HOLOGRAPHIC TECHNIQUE FOR ILLUMINATION OF IMAGE DISPLAYS USING AMBIENT ILLUMINATION

An apparatus and method is disclosed for illuminating an image display with ambient light using holographic techniques. The apparatus includes a pair of holographic optical elements each having a first surface aligned on a common axis so that the first surfaces of each optical element face each other. Each of the first and second optical elements diffracts first bandwidth light. The second holographic optical element, however, diffracts first bandwidth light received on the first surface facing the first surface of the first holographic optical element. The second holographic optical element diffracts first bandwidth light received on its first surface, the diffracted light emerging from the first surface. The first and second holographic optical elements are switchable between inactive and active states. In the inactive state, each of the first and second holographic optical elements transmits substantially all light without substantial alteration. However, in the active state, each of the first and second holographic elements diffracts a first bandwidth light. The first and second holographical elements record a hologram in a switchable holographic material. This material may be formed from a polymer dispersed liquid crystal material.