August 06, 2012 Glass fibres are used generally to transport
light over long distances – for example, fast data transmission
over the internet. Photonic crystal fibres (PCF) are a novel
variant of such optical fibres, currently used mainly in basic
research. Their cross-section is reminiscent of a honeycomb:
tiny hollow tubes surrounding the core run along the circular
fibre. They ensure that the light only travels in the core where
it is transported with low loss. The transmission behaviour of
photonic crystal fibres changes significantly if they are
twisted around their longitudinal axis – the transmission of
certain wavelengths becomes much poorer. The optical fibre
becomes spiral and works like a filter. The behaviour can be
controlled very easily through the twist: with a stronger twist,
the dips in transmission shift towards longer wavelengths. The
team of researchers working in Erlangen led by Philip Russell
has studied this effect in detail. They secured one end of a PCF
and used a motor to rotate the