Design of Compact Liquid Crystal on Silicon Projection Optics Utilizing a Common Freeform Optical Path for Augmented Reality Displays

Waveguides are a crucial optical solution for see-through near-eye displays. For waveguide-based systems, lightweight and compact projection optics are essential. Herein, a compact projection optics design utilizing freeform surfaces on two wedge-shaped prisms is presented. Compared to previous liquid crystal on silicon projection optics, which separate the illumination and imaging optical paths, a common freeform optical path is employed in the design. The optical design methodology is described in detail, and a simulation model of the system is established. Furthermore, stray light issues arising from the coupling between the waveguide and projection optics are analyzed. The proposed projection optics with freeform surfaces achieve a field of view of 32°, an exit pupil diameter of 4 mm, and a resolution of 37.5 pixels per degree. The total volume of the projection optics is less than 2 cubic centimeters, and its weight is only 3.48 g. Finally, a prototype is fabricated and integrated with a geometric waveguide to form a fully optical module.