Numerical simulation of hollow waveguide arrays as polarization converting elements and experimental verification

In this paper we study the characteristics of hollow waveguides that are used as polarization converting elements. In particular, numerical simulations are compared with experiments where a good agreement is found. The numerical simulations are performed with the Method of Lines—an eigenmode propagation algorithm where the eigenmodes are computed after a discretization in the cross-section. Due to the vectorial 3D-problem, extensions of the standard algorithm were required to keep the numerical effort low. Particularly, only a reduced set of eigenmodes is used in the computations and inverting rectangular matrices is done with the help of left eigenvectors. Further, it is shown how these left eigenvectors can be determined with simple matrix vector products, i.e., at very low numerical cost. The fabrication of the device is very demanding because of a very high ratio between the metal width and its height. Here, direct electron-beam lithography is used for this task.