Modern optical data and telecommunication employ phase modulators to increase the amount of data relayed and data rate efficiency by grouping several bits of information into fewer symbols, or packets, reducing the overall size, or spectral width.
Due to a natural trade-off this efficiency is reaching a maximum with silicon-based devices, so researchers are looking to bridge the gap between the increase in demand for data and the efficiency in transmitting it. As a result, researchers have turned to graphene, which can be integrated with pre-existing silicon photonics, due to its large optical modulation and high-speed operation.
The collaborative team, headed by Marco Ramagnoli of Graphene Flagship partner the National Inter-University Consortium for Telecommunications (CNIT), have 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 how “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 was found to have lower optical losses, reduced energy consumption and error-free bit operation for up to 50km transmission distance. By optimising processes and device geometry the radio frequency bandwidth could be raised to match high-end existing modulators.
With the move towards 5G technologies, this could be a potentially cost-effective method of delivery.
This technology could also hold the key to reducing the carbon footprint of mobile technology according to Daniel Neumaier, leader of Division 3, based at Graphene Flagship partner AMO GmbH.
“Optical communication systems form the backbone of the world wide web, which already 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 is already outperforming conventional silicon-based modulators. The next step is to bring this device towards applications is the wafer scale CMOS integration.”
The Graphene Flagship is one of the largest research initiatives of the European Union. With a budget of €1billion and more than 150 partners, both academic and industrial, the research effort covers the entire value chain, from materials production to components and system integration, and targets several specific goals that exploit the unique properties of graphene and related materials.