Discovery could reduce cost, energy
for high-speed Internet connections
January 9, 2018
Breakthrough research from The University of Texas at Arlington and The
University of Vermont could lead to a dramatic reduction in the cost and
energy consumption of high-speed internet connections.
effects, such as intensity-dependent refractive index, can be used to
process data thousands of times faster than what can be achieved
electronically. Such processing has, until now, worked only for one
optical beam at a time because the nonlinear-optical effects also cause
unwanted inter-beam interaction, or crosstalk, when multiple light beams
An article published in the prestigious Nature Communications journal,
by the research group of Michael Vasilyev, an electrical engineering
professor at UTA, in collaboration with Taras I. Lakoba, a mathematics
professor at UVM, detailed an experimental demonstration of an optical
medium in which multiple beams of light can autocorrect their own shapes
without affecting one another.
This work, funded by the National Science Foundation, enables
simultaneous nonlinear-optical processing of multiple light beams by a
single device without converting them to electrical form, opening the
way for this technology to reach its full multi-Terabit per second
potential, resulting in cheaper and more energy efficient high-speed
Currently, to eliminate the noise accumulated during light propagation
in optical communication links, telecom carriers must resort to frequent
optoelectronic regeneration, where they convert optical signals to
electrical via fast photodetectors, process them with silicon-based
circuitry, and then convert the electrical signals back to optical,
using lasers followed by electro-optic modulators. Since each optical
fiber can carry over a hundred different signals at various wavelengths,
known as wavelength-division multiplexing (WDM), such an optoelectronic
regeneration needs to be done separately for each wavelength, making
regenerators large, expensive and inefficient consumers of power.
An attractive alternative to this is processing the optical signal
directly, without converting it to electrical and back. In particular,
the speed of light propagating in a transparent medium can be slightly
modified by a change in the light intensity. This is a manifestation of
a nonlinear-optical effect known as “self-phase modulation” or SPM. If
light contains both signal and noise, the SPM can help clean the signal
from noise by scattering the noise energy into frequencies well outside
the signal band, from where the noise can be easily removed by a filter.
When applied to light containing useful data, this SPM-enabled
noise-removal operation is called “all-optical regeneration,” which can
result in optical auto-correction of the signals carrying hundred times
faster data rates than what can be processed electronically.
However, the adoption of the all-optical regeneration in communication
systems has been hindered by its inability to work with WDM signals.
This is because in the presence of multiple signal beams, or WDM
channels, the desired SPM is always accompanied by two undesirable
effects: cross-phase modulation, where one channel’s intensity modifies
propagation speed of another channel, and four-wave mixing, where
interaction of several channels leads to interference with other
In their published article, Vasilyev and colleagues report experimental
demonstration of a novel group-delay-managed nonlinear-optical medium,
where strong SPM effect is achieved without such inter-channel
interference. Splitting a conventional nonlinear medium, such as an
optical fiber, into several short sections separated by special
periodic-group-delay filters yields a medium in which all frequency
components of the same WDM channel travel with the same speed, ensuring
strong SPM. Different WDM channels travel with different speeds, which
dramatically suppresses any inter-channel interaction.
“Our new nonlinear medium has allowed us to demonstrate simultaneous
all-optical regeneration of 16 WDM channels by a single device, and this
number has only been limited by the logistical constraints of our
laboratory” Vasilyev said. “This experiment opens the opportunities to
scale the number of channels to over a hundred without increasing the
cost, all in a book-sized device.”
The multi-channel regenerator could even potentially shrink to the size
of a matchbox in the future if the nonlinear-optical medium could be
implemented on a microchip.
breakthrough is an example of how UTA researchers can positively impact
the physical and economic well-being of society in the area of
data-driven discovery and global environmental impact, themes in UTA’s
Strategic Plan 2020 Bold Solutions | Global Impact,” said Jonathan
Bredow, professor and chair of the Department of Electrical Engineering
in UTA's College of Engineering.
“Previous efforts to implement nonlinear-optical processing, such as
regeneration, failed to make an impact because there was no advantage to
employing them over electrical signals due to the inability to use more
than one channel. Now that Dr. Vasilyev’s group has overcome that
obstacle, there are tremendous new possibilities for faster, more
efficient transmission of messages,” Bredow said.