Scientists slow and steer light with resonant nanoantennas

Date:
August 20, 2020
Source:
Stanford University
Summary:
Researchers have fashioned ultrathin silicon nanoantennas that
trap and redirect light, for applications in quantum computing,
LIDAR and even the detection of viruses.



FULL STORY ========================================================================== Light is notoriously fast. Its speed is crucial for rapid information
exchange, but as light zips through materials, its chances of interacting
and exciting atoms and molecules can become very small. If scientists
can put the brakes on light particles, or photons, it would open the
door to a host of new technology applications.


==========================================================================
Now, in a paper published on Aug. 17, in Nature Nanotechnology, Stanford scientists demonstrate a new approach to slow light significantly,
much like an echo chamber holds onto sound, and to direct it at
will. Researchers in the lab of Jennifer Dionne, associate professor
of materials science and engineering at Stanford, structured ultrathin
silicon chips into nanoscale bars to resonantly trap light and then
release or redirect it later. These "high-quality-factor" or "high-Q" resonators could lead to novel ways of manipulating and using light,
including new applications for quantum computing, virtual reality and
augmented reality; light-based WiFi; and even the detection of viruses
like SARS-CoV-2.

"We're essentially trying to trap light in a tiny box that still
allows the light to come and go from many different directions,"
said postdoctoral fellow Mark Lawrence, who is also lead author of the
paper. "It's easy to trap light in a box with many sides, but not so easy
if the sides are transparent -- as is the case with many Silicon-based applications." Make and manufacture Before they can manipulate light, the resonators need to be fabricated, and that poses a number of challenges.

A central component of the device is an extremely thin layer of silicon,
which traps light very efficiently and has low absorption in the
near-infrared, the spectrum of light the scientists want to control. The silicon rests atop a wafer of transparent material (sapphire, in this
case) into which the researchers direct an electron microscope "pen" to
etch their nanoantenna pattern. The pattern must be drawn as smoothly
as possible, as these antennas serve as the walls in the echo-chamber
analogy, and imperfections inhibit the light-trapping ability.



========================================================================== "High-Q resonances require the creation of extremely smooth sidewalls
that don't allow the light to leak out," said Dionne, who is also Senior Associate Vice Provost of Research Platforms/Shared Facilities. "That
can be achieved fairly routinely with larger micron-scale structures,
but is very challenging with nanostructures which scatter light more."
Pattern design plays a key role in creating the high-Q nanostructures. "On
a computer, I can draw ultra-smooth lines and blocks of any given
geometry, but the fabrication is limited," said Lawrence. "Ultimately,
we had to find a design that gave good-light trapping performance but
was within the realm of existing fabrication methods." High quality
(factor) applications Tinkering with the design has resulted in what
Dionne and Lawrence describe as an important platform technology with
numerous practical applications.

The devices demonstrated so-called quality factors up to 2,500, which is
two orders of magnitude (or 100 times) higher than any similar devices
have previously achieved. Quality factors are a measure describing
resonance behavior, which in this case is proportional to the lifetime of
the light. "By achieving quality factors in the thousands, we're already
in a nice sweet spot from some very exciting technological applications,"
said Dionne.



==========================================================================
For example, biosensing. A single biomolecule is so small that it
is essentially invisible. But passing light over a molecule hundreds
or thousands of times can greatly increase the chance of creating a
detectable scattering effect.

Dionne's lab is working on applying this technique to detecting COVID-19 antigens -- molecules that trigger an immune response -- and antibodies
- - proteins produced by the immune system in response. "Our technology
would give an optical readout like the doctors and clinicians are used
to seeing," said Dionne. "But we have the opportunity to detect a single
virus or very low concentrations of a multitude of antibodies owing
to the strong light-molecule interactions." The design of the high-Q nanoresonators also allows each antenna to operate independently to
detect different types of antibodies simultaneously.

Though the pandemic spurred her interest in viral detection, Dionne
is also excited about other applications, such as LIDAR -- or Light
Detection and Ranging, which is laser-based distance measuring technology
often used in self- driving vehicles -- that this new technology could contribute to. "A few years ago I couldn't have imagined the immense application spaces that this work would touch upon," said Dionne. "For me,
this project has reinforced the importance of fundamental research --
you can't always predict where fundamental science is going to go or
what it's going to lead to, but it can provide critical solutions for
future challenges." This innovation could also be useful in quantum
science. For example, splitting photons to create entangled photons that
remain connected on a quantum level even when far apart would typically
require large tabletop optical experiments with big expensive precisely polished crystals. "If we can do that, but use our nanostructures to
control and shape that entangled light, maybe one day we will have an entanglement generator that you can hold in your hand," Lawrence said.

"With our results, we are excited to look at the new science that's
achievable now, but also trying to push the limits of what's possible." Additional Stanford co-authors include graduate students David Russell
Barton III and Jefferson Dixon, research associate Jung-Hwan Song, former research scientist Jorik van de Groep, and Mark Brongersma, professor of materials science and engineering. This work was funded by the DOE-EFRC, "Photonics at Thermodynamic Limits" as well as by the AFOSR. Jen is also
an associate professor, by courtesy, of radiology and member of the Wu
Tsai Neurosciences Institute and Bio-X.


========================================================================== Story Source: Materials provided by Stanford_University. Original written
by Lara Streiff.

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Mark Lawrence, David R. Barton, Jefferson Dixon, Jung-Hwan Song,
Jorik
van de Groep, Mark L. Brongersma, Jennifer A. Dionne. High quality
factor phase gradient metasurfaces. Nature Nanotechnology, 2020;
DOI: 10.1038/ s41565-020-0754-x ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200820164211.htm

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