Tech Briefs Magazine - May 2022 - PIT-26

less efficient and lead to loss of information
in quantum acoustic systems. By
pinpointing problematic areas, the technique
gives scientists the information
they need to improve resonator design.
In the February 4, 2022 edition of
Nature Communications, the researchers
reported that they could image acoustic
vibrations that have an amplitude as
small as 55 femtometers (quadrillionths
of a meter), about one-five-hundredth
the diameter of a hydrogen atom.
Over the past decade, physicists have
suggested that micromechanical resonators
in this frequency range may also
serve to store fragile quantum information
and to transfer the data from one
part of a quantum computer to another.
Establishing an imaging system that can
routinely measure micromechanical resoNanoscale
3D Structure to Control Light
The Pennsylvania State University, University Park, PA
etamaterials, made up of small,
repeated structures engineered to
produce desired interactions with light
or sound waves, can improve optical
devices used in telecommunications,
imaging and more. But the functionality
of the devices can be limited by
the corresponding design space, according
to Lei Kang, assistant research
professor of electrical engineering at
Penn State.
Kang and interdisciplinary collaborators
from Penn State and Sandia National
Laboratories leveraged three dimensions
of design space to create and
test a metamaterial with robust optical
properties.
" It's not easy to efficiently explore
M
lated many arrangements of connected
gold particles on the inside of a cubeshaped
unit cell's walls, targeting those
that best supported robust asymmetric
transmission of linearly polarized light
across a wide frequency range.
Researchers at Sandia National
Laboratories fabricated the optimized
design, constructing many nanoscopic
unit cells with cube-shaped cavities
atop a silicon nitride base. A gold pattern
was then stenciled and deposited
onto two inside walls of each unit cell.
The Sandia team then tested the
design space for 3D metamaterial components,
or unit cells, " Kang said. " But
we have developed a variety of complex
optimization techniques in our
lab, and our collaboration with Sandia
National Laboratories has allowed for fabrication
of very complex 3D structures at
the nanometer scale. This unique combination
of advanced capabilities provides a
good strategy to explore 3D unit cells that
can lead to sophisticated metamaterial
functionalities. "
One such functionality is enabling asymmetric
transmission of light, in which light
waves exhibit different power levels dependent
on their direction of travel through a
material. Realization of this phenomenon
for light with an electric field oscillating
in a specific direction - called linear
polarization - has often required bulky
components due to design challenges, according
to Kang. He said a nanoscale device
permitting asymmetric transmission
of linearly polarized light could lead to
significantly more efficient optical devices,
advancing technological applications in
communications and more.
26
Researchers at Penn State and Sandia National Laboratories
optimized and fabricated this design for a metamaterial
building block that could enable more efficient optical
devices. (Image: Lei Kang. All Rights Reserved.)
To identify an ideal unit cell design, the
team developed a computational optimizer
based on a genetic algorithm, which
identifies new configurations by mimicking
natural selection, with both self-designed
and commercial software to target
robust performance within set parameters.
Applying this approach to a 3D space
presented unique obstacles and benefits
when designing the optimizer. Generating
designs in an additional dimension,
while providing an additional degree of
freedom for developing functional materials,
required a higher computational
load. The researchers at Penn State also
had to account for fabrication limitations.
A simpler design would be easier to make
but potentially deficient in function, while
a complex design that performs ideally
could be impractical or impossible to construct
at the nanoscale.
In a recommendation engineered to
meet these challenges, the optimizer simusample
material by illuminating it with
linearly polarized light. They found
that the design performed as well as its
computationally optimized and simulated
counterpart, resulting in asymmetric
transmission of the light across
a wide range of frequencies.
This behavior made the design
promising for use in optic isolators,
according to Sawyer Campbell, assistant
research professor of electrical engineering.
" Optical isolators control and transmit
light in only one direction, like a diode in
an electrical circuit, " he said. " These components
are extremely important in telecommunications,
control systems, and
other areas. "
The researchers said they aim to continue
developing metamaterials using their
optimization techniques and a variety of
fabrication methods.
" Creating more complicated 3D structures
would allow us to expand on these
findings, " Kang said. " New combinations
of our advanced optimization methods
and state-of-the-art 3D fabrication techniques
could further propel the optical
capabilities of metamaterials. "
For more information, contact College
of Engineering Media Relations at
communications@engr.psu.edu.
Photonics & Imaging Technology, May 2022
nators for these applications will require
further research. But the current study is
already a milestone in assessing the ability
of micromechanical resonators to accurately
perform at the high frequencies
that will be required for effective communication
and for quantum computing in
the near future, Gorman said.
For more information, contact Ben P. Stein
at benjamin.stein@nist.gov.
PIT Tech Briefs 0522_1.indd 26
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4/20/22 11:10 AM
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Tech Briefs Magazine - May 2022

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