Electrically induced bandwidth broadening in polymer stabilized cholesteric liquid crystals

The reflection notch bandwidth of a cholesteric liquid crystal (CLC), equal to the product of the liquid crystal (LC) birefringence (Δn), and the pitch length (po), is typically on the order of 50-100 nm in the visible portion of the electromagnetic spectrum. Static bandwidths greater than 100 nm can be observed in CLCs that possess a pitch gradient throughout the thickness of the cell. In this work, we report on polymer stabilized CLC (PSCLC) systems that exhibit electrically controllable, dynamic bandwidths governed by the strength of a direct current (DC) electric field applied across the sample. Symmetric notch broadening which increases linearly with field and reaches a maximum value at 4 V/μm is observed. Removal of the field returns the PSCLC cell to its original optical properties. A seven fold increase in bandwidth was observed for 22 μm thick cells which contained LCs with a small birefringence (∼0.04). A variety of CLC mixtures with small positive or negative dielectric anisotropies are shown t...