title: Microlens-array-based exit-pupil expander for full-color displays.
abstract: Two-dimensional arrays of microlenses can be used in wearable display applications as numerical aperture expanders or exit-pupil expanders (EPEs) to increase the size of the display exit pupil. A novel EPE approach that uses two microlens arrays (MLAs) is presented. The approach is based on cascading two identical microlens arrays spaced precisely at one focal-length distance with submicrometer registration tolerances relative to each other. The ideal MLA for this application requires a 100% fillfactor, sharp seams between microlenses, and a perfect spherical profile. We demonstrate a dual-MLA-based EPE that produces excellent exit-pupil uniformity and better than 90% diffraction efficiency for all three wavelengths in a color-display system. Two-MLA registration is performed with submicrometer precision by use of far-field alignment techniques. Fourier optics theory is used to derive the analytical formulas, and physical optics beam propagation is used for numerical computations. Three MLA fabrication technologies, including gray-scale lithography, photoresist reflow, and isotropic etching, are evaluated and compared for an EPE application.
authors.affiliation: Department of Electrical Engineering and Optical Microsystems Laboratory, Koç University, Sariyer, 34450 Istanbul-Turkey. hurey@ku.edu.tr
authors.forename: Hakan
authors.initials: H
authors.lastname: Urey
authors.forename: Karlton D
authors.initials: KD
authors.lastname: Powell
mesh_terms: D003116:Color; D017076:Computer-Aided Design; D003626:Data Display; D004867:Equipment Design; D019544:Equipment Failure Analysis; D006801:Humans; D007089:Image Enhancement / Q000295:instrumentation*; D007909:Lenses; D011680:Pupil / Q000502:physiology*; D012160:Retina / Q000502:physiology*; D014584:User-Computer Interface