The aim of this manufacturing fellowship is to address the technology, architecture, performance and manufacturing needs of next generation optical communications systems for metro networks. Optical metro networks are undergoing tremendous growth as an unprecedented change in the distribution of network traffic, driven by requirements to ensure a superior quality of service to the end-user, leads to the concentration and localisation of traffic. The programme targets two specific network functions: compact, scalable and power-efficient multi-carrier "super-channel" transceivers at baud rates of 28-32Gbaud and above, and scalable, wide-band (120nm), segmented discrete Raman optical fibre amplifiers. Innovative product processes enabled by digital coherent technology and DSP-based monitoring of key transceiver parameters will be explored to address manufacturing yield and extended test times for arrayed transceivers. Novel designs will be developed to minimise bend losses, manual interventions, and to take advantage of robotic assembly, thereby introducing the required consistency in critical assembly processes for segmented amplifier manufacture. New equipment architectures and software-enabled re-purposing will be explored, focussed on energy efficiency, cost-effectiveness, longevity, and manufacturability. System performance will be evaluated in detailed numerical models of target networks serving great metropolises like Greater London, and compared with extensive laboratory tests in recirculating loop and extended optical fibre test beds.

The Fibre Optical Parametric Amplifier (FOPA) has been investigated by many research groups over the preceding thirty-five years as a potential "holy grail" of optical amplification, but has yet to evolve outside of the laboratory. The tantalising prospect of significantly increasing fibre capacity within optical systems by simply and directly employing FOPAs, each with gain bandwidth far exceeding that of the ubiquitous EDFA, has always been historically somewhat offset by a range of challenging physical barriers. Chief amongst these is the innate polarisation sensitivity of the parametric amplification process. This demands that close alignment must be maintained between the polarisation state of an incoming signal and an optical parametric pump which supplies energy to the signal via a nonlinear medium. In a DWDM system, this requirement scales extremely problematically - multiple signals of differing wavelength and in random states of polarisation (often with data carried on both orthogonal modes), must each correlate polarisation-wise with the pump or pumps to receive gain. We believe we have uncovered a ground-breaking new architecture for the FOPA which will ultimately effectively eradicate this significant hurdle, and forms the basis for this proposal's research direction. Other FOPA performance issues must also be overcome. For example, the transfer of intensity noise from the pump to the signals, and the unwanted generation of nonlinear crosstalk within the FOPA via signal-signal interactions are certainly drags on the performance ultimately achievable and will require significant investigation to minimise their effects. However, we do not consider these latter challenges to be such a considerable brick-wall against real-world operation as 'the polarisation question'. FPA-ROCS, is a focused research programme which will provide the required breakthrough to transition the FOPA from problematic laboratory experiment to an amplifier with real potential to impact across the optical communications world. This key advance will be based on our recent first experiments of an innovative FOPA design based on what we are calling the Half Pass Nonlinear Optical Loop or HPL NOL as shown in. We have recently demonstrated the world's first amplification of polarisation-multiplexed DWDM signals using this architecture , and believe it solves several of the large issues highlighted above, most notably offering polarisation independent black-box gain together with exceptional potential for significantly expanded bandwidth beyond the 20nm so far demonstrated. This potential has been outlined by separate characterisation studies undertaken by our team which demonstrated a single polarisation gain bandwidth of >110nm (i.e. 3x greater than that of the EDFA) with a gain variation across the band of only 1dB . We envisage using the HPL NOL to supply gain in regions of the fibre transmission spectrum which are currently untapped, such as at 1300nm (O-band) or 1500nm (S-band). By exploiting new bands in this way, together with considerably wider gain bandwidth per band, the capacity increase offered by FPA-ROCS will be extremely large (>500% current capability) and thus industry and, perhaps, world changing. The technology will be able to operate in parallel with existing optical communications infrastructure due to the transparency of the HPL-NOL outside its gain region (a feature not present in doped fibre amplifiers), enabling co-deployment with field-deployed EDFAs. This will enable a low-cost future upgrade path for network operators without the expensive and environmentally-unfriendly need to lay new fibre as capacity limits are approached. We envisage massively increased data throughputs from our radical redesign of the optical amplifier, allowing fibre systems to be future proofed to some degree at a UK-wide level and beyond.

The aim of this proposed research is to address the modelling, design, demonstration and potential applications of ultra-wide-band (UWB) optical fibre amplifiers based on the Raman effect, induced by high power laser pumping of specially designed optical fibre, for future applications in optical fibre communication networks, ranging from inter-data-centre connections to metro/regional networks. Despite massive advances in the capabilities of optical fibre communication systems over the past two decades, enabled by digital coherent technology, internet traffic growth remains well above 20% per annum, and is forecast to continue on a strong trajectory for the foreseeable future. Delivering a seamless optical amplifier of unprecedented bandwidth is now seen by operators and their network equipment suppliers as the most practical and cost-effective way to increase the traffic carrying capacity of the billions of km of glass fibre that has been deployed worldwide, by making use of the wide low-loss window. The programme targets two specific designs of all-Raman amplifier: (i) a node-located, discrete-only parallel, dual-stage design, and (ii) a hybrid distributed-discrete dual-stage design, making use of the intra-node transmission fibre as a gain medium for part of the spectrum. These innovative designs are enabled by recent increases in laser pump powers and novel nonlinear Raman gain fibres, and a growing, general acceptance of Raman technology by all network operators, ranging from relatively conservative incumbents, such as Verizon, to more adventurous technology giants, such as google. New, nonlinear, modelling tools will be developed to overcome and support the significant experimental design challenges in manufacturing and operating our proposed UWB amplifiers, which with 300nm bandwidth offer approaching 10x the bandwidth of standard Erbium-doped fibre amplifiers used in today's networks. Key optical amplifier characteristics such as gain, noise figure, uniformity and nonlinearity will be measured stand-alone. UWB optical fibre communication system capacity improvements and performance will be evaluated in representative models of target networks, informed by our project partners, and compared with extensive in-line and recirculating loop UWB laboratory-based tests.

