Complex liquid crystal superstructures induced by periodic photo-alignment at top and bottom substrates

Abstract

The formation of nematic liquid crystal (LC) superstructures in cells with non-uniform photo-alignment at the confining substrates is studied experimentally and by simulations. An interference pattern of left- and right-handed circularly polarized light is used to define the alignment at both substrates separately, so that the alignment varies along the x-coordinate on one substrate and along the y-coordinate on the other substrate. The interplay between the complex surface alignment and the liquid crystalline soft matter leads to the formation of interesting 3D configurations. The periodic LC structures that are formed in the bulk of the cell are analyzed experimentally by polarizing optical microscopy (POM) for different applied voltages. In the region with strong photo-alignment at both substrates, a 2D LC polarization grating (PG) with a complex 3D director configuration is formed. Distinct periodic structures with different symmetry properties are observed in the regions with weak illumination at the top and/or bottom substrate. The director configuration in the different regions was successfully simulated with the help of finite element (FE) Q-tensor simulations. The agreement between the simulations and the experiments was verified by comparing the POM images with simulated results for the transmission between crossed polarizers.

Ring-shaped liquid crystal structures through patterned planar photo-alignment

“…An interesting situation is obtained when top and bottom substrates are illuminated with different planar photo-alignment patterns, because this allows the formation of more complex LC configurations. [16][17][18][19][20][21][22] The frustration when the azimuthal angles for corresponding locations at top and bottom substrate are different, can often be resolved by a position-dependent twist in the bulk. For certain combinations of alignment patterns however, the topology at the interfaces requires either the creation of a disclination line along which the director is undefined, or a line along which the director is perpendicular to the substrate (homeotropic).…”

Physics-based multistep beam propagation in inhomogeneous birefringent media

“…patterned anchoring such as in Ref. [19], or localized defects with nonzero xz and/or yz inside the core), hypothesis (H2.b) is broken and wide-angle corrections to the walk-off operator will be inaccurately modeled if our scheme is still used, but the other operators for the diffraction and phase evolution are still accurately modeled. More precisely, an error of order O η ρ 3 will be introduced in Eq.…”

“…We conclude that in system A and B, the computational error in wide-angle simulations is only due to the numerical discretization, while for system C -for which the walk-off operator is nonzero -the error µ also includes a O η 2 in addition to the discretization error, as shown in Eq. (19). Paraxial simulations always include a scheme error in addition to the discretization error since for this class of BPM, hypothesis (H2.a) is always needed whatever the system in consideration.…”

Liquid Crystal Beam Steering Devices: Principles, Recent Advances, and Future Developments

“…More recently, multi-twist structures [75] and twisted-nematic diffractive waveplates [76,77] have been proposed and were demonstrated to show a broader bandwidth (from visible to infrared), in comparison with traditional PBDs. Furthermore, 2D PBDs [78][79][80][81], which can diffract beams into multiple directions, have recently emerged. In addition to varying the diffraction orders, there have been other proposals to change the period by using a sophisticated design of the alignment layer and electrodes [82].…”