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8 September 2003 Exit pupil expander: image quality performance enhancements and environmental testing results
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The numerical aperture of the light emanating from display pixels in a given display system determines the exit pupil size. In retinal scanning displays, 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. Positional freedom of the eye and relative display placement define the required expansion of the limited input NA for producing the desired exit pupil size for the display system. Currently Microvision utilizes an optical element comprised of two Microlens Arrays (MLAs) in tandem to expand the NA. The dual-MLA system has demonstrated exit pupil size that is independent of color; and uniformity of the beamlet structure is quite Top-Hat like. To further improve the perceived image quality, Microvision has now refined the optical system to minimize interference effects in the Exit Pupil plane that were caused by the coherent nature of the light source. We describe here a single refractive double-sided aspheric element that diminishes this interference effect by converting an input Gaussian beam profile to a Top-Hat profile. We also discuss the theory behind the use of a Gaussian-to-Top-Hat Converter, the tradeoffs associated with its use, as well as experimental results showing the uniformity improvements when using a Top-Hat converter element in conjunction with the MLA-based Exit Pupil Expander. In addition, we report the progress of environmental testing of the Exit Pupil Expander (EPE).
© (2003) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Karlton D. Powell, Peggy Ann Lopez, and Amjad Malik "Exit pupil expander: image quality performance enhancements and environmental testing results", Proc. SPIE 5079, Helmet- and Head-Mounted Displays VIII: Technologies and Applications, (8 September 2003);

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