Photoalignment-induced two-dimensional liquid crystal polarization structure via multi-beam polarization interferometry

Abstract

A two-dimensional (2D) pure polarization pattern via four-beam polarization interferometry of circularly polarized beams is demonstrated both theoretically and experimentally. The polarization orientation of the interference pattern is recorded by an azobenzene photoalignment layer and transferred to liquid crystal (LC), enabling the fabrication of a 2D liquid crystal (LC) chiral structure. This structure behaves as a 2D LC polarization grating (LCPG) that can generate multiple polarization-selective diffraction beams of orthogonal polarization states with high efficiency. This 2D LCPG provides an effective way to distribute an optical signal into multiple receivers by both incidence polarization control and external electric field, therefore offering potential applications on multi-channel optical communication and information processing.

A Review of Two-Dimensional Liquid Crystal Polarization Gratings

“…1st order occupied about 77% of the total energy at the half-wave conditions, with the polarization selectivity similar to the previous work [49] (Figure 11i,j). The ellipticities of the diffracted beams were near 1, indicating good CPL qualities (Figure 11k).…”

“…In their design, the LP light intensity was chosen to be one-fifth of the other CP light to give a well-defined LC alignment and good diffraction property (Figure 11h). The maximum diffraction of the 1st order occupied about 77% of the total energy at the half-wave conditions, with the polarization selectivity similar to the previous work [49] (Figure 11i,j). The ellipticities of the diffracted beams were near 1, indicating good CPL qualities (Figure 11k).…”

“…This reported value is much higher than the observation in Reference [44] with similar LC configurations, due to the well-defined LC orientation. This diffraction efficiency is similar to the 2D LC PG as reported in Reference [49] but higher than that of the electrically tunable device in LC cells, since this 2D micropattern not only avoids the mismatch problem of the photoalignment pattern on the two substrates but also avoids the undefined pretilt angle, which becomes severer with the applied electric field.…”

“…In this case, the interference polari- In 2018, Y. Shi et al discussed both the intensity and polarization distributions of the interference of four symmetrically arranged CP beams (Figure 10a). The four beams had the same intensities and no relative phase differences [49]. The interference field had intensity modulations, while only the case with one CP beam and three orthogonally CP beams did not have zero intensity areas (Figure 10b).…”

Tunable Dynamic Topological Defect Pattern Formation in Nematic Liquid Crystals

“…Here, besides expanding on the ability to control the regularity and length‐scale of the system, we demonstrate a technique to create and dynamically control patterns of arbitrary complexity to be used as 2D diffraction gratings. To date, 2D LC‐based gratings have been obtained by various approaches, such as superposing multiple 1D arrays, modulating the LC alignment with photopatterning, using the spontaneous periodic undulations in cholesteric LCs or creating field‐induced 2D umbilical defect arrays . In some of these approaches, the dynamic tunability of the 2D diffraction pattern is achieved by tuning each 1D LC grating or by mechanically changing the angle of the polarizers, thus changing the diffraction angle or the shape of diffraction patterns.…”