Mid-Infrared GeRmAnium phoTonIcs fOr seNsing (MIGRATION)

Group IV photonics is a field that is currently revolutionizing the future of modern optoelectronic devices. So far most of the focus has been on silicon based materials at near-infrared wavelengths for use in data communications, though some more recent demonstrations in the 2-3um regime include Raman and parametric amplification. There are a number of advantages to extending the operational range of these devices into the mid-infrared regime such as lower optical losses and higher nonlinear coefficients, and preliminary device work in this area has shown improved efficiencies over their near-infrared counterparts. Moreover, this wavelength regime supports a host of important applications such as chemical and biological sensing, environmental and hazardous substance monitoring, medicine, and industrial process controls. The most efficient wavelength band for many of these applications is the so called 'fingerprint' region (>8um) where the precise identification of many molecular substances is possible. However, as the transparency of silicon only extends to ~8um, more recently attentions have been turning to germanium (transparency range 2-15um) as an alternative platform to fully realize the mid-infrared capabilities of group IV devices for sensing and other life science applications. Significantly, compared to silicon, germanium offers a number of other advantages in terms of device development such as even higher nonlinear coefficients, better carrier mobility, and the potential to realise active devices based on germanium based alloys.

The work in this programme proposes to lay the foundations for a migration of mid-infrared group IV photonics from silicon to germanium-based platforms with the aim to future proof emerging technologies in this field. Thus, one of the main outcomes of this work will be to identify high quality germanium substrates that rival the performance of the well-established silicon-on-insulator wafers used over the 1-3um regime; a task that will be performed in conjunction with our project partners IQE who are the UK's global leaders in advanced semiconductor wafer fabrication. This framework will then be used to demonstrate a library of devices such as waveguides, couplers, filters, amplifiers and modulators that will form the building blocks of integrated on-chip circuits, systems and sensors over an extended wavelength regime. Although the primary focus of this project is the development of integrated sensors for toxic detection with improved efficiency, compactness, and robustness, which are required for DSTL and other defence and security stakeholders, by targeting devices that can perform a range of basic functions, these will be relevant to a variety of applications ensuring maximal impact. This visionary programme of research is at the forefront of this exciting new area of mid-infrared group IV photonics and thus promises to deliver a number of disruptive mid-infrared photonics solutions.

There is a high demand for sensors that are small, versatile and low cost for application in multi-billion dollar markets such as environmental monitoring, defence and security, medicine, and industrial process control. We believe that MIGRATION will be a catalyst for a series of research breakthroughs that will lead to the realisation of such sensors and result in significant economic and societal impact. This research is directly aligned with three of the main EPSRC themes.

Global Uncertainties: New emerging challenges from organised crime and terrorist groups underline the vital need for sensitive and selective, rapid (in field) identification of different types of chemical hazardous materials such as drug mixtures, chemical and biological warfare (CBW), explosives, and toxic spills. The platforms developed in the proposed work will enable realisation of compact chemical agent sensors with low false alarm rates. Such sensors would be of use for the protection of UK forces at home and abroad, by alerting them of the location of hazardous materials before they are encountered. Similarly, they could also be applied by first responders for the prevention terrorist attacks and in industrial accidents.

Healthcare Technologies: The high sensitivity of the systems that operate in the fingerprint wavelength region will also ensure that they can be applied in healthcare applications for efficient point of care diagnostics. For example, accurate breath tests can be used to detect diabetes and stomach cancer (http://www.bbc.co.uk/news/health-21671455), both of which give off signature smells of volatile organic compounds. Specifically, breath test trials are already being used to detect diabetes in children (http://www.bbc.co.uk/news/uk-england-oxfordshire-15589264), though we also expect such non-invasive tests to be important for care of our aging society.

Living with Environmental Change: In the longer term, these systems will be of use for networked environmental sensors to monitor pollutant concentration in air (e.g., CO2 emissions in cities), water, and soil. Extensive monitoring of developing cities and industrial estates will assist policy makers in determining how to create/maintain a healthier environment. In particular, the monitoring of water supplies for detection of biological outbreaks (deliberate or not) is critical for public health, as well as for services such as transport and power generation.

The new platforms proposed in this project have the potential to offer elegant solutions in each of these important areas, thus causing a migration in the Group IV photonics research community from silicon to germanium. As such, this research will be of wide interest as an enabling technology to both academic and industrial communities. The partnership with DSTL and IQE Silicon Ltd demonstrates the relevance of our proposal to UK industries, and especially the importance to maintain at the forefront of emerging mid-IR sensing technologies. Currently the UK is fourth in the world in terms of sensor production, with 60% of the production being exported, and we hope that this work will stimulate further growth in this area. In addition, by training new staff in this area we will ensure that the UK has a solid skill and knowledge base for any future industrial, as well as academic, developments.