air being where bulk material would otherwise be total internal reflection effects are not responsible for that waveguiding in the illustrated example photonic crystal fibres can be manufactured by a process one stage of which is shown in fig4 in the first stages of that process not shown a cylinder of bulk material e g silica is milled so that it has a hexagonal cross section and a hole is drilled along its centre the rod is then drawn into a cane using a fibre drawing tower the cane is cut into lengths and the resulting short canes 80 are stacked to form an array of canes as shown in fig4 the cane 100 at the centre of the illustrated array is not a capillary i e it has no hole the illustrated array will form an effective index guidance type of fibre the array of canes 80 is fused together and then drawn into the final photonic crystal fibre 110 the fibre shown in fig5 has a lattice 120 of holes which are arranged at the vertices of rectangles which are not squares the periodicity of the lattice is broken by the omission of a hole in the region 125 near the centre of the fibre cross section the center to center spacing pitch of the holes is different parallel to axis x pitch u03b4 x from the pitch u03b4 y parallel to axis y the fibre shown in fig5 could be manufactured using a cane which is milled to have a rectangular cross section the lattice of fig5 has two fold rotational symmetry and will therefore be birefringent fig6 and 7 show photonic crystal fibres which are effective index guidance fibres having a hexagonal lattice.