Beyond Exabit Optical Communications: from new devices, via new dimensions to new systems

The aim of this fellowship is to develop disruptive approaches through theory and experiment to unlock the capacity of future information systems. To go beyond current channel limits is arguably the greatest challenge faced by digital optical communications. To target it, the proposed research will combine techniques from information theory, coding, higher-dimensional modulation formats, digital signal processing, advanced photonic design, and machine learning to make possible breakthrough developments to ensure a robust communications infrastructure beyond tomorrow.

Optical communications have to-date been able to fulfil the ever-growing data demand whilst simultaneously reducing cost and energy-per bit. However, it is now recognised that systems are rapidly approaching the fundamental information capacity of current transmission technologies, a trend with potential negative impact on the economy and social progress. To meet future demands with prospective cost and energy savings and avoid the impending exhaust of fibre capacity, the only solution is the emergent technology of spatial division multiplexing (SDM). It provides much wider conduits of information by offering additional means for transporting channels over one single fibre, using multi-mode and multi-core fibres. However, SDM has not yet found a viable path to access this much higher information capacity. State-of-the-art SDM transceivers are only compatible with few-mode/few-core fibres (~10 paths) given the requirement to multiplex/demultiplex over all the fibre pathways to successfully estimate and unravel pathways crosstalk and walk-off. This completely defeats SDM's purpose, the installation of new fibres must allow for several decades of capacity growth to offset the high deployment costs of new cables.

This fellowship envisages how to transform SDM technology to drive future optical networks by addressing the key issue overlooked by the research community since the introduction of SDM concepts: optical transceivers must undergo >100-fold integration to enable the benefits of multi-mode/core. Focus on new transceivers capable of digital space modulation will enable scalability of all data pathways to reduce the cost and energy-consumption per bit. Digital spatial modulation in novel coherent transmission schemes, i.e. the pathway index itself is used to carry information, will open fundamentally new theoretical and experimental possibilities up to now unexplored. These new transceivers will be capable of exploiting the multidimensional channel properties in the linear and nonlinear regimes through new spatial modulation formats and coding guided by new information theory and nonlinear science methods. Two main challenges are to construct a high-speed digital spatial modulator capable of dynamically addressing different groups of paths (potentially with tens of paths) in massive multi-path fibres and to develop new learning algorithms (guided by new theory methods) suitable of being embedded in spatial-adaptable transceivers to reach the ultimate capacity of nonlinear multi-dimensional channels.

This fellowship is focused on one of our society's greatest technical challenges and economic drivers with impact on public, business and government activities. The question of how to ensure the universal availability of high-capacity, resilient and secure digital communications, beyond the potential offered by the current technology, forms the subject of our proposal. Every sector of the population and Government/private agencies is likely to be affected. My research programme will allow new digital application markets to become a reality, enabled by new cross-disciplinary approaches to build spatial-adaptable optical networks offering much wider conduits of information with sustainable energy consumption. This fellowship will have numerous means of creating impact, from the people involved, the knowledge created, to the impact on the economy and broader society.

A. People: The outcomes of this fellowship will impact the UK and international science and engineering ICT communities by training a new generation of researchers that are able to understand fibre-optic networks with the deep mathematical, physics and machine learning skills required to tackle increasingly complex communication systems and design new generations of networks.

B. (i) Knowledge: This fellowship will impact through knowledge creation with a focus on dissemination, advocating for science and STEM outreach. Dissemination - in addition to high-quality publication in leading international peer-review journals and conferences, a substantial effort will be dedicated to organise technical workshops including with industrial partners within and outside the programme. Major impact of the work will be through technology demonstrations over a recirculation loop, with massive multi-path fibres from OFS (see support letter), to give network carriers the confidence to move towards spatial-adaptable optical networks. (ii) Advocacy: To enhance my advocacy for optical communication and to enhance the impact of the project, I will work with UCL's Public Engagement Unit (https://www.ucl.ac.uk/culture/public-engagement) to extend my set of links to industry, opinion formers and the general public. (iii) STEM outreach: In this fellowship, I will continue to offer research placements for post-16 STEM students through the Nuffield programme (https://www.nuffieldfoundation.org/nuffield-research-placements).

C. Economy: This fellowship will impact the economy through improvement in productivity, wealth creation and inward investment as industry seeks to utilise its outcomes. Specifically, there are a number of beneficiaries beyond the project partners including: (i) Telecommunications/data service providers: this project will impact both traditional carriers and internet service providers in evolving their networks by providing a new technology platform allowing decades of continued capacity growth compatible with the long-term return of investment horizon in the business. (ii) Equipment and optical fibre manufacturers and vendors are facing the overall challenge of providing the necessary capacity to satisfy the growing data demands in the most cost-effective way and flexible way. The results of the research will inform industry's R&D directions.

D. Society: The future digital infrastructure proposed through this project, offers improved quality of life by providing much wider conduits of information with sustainable energy consumption that will underpin: family friendly flexible working, remote health support for elderly (and others), accelerate data-collection/transference for artificial intelligence, reliable communication among autonomous vehicles, among others. This fellowship outcomes will inform and contribute to standards bodies and Government policy on infrastructure capability, security and broadband delivery.