Geometry of intricately fabricated glass makes light trap itself
Light interacts with itself to form self-sustaining waves in an
artificial 'topological' material
Date:
June 22, 2020
Source:
Penn State
Summary:
Laser light traveling through ornately microfabricated glass has
been shown to interact with itself to form self-sustaining wave
patterns called solitons.
FULL STORY ========================================================================== Laser light traveling through ornately microfabricated glass has been
shown to interact with itself to form self-sustaining wave patterns
called solitons. The intricate design fabricated in the glass is a type
of "photonic topological insulator," a device that could potentially
be used to make photonic technologies like lasers and medical imaging
more efficient.
========================================================================== Topological materials, which were awarded the Nobel Prize in 2016,
have the ability to "protect" the flow of waves through them against
unwanted disorder and defects. Until now, our understanding of topological protection of light has been mostly limited to particles of light acting independently, but in a new paper that appears May 22, 2020 in the
journal Science, researchers at Penn State report that they have used
the glass to mediate interaction between photons, directly observing
the fundamental wave patterns of these intricate devices.
"People are perhaps more familiar with electronics, but there is a whole parallel world of 'photonics,' where we are concerned with the properties
of light instead of electrons," said Mikael Rechtsman, Downsbrough Early
Career Development Professor of Physics at Penn State, and senior author
of the paper.
"There are myriad applications of photonics, including in solar
energy, fiber optics for telecommunication, manufacturing using
laser cutting, and lidar, which is used, for example, to help control autonomous vehicles. Topological protection offers the promise to make
photonic devices more energy efficient, lighter, and more compact."
The concept of topological protection can be applied in electronic,
photonic, atomic, and mechanical systems. In electronics, for example, topological protection can improve efficiency by getting electrons to
flow reliably through a material without scattering. For electrons this protection requires extremely cold temperatures, nearing absolute zero,
and very often a strong external magnetic field, but with photons all
of the experiments can be performed at room temperature, and because
photons do not have a charge, without a magnetic field.
To perform their experiments, the researchers shine a laser through a
piece of glass that has a series of extremely precise tunnels carved
through it, each with a diameter of about one-tenth that of a human
hair. The tunnels, called "waveguides," act like wires, concentrating
the flow of light through them. The waveguides in the piece of glass
are arranged in a grid, forming an array, but the path of each waveguide through the glass is not straight -- it is perhaps better described as serpentine, with twists and turns designed by the researchers with a
geometry that leads to the topological protection of light.
"We had to build the fabrication facility in our lab to precisely carve
the three-dimensional waveguides through the glass, a process called femtosecond laser writing," said Sebabrata Mukherjee, a postdoctoral
researcher at Penn State and first author of the paper. "The ability
to write three-dimensional waveguides is crucial to making the device topological, a property that is confirmed experimentally by observing
the 'protected' one-way flow of light along the edge of the device."
Through a process called the "Kerr effect," the properties of the glass
are changed due to the presence of the intense laser light. This change
in the glass mediates an interaction between the many photons, which
usually do not interact, propagating through the array. As the power
was increased, the light collapsed into a beam that didn't spread out
(i.e., diffract), but rather rotated in spirals. The spiral rotation
of the solitons is a signature of the specific shape of the waveguides
designed by the researchers and an indicator that the device is, indeed, topological.
"Under normal circumstances, photons are oblivious to one another,"
said Rechtsman. "You can cross two laser beams and neither will be
changed by the other. In our system, we were able to get photons to
interact and form solitons because the intensity of the laser altered
the properties of the glass. The photons became 'aware' of each other
through the change in their environment." Solitons are known to be the
most fundamental waveforms in many systems where interaction is mediated
by the surrounding environment.
"Theoretically understanding and experimentally probing solitons in
topological systems like our waveguide arrays will be a key ingredient
in applying topological protection for practical use in photonic devices, especially those that require high optical power," said Rechtsman.
The research was funded by the Office of Naval Research with addition
al support from the David and Lucile Packard Foundation and the Charles
E. Kaufman Foundation.
========================================================================== Story Source: Materials provided by Penn_State. Note: Content may be
edited for style and length.
========================================================================== Journal Reference:
1. Sebabrata Mukherjee, Mikael C. Rechtsman. Observation of Floquet
solitons
in a topological bandgap. Science, 2020; 368 (6493): 856 DOI:
10.1126/ science.aba8725 ==========================================================================
Link to news story:
https://www.sciencedaily.com/releases/2020/06/200622152511.htm
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