Microlens array-based exit pupil expander for full color display applications

Abstract

Retinal Scanning Display (RSD) is a near-to-eye scanned beam display technology. An exit pupil expander (EPE) or numerical aperture (NA) expander is used in RSDs to create a large display exit pupil. A novel EPE approach that uses two microlens arrays (MLA) is presented in this paper. The approach is based on cascading two identical microlens arrays spaced precisely at one focal length distance with sub-micron registration tolerances relative to each other. We demonstrated a dual MLA based EPE that: produced excellent exit pupil uniformity and better than 90% diffraction efficiency for all three wavelengths in a color display system. Registration was performed with sub-micron precision using farfield alignment techniques. Both numerical and experimental results are presented, and three fabrication technologies: grayscale lithography, photoresist reflow, and isotropic etching, are compared.