This proposal seeks funding to create a Centre for Doctoral Training (CDT) in Connected Electronic and Photonic Systems (CEPS). Photonics has moved from a niche industry to being embedded in the majority of deployed systems, ranging from sensing, biophotonics and advanced manufacturing, through communications from the chip-to-chip to transcontinental scale, to display technologies, bringing higher resolution, lower power operation and enabling new ways of human-machine interaction. These advances have set the scene for a major change in commercialisation activity where electronics photonics and wireless converge in a wide range of information, sensing, communications, manufacturing and personal healthcare systems. Currently manufactured systems are realised by combining separately developed photonics, electronic and wireless components. This approach is labour intensive and requires many electrical interconnects as well as optical alignment on the micron scale. Devices are optimised separately and then brought together to meet systems specifications. Such an approach, although it has delivered remarkable results, not least the communications systems upon which the internet depends, limits the benefits that could come from systems-led design and the development of technologies for seamless integration of electronic photonics and wireless systems. To realise such connected systems requires researchers who have not only deep understanding of their specialist area, but also an excellent understanding across the fields of electronic photonics and wireless hardware and software. This proposal seeks to meet this important need, building upon the uniqueness and extent of the UCL and Cambridge research, where research activities are already focussing on higher levels of electronic, photonic and wireless integration; the convergence of wireless and optical communication systems; combined quantum and classical communication systems; the application of THz and optical low-latency connections in data centres; techniques for the low-cost roll-out of optical fibre to replace the copper network; the substitution of many conventional lighting products with photonic light sources and extensive application of photonics in medical diagnostics and personalised medicine. Many of these activities will increasingly rely on more advanced systems integration, and so the proposed CDT includes experts in electronic circuits, wireless systems and software. By drawing these complementary activities together, and building upon initial work towards this goal carried out within our previously funded CDT in Integrated Photonic and Electronic Systems, it is proposed to develop an advanced training programme to equip the next generation of very high calibre doctoral students with the required technical expertise, responsible innovation (RI), commercial and business skills to enable the £90 billion annual turnover UK electronics and photonics industry to create the closely integrated systems of the future. The CEPS CDT will provide a wide range of methods for learning for research students, well beyond that conventionally available, so that they can gain the required skills. In addition to conventional lectures and seminars, for example, there will be bespoke experimental coursework activities, reading clubs, roadmapping activities, responsible innovation (RI) studies, secondments to companies and other research laboratories and business planning courses. Connecting electronic and photonic systems is likely to expand the range of applications into which these technologies are deployed in other key sectors of the economy, such as industrial manufacturing, consumer electronics, data processing, defence, energy, engineering, security and medicine. As a result, a key feature of the CDT will be a developed awareness in its student cohorts of the breadth of opportunity available and the confidence that they can make strong impact thereon.

It is recognised that global communication systems are rapidly approaching the fundamental information capacity of current transmission technologies. Saturation of the capacity of the communication systems might have detrimental impact on the economy and social progress and public, business and government activities. The aim of the proposed research is to develop, through theory and experiment, disruptive approaches to unlocking the capacity of future information systems that go beyond the limits of current optical communications systems. The research will combine techniques from information theory, coding, study of advanced modulation formats, digital signal processing and advanced photonic concepts to make possible breakthrough developments to ensure a robust communications infrastructure beyond tomorrow. Increasing the total capacity of communication systems requires a multitude of coordinated efforts: new materials and device bases, new fibres, amplifiers and network paradigms, new ways to generate, transmit, detect and process optical signals and information itself - all must be addressed. In particular, the role of fibre communications, providing the capacity for a lion share of the total information traffic, is vital. One of the important directions to avoid the so-called "capacity crunch", the exhaust in fibre capacity - is to develop completely new transmission fibres and amplifiers. However, there is also a growing need for complimentary actions - innovative and radically novel approaches to coding, transmission and processing of information. Our vision is focused on the need to quantify the fundamental limits to the nonlinear channels carried over optical fibres and to develop techniques to approach those limits so as to maximise the achievable channel capacity. The information capacity of a linear channel with white Gaussian noise is well known and is defined by the Shannon limit. Wireless systems can approach this limit very closely - to within fractions of a dB. However, the optical channel is nonlinear. Fibre nonlinearity mixes noise with signal. Therefore, results of the linear theories on capacity can be applied in fibre channels only in the limit of very small nonlinear effects. Optical communication systems are undergoing another revolution with the development of techniques of coherent detection, the ability to detect both the amplitude and the phase of a transmitted signal and use of digital signal processing techniques to reconstruct the original signal. Use of the optical phase in emerging coherent transmission schemes opens up fundamentally new theoretical and technical possibilities most as yet unexplored. The challenge is to understand to what degree optical nonlinearity can also be compensated or, indeed, used to unlock the fibre capacity, maximise both the information transmission rate and the total bandwidth, to determine the fundamental Shannon limit for nonlinear channels and to develop methods to approach this capacity. We propose to explore fundamentally new nonlinear information technologies and to develop a practical design framework based on integration of DSP techniques, novel modulation formats, and novel source and line coding approaches tailored to the nonlinear optical channels. We believe this to be the key to designing the intelligent information infrastructure of the future.

