.
I am deeply grateful to Bell Labs for its fantastic interdisciplinary
research atmosphere and the many great colleagues, in particular Al
Cho, inventor of MBE, with whom I have had the privilege to collaborate
for so many years and sharing so many scientific adventures.