An array of individually controllable elements is comprised of elements, each formed of a stack of layers of dielectric material. At least one layer is an electro-optical material. The at least one layer's refractive index for radiation that is plane polarized in a given direction can be changed by application...http://www.google.com.au/patents/US7196772?utm_source=gb-gplus-sharePatent US7196772 - Lithographic apparatus and device manufacturing method
