Low-loss monolithic barium titanate on insulator integrated photonics with intrinsic quality factor >1 million

Barium titanate (BTO) has been experiencing a surge of interest for integrated photonics technologies because of its large nonlinear optical coefficients, especially the Pockels coefficient, and in part due to newly available thin-film substrates. In this work, we report a redeposition-free dry etching process for monolithic BTO-on-insulator photonics that produces very low-roughness and high-verticality (≈ 60^o) waveguides. Using this, we experimentally demonstrate the first, to the best of our knowledge, monolithic BTO-on-insulator microresonators with intrinsic quality factor (Q_i) >1 million, representing the highest intrinsic quality factor reported in any BTO-based integrated platform to date. Waveguide propagation losses as low as 0.32 dB/cm are also reported. We additionally demonstrate Mach-Zehnder amplitude modulators with V_πL=0.54 V⋅cm and effective electro-optic coefficient r_eff=162 pm/V.