Introduction

The generic single-mode optical fibre is a fibre drawn from fused silica. Silica fibres are available at very low cost, being produced by sophisticated processes in massive quantity for the global telecommunications network. They are very transparent, and much optical equipment is designed around their transparency windows, making research at these wavelengths particularly convenient. Devices or effects using silica fibres are therefore compatible with a wide range of existing optical fibre technologies, and so easy to incorporate into existing systems should the need or opportunity arise. Silica fibres are available in a wide range of different forms, especially with the development and commercial availability of silica photonic crystal fibres (PCF) and microstructured fibres.

Many of the above arguments rely for their worth on the already widespread deployment of silica optical fibres. However, there are also fundamental reasons to work with silica fibres, many of them the same reasons that they are already so popular. Silica – glassy SiO2 – can be synthesised with remarkably high levels of purity at very low cost: silicon is an abundant and easily-obtained element in the earth's crust, while the chemical processes used to synthesise silica are efficient and simple. Of course, the fact that these processes have been scaled up to produce large volumes of material further reduces the cost of production. The transparency window of silica is broad, spanning both visible and near-infra-red wavelengths. Practically, silica optical fibres are usually used in the spectral range 300–2500 nm.