Normally transparent smart window based on electrically induced instability in dielectrically negative cholesteric liquid crystal

We demonstrate a normally transparent smart window based on a cholesteric liquid crystal with negative dielectric anisotropy. The window is electrically switchable between clear and diffuse states. The clear state exhibits a well-aligned planar cholesteric texture and is stable in the absence of an electric field, while the diffuse state is switched on when applying a field higher than the undulation instability threshold. The degree of translucency can be controlled by varying the field strength. When the applied field is removed, the smart window relaxes back to the clear state spontaneously. It is also found that a much faster diffuse–clear process can be stimulated by reducing the field below the instability threshold. The smart window presents itself a promising projector screen for augmented reality applications as it features single stable state, sub-second switching speed, and polymerization-free fabrication.