  Ferroelectric nematic liquid crystals exhibit unique non-linear optical
properties, with the potential to become transformative materials for photonic
applications. A promising direction relies on the fabrication of tailored polar
orientational patterns via photoalignment, thus shaping the non-linear optical
susceptibility through thin slabs of the ferroelectric fluid. Here, we explore
the fabrication of 2D periodic SHG active arrays in ferroelectric nematic
fluids, for different materials, cell thicknesses and motifs. Based on
polarizing optical microscopy observations in combination with optical
simulations, second harmonic generation microscopy and interferometry, the 3D
structure of the motifs are revealed. Two different 2D periodic patterns are
explored, showing that the balance between flexoelectric and electrostatic
energy can lead to different domain structures, an effect which is rooted in
the difference between the flexoelectric properties of the materials. It is
shown that by combining the surface-inscribed alignment with different
spontaneous degrees of twist, 2D SHG active arrays can be obtained in the
micrometre scale, in which adjacent areas exhibit maximum SHG signals at
opposite angles.
