The research is focused on one of our society's greatest technical challenges and economic drivers with impact on knowledge, economy, society and people as well as business and government activities. It aims to transform the development of the information and communication infrastructure. A high-capacity, flexible, cost-effective and efficient telecommunications and data infrastructure is of great national and international importance. The ability to communicate seamlessly, without delay, requires intelligent communications networks with high capacity, available when and where it is needed. To achieve this requires research advances in ultrawideband wireless and optical networks, as well as intelligent transceivers, new ultrawideband optical devices and algorithms. This is a fast-moving and internationally fiercely competitive field and to maintain international leadership requires the capability of not only making theoretical advances, but the also the ability of demonstrating these experimentally. Our vision is to create an advanced, world leading signal generation and detection test-bed for advanced communications systems research. The key feature of the proposed system are the ultra-low noise, high-resolution capture and analysis of complex broadband signals, more than quadrupling the achievable network capacity. This unique facility will allow the investigation of optical and wireless networks over a wide range of time- and length scales, including long-haul networks, data centres and enable the research into the ultra-wideband signal manipulation for the next-generation optical & wireless access networks. It will enable UCL and UK to consolidate and enhance its internationally leading position in communications systems research supporting a wide range of other areas.

Over the last decade, much interest of scientists and engineers working in optics and photonics has been attracted to the research and development of miniature devices based on the phenomenon of slow light. The idea of slow light consists in reducing its average speed of propagation by forcing light to oscillate and circulate in specially engineered microscopic photonic structures (e.g., photonic crystals and coupled ring resonators). Researchers anticipated that slow light devices will have revolutionary applications in communications, optical and radio signal processing, quantum computing, sensing, and fundamental science. For this reason, the research on slow light has been conducted in many academic laboratories and industrial research centres including telecommunications giants IBM, Intel, and NTT. However, in spite of significant progress, it had been determined that current photonic fabrication technologies are unable to produce practical slow light devices due to the major barriers: the insufficient fabrication precision and substantial attenuation of light. To overcome these barriers, this project will develop a new photonic technology, Surface Nanoscale Axial Photonics (SNAP) which will allow us to demonstrate miniature photonics devices with unprecedentedly high precision and low loss. SNAP is a new microphotonics fabrication platform invented by the PI of this project. In contrast to previously considered slow light structures based on circulation of light in coupled ring resonators and oscillations photonic crystals, the SNAP platform employs whispering gallery modes of light in an optical fibre, which circulate near the fibre surface and slowly propagate along its axis. The speed of axial propagation of these modes is so slow that it can be fully controlled by dramatically small nanoscale variations of the fibre radius. This project will develop the advanced SNAP technology for fabrication of ultraprecise, ultralow loss, tuneable, switchable and fully reconfigurable miniature slow light devices establishing the groundwork for their revolutionary applications in future Information and Communication Technologies. The success of the project will place the UK in the centre of this revolutionary development.

The remarkable success of the internet is unquestioned, touching all aspects of our daily lives and commerce. This success is fundamentally underpinned by the tremendous capacity of unseen underground and undersea optical fibre cables and the technologies associated with them. Indeed, the initial surge in web usage in the mid 1990s coincides with the commissioning of the first optically amplified transatlantic cable network, TAT12/13 that allowed ready access to information otherwise inaccessible. Similarly, the remarkable growth of social media is supported by the introduction of optical fibres into data centres, allowing their tremendous growth. Exponential growth has been a characteristic of data communications since their first introduction in the 1970's and has been fuelled by the gradual introduction of radical technologies, such as optical amplification, wavelength-division multiplexing and coherent modulation. All of these technologies are today routinely deployed and it is widely acknowledged that fibres are becoming full. The limit to fibre capacity has its origin in the fact that the intense signals are significantly distorted by nonlinearly (a similar effect to overdriving loudspeakers). This distortion limits the maximum amount of information which may be transmitted across and optical fibre link, and unless combated, the nonlinear response will result in a capacity crunch, limiting access to the internet to today's levels. Faced with the ongoing exponential growth in demand, unless these restrictions are lifted many parallel systems will be required, resulting in exponentially increasing energy consumption, until the cost of this resource becomes prohibitive and finally curtails growth. Only one technology, optical phase conjugation (acting like a mirror for colours), has been shown to offer the prospect of supporting continued internet growth without the need for widespread use of multiple fibres and the associated growth in energy consumption. Very much like Newton's Prisms, optical phase conjugation allows the distortion of one fibre (analogous to spectral spreading in Newton's prisms) to be compensated by a second identical fibre. In PHOS, we will - Optimise the devices which perform this conjugation, both in terms of the assessment of fundamental nonlinear materials and in terms of optimised sub-system configuration. - Demonstrate orders of magnitude increase in the capabilities of optical fibres for both practical point-to-point links with non-uniform span lengths and for optical networks with a plethora of diverse routes. - Verify that the use of optical phase conjugation is cost effective, both in terms of reducing the cost of a network deployment compared to existing products and in terms of enhancing the service provided to customers through higher capacity with lower latency. Furthermore, as optical phase conjugation will transform the capabilities of the network, PHOS will work to remove bottlenecks within the network transmitters and receivers, increasing their performance by an order of magnitude, resulting in 10 times faster connections. The approach of compensating impairments in the optical domain, combined with simplified digital signal processing and enhanced exploitation of fibre bandwidth will reduce the cost, size and power consumption associated with providing 10's of Tbit/s of capacity per optical fibre. If successful, PHOS will enable massively increased data capacities from the employment of Optical Phase Conjugation, giving the UK the most advanced optical communication network and a strong position to become a leading supplier of the technology worldwide.

