  The reflectivity of various Bragg reflectors in connection to waveguide
structures, including nanowires, has been investigated using modal reflection
and transmission matrices. A semi-analytical model was applied yielding
increased understanding of the diffraction effects present in such gratings.
Planar waveguides and nanowire lasers are considered in particular. Two
geometries are compared; Bragg reflectors within the waveguides are shown to
have significant advantages compared to Bragg reflectors in the substrate, when
diffraction effects are significant.
