Femtojoule femtosecond all-optical switching in lithium niobate nanophotonics

Optical nonlinear functions are crucial for various applications in integrated photonics, including all-optical information processing1, photonic neural networks2,3 and on-chip ultrafast light sources4,5. However, the weak native nonlinearity of most nanophotonic platforms has imposed barriers for such functions by necessitating large driving energies, high-Q cavities or integration with other materials with stronger nonlinearity. Here we effectively utilize the strong and instantaneous quadratic nonlinearity of lithium niobate nanowaveguides for the realization of cavity-free all-optical switching. By simultaneous engineering of the dispersion and quasi-phase matching, we design and demonstrate a nonlinear splitter that can achieve ultralow switching energies down to 80 fJ, featuring a fastest switching time of ~46 fs and a lowest energy–time product of 3.7 × 10−27 J s in integrated photonics. Our results can enable on-chip ultrafast and energy-efficient all-optical information processing, computing systems and light sources. Researchers exploit the quadratic nonlinearity of lithium niobate nanowaveguides and demonstrate cavity-free all-optical switching. Switching energies down to 80 fJ, switching times down to ~46 fs and energy–time products of 3.7 × 10−27 J s are shown.