HeXLN: A 2-Dimensional nonlinear photonic crystal

We report on the fabrication of what we believe is the first example of a two dimensional nonlinear periodic crystal\cite{berger}, where the refractive index is constant but in which the 2nd order nonlinear susceptibility is spatially periodic. Such a crystal allows for efficient quasi-phase matched 2nd harmonic generation using multiple reciprocal lattice vectors of the crystal lattice. External 2nd harmonic conversion efficiencies > 60% were measured with picosecond pulses. The 2nd harmonic light can be simultaneously phase matched by multiple reciprocal lattice vectors, resulting in the generation of multiple coherent beams. The fabrication technique is extremely versatile and allows for the fabrication of a broad range of 2-D crystals including quasi-crystals.