Microstructured or holey optical fibres are a novel class of fibres that have attracted much interest recently because they can be tailored to have properties (dispersion, nonlinearity, mode size) very different from conventional fibres. These structures can consist exclusively of air holes arranged around a solid core region in a uniform background. Since such fibres do not have any raised index regions, they cannot support true bound modes. They can, however, possess leaky modes where the light is trapped within a region surrounded by air holes. Such modes suffer confinement losses due to energy leakage between and through the holes. The confinement loss is given by the imaginary part of the complex effective mode index n eff. Existing basis function expansion (Galerkin) techniques (using plane waves [1] or Hermite-Gaussians [2]) give most modal properties except for the confinement loss. Methods such as BPM can be used to find confinement loss [3] but are numerically intensive; and, recently, a multipole method has been used which is restricted to circular holes [4]. The technique presented here has the simplicity of a Galerkin technique but can also find confinement loss and complements existing methods by applying to a holes in the shape of annular sectors. Typical structures are shown below.
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