Modelling confinement loss in practical small-core holey optical fibres

Microstructured optical fibres (MOFs) are all-silica fibres that guide light by means of an arrangement of air-holes that run down the entire fibre length. In the kind of MOFs here considered, also named holey fibres (HFs), guidance arises from average-index effects: the holes form the cladding region around the solid core. The modes of such fibres are leaky because the core refractive index is the same as the index beyond the (finite) cladding region. HFs with a core diameter of the scale of an optical wavelength and large holes have been fabricated, resulting in the smallest effective area ever measured in a fibre at 1550 nm [1]. Such small effective areas make these fibres attractive for nonlinear applications. The cladding of a HF is usually comprised of hexagonally-packed rings of holes, and when the hole-to-hole spacing (Lambda) is of the order of the wavelength, several rings of holes are required to reduce the confinement loss to a practical value. Fibre fabrication feasibility on the other hand constrains the number of rings that can be used. Therefore in order to optimise the design of this class of fibres, it is necessary to study the loss characteristics for small-core HFs