Nonlinear photonic crystals (NPCs) are transparent materials that have a spatially uniform linear susceptibility, yet a periodically modulated quadratic nonlinear susceptibility. These engineered materials are used extensively for studying nonlinear wave dynamics and in many scientific and industrial applications. Over the past two decades, there has been a continuous effort to find a technique that will enable the construction of three-dimensional (3D) NPCs. Such capability will enable many new schemes of manipulation and control of nonlinear optical interactions.
Till now, only two artificial 3D NPCs have been constructed using femtosecond laser poling in ferroelectric LiNbO3 and Ba0.77Ca0.23TiO3 crystal. However, both nonlinear crystals only feature up-down ferroelectric domains and no spatially rotating polarization. Therefore, the crystal cutting angle and incident light polarization are still limited to utilize the maximum nonlinear coefficient. The 3D