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Unlike conventional plasmonic energy harvesting devices based on light scattering, enhancement or guiding, the new hydrodynamics-inspired light trapping platform circulates energy flow through nanoscale optical vortices 'pinned' to plasmonic nanostructures.
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Boston
University researchers have demonstrated a new way to efficiently trap
and enhance light in nanoscale structures and nanopatterned thin films,
which can significantly improve performance of photonic and electronic
devices such as nanosensors, thin-film organic solar cells and optical
nanochips.
Nanoscale
light focusing can be achieved by converting free photons into
localized charge-density oscillations (surface plasmons) on noble-metal
nanostructures, which serve as nanoscale analogs of radioantennas and
are typically designed by using antenna theory concepts. Despite
offering technological innovation in biosensing and terahertz
metamaterials design, plasmonics faces fundamental physical limitation
in the visible frequency band due to high absorptive losses of metals.
To
address this limitation of plasmonics, the Boston University research
team introduced an alternative hydrodynamics-inspired approach for
plasmonic nanocircuit engineering, based on trapping incoming light into
nanoscale optical tornadoes—areas of circular motion of light
flux—'pinned' to plasmonic nanostructures. They show that creating
optical vortices in nanostructures and coupling them into
transmission-like sequences results in dramatic optical effects,
including optical spectra shaping and orders-of-magnitude increase in
the field intensity and quality factors of trapped optical modes.
"We
build our design approach around the hydrodynamic analogy of the
'photon fluid,' whose kinetic energy can be locally increased via
convective acceleration in the vortex velocity field and then converted
into pressure energy to generate localized areas of high field
intensity," explained Dr. Svetlana Boriskina, the first author on the
paper "Molding the flow of light on the nanoscale: from vortex nanogears
to phase-operated plasmonic machinery", which appears in the Jan 2012
issue of the journal Nanoscale.
Just as mechanical and hydrodynamic transmissions form a basis of
complex machinery, rationally designed nanostructures that trap optical
vortices can be combined into complex plasmonic networks enabling
nanoscale light routing and switching.
The
scientists anticipate that their findings are going to drastically
change the approach to the engineering of plasmonic nanocircuits,
leading to better fundamental insight and novel device solutions in
light generation, harvesting and processing. In particular, they
demonstrated the advantages of their approach by developing a new
platform for surface enhanced Raman spectroscopy, presented in a paper
appearing in the journal Nano Letters.
Moving
forward, the scientists are exploring the advantages of the new
engineering concept for renewable energy generation, as it helps to
eliminate the mismatch between the electronic and photonic length scales
in thin-film photovoltaic devices. They expect that the solar energy
harvesting platforms designed in the frame of the proposed methodology
will help to minimize the thickness of semiconductor needed to absorb
light completely, will amplify the signal via plasmonic enhancement
mechanism, and will be compatible for integration with either silicon
electronics or flexible substrates such as those based on organic and
polymer materials.
Electromagnetic Field Enhancement and Spectrum Shaping through Plasmonically Integrated Optical Vortices
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