Integrated nonlinear silicon photonics: a route to smaller, faster, greener systems

Silicon photonics is one of the largest and fastest growing areas of research and development of our time. The ability to exploit the semiconductor functionality to process and transmit data in the form of light offers a route to dramatically increase the speeds, capacities, and efficiencies of next generation optoelectronic systems. An important subset of this work is nonlinear silicon photonics, where the aim is to make use of the large, ultrafast, nonlinearity of the material to intricately control and manipulate these light-based signals using light itself. Nonlinear processes in silicon have been widely studied, with significant device demonstrators including Raman lasers, parametric amplifiers, and high-speed modulators. However, most of these devices have been constructed from single crystal material platforms that are notoriously difficult to integrate, either with other elements on-chip or with the optical fibres that are used to link the systems together. Thus, if nonlinear silicon devices are to make the critical transition from a research curiosity to commercially viable products, these integration hurdles must be overcome.

The work in this fellowship application will develop procedures to directly incorporate nonlinear optical components fabricated from cheap and easy to deposit materials within highly functional photonic systems. Compared to their single crystal counterparts, these materials offer a number of key advantages as they are compatible with a wide range of substrates, can be shaped in three dimensions, and can even be post-processed to fine-tune the optical properties and/or the waveguide structure. The components will be fabricated in both fibre and planar form, thus opening an innovative route towards linking these two platforms - one of the most important design challenges in the field of silicon photonics. Following optimization of the integration methods and materials, a range of nonlinear optical systems will be constructed, with the goal to obtaining systems that are smaller, faster, and more efficient. Although the primary focus of this project is the development of integrated platforms for optical communication systems, by extending the device operation into the mid-infrared wavelength region there will be scope to target applications in important areas such as environmental sensing, healthcare, and public security. By looking beyond the traditional single crystal chip-based components to consider more flexible materials and geometries, the work in this programme will help bring the vision of truly integrated nonlinear silicon platforms to fruition.

The robust and compact integrated nonlinear systems developed within this proposal have the potential to transform modern optoelectronics by offering increased speeds, capacities, and efficiencies. Thus this research is perfectly aligned with the EPSRC theme "Photonics for Future Systems". Although initially I expect the outcomes of this work to have their largest impact in the area of optical communication systems, by extending the device operation into the mid-infrared wavelength region there will also be scope to target applications in imaging, sensing and healthcare.

Communication systems: ICT systems that are both simple to produce and more efficient will not only be of great economic benefit, but also of considerable societal value. For example, the development of all-optical switches, modulators, light sources and amplifiers that can be seamlessly linked with the transport fibres will negate the need to convert between optical and electronic signals, which is slow, costly and energy consumptive. In particular, improving the energy efficiency of ICT systems is of critical importance as the level of global carbon emissions (estimated to be at ~2%) is currently larger than the entire airline industry. In this regard, Intel and HP labs have already recognized the valuable role that deposited materials could play in the development of integrated optical systems, and my partnership with Seagate (one of the largest data storage companies in the world, with a keen interest in silicon photonics for optical interconnects) further demonstrates the relevance of this proposal to the communications sector. I expect that as the material technology matures, other major computer (IBM) and communication companies (Finisar) will find similar merit.

Sensing and healthcare: There is a high demand for sensors and medical components that are robust, versatile and low cost. The UK already has a strong technology base in this area (e.g. OptaSense and Mediwise), and thus continued investment is required to ensure it maintains its competitive edge. Within this programme, there are a number of systems that could be developed that are relevant to this sector. For example, silicon optical fibres coupled to mid-infrared fibre lasers could be used for precise delivery of radiation for in-vivo imaging or keyhole surgeries. Alternatively, integrated systems on-chip consisting of broadband sources, waveguides and multiplexers could form the basis of compact spectrometers for use in environmental monitoring or drug analysis. Thus, the impact of this project will also extend to the EPSRC themes "Healthcare Technologies" and "Global Uncertainties".

The successful outcomes of this proposed work will ultimately help to shift the focus away from single crystal nonlinear components to more flexible and integrable alternatives. As the programme is largely centred on developing the integration procedures, and the subsequent materials optimization, much of the immediate impact will be within the academic community. However, with guidance from the project's industrial partners, it should not take long for the commercial value of these platforms to be widely recognized. By training new staff and students in this technologically important area, the UK will have a solid skill and knowledge base from which to quickly capitalize on future commercial developments.