Leaky modes in twisted microstructured optical fibers

The purpose of this paper is to investigate the effect of a twist on the losses of leaky modes in microstructured optical fibers (MOF). A helicoidal system of coordinates is introduced to define the structure and to set up the problem. These coordinates, albeit non-orthogonal, preserve the translational invariance in a way that allows a two-dimensional finite element model similar to that of classical straight waveguides. The Perfectly Matched Layer (PML) technique is used to compute the leaky modes in the fibers. Helicoidal coordinates and PML are unified under the point of view of geometrical transformations which allows the design of 'twisted PML' that provides the right tool to determine the leaky modes in the twisted structures.