Second-harmonic and cascaded third-harmonic generation in generalized quasiperiodic poled lithium niobate waveguides

Lithium niobate (LN) thin film has recently emerged as an important platform for nonlinear optical investigations for its large χ (2) nonlinear coefficients and ability of light localization. In this Letter, we report the first, to the best of our knowledge, fabrication of LN-on-insulator ridge waveguides with generalized quasiperiodic poled superlattices using the electric field polarization technique and microfabrication techniques. Benefiting from the abundant reciprocal vectors, we observed efficient second-harmonic and cascaded third-harmonic signals in the same device, with normalized conversion efficiency of 1735% W −1 cm −2 and 0.41% W −2 cm −4 , respectively. This work opens a new direction for nonlinear integrated photonics based on LN thin film.