Tunable Optical Vortices Generated by Self-Assembled Defect Structures in Nematics

$O\phantom{\rule{0}{0ex}}p\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}c\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}l$ $v\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}c\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}s$ (corkscrews of light spinning about zeros in the electric field) offer many applications in $e.g.$ optical communication, superresolution microscopy, and astronomical imaging, so creating them controllably is of considerable interest. The authors reveal that an electric-field-induced, self-assembled grid of topological defects can generate optical vortices at different length scales, via two mechanisms: directly by transmission through an individual defect, and by diffraction from a dislocation in the grid pattern. The efficiency of generating optical vortices here can approach 100%, even for different wavelengths of light, and can be tuned by an applied voltage.