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Tuneable optical diffractive structures from liquid crystalline materials incorporated into periodic polymeric scaffolds

Diffractive optical elements (DOEs) are micro-structured components used in various photonic devices to manipulate propagation direction and often also polarisation state of optical beams. The simplest type of DOEs are one-dimensional diffraction gratings. We perform theoretical investigation of electrical and magnetic tunability of such gratings composed as a periodic assembly of polymer and ferromagnetic nematic liquid crystal (LC) layers. We analyse how various grating parameters and boundary conditions influence the LC configuration in the assembly. For static response to external electric and/or magnetic fields, the distortion profile of the director field is determined numerically and analytically by minimisation of the Landau-de Gennes free energy, while for the dynamic response only numerical solutions are provided. The resulting optical diffraction properties are determined numerically via solving the Maxwell’s equations by using the rigorous coupled-wave analysis. We demonstrate that the described methodology provides an efficient tool for designing various new types of polarisation sensitive LC-based DOEs, such as three-state polarisation switches for application in spectroscopic, optical communication, and remote sensing systems.

ferromagnetic liquid crystals, optical diffraction gratings, polarisation manipulation, regulation by electric and/or magnetic fields

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