Coupled-mode approach to square-gradient Bragg-reflection resonances in corrugated dielectric waveguides

We demonstrate the appearance of unexpected reflection resonances in corrugated dielectric waveguides. These are due to the curvature of the boundary. The effect is as strong as the ordinary Bragg resonances, and reduces the transmission through our waveguide by 20%. It is thus of high relevance for the design of optimized waveguiding structures. We validate our analytical predictions based on coupled-mode theory by a comparison to numerical simulations.