IEEE Signal Processing - May 2018 - 13

regeneration must be completed separately for each wavelength, requiring
the use of large, expensive, and powerthirsty regenerators.
A long sought-after solution to this
cumbersome approach would be to
process the optical signal directly with
no back and forth electrical conversion. Late last year, Michael Vasilyev,
a professor in the University of Texas
at Arlington's Department of Electrical
Engineering, working with Taras I. Lakoba, an associate professor in the Department of Mathematics and Statistics at
the University of Vermont, announced
the discovery of a way to all-optically
regenerate every WDM channel with a
single device (Figure 3).
All-optical regeneration takes advantage of a nonlinear-optical effect known
as self-phase modulation (SPM), which
allows the speed of light propagating in a
transparent medium to be slightly modified by a change in the light intensity.
SPM can clean noise from a signal by
scattering the noise energy into frequencies well outside the signal band, where it
can be easily removed by a filter. "When
applied to light containing useful data,
the SPM-enabled noise-removal operation can result in the optical autocorrection of signals with data rates hundreds

All-optical light noise reduction
Research underway at both the University of Texas at Arlington and the
University of Vermont promises to lead
to less costly and more energy-efficient

univErSity of tExaS at arlington

high-performance
and a lot of heat proresearch underway at both
computing and highduction," observes rethe university of Texas at
speed Internet consearch team member
Arlington and the university nections. The work,
Moritz Merklein, a
of Vermont promises to
funded by the U.S.
University of Sydney
lead to less costly and
National Science
Ph.D. student. "Our
Foundation, focuses
vision is to replace the
more energy-efficient
on the simultaneelectronic interconhigh-performance
ous nonlinear-optical
nects between difcomputing and high-speed
processing of mulferent processors and
internet connections.
tiple light beams by
computing machines
a single device. The
with photonic 'wires,'
approach aims to eliminate the need to
so light transmission will be used instead
convert light beams into electrical form,
of electronic connections," he says. "Our
thereby potentially enabling multiterabit
approach is a solution for a light memory
per second performance.
that is entirely controlled by light pulses."
Currently, telecom carriers must use
Merklein notes that the researchfrequent optoelectronic regeneration to
ers are using a nonlinear optical signal
eradicate noise accumulated during light
processing approach because they want
propagation over optical communicato avoid the electro-optic conversion of
tion links. The cumbersome technique
optical signals, a common bottleneck in
requires high-speed photodetectors to
optical communications, since it restricts
transform optical signals into electrithe bandwidth and speed that photonics
cal signals, processing the signals with
offers. A nonlinear optical effect, stimsilicon-based circuitry. The electriulated Brillouin scattering (SBS), links
cal signals must then be converted
light and sound waves together under speback into optical form with the help
cific conditions. If a data stream (light)
of lasers and electro-optic modulators.
traveling at the speed of light encounters a
Since a single optical fiber using wavecontrol light pulse (write), the information
length-division multiplexing (WDM)
can be transferred to an acoustic wave.
can carry over 100 different signals at
"This means the information travels
various wavelengths, an optoelectronic
further at the speed of sound, which is
100,000 times slower than the speed of
light," Stiller observes. By reversing the
process with another control light pulse
(read), the information is transferred back
to a data stream carried by light. "Therefore, it has been 'stored' for a while in the
acoustic wave," she explains.
The technology is not restricted to a
narrow bandwidth. "Unlike previous systems, this allows us to store and retrieve
information at multiple wavelengths
simultaneously, vastly increasing the
efficiency of the device," Stiller notes.
The project is still at the research level,
according to Stiller. The team is currently
refining the system and hopes to demonstrate a functional prototype sometime
within the next few years.

Figure 3. Michael Vasilyev (left), a professor in the University of Texas at Arlington's Department
of Electrical Engineering, working with a student. Prof. Vasilyev is coresearching simultaneous
nonlinear-optical processing of multiple light beams by a single device.

IEEE Signal Processing Magazine

May 2018

Table of Contents for the Digital Edition of IEEE Signal Processing - May 2018