OPTICAL WAVEGUIDE

摘要

The present invention is in the field of optical fibres. In particular, the present inventors describe hollow core optical fibres, for example hollow core photonic band-gap optical fibres. The present inventors describe examples of such fibres that guide light by virtue of a true photonic band-gap in a hollow core region having a boundary at the interface between the hollow core and a photonic band-gap cladding. In some examples, the boundary is tuned by addition of solid material during formation of a respective fibre preform (1800) to improve the performance of the resulting fibre, for example by mitigating deleterious effects such as mode coupling of light from core-guided modes to so-called boundary or `surface' modes.