Frequency generation by four-wave mixing in barium titanate-on-insulator microring resonators.

We report frequency generation by four-wave mixing in thin-film barium titanate (BTO) microring resonators. From the generated idler powers, we determined the nonlinear refractive index of the BTO thin film to be [Formula: see text] [Formula: see text]/W, in close agreement with previously reported value using photothermal spectroscopy. This value is an order of magnitude larger than the Kerr effect in thin-film lithium niobate and only slightly less than silicon, without the nonlinear loss due to free carrier absorption in the latter. These results suggest that BTO-on-insulator is a promising integrated photonic material for nonlinear and quantum applications such as generation of frequency combs, entangled photon pairs and squeezed light.