Much of the modern world relies on communication using fibre optic cables. These are essentially long tubes of glass through which pulses of light can be sent, transferring information from one end to the other. Filtering and manipulation of the light before or after the fibre optic cable enables the pulses of light to be converted to and from human-readable information. In an analogy with how electronic devices manipulate electrons, such light-manipulating devices work with photons, so their design and characterisation is the field of photonics. In the same way as miniaturisation has dramatically improved the performance of electronics, photonic devices will become more and more commonplace as their dimensions are reduced. One photonic component that has proved particularly difficult to shrink is the optical isolator, which allows light to propagate in one direction but not in the other. These are used extensively in fibre optical communication and are beginning to find a role in the object detection systems used in self-driving cars (LiDAR). They are typically built using a class of materials exhibiting a phenomenon known as the magneto-optic effect, which can be exploited to allow unidirectional propagation. Attempts to create smaller devices using the same materials have run into significant problems. These are mostly related to some practical issues encountered when very precisely manipulating magneto-optical materials at microscopic scales. A route around this is to use a material more suited to use in very tiny devices. An obvious candidate is silicon, as the vast existing infrastructure for computer processors means silicon-based manufacturing is very advanced. Unfortunately, silicon has weak magneto-optical properties, so it seems unsuitable for use as an optical isolator. This project will sidestep this difficulty using a technique known as inverse design, in which the human is removed from the design process. Instead, a computer uses efficient algorithms to determine an optimal structure to achieve a particular goal. This technique has been shown to dramatically increase the performance of all kinds of devices in various contexts. In this project, the team will apply the algorithm in such a way that designs for high-performance, miniaturised optical isolators will be the end result. These will be small enough to be built into compact photonic devices, improving for example the performance of fibre-optical communications or the technology used in automated vehicles.

This project will establish a long term relationship between research translational centres - the Centre for Nanohealth at Swansea University and the Fraunhofer Centre for Applied Photonics in Glasgow. This translational alliance will provide a commercialisation pipeline for photonics research concepts and devices applied to healthcare delivery. The strategic alliance will link to the significant portfolios of industrial partners currently held by the two translational centres and in doing so boost interactions between the optics business cluster in Scotland and the medical sector company base in Wales. The project will also take basic research outputs relating to a micro-laser system cytometer to a fully validated commercial prototype system. This will have application in cell based diagnostics such as blood cell counts.

At a glance: Microstructured optical fibres are transforming science and technology in fields spanning telecommunications through to healthcare. Their unique offering of guiding properties continues to push the limits of established photonics and drive novel innovation and scientific discovery. However, a limit to this potential is approaching because many theoretically transformative fibres cannot be realised in practice due to manufacturing challenges. With this fellowship, I aim to unlock this unmet potential by developing a freeform optical fibre manufacturing process, which is unbound from conventional manufacturing constraints. The vast majority of optical fibre is produced for the telecommunications sector to satisfy exponentially rising data capacity needs. The type of fibre used in telecoms is typically conventional step-index fibre, comprised of a silica glass core surrounded by a lower-index doped-silica cladding. Solid fibre is inexpensive and guides with reasonably low-loss, but is fundamentally limited in performance by material absorption, scattering and high-dispersion amongst other factors. Over the past few decades, another type of optical fibre has emerged - microstructured optical fibre (MOF). MOF utilises a structured-material core-cladding in which light is guided through complex waveguiding mechanisms. Depending on the type, MOF can offer several advantages over conventional fibre including broad spectral transmission, low bend-loss, low latency and high-power delivery. Remarkably, certain MOFs guide light within a hollow region of the fibre. These so-called hollow-core fibres overcome problems faced by solid-core fibres such as material absorption, dispersion, optical damage and latency, as well as enabling an innovation-rich field of gas-filled sensors and light sources. MOF is manufactured by an approach known as stack-and-draw. Stack-and-draw is a two-step process: firstly, circular glass capillaries, rods and tubes are stacked laterally, often with added spacers, to form a scaled-up approximation of the fibre known as a preform. Secondly, the preform is drawn to fibre through a high-temperature furnace. The design of MOF developed so far has been heavily steered by the restrictive stacking process, e.g., hexagonally-packed Kagomé fibre and circle-tubular antiresonant fibre. Unfortunately, several types of MOF that have shown huge potential theoretically cannot be reasonably stacked, and so the vast applicability of MOF is beginning to plateau. To unlock this potential, we will develop a new preform manufacturing process capable of producing freeform fibre, i.e., fibre with arbitrarily structured cross-section, without compromising on fibre quality. In the proposed approach, short segments of the preform are precisely and arbitrarily machined using tailored laser-manufacturing methods. These segments are then bonded axially to form the preform which is drawn to fibre using traditional methods. Building upon a recent early feasibility demonstration, the fellowship will facilitate an overhaul of the laser-based approach to fabricating preforms and investigation of optimal glass bonding techniques. Amongst a trove of benefits, freeform fibre will bring drastically lower loss, increased stability, faster data transfer speeds and novel spectral guidance. The later stages of the fellowship will focus on developing fibre with unprecedented guiding performance and exploring applications of fibre with novel geometry. We aim to develop an industry-ready manufacturing method for freeform silica optical fibre, and further improve high-resolution glass macro-fabrication and advanced bonding and assembly capabilities. This work is expected to open up a new field of fibre optics research and nurture a team of dedicated researchers.

