Holographic reflection gratings in polymer-dispersed liquid crystals (H-PDLCs) were formed by thiol-ene photopolymerization. Using UV laser light and a single prism, electrically switchable reflection gratings in blue, green, yellow, and red colors were fabricated. Results indicate that thiol-ene polymers function as better hosts for H-PDLC than multifunctional acrylate as matrixes. These differences are the result of a much different temporal structure development caused by fundamental differences in the polymerization propagation mechanism: a step-growth addition mechanism for the thiol-ene system compared to a chain-growth addition mechanism in multifunctional acrylates. Morphology studies by TEM support these conclusions, as striking differences in droplet shape and uniformity are observed. Discrete nematic droplets with a nearly spherical shape were seen. Thiol-ene polymers offer lower switching fields, higher diffraction efficiencies, better optical properties, and higher thermal stabilities. The response times of the thiol-ene gratings were five times slower than those of acrylates.

Polarization properties and electro-optical switching behavior of holographic polymer-dispersed liquid-crystal (HPDLC) reflection and transmission gratings are studied. A theoretical model is developed that combines anisotropic coupled-wave theory with an elongated liquid-crystal-droplet switching model and includes the effects of a statistical orientational distribution of droplet-symmetry axes. Angle- and polarization-dependent switching behaviors of HPDLC gratings are elucidated, and the effects on dynamic range are described. A new type of electro-optical switching not seen in ordinary polymer-dispersed liquid crystals, to the best of the author’s knowledge, is presented and given a physical interpretation. The model provides valuable insight to the physics of these gratings and can be applied to the design of HPDLC holographic optical elements.