Branching ratio of light incident on a photonic crystal in a multibranch dispersion region

In a frequency region where dispersion relation shows multibranch structure, the branching ratio of the Poynting vectors for various transmitted and reflected modes has been determined via the consideration of boundary conditions at the surface. For this purpose, it is required to obtain the field amplitudes of many eigenmodes with real and complex wave vectors, which numerically is a rather demanding task. An example is given for a simple cubic photonic crystal with intersecting square rods. It is found that a different choice of (001) surface in a unit cell leads to a remarkable change in the branching ratio, or reflectance curve.