The proposed project is about using silica aerogels in the field of fibre optics. Aerogel is a highly porous form of glass with remarkable optical properties, but has barely been exploited in fibre optics. It is made of the same material as optical fibres, namely silica glass. However, whereas the glass in the fibre is solid, an aerogel is like a sponge: an open porous network of solid matter with air in between. Indeed, most of the volume of an aerogel is air, making it very lightweight. The glass network and the pores are structured on a scale of tens of nanometres or less, much smaller than the wavelength of light. The aerogel is therefore an example of a metamaterial: light sees the aerogel as an averaged-out medium that is mainly air, yet the glass network makes it rigid like a solid. The refractive index of aerogel can be as low as 1.01: almost the same as air and very different from solid glass. Indeed, the lowest index of any common solid or liquid is around 1.27, so aerogel is really the only way to get lower-index materials. Although light and friable, aerogel is quite robust if not abused: it looks like frozen smoke and handles like Oasis floral foam. It has found diverse applications, from thermal insulation to the collection of interplanetary dust.Despite the intriguing properties of this material, few people have tried to use it in fibre optics. We now have a unique opportunity to bring these two technologies together, having recently demonstrated the necessary methods using tools we have developed for supercritical drying and fibre fabrication. The aim will be to optimise the material, allow it to interact with the light in a fibre, and so enable an entirely new class of photonic components that exploit the optical properties of aerogel in a fibre-compatible way. Key applications include high-numerical-aperture waveguides, compact splitters and couplers, fibre-coupled nonlinear sources and new plasmonic devices.