Mass.--In work that could lead to applications including
multifunctional textile fabrics and all-optical computer
interfaces, MIT researchers report the creation of flexible
fibers and fabrics that can not only sense light, but
also analyze its colors.
"These novel fiber structures offer a unique possibility
for constructing an optoelectronic functional fabric
because the fibers are both flexible and mechanically
tough, and can thus be woven," write the researchers
in the October 14 issue of Nature. "Interesting
device applications follow not only from the ability
to engineer the single-fiber properties, but also from
the specifics of fiber arrangements into larger assemblies."
team's leader, Yoel Fink, notes that "the technique
we developed allows us to bring together two disparate
technologies: those involved in creating optical fibers
and those for electronic components." The work
"challenges the traditional barrier between semiconductor
devices and fiber-optic processing," said Fink,
the Thomas B. King Assistant Professor of Materials
Science and Engineering.
result? The team can create devices which marry the
ease of fabrication, length and flexibility associated
with optical fibers with the many integrated functions
associated with semiconductor devices.
able, for the first time, to precisely control the
behavior of electrons, photons and their interactions
within a fiber framework leads naturally to the exciting
possibility of eventually creating intrinsically smart
fabrics," said co-author John D. Joannopoulos,
the Francis Wright Davis Professor of Physics.
the team has created two different prototype fibers
with the new technology. The first is a fiber that
simultaneously conducts two types of information carriers:
electrons and photons. The photons are guided in a
hollow core lined by a highly confining reflective
surface dubbed "the perfect mirror" when
Fink invented it in 1998 as an MIT graduate student.
The electrons are conducted through metal microwires
that surround the fiber core. The photons and electrons
do not interact as they are confined to different
spatial locations within the fiber.
second fiber utilizes an interaction between photons
and electrons. This fiber photodetector was designed
to be sensitive to external illumination at specific
wavelengths of light. It is made of a cylindrical
semiconductor core contacted by four metal microwires
that are surrounded by an optical cavity structure.
The electrical conductance of this fiber was found
to increase dramatically upon illumination with light
at the wavelength it was designed to detect.
of the most exciting and novel potential applications
stem from assembling the fibers into woven structures.
As the authors point out, "…it is the assembly
of such fibers into 2-D grids or webs that enables
the identification of the location of an illumination
point on a surface," and does so with a very
small number of fibers.
these grids in computer screens or onto projection
boards could therefore provide a new type of interface,
said Fink. "Instead of having a mechanical mouse,
you could just use a light beam, like a laser pointer,
to communicate with the computer because the screen
would know where it was being hit."
researchers included as supplementary material to
their publication (archived on Nature's website) a
short video demonstrating a novel optical system developed
using the fiber photodetector. Go to http://www.nature.com/nature/journal/v431/n7010/suppinfo/nature02937.html
to view the video.
paper's lead author is Mehmet Bayindir, a postdoctoral
associate in the Research Laboratory for Electronics
(RLE). Additional authors are RLE Postdoctoral Associate
Ayman Abouraddy, Graduate Students Fabien Sorin and
Jeff Viens of the Department of Materials Science
and Engineering, and Shandon Hart (MIT Ph.D. 2004,
now at 3M). All of the authors are also affiliated
with the Center for Materials Science and Engineering
THEY DID IT
as in the movie 'Honey, I Shrunk the Kids,' wouldn't
it be wonderful if you could fabricate something on
the macroscale, then shrink it to a microscopic size?"
said Fink. "That's what we did. But the magic
shrink-down apparatus we used is not a 'shrinking
beam' from science fiction ... it's a furnace."
team first created a macroscopic cylinder, or preform,
some 20 centimeters long by 35 millimeters in diameter
containing a low-melting-temperature conductor, an
amorphous semiconductor, and a high-glass transition
thermoplastic insulator. The preform shares the final
geometry of the fiber, but lacks functionality due
to the absence of intimate contact between its constituents
and proper element dimensions.
preform is subsequently fed into a tube furnace where
it is heated and drawn into a fiber that does exhibit
both electrical and optical functionalities. "These
follow from the excellent contact, appropriate element
dimensions, and the fact that the resulting fiber
retains the same structure as the macroscopic preform
cylinder throughout the drawing process," said
Bayindir, who designed and synthesized the semiconducting
glasses, assembled the preforms and drew the fibers
presented in the paper.
authors conclude that their new ability to interface
materials with widely disparate electrical and optical
properties in a fiber, achieve submicrometer features,
and realize arbitrary geometries over extended fiber
lengths presents "the opportunity to deliver
novel semiconductor device functionalities at fiber-optic
length scales and cost."
work is funded by the Defense Advanced Research Projects
Agency, the Army Research Office, the Office of Naval
Research, the Air Force Office of Scientific Research,
the Department of Energy, MIT's Institute for Soldier
Nanotechnology, and the Materials Research Science
and Engineering Center (MRSEC) program of the National
authors would like to express their deep gratitude
to Esra Bayindir, C. Bruce, A. McGurl, J. Connolly,
B. Smith, M. Young and the entire staff of MIT's Research
Laboratory for Electronics and Center for Materials
Science and Engineering (part of the NSF's MRSEC program