BRAGG GRATINGS IN AN ACRYLATE POLYMER CONSISTING OF PERIODIC POLYMER-DISPERSED LIQUID-CRYSTAL PLANES

We report on the results of holographic studies in an acrylate photopo lymer system containing a nematic liquid crystal. We demonstrate that Bragg gratings can be formed in this system and that the liquid crysta l greatly enhances the diffraction efficiency. For a liquid crystal lo ading of 16.5 wt %, we have observed diffraction efficiencies approach ing 100 %. With careful control of liquid-crystal loading and rapid po stcuring, we have obtained optically clear gratings of high diffractio n efficiency (>80 %) and narrow angular selectivity (<1-degrees) which are stable over a period of months. Low-voltage scanning electron mic roscopy reveals a unique morphology for these gratings, showing that t hey consist of periodic polymer-dispersed liquid-crystal planes. The l iquid-crystal microdroplets are confined to the Bragg planes, having a size approximately equal to one-half the grating spacing. We also obs erve droplet elongation and coalescence along the Bragg planes.