Reflection Holograms Formed using Polymer-Dispersed Liquid Crystals

The electrical switching characteristics of reflection gratings formed using polymer-dispersed liquid crystals are explored. First, an explanation for the lack of switching in previously formed gratings formed using E7 as the liquid crystal is proposed based on experiments on slightly slanted gratings. These confirm that the LC director orientation within the anisotropically-shaped LC domains is parallel to the grating vector( and applied electric field direction). Slight modification of the syrup leads to transmission gratings with different polarization dependencies and reflection gratings (non-slanted) that switch completely with a modest electric field. These differences are attributed to a 90 degrees rotation in the preferred LC director orientation within the LC domains. This change in orientation results in strong coupling of the electric field with the LC dipoles in a reflection geometry thereby leading to easier switching. The microstructure of these grating structures are explored using low-voltage scanning electron microscopy and bright-field transmission electron microscopy.