  Nanowires show a large potential for various electrooptical devices, such as
light emitting diodes, solar cells and nanowire lasers. We present a direct
method developed to calculate the modal reflection and transmission matrix at
the end facets of a waveguide of arbitrary cross section, resulting in a
generalized version of the Fresnel equations. The reflection can be
conveniently computed using Fast Fourier Transforms. We demonstrate that the
reflection is qualitatively described by two main parameters, the modal field
confinement and the average Fresnel reflection of the plane waves constituting
the waveguide mode.