In recent years, advances in semiconductor based photo-detectors have led to the development of simple and compact detectors that are sufficiently sensitive to detect a single photon incident on the sensing area. These devices had revolutionary impact on instrumentation for the life sciences, and now they are starting to open up new possibilities in optical wireless communications. At the same time, there have been significant advances in the development of light-emitting diode (LED) based lighting, which is now becoming ubiquitous. Within the last year, the applicant and his colleagues at the University of Strathclyde have pioneered a new method of optical wireless communications that uses LEDs as transmitters and a semiconductor single photon detector as receiver. Data can be transmitted at extremely low light levels of only 30 photons/bit. Utilising a special encoding scheme, which exploits the statistical distribution of single photon detection events, such a low signal level can be maintained even under the presence of normal ambient background light. This potentially disruptive technology can be scaled to multiple LED transmitters and multiple detectors operating in parallel, opening a vast range of possible applications in imaging, communications, space communications, and robotic control. The driving vision of the project is to realise such a highly parallel system and link it to specific applications. During the initial development of this technology it proved crucial to interface the transmitter and receiver with configurable digital electronics to perform digital signal processing (DSP). However, these DSP interfaces do not currently have the capability required for the envisaged parallel system. The applicant and his team will investigate the challenges in integrating essential functionality, such as e.g. clock synchronisation, into the DSP hardware. Their work will enable LED displays with 100 MHz frame rate, enhanced modulation formats, and transmitter interfaces for both active- and passive-matrix LED arrays. The project involves a broad industrial engagement strategy centred around a close link between the University of Strathclyde and Fraunhofer UK, and capitalising on two recently filed patents. Fraunhofer UK is a knowledge transfer organisation dedicated to facilitating the translation of academic research into commercial development. The University and Fraunhofer are already collaborating on other subjects and the fellowship will enable the candidate to lead the technology transfer activities in this area. Furthermore the applicant will directly engage with the Advanced Forming Research Centre, the Scottish Centre for Excelence in Satellite Applications, and Aralia Systems, which will help to apply the technology to the specific areas of digitally controlled manufacturing, satellite communications, and surveillance systems. The applicant will utilise his network of academic and industrial contacts in the UK to extend the application and commercialisation of the technology beyond the above mentioned areas, e.g. to ultra-low power networking units for usage in the internet of things.

The silicon electronics industry has two major challenges in the development of new products: demand for increasing levels of processing power on a single chip and the amount of energy required to run these chips. The two challenges are linked, since the more components and communications links that are integrated into the chip, the higher the associated energy usage. While the energy consumption of a single chip is relatively low, this rapidly scales to environmental levels when considering the huge volume of units produced each year is in the order of 10's of billions. Already, large scale data-centres consume around 1% of global electricity demand, so any efficiency gains in the energy consumption of integrated chips will have significant effects. As device dimensions reach fundamental physical limits, chip designers are developing new architectures in order to continue to deliver growth in chip performance. These designs require high bandwidth communications across millimetre length scales, currently realised as simple electronic tracks. By replacing these tracks with optical interconnects, system power consumption can be reduced and communications bandwidth improved. The fundamental challenge for any alternative technology is that it must be compatible with current electronics manufacturing, where vast investments have been made over the last decades. This project will develop an optical interconnect layer that has a link power consumption lower than equivalent electronic lines. The optical layer will be realised as a thin film chip that can be interposed between the silicon device and its packaging, meaning that this process is zero-change with respect to the manufacture of the electronic chips. Recent advances pioneered at the Universities of Strathclyde and Sheffield in ultra-high precision micro-assembly of opto-electronic membrane systems will enable a two stage process that is designed to be compatible with production at scale. Firstly, membrane optical sources, waveguides and detectors will be assembled on a glass chip that incorporates electrical vias. This interposer with integrated optical interconnects will be integrated between the electronic chip and its packaging using micro-assembly processes. The project is supported by industrial partners Alter Technologies and Fraunhofer UK who will provide resources and expertise in opto-electronic packaging and optical systems engineering. This will ensure new process developments with industrial standards and design rules. The proposal aligns with EPSRC's ICT and Manufacturing the Future themes and the Photonics for Future Systems priority, addressing specific portfolio areas such as Manufacturing Technologies, Optical Communications, Optical Devices & Subsystems, Optoelectronic Devices & Circuits, Components & Systems. By the end of the project we will have demonstrated an optical transmission link with energy consumption lower than an equivalent electronic line. This link will be integrated with a commercially available silicon transceiver chip to demonstrate feasibility of developing this technology as a back-end process in the silicon electronics industry.