Oblique quasi-lossless excitation of a thin silicon slab waveguide: a guided-wave variant of an anti-reflection coating

Radiation losses at a junction of high-contrast Si/SiO2 slabs of different thicknesses can be avoided, if, for excitation by semi-guided waves, the angle of incidence is raised beyond a critical angle. By introducing an additional short waveguide segment of intermediate thickness at the junction, reflections can be suppressed; our simulations predict near-full transmittance for the thus coated interface. These are nonresonant effects; the structures perform adequately for incidence of semi-guided Gaussian beams of moderate widths, and for a comparatively broad wavelength range. (C) 2019 Optical Society of America