Multimaterial multifunctional fiber devices
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Sorin, Fabien, and Yoel Fink. "Multimaterial Multifunctional Fiber
Devices." In European Conference on Optical Communication,
ECOC 2009, 20-24 September, 2009, Vienna, Austria.
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Institute of Electrical and Electronics Engineers
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ECOC 2009, 20-24 September, 2009, Vienna, Austria
Paper 5.1.6
Multimaterial Multifunctional Fiber Devices
Fabien Sorin(1), Yoel Fink(2)
(1)
Department of Materials Science and Engineering, Research Laboratory of Electronics and Institute for Soldier
Nanotechnology, Massachusetts Institute of Technology, Cambridge, MA 02139 (USA), sorin@mit.edu
(2)
Department of Materials Science and Engineering, Research Laboratory of Electronics and Institute for Soldier
Nanotechnology, Massachusetts Institute of Technology, Cambridge, MA 02139 (USA), yoel@mit.edu
Abstract Recent discoveries have enabled the integration of metals, insulators and semiconductors structures
into extended length of polymer fibers. The challenges and opportunities associated with this new class of fiber
devices will be presented.
The recent development of fiber devices
integrating a prescribed assembly of conducting,
semiconducting and insulating materials into
specific geometries with intimate interfaces and
microscopic feature dimensions has heralded a
novel path to large area, flexible and light
weight electronic and optoelectronic systems1.
For the first time, functionalities such as optical
transport2,3, external reflection4, lasing5, but also
optical6-9 and thermal10 detection may be
delivered at length scales and uniformity
typically associated with optical fibers. While
these fibers share the basic device attributes of
their traditional electronic and optoelectronic
counterparts, they are fabricated using
conventional preform-based fiber-processing
methods, yielding kilometers of functional, thin
and flexible fiber devices. This renders these
fibers systems a compelling candidate for
applications such as remote and distributed
sensing, large-area optical-detection arrays, and
functional fabrics1,6-10.
This presentation provides a review of the recent
progress in multimaterial fibers research aimed
to enhance fiber-systems functionalities by
increasing device density and complexity. We
will first describe the fabrication approach of
multimaterial fiber devices, and briefly present
Photonic Band Gap fibers for medical
applications our group has developped. The
latest results on photodetecting fibers will then
be presented. Especially, two complementary
approaches towards realizing sophisticated
functions are explored: on the single-fiber level,
the integration of a multiplicity of functional
components into one fiber, and on the multiplefiber level, the assembly of large-scale two- and
three-dimensional geometric constructs made of
many fibers. Finally, recent progressses on
978-3-8007-3173-2 © VDE VERLAG GMBH
Fig. 1: (a) A chalcogenide semiconducting glass rod is
assembled with an insulating polymer shell and four metal
electrodes; and (b) a polymer sheet is rolled around the
structure to form a protective cladding. (c) The high-index
chalcogenide glass is evaporated on both sides of a lowindex thin polymer film before (d) being rolled around the
cylinder prepared in (a-b). A polymer layer is wrapped
around the coated film for protection. (e) The preform is
consolidated in a vacuum oven and is thermally drawn to
mesoscopic-scale fibers. The cross-section of the resulting
fibers retains the same structure and relative sizes of the
components at the preform level.
in-fiber device complexity will be presented as
well as an overview of the different projects and
future direction for this emerging technology
.
The fabrication of multimaterial fibers
involves the construction of macroscale
preforms that are subsequently stretched into
long (hundreds of meters), thin, flexible, and
light-weight fibers that deliver prescribed
functionalities1. In order to give an outline of the
steps involved in fiber fabrication, we consider
an integrated device that consists of both a
cylindrical omnidirectional mirror structure and
a metal-semiconductor-insulator optoelectronic
device as depicted in Figure 1. Fabricating the
device fiber begins with synthesizing a
ECOC 2009, 20-24 September, 2009, Vienna, Austria
chalcogenide glass rod using standard sealedampoule techniques. A hollow polymer tube is
prepared having an inner diameter that exactly
matches the outer diameter of the glass rod, and
a thickness exactly equal to that of thin metallic
ribbons. The glass rod is then slid into the tube,
the electrodes are inserted into pockets cut in the
tube (Fig. 1a), and finally a protective polymer
cladding is wrapped around the structure (Fig.
1b). In this way, the metal electrodes are
completely enclosed between the polymer and
the glass rod, preventing any leakage when it
melts during drawing. The electrodes may be
contacted to thin glass films with this method as
well.
Fabrication of hollow multilayer
structures in fibers begin by thermally
evaporating a high-index chalcogenide glass on
both sides of a free-standing low-index thin
polymer film. To create a hollow fiber, the film
is wrapped around a silicate glass tube and
consolidated through heating in a vacuum oven.
The silicate tube is then removed from the
preform core by etching with hydrofluoric acid.
When the structure is placed on the external
surface of the fiber, no quartz tube is needed.
Instead, the coated film is rolled directly around
a polymer cylinder with a thin protective
polymer layer wrapped around it.
Both procedures are combined in
preparing the preform shown in Fig. 1, where an
external multilayer structure surrounds the
optoelectronic device. The preform is then
consolidated under vacuum at a high
temperature (typically 10-3 Torr and 260 Cº).
The resulting fiber preform is thermally drawn
into extended lengths of fiber using the tower
draw procedure common in the fiber-optic
industry. During the draw process, the mirror
layers are reduced in thickness by a factor of
~20-100 and the nominal positions of the PBGs
are determined by laser micrometer monitoring
of the fiber outer diameter during the draw
process. The end result of this fabrication
process is 100’s of meters of uniform fibers.
