Electrically switchable achromatic liquid crystal polarization gratings on reflective substrates

Abstract

We have experimentally demonstrated broadband light modulation by achromatic liquid crystal (LC) polarization gratings (PGs), which manifest polarization-independent modulation with high efficiencies (≥ 95%). Recently, we introduced achromatic PGs with a unique double-layer, reversed-twist structure as efficient, broadband polarizing beamsplitters. We now report on our successful implementation of electrically switchable achromatic LCPGs on a reflective substrate. To pattern a spiraling, periodically varying LC profile, we utilize polarization holography and photoalignment techniques. Use of reflective substrates enables the same retardation compensation of doublelayer achromatic PGs. In addition, perhaps most importantly, the single cell structure allows the electro-optical switching/modulation by applying an electric field across the cell. The achromatic LCPG sample shows steeper voltage responses and less spectral shifts while operating in grayscale with respect to previously reported LCPGs. Relatively faster switching times (∼ 6m sec for 3µm-thickness) were measured compared to a conventional LCPG with the same thickness (∼10 msec). Interesting electro-optical behaviors were also observed including zero-voltage threshold and a hysteresis in the voltage response.