Transmission and reflection type holograms may be formed utilizing a novel polymer-dispersed liquid crystal (PDLC) material and its unique switching characteristics to form optical elements. Applications for these switchable holograms include communications switches and switchable transmission, and reflection...http://www.google.com.au/patents/US7312906?utm_source=gb-gplus-sharePatent US7312906 - Switchable polymer-dispersed liquid crystal optical elements