We now turn to recent development in
codrawn
metal-insulator-semiconductor
photodetecting fiber-based devices with
mesoscopic-scale
cross-sectional
features
enabled by this fabrication approach. These new
class of fibers have heralded a novel path to
optical radiation detection, allowing device-like
performance at length scales and in a
mechanically flexible form hitherto associated
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Paper 5.1.6
Fig. 2: Top: SEM micrographs of a dual-ring fiber where
the position of the electrodes contacting the inner layer are
rotated by 45o with respect to those contacting the outer
layers (scale bar 100 microns). Bottom left: a
semiconducting film (scale bar 1 micron). Bottom right:
intimate contact between the film and an electrode (scale
bar 1 micron).
with optical fibers. Until recently, however, a
limitation of these novel fiber devices has been
the
challenge
of
integrating
multiple
optoelectronic components into a single fiber
cross-section. This is in fact a common problem
in nanotechnology where the drive towards
smaller and smaller nanoscale devices
complicates the ability to integrate and
individually address many of them, especially
over very large-area coverage. Integration of
multiple devices to work collectively, however,
is key to the delivery of complex functionality.
The fabrication approach described above
however, espsecially for thin-film structures,
allows for great flexibility in the number of
films to be integrated, their composition,
thickness (from a few microns down to below
100 nm), and radial position, as well as the
number of electrodes and their placement
around the film circumference. This is
exemplified in Figure 2, in which the precise
alignment of the electrodes between layers, the
semiconducting film and the intimate contact
between the semiconductor and an electrode are
shown. Here, the metallic electrodes are
typically tens of microns in size which renders
trivial electrical contact of each individual
device, while the film is uniformly maintained
down to below 100 nm in thickness, illustrating
the fine level of control over the fiber crosssectional structure that can be achieved.
ECOC 2009, 20-24 September, 2009, Vienna, Austria
Fig. 3: Principle of single grid lensless imaging: An object
(smiley face) is illuminated by polychromatic radiation.
The two diffracted patterns are obtained at the grid
location. The phase-retrieval algorithm is used to
reconstruct the object. The first row shows theoretical
calculations while the second shows the experimental
results.
This prescribed arrangement of multiple
nanometer scale components in a single fiber
enables the exploitation of their collective
response to impart complex functionalities to
fiber devices. We will show that a tandem
arrangement of sub-wavelength photodetecting
devices integrated in a single fiber enables the
extraction of information on the direction,
wavelength and potentially even color of
incident radiation over a wide spectral range in
the visible regime. The remarkable increase in
functionality of polymer fibers integrating novel
arrangements of nanometer devices is best
exploited when one considers the potential
coverage area of these systems and the
opportunities associated with their assemblies
into constructs and fabrics1,6-10. In Figure 3, we
demonstrate how a single wavelength
discriminating fiber web can image a complex
object with polychromatic light, noninterferometrically and without lenses, by taking
an intensity measurement at a single diffraction
plane8.
Finally we will present recent
development and direction for multimaterial
fibers. One example is the incorporation of
electronic junctions having build-in potential is
a necessity for the realization of transistors,
photovoltaics, LEDs, and many other electronic
and optoelectronic devices. Until recently, the
length and complexity of fiber devices showing
rectification behavior have been limited by the
processing methods. Their cylindrical geometry
is ideal for single device architectures but not
amenable to building multiple devices into a
single fiber, a requirement for more complex
tasks such as signal processing. The
multimaterial
preform-to-fiber
approach
addresses the challenges of device density,
978-3-8007-3173-2 © VDE VERLAG GMBH
Paper 5.1.6
complexity, and length simultaneously, but the
performance of these fiber devices has also been
limited by the relatively small set of materials
compatible with the drawing process and use of
low
mobility
amorphous
inorganic
semiconductors. From a processing standpoint,
non-crystallinity is necessary to ensure that the
preform viscosity during thermal drawing is
large enough to extend the time-scale of breakup
driven by surface tension effects in the fluids to
times much longer than that of the actual
drawing. The structured preform cross-section is
maintained into the microscopic fiber only when
this requirement is met. Unfortunately, the same
disorder that is integral to the fabrication process
is detrimental to the semiconductors’ electronic
properties. As a result, multimaterial fiber
devices built to date are limited to ohmic metalsemiconductor contacts and suffer from
problems common to photoconductor devices
including high noise currents, continuous power
consumption, and reduced sensitivity. The
recent
incorporation
of
phase-changing
semiconductors11, those that may be easily
converted between the amorphous and
crystalline states, into composite fibers offers a
path towards reduction of these defects and the
ability to introduce spatially extended internal
fields within the device. Indeed, by proper
selection of the semiconductor and metallic
contacts the synthesis of a crystalline compound
semiconductor in fiber can be achieved. This
opens the way toward arbitrarily long rectifying
junction or field effect devices embedded in
polymer fibers12.
It is safe to say that the range of
materials and variety of structures amenable to
the approach outlined in this paper will increase
and that the resulting repertoire of novel
applications will expand. In addition to
incorporating new materials into our fibers,
novel structures and geometries may be
considered that are not necessarily cylindrically
or longitudinally symmetric. The interplay
between
material
properties,
structure
integration, and fabric-array construction that
our group has pioneered is just beginning and
promises to be an exciting field for fundamental
and applied research besides many current and
future applications. The further development of
transistors and fiber-integrated logic devices
would bring even more exciting functionalities
and the prospect of truly intelligent fabrics.
ECOC 2009, 20-24 September, 2009, Vienna, Austria
References
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Paper 5.1.6
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