Evanescent Wave Sensitivity of Silica-Titania Rib Waveguides in the Single-Mode Propagation Regime

The analysis reported in this paper shows that the homogeneous sensitivity of both fundamental rib waveguide modes, HE00 and EH00, can slightly exceed the sensitivity of the optimized parent slab waveguide. The most crucial difference in the behavior of these two polarizations is that the sensitivity of the HE00 mode is the maximum for strip waveguides. In contrast, the sensitivity of the EH00 mode can either decrease monotonically or not-monotonically with increasing rib height or behave like a homogeneous sensitivity characteristic of the slab waveguide's EH0 mode. The second important conclusion comes from comparing the sensitivity characteristics with the distributions of the fundamental mode's optical power. Namely, the homogeneous sensitivity of the rib waveguide is at the maximum if, due to a slight variance in the cover refractive index, a variation in the weighted optical power carried by the mode is the maximum.