Patent ID: 8503846

Claim:
A photonic bandgap optical fiber comprising: a core region; and a cladding region surrounding the core region, the cladding region including a background optical material having a first refractive index n, and elements arranged in a two-dimensional periodic structure, wherein: each of the elements comprises a centre part and a peripheral part, the peripheral part having a higher refractive index than the centre part, the elements are arranged such that the fiber has a band gap in a normalized modal parameter (β 2 -n 2 k 2 )Λ 2 of the fiber, with a lower band edge of the band gap substantially constant over a range of normalized frequency kΛ, where β is a longitudinal component of wave vector, k is a free space wave number, and Λ is a distance from a center of one element to a center of an adjacent element in the cladding region, and the first refractive index is substantially equal to the refractive index of the centre part.