Tech Briefs Magazine - October 2021 - 27

ultimate performance of LEDs. But
achieving high performance requires pre -
cisely the right conditions.
For the high exciton concentration at
which optical and electronic devices typically
operate, though, too many excitons
annihilate each other. The new work suggests
that the trick to achieve high performance
for high concentrations lays in
tweaking the material's band structure, an
electronic property that controls how excitons
interact with each other and could
reduce the probability of exciton annihilation.
When more excited particles are created,
the balance tilts toward creating
more heat instead of light.
The researchers started by placing a
thin semiconductor (tungsten disulfide,
or WS2) film atop a flexible plastic substrate.
By bending the plastic substrate,
they applied a small amount of strain to
the film. At the same time, they focused
a laser beam with different intensities on
the film, with a more intense beam leading
to a higher concentration of excitons
- a high " brightness " setting in an electronic
device.
Detailed optical microscope measurements
allowed the researchers to ob -
serve the number of photons emitted by
the material as a fraction of the photons
it had absorbed from the laser. They
found that the material emitted light at
nearly perfect efficiency at all brightness
levels through appropriate strain. To further
understand the material's behavior
under strain, the team performed analytical
modeling. They found that the
heat-losing collisions between excitons are
enhanced due to " saddle points " -
regions where an energy surface curves in
a way that resembles a mountain pass
between two peaks - found naturally in
the single-layer semiconductor's band
structure.
Applying the mechanical strain led the
energy of that process to change slightly,
drawing the excitons away from the saddle
points. As a result, the particles' tendency
to collide was reduced and the reduction
in efficiency at high concentrations of
charged particles ceased to be a problem.
For more information, contact Rachel
Ber kowitz at media@lbl.gov; 510-486-5183.
Photonic Integrated Chip for Improved Light Control
This combination of technologies could enable developments for many optical applications.
Pennsylvania State University, University Park
new technology that can allow for
better light control without requiring
large, difficult-to-integrate materials and
structures has been developed. The photonic
integrated chip could allow for many
advances in the optical field and industry,
ranging from improvements in virtualreality
glasses to optical remote sensing.
Traditionally, scientists have had two
options when it comes to controlling
light for use in various optical devices.
The first is a photonic integrated circuit
(PIC) that can be incorporated onto
small chips but has limited ability to control
free-space light - light propagating
in air, outer space, or a vacuum, as
A
opposed to being guided in fibers or
other waveguides. The second is a newly
emergent metasurface - an artificially
engineered thin layer that allows for light
manipulation at subwavelength scale but
cannot be integrated on a chip.
Researchers solved this problem by
incorporating the best qualities of the
two previous options into a new, hybrid
photonic architecture that has metasurfaces
integrated onto a PIC chip while
maintaining high light controllability.
Incorporation of the PICs and metasurfaces
makes it possible to drive the metasurfaces
using guided waves inside the
PICs. It enables routing of light among
different metasurfaces, performing multiple
complex functions on a single chip.
This new development could have
applications in optical communications,
optical remote sensing, free-space optical
interconnects, and virtual reality and
augmented reality displays. The hybrid
system has the advantages of both the
metasurfaces and the PICs. In addition,
the design is highly flexible and modular.
A library of the building blocks can be
established for reusing and creating consistent
functional components across various
de vices or systems.
For more information, contact Megan
Lakatos at mkl5024@psu.edu; 814-865-5544.
Optical Coating Exhibits the Same Color in Reflection
and Transmission
Fano Resonance Optical Coatings (FROCs) can both transmit and reflect the same
color simultaneously.
University of Rochester, New York and Case Western Reserve University, Cleveland, Ohio
O
ptical coatings have been used to
better reflect certain wavelengths
of light from lenses and other devices
or conversely, to better transmit certain
wavelengths through them. The
coatings on tinted eyeglasses, for ex -
ample, reflect or block out harmful
blue light and ultraviolet rays. But
until now, no optical coating had ever
Tech Briefs, October 2021
Cov
been developed that could simultaneously
reflect and transmit the same
wavelength or color.
Researchers developed a new class of
optical coatings - Fano Resonance
Optical Coatings (FROCs) - that can
be used on filters to reflect and transmit
colors of remarkable purity. In addition,
the coating can be made to fully reflect
www.techbriefs.com
ToC
only a very narrow wavelength range.
Previously, the only coating that could
do this was a multilayered dielectric mirror
that is much thicker, suffers from a
strong angular dependence, and is far
more expensive to make.
The researchers envision several ap -
plications for the new technology. The
FROCs could be used to separate ther27
http://www.techbriefs.com http://info.hotims.com/79418-936
Tech Briefs Magazine - October 2021

Table of Contents for the Digital Edition of Tech Briefs Magazine - October 2021
