Two-dimensional photonic lattices in polymer-dispersed liquid crystal composites

Abstract

The relationship between liquid crystal orientational ordering and optical diffraction properties is investigated for a two-dimensional square photonic lattice fabricated in a polymer-dispersed liquid crystal (PDLC) composite. Modifications of the nematic director field in the liquid crystal domains were induced by an external applied voltage and by heating over the nematic-isotropic (N-I) phase transition. They were studied by optical polarization microscopy and by analysing far-field optical diffraction patterns. The intensities of various diffraction orders (from the zeroth up to the eighth diffraction order) were monitored with a CCD camera, and their variations were correlated with the modifications of the director field.

Effect of structural modifications on the switching voltage of a holographic polymer-dispersed liquid crystal lattice

“…We therefore suggest that in our HPDLC material the change of the behaviour at T = 50 • C is related to modification of the boundary condition at the polymer-LC interface. As demonstrated in figure 9, and reported in more detail in our previous paper [23], during heating of the sample the transition from nematic to isotropic phase starts at the boundary with the polymer pilasters. Then, in a relatively broad range of the temperatures, the LC material in the vicinity of the pilasters is already in the isotropic phase, while the central LC region is still in the nematic phase.…”

“…The cells were filled with the optically isotropic mixture at room temperature by means of capillary flow. To obtain a 2D square interference pattern, a linearly polarized output beam from an argon ion laser at λ = 351 nm was at first expanded, then collimated and afterwards sent through a fourfold glass pyramid with side walls inclined at an angle γ = 2 • with respect to the base plane [23,24]. Optical refraction on the side walls produced four coherent beams, whose interference led to a 2D square lattice with the lattice constant a = 13.2 μm.…”

“…In our recent paper we reported on a detailed analysis of the structural and diffractive properties of a transverse square HPDLC lattice with a lattice constant of 13.2 μm [23]. A comparative study of the electric field and temperatureinduced modifications of the nematic director field within the LC-rich regions was performed by combining optical diffraction experiments and optical polarization microscopy imaging.…”