US Patent 10444419 Dithering methods and apparatus for wearable display device

A device includes an input coupling grating having a first grating structure characterized by a first set of grating parameters. The input coupling grating is configured to receive light from a light source. The device also includes an expansion grating having a second grating structure characterized by a second set of grating parameters varying in at least two dimensions. The second grating structure is configured to receive light from the input coupling grating. The device further includes an output coupling grating having a third grating structure characterized by a third set of grating parameters. The output coupling grating is configured to receive light from the expansion grating and to output light to a viewer.