Analysis of light propagation for a crossing of thin silicon wires using vertical tunnelling coupling with a thick optical channel waveguide

Using silicon photonic wires in a silicon-on-insulator structure as an example, we examine the problem of crossings of thin, high-index-contrast channel waveguides. To ensure high optical wave transmission efficiency at as low a level of parasitic scattering as possible, we propose using a structure with vertical coupling between a thin tapered silicon waveguide and a thick polymer waveguide, separated by a thin buffer oxide layer. Numerical simulation is used to find conditions under which such a structure (3x90 mu m in dimensions) ensures 98% and 99% transmission efficiency at similar to 1.55 mu m in 35- and 26-nm spectral ranges, respectively, for direct propagation and 99.99% transmission in the transverse direction. The optical element in question is proposed for use in optical microchips with multiple channel waveguide crossings.