Origin of non-absorptive scattering loss in Si-integrated barium titanate

Barium titanate BaTiO₃ (BTO) is an emerging material in silicon photonics with one of the largest known linear electro-optic coefficients. Due to a very large Pockels coefficient, BTO-based modulators require a relatively low voltage to achieve a π phase shift for a given device length, resulting in a low value of the so called V_π·L, a common figure of merit for phase-shift modulators. However, in BTO-based devices, high optical losses are consistently observed, typically an order of magnitude larger than those observed in lithium niobate. In this talk, we present a theoretical investigation into the origin of optical loss in BTO waveguides suggesting that a higher loss is non-absorptive and is caused by planar defects such as e.g., ferroelectric domain walls. Our results suggest that poling of the z-cut material may reduce the loss level to that reported for Si-integrated lithium niobate.