Interplay between disorder and local field effects in photonic crystal waveguides

TL;DR

This paper develops a theory to analyze how disorder and local field effects influence scattering and resonance shifts in photonic crystal waveguides, revealing significant impacts on slow-light regimes and mode edges.

Contribution

The paper introduces a novel theoretical framework that accounts for local field effects in disorder-induced scattering within high-index-contrast photonic crystal waveguides.

Findings

Disorder causes substantial frequency shifts and band broadening even in state-of-the-art fabricated waveguides.

Local field effects significantly increase predicted scattering losses and resonance shifts.

Approaching the slow light regime, disorder effects intensify, potentially eliminating the slow-light mode edge.

Abstract

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 waveguide mode. 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. For a representative waveguide, we predict substantial meV frequency shifts and band structure broadening for a telecommunications operating frequency, even for state of the art fabrication. 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 have a dramatic impact on high-index-contrast nanoscale waveguides, and, for photonic crystal waveguides, suggest that the nominal slow-light mode edge may not even exist. Furthermore, our results shed new light on why it has hitherto been impossible to observe the very slow light regime for photonic crystal waveguides.