High‐Q Monolithic Ring Resonators in Low‐Loss Barium Titanate on Silicon

Abstract The extremely large nonlinear optical response and CMOS compatibility of barium titanate make it particularly appealing for high‐density, wide‐bandwidth, and reduced power consumption optical components and devices for chip‐scale photonics applications. However, without a dramatic reduction in material loss, barium titanate is unlikely to be a competitive alternative to existing nonlinear materials used in integrated photonics. This work investigates loss mechanisms in monolithic photonic structures fabricated from barium titanate grown epitaxially by RF‐sputtering on silicon‐on‐insulator substrates. Barium titanate waveguide loss is investigated using three photonic architectures, and straight waveguide loss of less than is demonstrated, well below previously published loss measurements of barium titanate‐containing waveguiding structures. High‐Q barium titanate resonators with unloaded quality factors of are demonstrated. The low loss of the barium titanate photonic structures, coupled with barium titanate's large non‐linear optical response offers a path to compact and high‐efficiency barium titanate photonic devices and structures for high‐speed modulation, optical computing, and non‐linear applications.