Multitasking fibers weave a new
story for imaging systems
A group at MIT has developed a multimaterial
optical fiber that can detect the components of any
light that strikes it. Woven together, the fibers make
a flexible, lensless camera. Courtesy of Fabien
Sorin, MIT.
CAMBRIDGE, Mass. – Imagine walking
to work one day and, for no obvious reason, you get a feeling that everyone is
looking at you. You ignore the feeling for
a while, but it persists, despite the fact that
none of the people bustling around nearby
are casting a single glance at you and
you’ve gotten used to the growing number
of surveillance cameras filling every city
block. Now you feel silly, perhaps even a
little paranoid. But you might not be
wrong – a new imaging technology has
begun to weave itself into the fabric of
everyday life.
In the lab of professor Yoel Fink of the
materials science and engineering department at MIT reside swaths of woven
strands of optical fibers. Not off-the-roll
fibers ordered from a catalog, but custom
lines drawn from a preform crafted by
Fink’s group. Interwoven like a patch of
cloth, the fibers combine to form a lensless, flexible camera.
The researchers made the fiber using
polyethersulfone as the base material
and alternating layers of semiconducting
As40Se60 or As40Se54Te6. Contacts made of
tin were attached to the semiconductor
rings. After deposition, the layers were
rolled together onto a tube. After making
a series of these tubes, the engineers
stacked them, joined the ends by heating
them and drew them out into their final
fiber diameter (see figure). The preforms
were about 3 cm in diameter, while the
processed fibers ranged from 100 μm to
1 mm in diameter.
When an external electric field is applied to the contacts, which act as electrodes, the semiconductor layers become
responsive to light via the photocurrent effect. A single layer of the material can discriminate the incoming light’s angle of incidence; a second layer distinguishes
wavelength. A third layer, in theory, would
add RGB information to the mix.
According to Fabien Sorin, a member
of Fink’s group representing MIT’s electronics lab, the semiconductor bandgap
can be adjusted so that wavelengths from
the UV to the visible to the IR can be detected.
The investigators tested the fiber’s ability to form an imaging system by arranging them into a 32 ; 32 grid, with about
1 cm between each pair of strands. Powered up, the optical fiber “fabric” patch
could image an object with features as
small as 100 nm.
“The size [of the grid] was limited for
convenience of use in the lab,” Sorin said,
“but could be made much larger, with
smaller spacing between fibers.” That
would significantly improve image resolution.
Fink’s group sees strong potential for
this technology – which its members have
dubbed “multimaterial fibers” – in such
applications as large-area medical imaging, remote sensing, industrial control and
intelligent fabrics.
It may even show up as watchful sew-on patches on clothes and baseball caps,
giving their wearers an extra eye with
which to watch the world and you something to be wary of on your walk to work.
Lynn Savage
lynn.savage@laurin.com