Fabrication of Photonic Crystal Fibres

The idea of producing optical fibres from a single low-loss material with microscopic air holes goes back to the early days of optical fibre technology, and already in 1974 Kaiser et al. [4.1] reported the first results on singlematerial silica optical fibres. In the early days — as well as today — the key issues have been to obtain a desired fibre structure for a given application, and maintain this structure for very long fibre lengths. It will, generally, be needed that the fibre attenuation is kept at a rather low level, and the acceptable attenuation level will be given by the specific application. In this chapter, we will address the fundamental issues of fabrication of photonic crystal fibres, by first discussing the most commonly used preform fabrication method. Secondly, we will report details about the fibre drawing and coating procedure. Furthermore, we will discuss how additional doping techniques are needed for providing hybrid fibre types (such as the holeassisted lightguide fibre (HALF) [4.6]) combining the approach of microstructuring with index-raised doped glass or active dopants such as rare-earth ions needed for new amplifiers and lasers. The chapter will also shortly address the issues of photonic crystal fibres in low-melting-point glasses and polymers.