Optimising two dimensional nonlinear photonic crystals for cascaded third harmonic generation with fabrication constraints

In our paper we present the best physically realisable 2D NPC for the initial growth of the 3rd harmonic, in lithium niobate (LN), taking into account several practical constraints. First we require a collinear 1-st step of the process as this increases the overall efficiency by maximising the overlap of the waves generating the 3-rd harmonic. Numerical optimisation of patterns is presented for THG in a 2D NPC, where the 1-st step of the process is collinear and which takes into account the usual fabrication constraints.