Flexoelectric-effect-based light waveguide liquid crystal display for transparent display

Abstract

We report a light waveguide liquid crystal display (LCD) based on the flexoelectric effect. The display consists of two parallel flat substrates with a layer of flexoelectric liquid crystal sandwiched between them. A light-emitting diode (LED) is installed on the edge of the display and the produced light is coupled into the display. When no voltage is applied, the liquid crystal is uniformly aligned and is transparent. The incident light propagates through the display by total internal reflection at the interface between the substrate and air, and no light comes out of the viewing side of the display. The display appears transparent. When a voltage is applied, the liquid crystal is switched to a micrometer-sized polydomain state due to flexoelectric interaction and becomes scattering. The incident light is deflected from the waveguide mode and comes out of the viewing side of the display. We achieved thin-film-transistor active matrix compatible driving voltage by doping liquid crystal dimers with large flexoelectric coefficients. The light waveguide LCD does not use polarizers as in conventional LCDs. It has an ultrahigh transmittance near 90% in the voltage-off state. It is very suitable for transparent display, which can be used for head-up display and augmented reality display.