GEN2 - Proprietary Pancake Lens
The main goal of GEN2 was to reduce the lens to display distance. Following approaches were evaluated for that:
(1) Shorter focal distance compound optics
(2) Folded path optics (catadioptric approach) based on total internal reflections (TIL) or polarization manipulation (pancake)
(3) Multiple segments optics (that could be catadioptric) with software for seamless image (approaches by Limbak)
The option (3) has challenge of small eyebox and therefore wasn't considered. The pros and cons of option (1) vs (2) are:
The pancake lens based approach was selected for GEN2 since has a number of significant advantages: (1) More FoV while preserving high central PPD; (2) edge-2-edge visual clarity; (3) big eyebox. The slightly better system compactness is advantage (4).
Ghosting and low light efficiency are two fundamental challenges related to pancake optics; still allow normal operation/UX, while for long term are treated:
Ghosting Images - we are doing research for reducing of each ghost contributor by optimizations in AR,BS coatings and polarization manipulation components
To improve light efficiency we are developing per-pixel beam shaping micro-optics in framework of OPTIMAL EU consortium.
For more details about Hypervision pancake lenses please relate to HO140 pancake lens and RDK sections.