Polarization-Dependent Curvature Loss in Silicon Rib Waveguides

We show that the quasi-TM mode in silicon rib waveguides can experience significantly less curvature loss at the same bend radius than does the quasi-TE mode. Photonic devices making use only of the TM mode and a polarization-diversity scheme can, thus, profit from smaller possible bend radii and the resulting circuit-size reduction. The main loss mechanism for the quasi-TM rib mode can be coupling to the orthogonally polarized TE slab mode, which radiates power away from the waveguide. This is possible due to the slight hybridicity of the quasi-TM rib mode. Neglecting this hybridicity would lead to a significant underestimation of the curvature losses. Thus, accurate simulation of waveguides with low quasi-TM-mode curvature loss requires full-vectorial simulation models