Innovative Graphene-Based Phase Modulators to Power up Faster Mobile Technology

Scientists from Graphene Flagship Partners at the National Inter-University Consortium for Telecommunications (CNIT) in Italy, IMEC in Belgium, and the University of Cambridge in the UK developed and tested a graphene-based phase modulator with the ability to surpass current silicon-based modulators.

Sophisticated optical data and telecommunication use phase modulators to enhance the amount of data relayed and data rate efficiency, or the speed of relay of information. Phase modulators might function by grouping a number of bits of information into a lesser number of symbols, or packets, thereby decreasing the overall size, or spectral width.

The data rate efficiency is inversely proportional to the spectral width. Yet, because of a natural trade-off, this efficiency is getting closer to a maximum with silicon-based devices; therefore a highly innovative solution is required to bridge the gap between the increase in demand for data and the efficiency in transmitting it. This innovative solution has come as graphene, which is best suited to be combined with pre-existing silicon photonics owing to its large optical modulation and high-speed operation.

The multi-national collaborative team, led by Marco Ramagnoli of Graphene Flagship partner the National Inter-University Consortium for Telecommunications (CNIT), performed a number of tests to observe the efficiency of a graphene-based modulator. The team grew a single layer of graphene through chemical vapor deposition and shifted it onto a silicon photonic platform.

Romagnoli elucidated the way “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 could have reduced energy consumption, lower optical losses, and error-free bit operation for up to 50 km transmission distance. Moreover, through optimizing processes and device geometry, the radio frequency bandwidth could be increased to match current high-end modulators.

With increasing demands for faster and higher rates of data streaming in the form of 5G technologies, this could be a promising cost-efficient delivery technique.

From the point of view of a customer, 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.

Marco Ramagnoli

This technology could also play a vital role on minimizing the carbon footprint of mobile technology as Daniel Neumaier, leader of Division 3, based at Graphene Flagship partner AMO GmbH, explained, “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 outcomes of the study are a highly propitious start for the use of graphene/graphene-silicon hybrids in the application of telecom and data communication where phase modulators are crucial.

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.

Professor Andrea C. Ferrari, Science and Technology Officer of the Graphene Flagship, and Chair of its management panel