Tech Briefs Magazine - August 2023 - 38

Optics
Engineering the Flow of Light
The new technique could have applications in industries such as holographic screens and
high-power lasers.
University of Southern California, Los Angeles, CA
T
he novel structure shown in the illustration
was designed to do one thing:
change the shape of light as it is transported.
In a recent paper, Professor
Mercedeh Khajavikhan and her team
showed how this can be done by using a
new theoretical model that could have
profound implications for many aspects
of our lives.
Light can be generated by lasers for imaging
and sensing, run through fiber optic
cables for advanced communications, and
built into chips to increase computing capabilities
to a level earlier generations
couldn't have dreamed of. Although each
of these advances may have ended with a
new device built by a mechanical, astronautical,
biomedical, or computer engineer,
they got their start in photonics.
Light particles tend to move as waves,
and photonics is the science of harnessing
those waves. From cutting-edge experiments
of quantum communication
with entangled photons, to everyday
technologies like smartphone screens,
LiDAR, and fiber internet, photonics
has changed our lives more than most
people realize. And even though the
field has been around for over a century,
researchers are still pushing into
new frontiers.
One of these frontiers is called topological
photonics. It combines traditional
photonics with topological physics - a
field pioneered in part by Nobel Prize
winner and former USC Professor Duncan
Haldane. Topological physics - the
mathematical study of shapes and their
arrangement in space - has been used to
explain many interesting properties in
electronics and has led to the development
of several new materials and devices.
Now, by combining topological physics
and photonics, researchers can engineer
even more creative and never-before-seen
light structures.
So, what is so special about this new
structure and how did they build it? The
team first uses topological physics to
come up with a design they want to explore.
They then run simulations to un38
2
-it2
it2
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1
1
2
to
to
2
1
t1
This
novel structure produces uniquely shaped light and is only one quarter of a millimeter squared
in size. (Image: Nathan Liu)
derstand how the elements in the structure
should interact with each other.
Next, they design the individual cells
- the little building blocks that make
up the whole structure.
Once the cell design is complete, they
must decide how they should be arranged
together to form the structure.
Finally, the design is taken to a nano-fabrication
clean room where the physical
product - less than 0.25 square millimeter
in size - is built. What we are left
with is a totally unique structure that
forms light into a novel shape when it
flows through. This new shape, in turn,
has new qualities, such as better lasing
purity and higher efficiency.
As impressive as that is, Khajavikhan
and her team decided to go even further.
And this is where that combination
of physics and photonics really
comes into play. Topological materials
can exhibit amazing new transport
properties, but they cannot easily be
switched between an " on " and " off "
state. Think about these light structures
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like a state- of-the-art race car. They can
move faster, turn harder, and do more
than their competitors. But if you can't
ever turn the car off once you've started
the engine, it's not a very practical piece
of machinery.
That's exactly what the USC team was
able to do - control this new light. They
introduced a technique from photonic
systems called " optical pumping " to give
the topological properties of the structure
the ability to turn on and off. The
ability to control not just the shape of
light, but when and how it flows through
a system is of utmost importance.
For the researchers, the work on this
new structure is only just the beginning.
" Our findings open up completely new
avenues to study topological systems
and we plan on engineering more designs
that could change the face of a
whole host of industries such as holographic
screens and high-power lasers, "
said Khajavikhan.
For more information, contact Amy
Blumenthal at amyblume@usc.edu.
Tech Briefs, August 2023

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