Analysis of Anisotropic Diffraction Gratings Using Holographic Polymer-Dispersed Liquid Crystal

摘要

Highly polarized gratings based on a holographic polymer-dispersed liquid crystal (HPDLC) are realized by interferometric exposure. The resulting volume gratings exhibit a diffraction efficiency of 80% and a distinctive ratio of diffraction efficiency of 300. Phase separation by photo polymerization for forming the gratings is studied by evaluating the anisotropic diffraction property and configuration of the separated phase of the gratings. The distinctive ratio of diffraction efficiency in polarization parallel to the grating vector to that in polarization perpendicular to the grating vector increases with grating formation temperature. The microscopic origin of the anisotropic property is investigated by optical polarization microscopy and scanning electron microscopy (SEM). Observations strongly suggest that by increasing the grating formation temperature, the layers of liquid-crystal (LC) and cured-polymer phases in the gratings are well formed and a coalesced LC droplet configuration with small droplets is obtained. LC molecules are considered to be more strongly oriented in the small droplets, and consequently, the LC orientation produces a highly polarized diffraction.