Novel high light efficiency pancake optics for HMD named “double path”

The folded optics for HMD (head-mounted display), commonly referred to as pancake optics, is widely used to realize a compact HMD headset. The optics has the advantage of compactness, but also has a big drawback of lowering light efficiency. To overcome the issue, we proposed novel HMD pancake optics named “DP (double path) pancake optics” to achieve both compactness and high light efficiency simultaneously. In this paper, we introduce the principle of our “DP pancake optics” and review our prototype. We describe optical simulation results to find a highly balanced design among thickness, lens power, and magnification ratio. We also describe fabrication study of, such as polarization state and alignment accuracy. We successfully have fabricated two prototypes with 90° FOV (field of view), one of which is 20.6 mm optics thickness and the other is 25.5 mm optics thickness. The latter prototype especially shows high MTF with a 1200 ppi (pixel per inch) resolution LCD (liquid crystal display). Both prototypes have 1.8 times higher light efficiency than that of conventional one. In addition, to further expand the DP pancake optics, we also describe the improved design with wider FOV for future prototype fabrication. Therefore, we also show the optical simulation result of the improved design.