Nanophotonics inside structured optical fibres

Invited Paper

Nanophotonics inside structured optical fibres J. Canning * Interdisciplinary Photonics Laboratory (iPL), School of Chemistry, The University of Sydney, Sydney, NSW, Australia ABSTRACT Tailoring and structuring optical fibres to nanoscale dimensions is rapidly becoming a focus area of research and is important for the eventual success of future in-fibre optical systems and novel technologies. Here, I review one aspect of our work in establishing and pursuing this field: localizing light for sensing. Keywords: Fresnel fibres, nanophotonics, nanoholes, edge localisation, optical localisation

INTRODUCTION When we think of optical fibres, we think of optical propagation, essentially moving light from one point to another, whether by step-index or diffraction assisted propagation. The focus on this waveguide properties means that even components, both linear and nonlinear, using optical fibres are largely considered in terms of features on a scale commensurate with the waveguide, or the waveguide mode. Little if any attention is usually paid to sub-wavelength features. In fact, arguably such components are always considered in terms of modification of the wave guiding properties only. However, recent innovations developing novel Fresnel lenses based on existing curiosities associated with fibre fabrication has transformed our view of optical fibres as solely a means of confinement and transport. The deposition process of an MCVD system is sufficiently refined to enable the etching of well correlated graded profiles at the end of each fibre that can act to focus light [1]. These features can be less than 100nm in resolution. It was a small step from this innovation to the idea that with sufficient index contrast a properly designed optical fibre can do more than simply assist propagation of light, via diffraction, from one point to another – the Fresnel fibre [2,3] can enable both transportation and focusing of light [3-6], introducing the idea that fibres generally can have multiple capabilities beyond optical transport. In this context, alternative fabrication methods, such as plasma based CVD and structured optical fibre and fibre taper fabrication, have offered straightforward ways in which a fibre can be tailored on the nanoscale. Indeed, feature sizes