A shaped tube (figures 6A & 6B) for use as a component in the fabrication of an antiresonant hollow core optical fibre, the shaped tube having a side wall with a transverse cross-sectional shape comprising a number of major curved portions alternating with the same number of minor substantially straight portions, each curved portion having an inwardly curving shape, and each straight portion being equidistant from a central longitudinal axis of the shaped tube. A preform and a method of fabricating of fabricating a preform comprising the shaped tube secured inside an outer jacket tube of glass or polymer material, a cane drawn from the preform are also disclosed. A nested antiresonant hollow core optical fibre is also disclosed.
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