Control of modal properties and modal effects in air guiding photonic bandgap fibres

The advent of microstructured fibre technology has opened up the possibility of photonic bandgap fibres (PBGFs), which guide light in a low index core, or even a gas or vacuum. Their unique optical properties make them particularly attractive for applications in high power laser delivery, pulse compression, gas-based nonlinear spectroscopy and optical sensing. PBGFs, however, operate by virtue of a radically different mechanism as compared to conventional index guiding fibres and as a consequence they present unusual and rather complex modal properties. Control over the modal properties of these waveguides is paramount to a number of application areas, particularly those requiring a relatively short device length. In this paper we address the issue of multi-modeness in PBGFs and investigate various strategies to control the number and type of modes supported in these fibres.