Multistable nematic liquid crystal pores as reconfigurable optical vortex metasurfaces

Abstract

Nematic liquid crystals confined in cylindrical pores adopt multiple stable director topologies --- radial, escaped, and arches --- each imprinting a distinct optical signature on transmitted circularly polarized light, with topological charge set by the projected director winding number, $\ell = 2m$. Using Landau--de Gennes and Jones-calculus modeling validated against micron-scale experiments, we show that this mechanism persists as the pore diameter shrinks toward the optical wavelength. However, full-wave Maxwell simulations of periodic sub-wavelength pore arrays reveal that the resulting vortex is a near-field phenomenon only: each topology imprints a distinguishable phase-singular signature --- differing in core multiplicity, core width, and ring amplitude --- directly below the pore array, but this signature does not survive propagation into the far field, where diffraction and inter-pore interference erase it within about one wavelength. Landau--de Gennes simulations further demonstrate that an applied electric field switches the pore between topologies, and hence between their near-field optical signatures. Because each topology is locally stable, sub-wavelength NLC pore arrays constitute an electrically reconfigurable, non-volatile platform for topology-encoded near-field optical readout, with potential application to optical labeling and anti-counterfeiting.