Quasi-modal analysis of segmented waveguides

In the present paper, we show that it is possible to use a periodic structure of disconnected elements (e.g. a line of rods) to guide electromagnetic waves, in the direction of the periodicity. To study such segmented waveguides, we use the concept of quasimodes associated to complex frequencies. The numerical determination of quasimodes is based on a finite element formulation completed with Perfectly Matched Layers (PMLs). These PMLs lead to non Hermitian matrices whose complex eigenvalues correspond to quasimode frequencies. Using Floquet-Bloch theory, a numerical model is set up that allows the spectral study of structures that are both open and periodic. With this model, we show that it is possible to guide electromagnetic waves on significant distances with very limited losses.