Over-designed and under-performing: design and analysis of a freeform prism via careful use of orthogonal surface descriptions

In this paper, two freeform prism combiner designs with different geometries were studied. The first design, whose geometry is driven by the need for total-internal-refraction, achieves optical performance suitable for use in AR/VR applications, but involves highly complex surfaces and highly non-uniform performance. The second design, which removes the total-internal-refraction requirement, adopts a modified geometry which enables significantly improved aberration correction potential. The nodal-aberration-theory based design process is shown for both prism designs, and the optical performance of each design was analyzed. Performance exceeds 10% MTF at 50lp/mm over centered and decentered 3mm effective subpupils, evaluated at nine different positions within an 8mm diameter eyebox.

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