Modal characteristics of few-mode silica-based photonic crystal fibres

The modal characteristics of silica-based photonic crystal fibres (PCF) are examined through a scalar modal analysis combined with an effective V-para meter model using a finite-difference method. Cut off frequencies of the lo west-order modes and the normalised dispersion curves are given and are fou nd to be quasi-independent of the hole-size-to-pitch ratio. A simple and ac curate empirical relation for the cutoff wavelength is given for the first higher-order mode for fibres with hole-size-to-pitch ratio below 0.7. These results should he very useful in designing PCF's for various applications.