Nonlinear photonic crystals in lithium niobate

This study demonstrates the idea of a 2-D photonic crystal by poling a wafer of lithium niobate with a hexagonal pattern. The fabricated crystal is used in performing experiments on 2nd, 3rd, and 4th harmonic generation. The peak conversion efficiencies of > 80% for SHG using picosecond pump pulses and conversion efficiencies of 10-4 % for third and fourth harmonic generation using low power picosecond pulses are measured. In addition, the first observation of type II sum frequency generation in a periodically poled material is successfully made. This shows that 2D NPCs are ideal for multiwavelength harmonic generation. Problems on the intensity of the interacting waves and the effective nonlinearity are solved to realize multiwavelength harmonic processes