Minimizing Roughness Lossfor Ultra-Compactly BentHighIndex-Contrast Waveguides

Roughness-loss inrectangular highindex-contrast waveguides maybecalculated semi-analytically using amodified coupled-mode theory. Themethodisverified byexperiments andgives rules forthedesign of straight low-loss optical waveguides. Forultra-compactly bentwaveguides, roughness losses maybeminimized bychoosing whispering-gallery guidance oflight along anoptimized outer waveguide contour. Ourfindings are