An
electrical engineer at the University at Buffalo, who previously
demonstrated experimentally the “rainbow trapping effect” — a
phenomenon that could boost optical data storage and communications —
is now working to capture all the colors of the rainbow.
In
a paper published March 29 in the Proceedings of the National Academy
of Sciences, Qiaoqiang Gan (pronounced “Chow-Chung” and “Gone”), PhD, an
assistant professor of electrical engineering at the University at
Buffalo’s School of Engineering and Applied Sciences, and his colleagues
at Lehigh University, where he was a graduate student, described how
they slowed broadband light waves using a type of material called
nanoplasmonic structures.
Gan
explains that the ultimate goal is to achieve a breakthrough in optical
communications called multiplexed, multiwavelength communications,
where optical data can potentially be tamed at different wavelengths,
thus greatly increasing processing and transmission capacity.
He
notes that it is widely recognized that if light could ever be stopped
entirely, new possibilities would open up for data storage.
“At
the moment, processing data with optical signals is limited by how
quickly the signal can be interpreted,” he says. “If the signal can be
slowed, more information could be processed without overloading the
system.”
Gan
and his colleagues created nanoplasmonic structures by making nanoscale
grooves in metallic surfaces at different depths, which alters the
materials’ optical properties.
These
plasmonic chips provide the critical connection between nanoelectronics
and photonics, Gan explains, allowing these different types of devices
to be integrated, a prerequisite for realizing the potential of optical
computing, “lab-on-a-chip” biosensors and more efficient, thin-film
photovoltaic materials.
According
to Gan, the optical properties of the nanoplasmonic structures allow
different wavelengths of light to be trapped at different positions in
the structure, potentially allowing for optical data storage and
enhanced nonlinear optics.
The
structures Gan developed slow light down so much that they are able to
trap multiple wavelengths of light on a single chip, whereas
conventional methods can only trap a single wavelength in a narrow band.
“Light
is usually very fast, but the structures I created can slow broadband
light significantly,” says Gan. “It’s as though I can hold the light in
my hand.”
That,
Gan explains, is because of the structures’ engineered surface “plasmon
resonances,” where light excites the waves of electrons that oscillate
back and forth on metal surfaces.
In
this case, he says, light can be slowed down and trapped in the
vicinity of resonances in this novel, dispersive structural material.
Gan
and his colleagues also found that because the nanoplasmonic structures
they developed can trap very slow resonances of light, they can do so
at room temperature, instead of at the ultracold temperatures that are
required in conventional slow-light technologies.
“In
the PNAS paper, we showed that we trapped red to green,” explains Gan.
“Now we are working on trapping a broader wavelength, from red to blue.
We want to trap the entire rainbow.”
Gan,
who was hired at UB under the UB 2020 strategic strength in Integrated
Nanostructured Systems, will be working toward that goal, using the
ultrafast light source in UB’s Department of Electrical Engineering in
the laboratory of UB professor and vice president for research Alexander
N. Cartwright.
“This
ultrafast light source will allow us to measure experimentally just how
slow is the light that we have trapped in our nanoplasmonic
structures,” Gan explains. “Once we know that, we will be able to
demonstrate our capability to manipulate light through experiments and
optimize the structure to slow the light further.”
Co-authors
with Gan on the study are Filbert Bertoli, Yongkang Gao, Yujie Ding,
Kyle Wagner and Dmitri Vezenov, all of Lehigh University.
