Sequential Three-Dimensional Nonlinear Photonic Structures for Efficient and Switchable Nonlinear Beam Shaping

Nonlinear beam shaping can be dynamically controlled by temperature or polarization to form switchable nonlinear structured beams, which constitute an unprecedented system for realizing optical encryption at new frequencies and high-dimensional nonclassical light sources. However, previous works were limited by a trade-off between the conversion efficiency and the modulation dimension of the beam. It is still technologically challenging to achieve efficient and switchable multidimensional nonlinear beam shaping. Here, we demonstrate switchable generation of nonlinear structured beams via three-dimensional (3D) nonlinear photonic crystals (NPCs) fabricated by femtosecond laser writing technique with considerable conversion efficiency. The 3D NPCs contain different sequential 3D arrays of spatially modulated χ⁽²⁾ nonlinearity designed by computer-generated hologram (CGH) along the optical y-axis (LiNbO₃ crystal). The output direction of the nonlinear beams can be changed by the carrier frequencies, while their efficiencies can be increased by the quasi-phase matching condition.