Leakage studies on SOI slot waveguide structures

In this study. we theoretically investigate the leakage behavior of SOI slot waveguides at a wavelength of 1.55 mu m. First, the dependence of the substrate leakage of vertical and horizontal wire-type slot waveguides on their geometry is shortly summarized. The main part is devoted to the lateral leakage in perfectly symmetric and asymmetric rib-type slot waveguides. which is caused by coupling between the TM-like slot mode and the TE slab modes outside the rib. The influence of the geometry parameters on the leakage behavior and the impact of structural deviations caused by the fabrication process are studied in depth. A semi-analytical criterion for the design of leakproof rib-type slot waveguides is derived and compared with full-vectorial numerical methods employing a commercial FEM solver and a recently developed variational mode-matching 2D eigenmode solver.