High‐Efficiency Second Harmonic and Third Harmonic Generation in Dual Periodically Poled Lithium Niobate Waveguides

ABSTRACT Periodically poled lithium niobate (PPLN) waveguides on thin films are considered an excellent platform for wavelength conversion due to tight optical confinement and large nonlinear coefficient . Here, the dual periodically poled waveguides of lithium niobate on insulator were demonstrated for the first time using electric field poling and microfabrication techniques. Second harmonics and cascaded third harmonics were detected at the continuous wave pump wavelength in the 1550‐nm band. The normalized efficiency reached up to 1549% W −1 cm −2 for second harmonic generation (SHG) and 3266% W −2 cm −4 for third harmonic generation (THG), and the conversion efficiency of THG is more than four orders higher compared with the generalized quasi‐periodically poled lithium niobate waveguides prepared previously. This work promotes the development of lithium niobate nonlinear integrated photonics.