Mixing second and third-order nonlinear interactions in nanophotonic lithium-niobate waveguides

In this paper, we have investigated the interplay between the second and third-order nonlinearities in lithium-niobate waveguides with strong waveguide dispersion using uniform and linearly-chirped poling patterns at input powers in the pico-joule range. We have implemented the accurate unidirectional pulse propagation model to take into account all the possible nonlinear interactions inside these structures. In particular, the poling period has been designed to quasi-phase-match single and multiple sum- and difference-frequency generation processes. We have shown how the poling period can be used as an additional degree of freedom to tailor the output spectra of chip-based nonlinear waveguides in an unprecedented way.