Computational design and prototype development of optical prism for augmented reality projection

Head mounted display (HMD) has two basic components, a display unit and an optical freeform prism. The crucial issue in the design of the freeform prism is a geometric shape to properly display the image to naked eye in a short distant. Typically, the freeform prism is comprised of 3 specially designed aspherical surfaces. The source image is reflected by these three surfaces to form image on the human retina. In this paper, we propose a new and simplified design of convex-plano HMD prism with the aid of ray tracing and optical theories. A prototype with the optimized surface alignment is also fabricated. Experiments confirming the performance of our prism as consistent with that predicted by optical design package are presented. Although the prototype is relatively low cost, it gives a better resolution than that of half-transparent mirror and freeform prism, and produces a wide and clear image along the line of sight.