Photorefractive polymer dispersed liquid crystals

ABSTRACTOrganic photorefractive materials have received increasing attention for photonic applications due to their highperformance level and their ease ofprocessing. Here, we present functionalized polymer dispersed liquid crystalsthat exhibit strong photorefractive properties. Their properties are investigated by wave-mixing experiments andtheir performance compared with photorefractive polymers and photorefractive liquid crystals.Keywords: Liquid crystal, photorefractive, polymer, organic, nonlinear optics, holography, optical processing,photoconductor 1. INTRODUCTION Photorefraclive materials arc among the most sentive nonlinear optical materials since they exhibit large refractive indexchanges when exposed to low power laser beams.' The photorefractive effect is based on the build-up of a space-chargethrough the photoexcitalion of carriers and their transport over macroscopic distances. Transport can occur by eitherdiffusion of the carriers, if the excitation is nonuniform, or by drift, if an electric field is applied to the material. Chargeseparation results in a space-charge field that changes the refractive index of the material. This refractive index change is aphase replica of the initial light distribution. Thus, photorefractive materials are used as optical recording medium.Optical media that can record a grating, that is the interference pattern of two coherent laser beams, are in high demand.For real-time optical recording or processing applitions, the material must have a dynamic response. hi other words thelight-induced gratings should be erasable or be able to accommodate any changes in the light waves that are inducing them,in real time. Materials with such optical encoding properties allow for implementanon of a wide range of optical applicationsranng from reconfigurable interconnects, dynamic holographic orage, to optical correlation, image recognition, imageprocessing; and phase conjugation. Therefore, materials where the optical encoding is dynamic and based on a periodicmodulation ofthe refractive index are the focus of intense research.During its first twenty-five years of existence, the photorefractive effect was studied mainly in inorganic Crystals,