Electro-optical switching characteristics of volume holograms in polymer dispersed liquid crystals

Electrically switchable volume holograms lead to the possibility of real-time electrooptical control of diffractive optic components. We report here on the development of a novel photopolymer-liquid crystal composite material system for writing in a fast single step, high diffraction efficiency volume holograms, capable of switching in applied electric fields of low voltage. Switching of a first-order Bragg diffracted beam into the zero-order with an applied field of similar to 10 V/mu m was observed. With the addition of a surfactant to our pre-polymer syrup, we observed lowering of the switching fields to similar to 5 V/mu m. We report response times for switching and relaxation in the order of microseconds. Low voltage, high resolution scanning electron microscopy studies show that the Bragg gratings formed consist of periodic polymer dispersed liquid crystal planes. The addition of surfactant leads to formation of very uniform small (20-40 nm) nematic droplets. A simple model based on the shape of the liquid crystal droplets was applied to explain the switching fields and response times.