An apparatus for providing an optical display includes an optical substrate for propagating light received from a light source, a first set of one or more switchable diffractive elements in the substrate, and a second set of one or more switchable diffractive elements in the substrate. Each diffractive element in the second set corresponds to a diffractive element in the first set. Each of the diffractive elements in the first and second sets is configured to switch between on and off states. One of the states is for diffracting light and the other state for allowing light to pass through. Each of the first set of diffractive elements is configured to diffract the light at an angle for propagation in the substrate. Each of the second set of diffractive elements is configured to diffract the light for display.