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How could optical network technology be improved? The EU-funded GRIFFON project, which ended in February 2017, delivered leads for a number of possible advances. As one of its main outcomes, its researchers found a way to achieve unrepeated transmission over long distances using generic equipment and legacy optical fibres deployed in existing optical transport networks.
The ability to do so is crucially important, says project coordinator Sergey Sergeyev of the United Kingdom’s Aston University, Birmingham. With data streams rapidly expanding, limitations in the current throughput capacity of optical networks have to be overcome — but doing so by replacing existing fibres with multi-core ones, for example, is an extremely costly proposition, he explains.
GRIFFON’s solution was tested successfully for transmission across a span of 240 km, Sergeyev reports. And it is scalable, he adds, highlighting another aspect of relevance to potential commercial applications. The project’s researchers were not the first to achieve unrepeated transmission, Sergeyev notes.
“However, we demonstrated how to upgrade existing systems in a cost-effective way,” he points out.
Eliminating repetition…
Unrepeated transmission would dispense with the optical amplifiers that are currently used to compensate for signal attenuation, Sergeyev explains. At the moment, such devices, which are known as repeaters, are required every 50 to 70 km or so.
“These amplifiers require electrical current to be driven through an electrical cable embedded in the fibre optic cable,” he says.
Instead, GRIFFON’s proposed alternative harnesses a physical effect known as ‘stimulated Raman scattering’ to create distributed amplification along the entire link.
“The lasers enabling Raman scattering are located at the ends of the link, and so there’s no need for electrical fibre inside the optical cable,” Sergeyev explains.
They consume less energy than the succession of amplifiers that might otherwise have been required, he adds. The system’s power consumption would therefore be reduced, lowering its environmental impact and the operator’s energy bills.
…for greener transmission
Greater sustainability through unrepeated (or unrepeatered) transmission is, however, just one of the improvements for which GRIFFON provided leads. Among other outcomes, the team also found ways to transmit larger amounts of information and to mitigate noise in the transmission, Sergeyev notes.
The project’s insights are inspiring developments pursued by a number of companies, he reports. More specifically, some of its suggestions are likely to be taken forward by the commercial entities involved in the consortium, a collaboration of both private and public sector partners, Sergeyev adds.
Based on an approach developed at Aston, the project demonstrated that software developed by German project partner VPIphotonics can be used for simulations of ultra-long unrepeated Raman-amplified links to determine their power and noise characteristics, Sergeyev reports.
“It has been demonstrated that the same approach can also be applied for the development of the noise suppression methods in short Raman-amplified fibres,” he adds.
And most importantly, says Sergeyev, “the VPIphotonics models for fibres, lasers, transmitters, receivers and other components have been validated in the context of modern transmission systems.”
This validation, which was carried out in collaboration with Swedish project partners Acreo and KTH Royal Institute of Technology, reveals these models’ usefulness for the design and optimisation of such systems, he observes.
GRIFFON was backed by the EU’s Marie Skłodowska-Curie actions programme, as part of a funding scheme specifically encouraging industry-academia partnerships to stimulate an exchange of knowledge and technology transfer between the two sectors.
Both sides gain from such opportunities, says Sergeyev. One particular advantage to researchers from academia is that they obtain insight into industry needs, he explains.
In his view: “It shows them what direction they should move in.”
“For the non-academic partners, it’s a chance to access knowledge and expertise they might not be able to bring in otherwise,” Sergeyev adds.
Private sector research tends to be narrowly focused on very specific developments, and businesses can’t necessarily afford to explore possibilities beyond these boundaries, he notes.