Dual frequency addressing of polymer-dispersed liquid-crystal films

We report the feasibility of using dual frequency addressing (DFA) to switch polymer-dispersed liquid crystal (PDLC) films between their on- and off-states. In this scheme, the on-state is activated with an applied voltage of low frequency while the off-state is activated with a high-frequency voltage. We find that DFA increases the forward-scattering efficiency of PDLC films in the off-state without decreasing their on-state transmittance. Consequently, DFA can be used to improve the contrast ratio of PDLC films in projection displays and similar devices. We also find that the addressing frequency required to activate the off-state in a PDLC film has the same exponential temperature dependence observed in conventional liquid-crystal devices not employing microdispersed liquid crystals; this limits the use of DFA in PDLC films to applications which do not require operation over a wide temperature range.