Researchers from Graphene Flagship Partners at the National
Inter-University Consortium for Telecommunications (CNIT) in Italy, IMEC
in Belgium and University of Cambridge in UK created and tested a graphene
based phase modulator that outperforms existing silicon based ones.
Modern optical data and telecommunication employ phase
modulators to increase the amount of data relayed and data rate efficiency,
i.e. the speed at which information is relayed.
Phase modulators may work by grouping several bits of
information into fewer symbols, or packets, reducing the overall size, or
spectral width. The smaller the spectral width, the higher the data rate
efficiency. However due to a natural trade-off this efficiency is reaching a
maximum with silicon based devices, hence a more novel solution is needed to
bridge the gap between the increase in demand for data and the efficiency in
This novel solution has come in the form of graphene.
Graphene is ideally suited to integrate with pre-existing silicon photonics,
due to its large optical modulation and high-speed operation.
The multi-national collaborative team, headed by Marco
Ramagnoli of Graphene Flagship partner the National Inter-University Consortium
for Telecommunications (CNIT), conducted several tests to see the efficiency of
a graphene based modulator. A single layer of graphene was grown, via chemical
vapour deposition, and transferred onto a silicon photonic platform. Romagnoli
explains, “A small piece of graphene was placed on top of the silicon like an
adhesive tape. This made the resulting phase modulator work at any wavelength
and the spectral efficiency was ten times more than that of a state of the art
silicon phase modulator.”
This hybrid phase modulator can have lower optical losses,
reduced energy consumption and error-free bit operation for up to 50 km transmission
distance. Furthermore, by optimising processes and device geometry the radio
frequency bandwidth could be raised to match high-end existing modulators.
With the eyes of the world shifting towards faster and
higher rates of data streaming in the form of 5G technologies, this could be a
potential cost-effective method of delivering. “From the point of view of a
customer,” continues Romagnoli, “you want to watch films and other things on
mobile devices, but don’t want to increase what you pay to the operator. So
this means you want to increase the performances, bandwidth, but at the same
time you want to reduce the cost per data bit. We have to find the technology
that is scalable in performance but is, at the same time, cheaper.”
“That is why we believe that graphene is a good
candidate…This, as an experiment, is very simple and very inexpensive,” added
This technology also may hold the key to reducing the carbon
footprint of mobile technology as Daniel Neumaier, leader of Division 3, based
at Graphene Flagship partner AMO GmbH, explains, “Optical communication systems form the backbone of the world wide web,
which already now contributes significantly to the global CO2
footprint. This work demonstrates that graphene based optical phase-modulators
could become key components of optical data links in order to reduce the energy
consumption. The reported modulation efficiency, which is one of the decisive
key parameters for the overall energy consumption, is already outperforming
conventional silicon based modulators. The next crucial step in order to bring
this device towards applications is the wafer scale CMOS integration. This
challenge is currently addressed by leading European research centres and
companies within the Graphene Flagship.”
The results are a very promising start for the use of
graphene/graphene-silicon hybrids in the application of telecom and data
communication where phase modulators are key.
Professor Andrea C. Ferrari, Science and Technology Officer
of the Graphene Flagship, and Chair of its management panel added:
"Photonics and Optoelectronic applications have been identified as having
great application potential since the very start of the Flagship. This work
demonstrates that this technology is competitive with and can surpass the state
of the art. This work already underpins a spearhead project targeting
a~400Gbit/s data link for 2020, ready to be integrated in the business units of
telecom and datacom companies"
The paper can be found in Nature Photonics 2018, 12, 40-44
DOI: 10.1038/s41566-017-0071-6, titled: ‘Graphene-silicon phase modulators with
gigahertz bandwidth.’ by V. Sorianello, M. Midrio, G. Contestabile, I.
Asselberghs, J. Van Campenhout, C. Huyghebaert, I. Goykhman, A.K. Ott, A.C.
Ferrari and M. Romagnoli.