Monolithic Barium Titanate Modulators on Silicon-on-Insulator Substrates

The linear electro-optic (Pockels) effect provides a mechanism for the rapid (and ideally lossless) modulation of a material's refractive index. Barium titanate (BTO), a complex oxide with a large Pockels coefficient and low optical loss, is thus of significant interest for devices essential to integrated silicon photonics (modulators, phased arrays, tunable resonators), offering decreased operating voltages and/or footprints, low-loss operation, and compatibility with existing CMOS fabrication infrastructure. However, fabrication and growth challenges have limited the direct integration of monolithic BTO-based optoelectrics on silicon substrates. Here we demonstrate a low loss, monolithic BTO device architecture fabricated in thin film epitaxial BTO integrated on silicon-on-insulator substrates by using off-axis RF-sputtering. Mach-Zehnder interferometer modulators are fabricated in the as-grown BTO and characterized spectrally and as a function of DC and AC applied biases. The electro-optical modulators show low losses and competitive V pi L values compared to state-of-the-art lithium niobate modulators, in a monolithic architecture compatible with CMOS electronics and silicon integrated photonic circuitry.