Simultaneous frequency conversions in nonlinear photonic crystals of lithium tantalate with a square lattice

Nonlinear photonic crystals such as 2D-PPLT (periodically-poled lithium tantalite) are of great interest for multi-wavelengths frequency conversion thanks to the contribution of different reciprocal lattice vectors (RLV) [1]. Such characteristics facilitates optical parametric generation (OPG), second harmonic generation (SHG), sum-frequency generation (SFG) or difference frequency generation (DFG). However, these nonlinear processes do not usually occur at the same time because of the different phase matching conditions. Recently, multi nonlinear process has been demonstrated in a hexagonally-poled LiTaO
3
[2]. In this case, SHG and OPG were generated and SFG was then generated by a cascaded process.