Antiresonant hollow core fibre, preform therefor and method of fabrication

A nested antiresonant nodeless hollow core optical fibre, or a preform or a cane for drawing into a nested antiresonant nodeless hollow core optical fibre, comprising:

• a cylindrical elongate outer jacket of glass material or polymer material;
• a cladding structure comprising a plurality of cladding elements of glass material or polymer material spaced apart around an inner surface of the outer jacket and defining elongate cladding voids, each cladding element comprising a first inwardly curving wall extending from the inner surface towards a central longitudinal axis of the outer jacket and back to the inner surface along a first curved shape, and a second inwardly curving wall extending from the inner surface towards the central longitudinal axis and back to the inner surface along a second curved shape which has a different shape and/or a different length from the first curved shape;
• and
• an elongate hollow core region along the central longitudinal axis and bounded by negative curvatures of the first inwardly curving walls of the cladding elements.