Field Induced Twist Profiles in Voltage Controlled Circular Dichroism Liquid Crystal Cells

Abstract

The vivid reflection colours resulting from the circular dichroism exhibited by short pitch cholesteric liquid crystals are well known, as are the thermally and impurity induced shifts in the peak wavelength λ_m of the reflection spectrum. Electrochromic effects in which an electricfield induces a blue shift in λ_m for cholesterics showing a positive dielectric anisotropy have also been reported and exploited in voltage controlled circular dichroism (VCCD) devices patented by Fergason. In this note experimental results demonstrating the low voltage operation of such a device are presented and a mechanism for the pitch contraction implied by this blue shift is proposed and contrasted with the distortion of the twist profile in a twisted nematic cell.