Two-dimensional quasi-phase-matched multiple-cascaded four-wave mixing in periodically poled KTiOPO(4)

A two-dimensional quasi-phase-matched structure is realized in a noncollinear, nondegenerate periodically poled KTiOPO(4) parametric oscillator by utilizing the mutual coherence of two noncollinear pump beams. The mutually coherent pump beams form an interference pattern inside the crystal that is directed perpendicular to the existing quasi-phase-matched grating vector and acts as a parametric gain grating. The cavity itself supports two signal wavelengths around 1550 nm with tunable separation, while the gain grating reduces the operational threshold of the oscillator. Furthermore, with this two-dimensional quasi-phase-matched structure, we can demonstrate the generation of new spectral components through multiple chi((2)):chi((2))-cascaded four-wave mixing processes.