A novel approach for exit pupil expansion in wearable displays

The numerical aperture (NA) of the light emanating from display pixels in a given display system determines exit pupil size. In Retinal Scanning Displays (RSD), the exit pupil is defined by the scanner optics, creating a rastered, projected image at an intermediate plane, typically resulting in an exit pupil approximately the size of an eye's pupil. Accounting for positional freedom of the eye and relative display placement defines the required expansion of the. limited input NA for producing the desired exit pupil size for the display system. Although there are many approaches to performing this task of NA conversion, or exit pupil expansion, many of them exhibit wavelength dependencies, causing the envelope of the intensity profile in the exit pupil plane to be non-overlapping or inconsistent versus pixel location, resulting in uniformity or color variations and often efficiency loss. This paper will look at a microlens array approach to exit pupil expansion for color display systems that will be shown as wavelength independent in terms of diffraction envelope.