Holographic polymer-dispersed liquid crystals (H-PDLCs)

The formation of switchable holographic gratings from polymer-dispersed liquid crystals (H-PDLCs) allows for the development of switchable transmissive and reflective diffractive optics. These structures are created by the coherent interference of laser radiation within a syrup containing photoreactive monomer, initiator, and liquid crystal. Local differences in photopolymerization rates induce phase separation of discrete LC domains to occur periodically commensurate with the period of the interference pattern. These spatially periodic gratings of nano-scale sized LC domains can be formed on grating length scales ranging from 100 nm to microns depending on the optics of fabrication. True Bragg gratings are formed with spacings typically less than 1 mu m. Owing to the refractive profile generated by this periodic two-phase structure, diffraction of light occurs. Electrical switching of the average director orientation within the LC domains results in a modulation of diffracted radiation. This technology serves as the basis for the fabrication of switchable diffractive optical elements. We review the current state-of-the-art: of H-PDLC technology including the materials used to date, the resulting electro-optical properties, the importance of grating formation dynamic measurements, and structure/property relationships developed using solid state morphology techniques.