Lithium niobate nanophotonics – giving new life to an old material

Lithium niobate (LN) is an excellent nonlinear optical material widely deployed for telecommunications and wavelength conversion. While its high χ2 nonlinearity, wide transparency window and low optical loss offer unique advantages, conventional LN devices are bulky and discrete due to the low index-contrast in ion-exchanged waveguides. In this talk, I will provide a summary of our recent breakthrough in integrated LN photonics that overcomes this limitation by direct etching thin-film LN. We show that waveguides and resonators with sub-wavelength light confinement and extremely low propagation loss (< 0.03 dB/cm) can be fabricated using standard lithography techniques. Together with the strong electro-optic and nonlinear responses, we demonstrate electro-optic modulators with CMOS-compatible driving voltage of 1.4 V and electro-optic bandwidths up to 100 GHz. Leveraging the high nonlinear-optic coefficient, we demonstrate broadband Kerr and electro-optic frequency comb generation, as well as nonlinear wavelength conversion with record-high conversion efficiencies. The high-performance LN nanophotonic platform could open up avenues for a chip-scale photonic integrated circuit densely integrated with non-classic light sources, high-speed switches, filters and wavelength converters, which could find applications in next-generation optical data links, quantum communications and microwave/terahertz photonics.