Second-harmonic generation and its nonlinear depolarization from lithium niobate thin films

Abstract

In this Letter, we present systematic studies of the second-harmonic generation (SHG) behaviors of lithium niobate (LN) thin film, including comprehensively evaluating its second-order nonlinear susceptibility elements and characterizing the SH polarization states as functions of fundamental wavelengths and polarizations. Moreover, the film shows an advantage of SH enhancement resulting from Fabry–Perot resonance compared with its bulk counterpart. We further show a type of nonlinear effect from LN film, called the nonlinear depolarization effect, in which the degree of polarization (DOP) of SH is nonlinearly dependent on the intensity of the fundamental frequency wave. Such a nonlinear effect would enable novel light sources with controllable DOP. Our results would be useful in developing compact SHG devices and the related multi-functional monolithic integrated LN photonic chips.