Optical networks underpin the global digital communications infrastructure, and their development has simultaneously stimulated the growth in demand for data, and responded to this demand by unlocking the capacity of fibre-optic channels. The work within the UNLOC programme grant proved successful in understanding the fundamental limits in point-to-point nonlinear fibre channel capacity. However, the next-generation digital infrastructure needs more than raw capacity - it requires channel and flexible resource and capacity provision in combination with low latency, simplified and modular network architectures with maximum data throughput, and network resilience combined with overall network security. How to build such an intelligent and flexible network is a major problem of global importance. To cope with increasingly dynamic variations of delay-sensitive demands within the network and to enable the Internet of Skills, current optical networks overprovision capacity, resulting in both over- engineering and unutilised capacity. A key challenge is, therefore, to understand how to intelligently utilise the finite optical network resources to dynamically maximise performance, while also increasing robustness to future unknown requirements. The aim of TRANSNET is to address this challenge by creating an adaptive intelligent optical network that is able to dynamically provide capacity where and when it is needed - the backbone of the next-generation digital infrastructure. Our vision and ambition is to introduce intelligence into all levels of optical communication, cloud and data centre infrastructure and to develop optical transceivers that are optimally able to dynamically respond to varying application requirements of capacity, reach and delay. We envisage that machine learning (ML) will become ubiquitous in future optical networks, at all levels of design and operation, from digital coding, equalisation and impairment mitigation, through to monitoring, fault prediction and identification, and signal restoration, traffic pattern prediction and resource planning. TRANSNET will focus on the application of machine techniques to develop a new family of optical transceiver technologies, tailored to the needs of a new generation of self-x (x = configuring, monitoring, planning, learning, repairing and optimising) network architectures, capable of taking account of physical channel properties and high-level applications while optimising the use of resources. We will apply ML techniques to bring together the physical layer and the network; the nonlinearity of the fibres brings about a particularly complex challenge in the network context as it creates an interdependence between the signal quality of all transmitted wavelength channels. When optimising over tens of possible modulation formats, for hundreds of independent channels, over thousands of kilometres, a brute force optimisation becomes unfeasible. Particular challenges are the heterogeneity of large scale networks and the computational complexity of optimising network topology and resource allocation, as well as dynamical and data-driven management, monitoring and control of future networks, which requires a new way of thinking and tailored methodology. We propose to reduce the complexity of network design to allow self-learned network intelligence and adaptation through a combination of machine learning and probabilistic techniques. This will lead to the creation of computationally efficient approaches to deal with the complexity of the emerging nonlinear systems with memory and noise, for networks that operate dynamically on different time- and length-scales. This is a fundamentally new approach to optical network design and optimisation, requiring a cross-disciplinary approach to advance machine learning and heuristic algorithm design based on the understanding of nonlinear physics, signal processing and optical networking.

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.

Dramatic progress has been made in the past few years in the field of photonic technologies, to complement those in electronic technologies which have enabled the vast advances in information processing capability. A plethora of new screen and projection display technologies have been developed, bringing higher resolution, lower power operation and enabling new ways of machine interaction. Advances in biophotonics have led to a large range of low cost products for personal healthcare. Advances in low cost communication technologies to rates now in excess of 10 Gb/s have caused transceiver unit price cost reductions from >$10,000 to less than $100 in a few years, and, in the last two years, large volume use of parallel photonics in computing has come about. Advances in polymers have made possible the formation of not just links but complete optical subsystems fully integrated within circuit boards, so that users can expect to commoditise bespoke photonics technology themselves without having to resort to specialist companies. These advances have set the scene for a major change in commercialisation activity where photonics and electronics will converge in a wide range of systems. Importantly, photonics will become a fundamental underpinning technology for a much greater range of users outside its conventional arena, who will in turn require those skilled in photonics to have a much greater degree of interdisciplinary training. In short, there is a need to educate and train researchers who have skills balanced across the fields of electronic and photonic hardware and software. The applicants are unaware of such capability currently.This Doctoral Training Centre (DTC) proposal therefore seeks to meet this important need, building upon the uniqueness of the Cambridge and UCL research activities that are already focussing on new types of displays based on polymer and holographic projection technology, the application of photonic communications to computing, personal information systems and indeed consumer products (via board-to-board, chip to chip and later on-chip interconnects), the increased use of photonics in industrial processing and manufacture, techniques for the low-cost roll-out of optical fibre to replace the copper network, the substitution of many conventional lighting products with photonic light sources and extensive application of photonics in medical diagnostics and personalised medicine. Many of these activities will increasingly rely on more advanced systems integration, and so the proposed DTC includes experts in computer systems and software. By drawing these complementary activities together, it is proposed to develop an advanced training programme to equip the next generation of very high calibre doctoral students with the required expertise, commercial and business skills and thus provide innovation opportunities for new systems in the future. It should be stressed that the DTC will provide a wide range of methods for learning for students, well beyond that conventionally available, so that they can gain the required skills. In addition to lectures and seminars, for example, there will be bespoke experimental coursework activities, reading clubs, roadmapping activities, secondments to collaborators and business planning courses.Photonics is likely to become much more embedded in other key sectors of the economy, so that the beneficiaries of the DTC are expected to include industries involved in printing, consumer electronics, computing, defence, energy, engineering, security, medicine and indeed systems companies providing information systems for example for financial, retail and medical industries. Such industries will be at the heart of the digital economy, energy, healthcare and nanotechnology fields. As a result, a key feature of the DTC will be a developed awareness in its cohorts of the breadth of opportunity available and a confidence that they can make impact therein.