Scattering at sidewall roughness in photonic crystal slabs

We have simulated the effect of sidewall roughness in photonic-crystallike structures with different vertical refractive-index contrast. We treated the scattering off a sidewall irregularity as a radiating dipole excited by the incident waveguide mode. We show that the loss that is due to this scattering is significantly larger for structures with a low refractive-index contrast (such as GaAs/AlGaAs waveguides) than for structures with a high vertical index contrast (such as silicon-on-insulators and membranes).