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. However, in current BTO-based devices, high optical losses are consistently observed, typically an order of magnitude larger than those observed in thin-film lithium niobate. We present a theoretical investigation into the origin of optical loss in BTO waveguides, suggesting that the higher loss is non-absorptive and is caused by planar defects such as ferroelectric domain walls. Our results suggest that the poling of the z-cut material could reduce the loss level to that reported for Si-integrated lithium niobate.