A system is provided for removing extraneous side images produced by light emitted at high angles from a display in a head mounted display (HMD), which results in light rays traveling along undesired paths that bounce one or three times from a worldside surface of a lightguide in the HMD, instead of the two bounces along the path taken by the light that forms the primary image. The system includes an optical element that couples the display to a prism to provide light to a lightguide in the HMD. The optical element is fabricated using a stack of prisms having surfaces at different angles relative to a surface of a prism used to couple the light rays into a lightguide of the HMD. Light incident upon the prism stack at relatively high angles, e.g., light traveling along paths that would bounce one or three times in the lightguide, is totally internally reflected at the interfaces between the prisms so that the high angle light rays are directed out of the path that couples the light into the HMD lightguide.
Martinez, Oscar; Dunphy, James; and Cakmakci, Ozan, "TOTAL INTERNAL REFLECTION IN A FILTER STACK FOR SIDE IMAGE MITIGATION IN A CURVED LIGHTGUIDE", Technical Disclosure Commons, (November 15, 2017)