Dense packing of topological defects in nematic liquid crystal cells with pads, crossed-strips, and porous electrodes

Topological defect arrays in liquid crystal is an emerging optical material for smart windows, displays, gratings, and optical vortex generators. Formation of defect arrays is investigated using vertically aligned nematic liquid crystal cells with pad, crossed-strips, and porous electrodes. The location and types of the defects are identified using a polarized optical microscope. The pads and crossed-strips generate alternative radial and hyperbolic defects. Unexpectedly, the holes create dipoles of radial and hyperbolic defects, and the dipoles align in parallel order. The best dense packing of defects is achieved with the 15µm × 15µm unit cell.