SELECTIVE REFLECTION ZONES IN MODULATED FLEXOELECTRIC STRUCTURES INDUCED BY A PLANAR ELECTRIC FIELD

Liquid crystals (LCs) exhibit anisotropic optical and dielectric properties, allowing them to effectively manipulate light by changing the orientation of the long axes of the molecules (the n-director) under the influence of an electric field. This makes LCs unique materials for photonics.
Along with the traditional switching of LC states, in which the director reorientation occurs due to the dielectric effect, there is a variant of the electric field interaction with flexoelectric polarization. The flexoelectric effect (FE) in liquid crystals, first theoretically predicted in 1969 by Meyer [1], arises in LCs as a result of splay and bend deformations. At low values of dielectric anisotropy, the FE becomes predominant in electrically induced orientational transitions and can manifest itself as a periodic supramolecular structure or flexolattice [2, 3].
In this research, for the first time, periodic flexostructures are investigated using planar interdigital electrodes. A nonuniform electric field generated by such an electrode system leads to the formation of modulated flexoelectric structures in the above-electrode and interelectrode regions, with wave vectors directed perpendicular and parallel to the LC layer normal, respectively. The cycloidal director distribution arising in the interelectrode region with refractive index modulation along the normal to the LC layer leads to the appearance in the transmission spectrum of a selective reflection band. The spectral position of the band depends on the amplitude of the applied voltage and on the light incidence angle relative to LC layer normal. Numerical modeling methods were used to study in detail the LC director distributions and the spectral features of the field-induced transition.

1. Meyer R.B. Piezoelectric effects... Physical Review Letters. 1969. 22(18). 918.
2. Bobylev Y.P. et al. Threshold… JETP. 1977. 45. 195.
3. Barnik M.I., et al. Flexo-electric domains… Journal de Physique. 1978. 39(4), 417-422.