Graphene is an ideal material for optical
communications systems. A new, waveguide-integrated photodetector design sets a
record high bandwidth for ultrafast, high data rate graphene devices.
Graphene-based technologies are proving
integral to the new generation of communications – enabling high performance
optical communication systems through ultra-fast and compact optoelectronic
devices. Researchers from the Graphene Flagship working at TU Vienna, Austria
and AMO, Germany, have demonstrated ultrafast photodetectors that have the
highest reported bandwidth for graphene-based devices, enabling data rates of
up to 100 Gbit/s. The research, recently published in Nano Letters, points the
way towards graphene applications in high-speed communications systems.
Modern telecommunications systems are built
on the conversion of light into electrical signals, for example in optical
links in fibre-optic communications systems. Photodetectors within these
systems convert light into voltage signals, which are then processed for use in
computers, phones, and other devices. Current optical detection systems are
based on silicon and other semiconductors such as germanium, and are reaching
their limits in terms of speed and bandwidth.
Simone Schuler, a researcher at TU Vienna,
explained the importance of increasing data capabilities. “These kinds of
photodetectors are typically used in optical data links, which form the
back-bone of the internet. The maximum operation speed of a photodetector
defines the maximum data rate the detector can receive. So, the faster the
photodetector the more data it can receive.”
As more and more devices are connected to
each other, the demands on large-scale communications systems grow rapidly.
Next generation communications systems must be able to handle the large number
of connected devices in the Internet of Things (IoT), so faster optical
detection and higher bandwidths are needed to keep data transfer reliable
between all connections. As well as the internet and next generation mobile
communications, such as 5G, such photodetectors also have applications in radar
for industrial automation, known as Industry 4.0.
Graphene’s properties make it ideal for
next-generation optoelectronics and optical communications systems. Its
excellent electrical properties and broadband optical absorption are highly
suited for high-performance optoelectronic devices, and it can be readily
integrated with silicon photonic systems. The photodetector demonstrated here
is highly sensitive, due to its very compact structure. This enables the use of
such detectors alongside other opto-electronic devices including switches in
functionally dense, integrated chips. “This could open the path towards a
complete integration on one CMOS chip. Graphene will be the enabling material
for realising high performance photodetectors on a silicon platform,” added
In the new photodetectors, light is guided
into a slot waveguide that is covered with graphene. Under specific electrical
conditions in the graphene, in which the graphene acts as semiconductor
junction, the light in the waveguide generates a current in the graphene via
the photothermoelectric effect, converting light into an electrical signal. The
sensitivity of the detector can be tuned electrically without compromising the
speed, enabling the high bandwidth and ultrafast data rate.
Speaking about this new photodetector
design, another of the paper’s authors, Daniel Neumaier of AMO, Germany said
“This is an important step towards high performance on-chip photo-detectors,
demonstrating that competitive speed and sensitivity can be achieved in
graphene photodetectors in a highly controlled way.” On-chip integration of
different graphene-enable technologies is an important focus of the Graphene
Flagship. Neumaier leads the Graphene Flagship Electronics and Photonics
Integration Division and Work Package Electronic Devices, and is a member of
the Flagship Management Panel and Executive Board.
In order to take new technology such as
this to direct, real-world applications in communications networks, it must be
possible to put the technology onto optoelectronic chips. “The next step
towards applications will be the transition into a CMOS line, which is one
focused activity in the Electronics and Photonics Integration Division of the
Graphene Flagship project,” said Neumaier. CMOS manufacture has strict
requirements for materials and processing, so translating laboratory techniques
into methods suitable for chip production is very tricky.
Marco Romagnoli, of the National Consortium
for Telecommunications (CNIT), Italy, is the leader of the Graphene Flagship
Wafer-Scale Systems Integration Work Package, and spearheading the development
of silicon-compatible processes for mass production of graphene-based electronics.
“We are developing the key building blocks to be integrated in graphene
photonic circuits. This detector is a good example of design compliant with the
platform under development in the Flagship, and the combination of good
performance with technological compatibility is key to move forward in the
progress of graphene technology for electronics and photonics applications,” he
This research is a prime example of the way
graphene can provide improvements over existing optoelectronic technologies,
both in terms of performance and compactness. Frank Koppens, of the Institute
of Photonic Sciences, Spain, is leader of the Flagship’s Optoelectronics and
Photonics Work Package. “This work has shown record-high performance and
operation with zero dark current. It’s a major step forward for the Flagship
program that aims at developing the components (detectors, modulators) for a
fully CMOS-integrated optical data-communication platform,” he said.
Andrea Ferrari, Science and Technology Officer
of the Graphene Flagship and Chair of its Management Panel, stated
"Graphene photonics and optoelectronics is clearly one of the strongest
areas for mid-term development. The Graphene Flagship has made significant
investment in pioneering large scale integration of optoelectronic components
based on graphene and related materials. This is a key step to enable their
widespread uptake in the future of data com and IoT areas. This result clearly
shows that we are on the right track on our technology roadmap"
The Graphene Flagship is dedicated to
exploring the potential for graphene and related materials in new technologies
in a wide range of areas, from telecommunications and sensors to building
materials and batteries. The specific properties of graphene have a lot to offer
in innovative technologies, and taking graphene from the laboratory to
commercial application is a cornerstone of the Graphene Flagship.
 S. Schuler, D. Schall, D. Neumaier, L. Dobusch, O.
Bethge, B. Schwarz, M. Krall, T. Mueller, Nano Lett., 16, 7107 (2016)