For both modes of crystal fibre, the pattern of holes is generated by stacking hollow glass tubes a millimetre or so in diameter to form a rod several centimetres thick.

ECONOMIST: A new approach to making optical fibres

Using this fibre, weavers produce the pattern, the crown and the brim of the hat and complete the process by washing, bleaching, oven treatment, ironing and pressing.

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In the same way, the pattern of holes in a crystal fibre can create the equivalent for light of a graphite core and a diamond cladding.

ECONOMIST: A new approach to making optical fibres