Out-of-plane scattering from vertically asymmetric photonic crystal slab waveguides with in-plane disorder

We characterize optical wave propagation along line defects in two-dimensional arrays of air-holes in free-standing silicon slabs. The fabricated waveguides contain random variations in orientation of the photonic lattice elements which perturb the in-plane translational symmetry. The vertical slab symmetry is also broken by a tilt of the etched sidewalls. We discuss how these lattice imperfections affect out-of-plane scattering losses and introduce a mechanism for high-Q cavity excitation related to polarization mixing.