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 optical fibre 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, optical communications have now exceeded the fundamental capacity of existing single-mode technology a trend leading to a rapid duplication of line systems which in time will translate in less affordable broadband access. To meet future demands with prospective cost and energy savings and avoid the impending exhaust of fibre capacity, this fellowship offers a scalable path towards parallelism in optical fibre communications resembling the advent of parallel computing using multiple cores to sustain Moore's law - once we were unable to double the number of transistors in a single-core microprocessor. The emergent technology of spatial division multiplexing (SDM) provides much wider conduits of information by offering additional means for transporting channels over one single fibre, using multi-mode and multi-core fibres. The fellow has shown that the internal structure of optical fibres can be optimised to support thousands of different spatial paths, each with full transmission capacity. And, critically, that there are principal launching conditions that allow for full transmission rate over each path with a small fraction of the equalisation cost assumed before. These discoveries offer the potential to foster a revolution in how optical fibre communications networks operate to meet the ever-increasing traffic demand with decreasing cost and energy consumption per bit, enabling ubiquitous and universal broadband access. This fellowship renewal envisages how to achieve chip-scale integration for multimode SDM transceivers packing intelligent optical beamforming powered by generalised machine learning and principled digital signal processing for highly spatially diverse fibre channels. Moreover, this fellowship renewal will initiate a new class of low crosstalk multi-mode fibres using elliptical cores and a new class of multimode optical fibre amplifiers with adaptive mode gain profile - opening fundamentally new theoretical and experimental possibilities up to now unexplored for SDM systems. These new developments will push multimode SDM technology far beyond that of the standard single-mode fibre infrastructure and bring it to an industry-ready development stage, unlocking decades of capacity growth in future optical networks with sustainable cost- and energy-per-bit.

Atoms are the building blocks of all materials. Therefore, the common sense suggests that microscopic devices cannot be fabricated with the precision better than an angstrom, the size of an atom. However, the performance of optical microdevices is usually determined by the average position of a very large number of atoms. The progress in measurement technologies allows this average to be determined with the ground-breaking picometre (one hundredth of the atomic size) precision. It has recently been recognized that similar picometre precision may become a must for the fabrication of a range of emerging photonic microdevices promising to revolutionize computer, communication, and sensing technologies. However, the problem of robust and scalable fabrication of microdevices with such astonishing precision remains open since major modern manufacturing technologies have achieved a precision plateau of several nanometres (tens of angstroms). SNAP (Surface Nanoscale Axial Photonics), a unique technology invented by the Principal Investigator of this project, allows the fabrication of miniature photonic devices at the surface of an optical fibre with unprecedented subangstrom precision. In contrast to the propagation of light in regular optical fibres, in SNAP devices, light is spiralling along the perimeter of the fibre and slowly propagating along its length. Recently, we demonstrated new SNAP fabrication methods and proposed unique microdevices for applications in communications, optical signal processing, and ultraprecise sensing. However, the SNAP devices demonstrated to date have been the products of breakthrough experiments. To bring these devices to realistic applications and further increase their precision, it is necessary to develop a robust manufacturing process attaining both ultra-accurate reproducibility and scalability. The goal of this project is the development of this process, which requires the insight into the depth of associated physical phenomena, as well as the design and fabrication of new microdevices critical for the future communication, optical signal processing, microwave, and sensing technologies. We will (i) develop a technology for scalable manufacturing of microphotonic devices with unprecedented picometre-scale precision and (ii) demonstrate SNAP microdevices including miniature optical delay lines, dispersion compensators, frequency comb generators, microwave photonics filters, as well as optical microfluidic sensors and manipulators with outstanding performance for applications ranging from food industry to fundamental science. If successful, this project will not only bring in a new revolutionary technology but also deliver miniature optical devices with performance not previously possible to achieve and ready for practical applications. We envision a high need for the miniature optical devices we plan to design and fabricate in this project in future applications in the information and communication technologies, precise manufacturing, microwave, and sensing technologies. Lack of reliable, scalable manufacturing processes with the required picometre precision remains a major obstacle for their mass manufacturing. SNAP devices, which we plan to fabricate in this project, have real potential to address this need due to their highest to date precision and exceptional performance. We anticipate that the developed robust, unprecedently precise, and scalable manufacturing process with the UK-owned IP, as well as miniature optical devices we plan to deliver, will have broad industrial, scientific, and social impact centred in the UK.

Optical frequency comb is a light source that can be pictured as a comb of light, where each tooth represents a different colour (frequency) of light. Originally developed to measure optical frequencies as an ultra-precise frequency 'ruler', this new type of light source has emerged as a transformative tool for many scientific and engineering fields. They enable precise distance measurement and fast data transmission, crucial for future ultra-fast internet connectivity, wireless device positioning, and medical diagnostics. However, the existing frequency comb technologies have limitations. The predominant existing technologies are not easily adjustable, producing predetermined shapes of light pulses and spectra, limiting their applications and flexibility. Moreover, they are challenging to deploy in practical, variable environments such as on mobile and satellite terminals due to their size and sensitivity to temperature fluctuations. The first objective of this fellowship is to address these challenges by creating new types of frequency comb sources that are adjustable, stable, compact, and can work in a wide range of environments and temperatures, which has not been achieved with existing technologies. In addition to the development of these new comb sources, the fellowship will also explore and demonstrate their applications in telecommunication technologies by increasing telecommunications network data capacity and by enabling more precise clock and time synchronisation. The above objectives will be achieved by significantly developing the concepts formulated by the fellow through a synergy of expertise in photonic integrated circuits, nonlinear optics, RF electronics, signal design and control. The goal of this fellowship is to validate the proposed techniques by developing prototype hardware, with which experimental trials will be performed in real-world environments. The fellowship research outcomes could advance communications, medical imaging, and broader potential in precision manufacturing and astronomy. The development of this new light source technology and associated technologies align with the UK's strategy to lead in telecommunications and healthcare innovation. The outcomes will benefit researchers, healthcare professionals and suppliers by providing insights and advancements in photonics and communications technologies. The ultimate beneficiary will be the public, who will gain better digital infrastructure and healthcare services. The new techniques will enable faster Internet and future society-transformative applications such as connected car fleets and autonomous drone swarms. They will advance medical imaging techniques, allowing for non-invasive, non-ionising, in-vivo diagnostic imaging with deeper penetration than existing technologies. This fellowship answers the growing demand for state-of-the-art but practical frequency comb technologies, driven by the need for highly precise sensing and higher data rates in various fields like medical diagnostics and telecommunications. It aims to benefit a wide range of end users and audiences, including academic researchers in the telecom and medical sectors, component suppliers and vendors, equipment vendors and network operators, healthcare professionals and patients, as well as policymakers and government agencies. In conclusion, this fellowship aims to demonstrate a new, highly flexible, and practical optical frequency comb tool that promises advancements in telecommunications, medical imaging, and various scientific applications, positioning the UK as a leader in these cutting-edge technologies.

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.