The exponential growth in the use of bandwidth-hungry internet services such as high-definition video streaming, cloud computing, artificial intelligence, Big Data and the Internet of Things requires new advances in optical data transmission technologies to achieve ultra-high throughputs and minimal latencies. To go beyond current channel limits is arguably the greatest challenge faced by digital optical communications. To target it, the proposed research programme will develop new approaches to significantly increase the capacity of future communication systems focusing on the ultrawideband optical transmission and amplification in combination with adaptative coded modulation and digital signal processing, to ensure a robust communications infrastructure beyond tomorrow. Systems capacity is bounded by three dimensions: bandwidth, information spectral density and space. Whilst much research has focused on maximising the information spectral density and investigating space division multiplexing, little attention has been paid to the bandwidth domain. We propose to significantly extend the channel bandwidth with transceivers, broadband optical amplifiers, beyond the well-established erbium doped fibre amplifier (EDFA), focusing on bismuth and thulium doped fibre amplifiers with the assistance of Raman-amplification. Together with space division multiplexing, based on multiple fibres or new multi-core fibres, will ensure system capacities of tens of Petabit/s will be possible in the future. In EWOC research, we will gain a deeper understanding of the fundamental nonlinear effects that govern the upper limit on capacity in such ultra-wide systems, never previously investigated. Three main challenges are: (i) to fully utilise the bandwidth of the ubiquitous silica fibres low-loss window, overcoming the single mode fibre constraints, to reach bit rates of up to 250 Tb/s per core; (ii) to operate beyond the Raman gain shift - means that the associated nonlinear signal-to-signal interference in the widely diverse dispersion and nonlinearity regimes must be understood, quantified and effectively mitigated and (iii) experimentally demonstrate the combination of the significantly increased bandwidth with novel coded modulation, advanced DSP and nonlinearity mitigation in a wide variety of distance and bitrate transmission scenarios and applications in core, access and data centre networks. The EWOC proposal is a collaboration between UCL's Optical Networks Group and the University of Southampton Optoelectronics Research Centre and 6 world-leading industrial partners spanning network and service providers (BT and KDDI), equipment systems (Xtera and Nokia) and optical fibre/amplifier (Corning/OFS) manufacturers, a testament to the strategic importance of this research. The importance of ubiquitous, broadband, high-capacity, low delay and secure telecommunications infrastructure is critical to the UK's future and economic success. The recently published report of the National Taskforce on Telecoms Equipment Diversification Task Force (https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/975007/April_2021_Telecoms_Diversification_Taskforce_Findings_and_Report_v2.pdf) has highlighted the need for R&D to ensure this: 'Research, development and innovation are central to the development of new telecoms solutions and technologies and a major competitive advantage for incumbent vendors. Therefore, R&D activity and investment is vital in driving diversification' recommending 'The Government should invest in projects aimed at early development and growth of systems integration skills in the UK. Such projects will ensure it builds a competitive advantage in this domain, and as an early element of its ambition to build UK capability'. The EWOC proposal is focused on both of these goals.

Technologies underpin economic and industrial advances and improvements in healthcare, education and societal and public infrastructure. Technologies of the future depend on scientific breakthroughs of the past and present, including new knowledge bases, ideas, and concepts. The proposed international network of interdisciplinary centre-to-centre collaborations aims to drive scientific and technological progress by advancing and developing a new science platform for emerging technology - the optical frequency comb (OFC) with a range of practical applications of high industrial and societal importance in telecommunications, metrology, healthcare, environmental applications, bio-medicine, food industry and agri-tech and many other applications. The optical frequency comb is a breakthrough photonic technology that has already revolutionised a range of scientific and industrial fields. In the family of OFC technologies, dual-comb spectroscopy plays a unique role as the most advanced platform combining the strengths of conventional spectroscopy and laser spectroscopy. Measurement techniques relying on multi-comb, mostly dual-comb and very recently tri-combs, offer the promise of exquisite accuracy and speed. The large majority of initial laboratory results originate from cavity-based approaches either using bulky powerful Ti:Sapphire lasers, or ultra-compact micro-resonators. While these technologies have many advantages, they also feature certain drawbacks for some applications. They require complex electronic active stabilisation schemes to phase-lock the different single-combs together, and the characteristics of the multi-comb source are not tuneable since they are severely dictated by the opto-geometrical parameters of the cavity. Thus, their repetition rates cannot be optimised to the decay rates of targeted samples, nor their relative repetition rates to sample the response of the medium. Such lack of versatility leads to speed and resolution limitations. These major constraints impact the development of these promising systems and make difficult their deployment outside the labs. To drive OFC sources, and in particular, multi-comb source towards a tangible science-to-technology breakthrough, the current state of the art shows that a fundamental paradigm shift is required to achieve the needs of robustness, performance and versatility in repetition rates and/or comb optical characteristics as dictated by the diversity of applications. In this project we propose and explore new approaches to create flexible and tunable comb sources, based on original design concepts. The novelty and transformative nature of our programme is in addressing engineering challenges and designs treating nonlinearity as an inherent part of the engineering systems rather than as a foe. Using the unique opportunity provided by the EPSRC international research collaboration programme, this project will bring together a critical mass of academic and industrial partners with complimentary expertise ranging from nonlinear mathematics to industrial engineering to develop new concepts and ideas underpinning emerging and future OFC technologies. The project will enhance UK capabilities in key strategic areas including optical communications, laser technology, metrology, and sensing, including the mid-IR spectral region, highly important for healthcare and environment applications, food, agri-tech and bio-medical applications. Such a wide-ranging and transformative project requires collaborative efforts of academic and industrial groups with complimentary expertise across these fields. There are currently no other UK projects addressing similar research challenges. Therefore, we believe that this project will make an important contribution to UK standing in this field of high scientific and industrial importance.