New polarization properties of photonic bandgap optical fibres are analysed
. Exemplified by an analysis of honeycomb-structured photonic bandgap fibre
s, strong birefringence is found for modest non-uniformities (deviations fr
om the 60 degrees symmetry) in and around the core region. This suggests th
e application of photonic bandgap fibres as polarization-maintaining optica
l components.