In this example we calculate eigenmodes of a photonic crystal fiber (PCF) depicted below. The large number of air pores in the cross section was generated using Lattice Copies, whereby a basic geometrical pattern can be placed several times in the layout.
The computed modes for this example are very well confined within the 7 cores of the fiber surrounded by the photonic crystal pattern. However, we want to take into account that radiation can leak to the exterior of the computational domain due to the fact that the refractive index in the main wave guiding region is not larger than in the exterior. Therefore, we apply transparent boundary conditions to the outer boundaries of our layout.
The basic parameters needed for the input files are described in the basic example Propagating Mode. As initial guess for the effective refractive index we take a value slightly below the refractive index of the fiber material .
The following images show a selection of intensities of modes which were computed for the fiber:
In the present PCF example it appears to be reasonable to apply
TangentialMagnetic boundary conditions in order to reduce the computational costs, as the intensity of the electric field decreases very quickly towards the boundaries. Additionally the symmetry of the given PCF allows us to reduce the size of the computational domain to one quarter. How this can be done is explained here.