Nonlinear modes, resonant trapping, and soliton emission in engineered PPLN structures

We investigate nonlinear waveguiding effects, due to second-order nonlinearity, in quasi-phase-matching (QPM) structures in periodically poled lithium niobate (PPLN) with engineered patterns. We specifically study the existence and the propagation of pure nonlinear guided modes in QPM gratings with different domain lengths in different transverse regions of the medium, without any waveguiding effect due to linear refractive index changes. On one hand, the obtained results enlighten the possibility of soliton operation at lower intensity thresholds than in standard not-tailored PPLN structures. On the other hand, in such nonlinear engineered structures, we reveal the presence of intensity-dependent attractive and repulsive potential wells that can be exploited for soliton control (resonant trapping and emission) in quadratic nonlinear media.