Interplay between disorder-induced scattering and local field effects in photonic crystal waveguides

We introduce a theory to describe disorder-induced scattering in photonic crystal waveguides, specifically addressing the influence of local field effects and scattering within high-index-contrast perturbations. Local field effects are shown to increase the predicted disorder-induced scattering loss and result in significant resonance shifts of the propagating waveguide mode. Performing an incoherent averaging calculation, we demonstrate that two types of frequency shifts can be expected, a mean frequency shift and a rms frequency shift both acting in concert to blueshift and broaden the nominal band structure. The disorder-induced broadening is found to increase as the propagation frequency approaches the slow-light regime (mode edge) due to restructuring of the electric-field distribution. These findings shed new light on why it has hitherto been impossible to observe the very slow-light regime for photonic-crystal waveguides and suggest that the nominal slow-light mode edge may not even exist.