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

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 $0.15\mathrm{dB}{\mathrm{cm}}^{-1}$ is demonstrated, well below previously published loss measurements of barium titanate-containing waveguiding structures. High-Q barium titanate resonators with unloaded quality factors of $Q\approx 5\times {10}^5$ 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.