Physicists from Gdansk University of Technology in Poland and from Aston University in the UK have worked out a new way of modelling photonic crystal fibres with hexagonal cells and large airholes. These small-mode-area fibres have applications in pressure and temperature sensing as well as in all-optical switching, in supercontinuum generation and in Raman scattering for optical amplifiers.This image of the step index fibre is generated by Femlab software. Courtesy of B. Reichel, Gda«nsk University of Technology.The technique combines accurate numerical computation of mode eigenvectors with an equivalent step index fibre model. The scientists used Femlab software from Comsol to compute eigenvalues and compared numerical and analytical determinations. They used a model that omits the cladding and its associated modes and that uses only one ring of airholes, with a circular model for the star-shaped core. This works well for large airholes, but for small ones, it is necessary to include more than one ring of holes.(Journal of Modern Optics, 20 May 2008, pp. 1479-1486)