| Holographic polymer-dispersed liquid crystals are composite materials that are rich in physical phenomena and useful for electrically or thermally switchable hologram and grating applications. They are formed through a self-diffusion process using an interference pattern to initiate and drive the kinetics of formation, which is generated through two or more coherent laser beams. The information from the interference pattern is permanently recorded through a phase separation process or optical alignment of polymer in liquid crystal/polymer composites. The recorded holograms are erasable or tunable by applying sufficient external field or temperature variation.; The formation kinetics of holographic polymer-dispersed liquid crystals can be modeled by a set of reaction-diffusion equations. By analyzing the optical performance of resulting gratings, we found that the phase separation process is dominated by a photo-polymerization induced diffusion in the fast polymerization regime rather than the thermal diffusion in the slow polymerization regime. The effective diffusion constant of oligomers can be enhanced by two orders of magnitude. This diffusion model is verified by in-situ spectroscopy measurements of reflective holographic polymer-dispersed liquid crystals. Through experiments and modeling, the shrinkage of the polymer matrix is determined. In addition, we have expanded our diffusion formalism to model two-dimensional and three-dimensional cases and temporally multiplexed systems.; The Fréedericksz transition, based on the elastic theory of liquid crystals, is used to model various morphologies of confined liquid crystals. A polymer scaffolding model and a cylindrical cavity model are proposed, which enable us to make an order of magnitude estimation of the surface anchoring strength of liquid crystal/polymer interfaces in different systems.; From the applied physics standpoint, we have also made a number of valuable contributions to optical and photonic applications, which include switchable photonic crystals, total internal reflection mode devices, and an active U-turn device. One of our novel modes is based on total internal reflection, which enables a new type of holographic polymer-dispersed liquid crystal device with dramatically improved electro-optic performances. This new mode diffracts incoming light at an angle such that it becomes trapped in the cell through total internal reflection. This new device mode is used to create U-turn electro-optic switches and a new reflective display mode. These devices may have broad applicability in many areas, including photonics, telecommunications, and display technologies. |
