Ultracompact, On‐Axis LCoS Illumination System With Local Dimming for Waveguide‐Based AR Displays

ABSTRACT We proposed an ultracompact, on‐axis liquid‐crystal‐on‐silicon (LCoS) illumination scheme with local dimming, by taking advantage of the polarization selectivity of polarization volume grating (PVG), which serves as both an analyzer for the LCoS and an input‐coupler for the waveguide. The fabrication process of the diffractive waveguide and a monochromatic monocular demonstration of the proposed LCoS illumination design in a waveguide‐based AR system are described. This design improves the coupled optical efficiency to about 30%, enhances the contrast ratio by local dimming, and achieves a total volume less than 0.3 cc, including projection optics, for a 720 × 720 LCoS panel with pixel pitch at 4.25 μm. If the pixel pitch is reduced from 4.25 to 3 μm while keeping the same resolution (720 × 720), the volume is expected to reduce by ~2×.