Dynamic pattern generation of topological defect arrays in nematic liquid crystals*

Some photonic devices use the periodic nature of repeating lattices to modulate light.[1] Here we create tunable patterns of topological defect arrays in nematic liquid crystals (LCs) that can be simply controlled by electrical waveforms.[2,3] The refractive index of LCs is spatially modulated owing to the presence of the topological defect arrays. The symmetry and regularity of patterns is controllable thanks to micro-pillars created by photolithography. Adjusting the frequency and amplitude of electrical waveforms changes the defect spacing. Where the defect spacing is reduced, the number density of defects increases, compatibly with the presence of the pillars. The patterns are in two dimensions and this opens up more possibilities for the arrangement of the defects. When a laser beam propagates through the spatially modulated refractive index LC layer, the direction of the wave front changes and the beam can be split and steered. We utilize these complex patterns as a diffraction grating, which can change both diffraction (polar) angle and azimuthal angles.

[1] A. Ryabchun, A. Bobrovsky, Adv. Opt. Mater. 2018, 6, 1800335.
[2] M.S. Kim, F. Serra, RSC Adv. 2018, 8, 35640.
[3] M.S. Kim, F. Serra, Adv. Opt. Mater. 2019, accepted.