There is no obvious and simple method for bonding a lens made of a high Refractive Index (RFI) material to the surface of photodiodes that are used to capture optical frequency signals. Any air gap unavoidably constrains the optical field of view and the potential to capture light across much larger angles is wasted unless a direct and optically efficient bonding technique can be found. For lower refractive index optics, adhesives can be used but since those available have a maximum RFI below 2.0, none can be used for lenses with a higher RFI. If used, there would be significant back reflections at the interface of the adhesive and lens and usable incidence angles inside the high RFI optics would be limited. 3D printing of optics directly onto the surface is not feasible because there are currently no resins with an RFI greater than 2\. Tethir wishes to find and validate a workable approach to bonding photodiodes to the exit aperture of high RFI lenses with the bonding area diameter in the range 0.5 - 3 mm but it lacks the resources needed to carry out the investigations. The most likely methods for achieving high coupling efficiency require the surfaces in contact to be extremely clean and flat (< 1nm surface roughness). The surface roughness of the lens exit surface will need to be measured and because none of the standard photodiode suppliers publish information on the roughness of their photodiode surfaces, this too will need to be measured. Depending on the results of these measurements, methods for improving surface roughness and subsequent cleaning can be explored. It is not yet feasible to implement direct bonding but measurements of photodetector surfaces with techniques such as Atomic Force Microscopy (AFM) will establish whether it is feasible in future. It will also be possible to examine some adhesive bonded contacts so that X-ray Computed Tomography can investigate the dimensions and integrity of bonded surfaces. A successful outcome to this investigation will allow Tethir to assess how optical surfaces should be bonded in future designs and provide NPL with valuable assessments of how its various tools can best be applied to the characterisation of surfaces for optical communications.

Wildfires cause catastrophic damage worldwide, accounting for 20% of global carbon emissions. The problem, exacerbated by climate change, is deteriorating. Unusually severe fires in USA, Australia, Spain etc, have claimed hundreds of lives, causing damage worth US$Bn's. Wildfires are breaking out in countries unaccustomed to the problem. Northern European countries experienced a 200x increase in area burned in 2018\. Even the UK is being badly affected (e.g. Winter Hill -- 2018). We propose a new solution for early detection of the most predictable fires: those occurring due to power line failure - more damaging than most because they often occur in high winds. In California over 6 years, 1,500 wildfires started in the power line corridors of one utility company, some of the most devastating on record. In Spain, 3,185 fires were started by power lines between 1985-2010\. Power line operators worldwide now face severe financial liabilities (US$Bns), creating a large market (£M100's) for reliable and effective detection systems. Utility companies have assessed sensors (based on visible/thermal imagers) but have not adopted any at scale because they are too expensive to rollout, require human monitoring and only detect fires once they have grown to an unstoppable size. Companies need technologies that can detect fires in the first minutes after ignition, while they still occupy <1 acre and when firefighters have a chance of extinguishing the fire before it causes extensive damage. This is challenging. Many wildfires occur in remote areas far from electricity and telecommunications infrastructure, so low power consumption, reliability and power/comms-autonomy are key. The sensing system we propose will use low cost, world-leading pyroelectric infra-red (PIR) detectors (Pyreos) with low cost, highly-efficient non-imaging radiation-collectors (Tethir). PIR's are widely used in fire/flame detection systems for the oil-and-gas sector. Tethir's optics will give a usable detection range (1-2km) with existing detector performances and much further with the development of better detectors. The project will develop a saleable market-entry product and we predict sales of £M10's to power companies over the first 5 years after prototype demonstration, with further sales as we extend the detection capability to other wildfire causes (e.g. arson). The combination of cutting edge technologies with two world-leading UK experts in PIRs and wildfires at Imperial and Kings College London is key to the success of this development and brings the UK a significant wealth-creation opportunity while helping to solve a serious world-wide problem.

Only a third of passengers on the UK's railways seem happy with the wifi service they receive on the train. People increasingly expect free and reliable internet wherever they go and are frustrated that train journeys interrupt the entertainment and communications they value for lifestyle and work. The problem is not for lack of attention. The Government knows how much this matters to people and has called for rail franchises to include free wifi from 2020\. Although the initiative itself will guarantee no more than 1 Mbps per head, it sends a clear signal to the train operators who have so far found it difficult to justify investment in the infrastructure needed over the timeframe of the franchise contracts. Network Rail Infrastructure Limited (NRIL) is the owner and operator of most of the rail infrastructure in Great Britain and is at the forefront of attempts to find innovative solutions for this market failure. HS2 is the next major railway infrastructure project in the UK and an excellent opportunity to prove high bandwidth, reliable internet services for entire journeys. VILIRI's approach is based on Optical Wireless Communications (OWC) that uses Infra-Red (IR) frequencies to send data between train and trackside at 10Gigabits per second (10Gbps). This is more than enough for all types of internet browsing, real time communications and effectively unlimited capacity for each passenger. The innovation is to use advanced optics with high levels of concentration and carefully matched sensors that can take low power IR signals and process them reliably in real time. This needs transceivers on the train and along the track so that data is transferred by line of sight from each transceiver in turn. The quality of service achievable will support operational communications and security CCTV picture transfers, for example, as well as information and internet for the passengers. The project will enhance the capability of the optical links by advanced signal processing and multiple channels where needed. Care will be taken to ensure that the optics remain clean and clear in all weathers. Most importantly, the business case for installing the system as part of the railway infrastructure will be covered by the revenue that additional internet services will bring while passengers enjoy the basic internet service without direct charges. Capital costs will be reduced by internet connection within the provision of optical fibre that has to be laid for signalling and other functions.