High-speed networks will shape the future of the digital economy

Dr Lidia Galdino, lecturer at University College London and Royal Academy of Engineering Research Fellow.

When in August 2020 I Ied the research at UCL that recorded the world’s fastest data transmission speed, reaching 178 terabits a second – or 178,000,000 megabits a second – I paused to reflect on what had led us to achieve this goal, and also my own personal journey from a young girl in Brazil to an engineering researcher in London.

In collaboration with the UCL team, Xtera and KDDI Research, by using a bandwidth of 16.8 THz, we were able to achieve speeds at double the capacity of any system currently deployed in the world.1

This speed per wavelength was very close to the theoretical limit of data transmission set out by famous American mathematician Claude Shannon in 1949. Working at Bell Labs in 1948, Shannon defined in mathematical terms what information is and how it can be transmitted in the face of noise. What had been viewed as quite distinct modes of communication–the telegraph, telephone, radio and television–were unified in a single framework.

So how did a young girl in Brazil, with an interest in maths and science, but with no knowledge of engineering, or indeed what engineering could do, manage to achieve this personal goal?

I was very fortunate to have a wonderful mother who didn’t have the opportunity to go to university, but who had a vision for me to achieve my utmost potential in the world, and who steered me in the direction of engineering. I was at the time absolutely fascinated by the internet and its potential, but never imagined that I could somehow end up as a researcher in the field of high-speed data transmission. Like most young girls, I had only a vague concept of engineering, and did not understand that, in fact, everything is engineering. It underpins everything that we see in the world, and in our field of communications and electronic engineering, it now drives the very foundation of everything we do on a digital or mobile platform.

I also had a number of mentors along the way, among them, Prof Polina Bayvel, who invested their time and their interest in helping me navigate my way through the engineering world, and who encouraged me to set high goals for my research and my life. Now I try to pass on these benefits to the younger generation of girls and women who are entering the field, and may need encouragement, as I did, to see their future in engineering and science. I am proud to have been chosen as the Associate Vice-President of Women in Photonics in the IEEE Photonics Society. These organisations are continually striving to support and mentor women in these fields, and I am pleased that we are making great progress today.

The challenge – and the solution

Even before the COVID-19 pandemic so radically changed our working and living environments, it was obvious that digital transformation was an inevitable process that would transform all aspects of the economy and society. And with this transformation would come ever increasing demands for higher and higher bandwidth and internet speeds, to enable this new way of working, living and learning, to function. Therefore, when I was lucky enough to receive a Royal Academy of Engineering Research Fellowship, I made it my objective to work with UCL team and industrial partners to maximize the amount of data that can be transmitted through optical fibres, achieving the world’s fastest data transmission speed, and help drive the future of the internet economy and society.

I have learned that it is very important for those involved in engineering and scientific research to learn how to communicate their passion for their interests, and also to relate this to the real world that everyone can identify with. This is perhaps not so difficult with this type of communications research, as most people, especially those actually in the digital tech sector, readily understand how vital it is to carry ever more data, at ever greater speed, across optical fibre networks. And of key importance is to maximise the signal quality and transmission bandwidth.

So the issue becomes: “how can we maximise the amount of information carried through an optical fibre, encoding the digital data in such a way as to ‘squeeze’ the maximum capacity out of existing optical fibre infrastructure, at the least additional cost?”

We achieved this by transmitting data through a much wider range of colours of light, or wavelengths, than is typically used in optical fibre. Current infrastructure typically uses a limited spectrum bandwidth of 4.5 THz. There are now 9THz commercial bandwidth systems, but we developed a new transmission system with a continuous bandwidth of 16.8 THz. We did this by combining different amplifier technologies to boost the signal power over this wider bandwidth. We also developed new Geometric Shaping (GS) constellations, or patterns of signal combinations, that make best use of the phase, brightness and polarisation properties of the light, enabling us to manipulate the properties of each individual wavelength, which enabled us to transmit data per wavelength close to the theoretical limit described by Shannon.

Our research plans for the next three years are to expand the transmission distance that we have achieved, and above all, improve the quality of the signal to reduce as much as possible any ‘noise’ which interferes with the signal carrying the data. This noise is mainly introduced by the optical amplifiers, the transponders and the optical fibre itself, which continues to be the bugbear of internet researchers, reduces the speed of data per colour and at present puts a theoretical limit on how much data can be transmitted over optical fibre. This is the scientific challenge – to mitigate the linear and nonlinear noise when we transmit data over this wider bandwidth. Solving this problem will lead us to further increase the transmission data rate per fibre, maximising the potential of our existing infrastructure at the lowest cost possible.

Optical fibre underpins the global communications infrastructure and transports more than 95% of global internet traffic data. Over the last 15 years, internet traffic data has increased exponentially, and it is essential that we develop new technologies to meet future data rate demands while maintaining a low cost per bit. High-capacity, ubiquitous broadband communication infrastructure is essential to economic growth. It will enable new internet traffic types and new data services that will emerge with 5G, the internet of things and smart cities or as yet unthought-of future applications that will transform people’s lives.

1 This work was sponsored by the Royal Academy of Engineering and the EPSRC programme grant TRANSNET.

Dr Lidia Galdino received M.Sc. and Ph.D. degrees in electronic and electrical engineering from the University of Campinas, Brazil, in 2008 and 2013, respectively. Dr Galdino commenced a lectureship and a Royal Academy of Engineering Research Fellowship in September 2018 on the topic of “Capacity-approaching, Ultra-Wideband Nonlinear Optical Fibre Transmission System”, and a co-investigated in the EPSRC TRANSNET programme grant. She previously worked as a Senior Research Associate on the EPSRC UNLOC programme grant. She is part of the Technical Programme Committee for European Conference on Optical Communication (ECOC), Optical Fibre Communication Conference (OFC), IEEE Photonic Conference (IPC), Advanced Photonics Conference (NETWORKS meeting). She served as Associated Vice President of IEEE’s Women in Photonic (2018-2020) and has been elected to the Board of Governors of the IEEE Photonics Society (2021-2023).  Dr Galdino was a co-recipient of the RAEng Colin Campbell Mitchell Award in 2015 for pioneering contributions to optical communications technology and was named as one of the 2017 “Top 50 Women in Engineering under 35” by The Telegraph and Women in Engineering Society which features the U.K.’s top rising female stars of engineering.