Fig. 11
Effective refractive indices of the fundamental TE and TM modes in a slab waveguide, in dependence on the waveguide height at 1550 nm wavelength. A TM leakage is possible for all rib slab heights, where neff,TM(t1) < neff,TE(t2) (right from the vertical gray line). Both shallowly etched (s-rib) and deeply etched (d-rib) waveguides find themselves in this area