A trillion turns of light nets terahertz polarized bytes

Date:
October 19, 2020
Source:
Rice University
Summary:
Nanophotonics researchers have demonstrated a novel technique
for modulating light at terahertz frequencies with plasmonic
metasurfaces.



FULL STORY ==========================================================================
U.S. and Italian engineers have demonstrated the first nanophotonic
platform capable of manipulating polarized light 1 trillion times
per second.


========================================================================== "Polarized light can be used to encode bits of information, and we've
shown it's possible to modulate such light at terahertz frequencies,"
said Rice University's Alessandro Alabastri, co-corresponding author of
a study published this week in Nature Photonics.

"This could potentially be used in wireless communications," said
Alabastri, an assistant professor of electrical and computer engineering
in Rice's Brown School of Engineering. "The higher the operating
frequency of a signal, the faster it can transmit data. One terahertz
equals 1,000 gigahertz, which is about 25 times higher than the operating frequencies of commercially available optical polarization switches."
The research was a collaboration between experimental and theoretical
teams at Rice, the Polytechnic University of Milan (Politecnico) and
the Italian Institute of Technology (IIT) in Genoa. This collaboration
started in the summer of 2017, when study co-first author Andrea Schirato
was a visiting scholar in the Rice lab of physicist and co-author Peter Nordlander. Schirato is a Politecnico-IIT joint graduate student under
the supervision of co- corresponding author Giuseppe Della Valle of
Politecnico and co-author Remo Proietti Zaccaria of IIT.

Each of the researchers work in nanophotonics, a fast-growing field that
uses ultrasmall, engineered structures to manipulate light. Their idea
for ultrafast polarization control was to capitalize on tiny, fleeting variations in the generation of high-energy electrons in a plasmonic metasurface.

Metasurfaces are ultrathin films or sheets that contain embedded
nanoparticles that interact with light as it passes through the film. By varying the size, shape and makeup of the embedded nanoparticles and by arranging them in precise two-dimensional geometric patterns, engineers
can craft metasurfaces that split or redirect specific wavelengths of
light with precision.

"One thing that differentiates this from other approaches is our reliance
on an intrinsically ultrafast broadband mechanism that's taking place
in the plasmonic nanoparticles," Alabastri said.

The Rice-Politecnico-IIT team designed a metasurface that contained rows
of cross-shaped gold nanoparticles. Each plasmonic cross was about 100 nanometers wide and resonated with a specific frequency of light that
gave rise to an enhanced localized electromagnetic field. Thanks to this plasmonic effect, the team's metasurface was a platform for generating high-energy electrons.

"When one laser light pulse hits a plasmonic nanoparticle, it excites
the free electrons within it, raising some to high-energy levels that
are out of equilibrium," Schirato said. "That means the electrons are 'uncomfortable' and eager to return to a more relaxed state. They return
to an equilibrium in a very short time, less than one picosecond."
Despite the symmetric arrangement of crosses in the metasurface, the nonequilibrium state has asymmetric properties that disappear when the
system returns to equilibrium. To exploit this ultrafast phenomenon for polarization control, the researchers used a two-laser setup. Experiments performed by study co-first author Margherita Maiuri at Politecnico's
ultrafast spectroscopy laboratories -- and confirmed by the team's
theoretical predictions -- used an ultrashort pulse of light from one
laser to excite the crosses, allowing them to modulate the polarization
of light in a second pulse that arrived less than a picosecond after
the first.

"The key point is that we could achieve the control of light with light
itself, exploiting ultrafast electronic mechanisms peculiar of plasmonic metasurfaces," Alabastri said. "By properly designing our nanostructures,
we have demonstrated a novel approach that will potentially allow us to optically transmit broadband information encoded in the polarization of
light with unprecedented speed."

========================================================================== Story Source: Materials provided by Rice_University. Note: Content may
be edited for style and length.


========================================================================== Journal Reference:
1. Andrea Schirato, Margherita Maiuri, Andrea Toma, Silvio Fugattini,
Remo
Proietti Zaccaria, Paolo Laporta, Peter Nordlander, Giulio Cerullo,
Alessandro Alabastri, Giuseppe Della Valle. Transient optical
symmetry breaking for ultrafast broadband dichroism in plasmonic
metasurfaces.

Nature Photonics, 2020; DOI: 10.1038/s41566-020-00702-w ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201019145555.htm

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