Out-of-plane scattering at sidewall roughness in photonic crystal slabs

We have simulated the effect of sidewall roughness in photonic crystal slabs sing a 2-D approximation. The scattering off a sidewall irregularity is modelled as a radiating dipole excited by the incident slab mode. We studied the effect of the vertical index contrast in the slab layer to establish the impact of irregularities in high and low vertical index contrast structures respectively. It turns out that losses due to roughness are significantly larger for structures with a low refractive index contrast (like GaAs/AlGaAs or InGaAsP/InP waveguides) compared to structures with a high vertical index contrast (like Silicon-on-insulator or membranes)