Optical fibres lie at the heart of our increasingly technological society, for example: supporting the internet and mobile communications that we all now take for granted, saving lives through medical diagnosis and interventions using fibre-optic endoscopes, and enabling the mass production of a huge array of commercial products through fibre laser based materials processing. However, current fibre optics technology has its limitations due largely to the fact that the light is confined to a solid glass core. This places fundamental restrictions on the power and wavelength range over which signals can be transmitted, the speed at which signals propagate, and in terms of sensitivity to the external environment. These limits are now starting to impose restrictions in many application areas. For example, in telecommunications, nonlinear interactions between wavelength channels limit the maximum overall data transmission capacity of current single mode fibres to ~100-200 Tbit/s (for amplified terrestrial systems). Moreover, nonlinear, thermal and material damage thresholds combine to limit the maximum peak and average powers that can be delivered in a tightly focusable beam. This restricts the range of potential uses, particularly in the important ultrashort pulse regime increasingly used for a wide variety of materials processing applications These limitations can in principle be overcome by exploiting new light guidance mechanisms in fibres with a hollow core surrounded by a fine glass microstructure. Such fibres are generally referred to as Hollow Core Fibres (HCFs). Within this Programme we will seek to reinvent fibre optics technology and will replace the glass core with air or vacuum to produce Optical Fibres 2.0, offering vastly superior but largely unexplored potential. Our ultimate vision is that of a Connected World, where devices, machines, data centres and cities can be linked through these hollow light pipes for faster, cheaper, more resilient and secure communications. A Greener and Healthier World, where intense laser light can be channelled to produce goods and run combustion engines more efficiently and to image cancer tissues inside our bodies in real time. And an Explorative World, where hollow lightguides will enable scientific breakthroughs in attosecond science, particle physics, metrology and interplanetary exploration. Our overall ambition is therefore to revisit the way we think about light guidance and to develop a disruptive technology that challenges conventional thinking. The programme will provide the UK with a world-leading position both in HCF technology itself and in the many new applications and services that it will support.

Photonics is one of six EU "Key Enabling Technologies. The US recently announced a $200M programme for Integrated Photonics Manufacturing to improve its competiveness. As a UK response, the research proposed here will advance the pervasive technologies for future manufacturing identified in the UK Foresight report on the Future of Manufacturing, improving the manufacturability of optical sensors, functional materials, and energy-efficient growth in the transmission, manipulation and storage of data. Integration is the key to low-cost components and systems. The Hub will address the grand challenge of optimising multiple cross-disciplinary photonic platform technologies to enable integration through developing low-cost fabrication processes. This dominant theme unites the requirements of the UK photonics (and photonics enabled) industry, as confirmed by our consultation with over 40 companies, Catapults, and existing CIMs. Uniquely, following strong UK investment in photonics, we include most of the core photonic platforms available today in our Hub proposal that exploits clean room facilities valued at £200M. Research will focus on both emerging technologies having greatest potential impact on industry, and long-standing challenges in existing photonics technology where current manufacturing processes have hindered industrial uptake. Platforms will include: Metamaterials: One of the challenges in metamaterials is to develop processes for low-cost and high-throughput manufacturing. Advanced metamaterials produced in laboratories depend on slow, expensive production processes such as electron beam writing and are difficult to produce in large sizes or quantities. To secure industrial take up across a wide variety of practical applications, manufacturing methods that allow nanostructure patterning across large areas are required. Southampton hosts a leading metamaterials group led by Prof Zheludev and is well positioned to leverage current/future EPSRC research investments, as well as its leading intellectual property position in metamaterials. High-performance special optical fibres: Although fibres in the UV and mid-IR spectral range have been made, few are currently commercial owing to issues with reliability, performance, integration and manufacturability. This platform will address the manufacturing scalability of special fibres for UV, mid-IR and for ultrahigh power sources, as requested by current industrial partners. Integration with III-V sources and packaging issues will also be addressed, as requested by companies exploiting special fibres in laser-based applications. In the more conventional near-infrared wavelength regime, we will focus on designs and processes to make lasers and systems cheaper, more efficient and more reliable. Integrated Silicon Photonics: has made major advances in the functionality that has been demonstrated at the chip level. Arguably, it is the only platform that potentially offers full integration of all the key components required for optical circuit functionality at low cost, which is no doubt why the manufacturing giant, Intel, has invested so much. The key challenge remains to integrate silicon with optical fibre devices, III-V light sources and the key components of wafer-level manufacture such as on line test and measurement. The Hub includes the leading UK group in silicon photonics led by Prof Graham Reed. III-V devices: Significant advances have been made in extending the range of III-V light sources to the mid-IR wavelength region, but key to maximise their impact is to enable their integration with optical fibres and other photonics platforms, by simultaneous optimisation of the III-V and surrounding technologies. A preliminary mapping of industrial needs has shown that integration with metamaterial components optimised for mid-IR would be highly desirable. Sheffield hosts the EPSRC III-V Centre and adds a powerful light emitting dimension to the Hub.