Folded optical system adapted for head-mounted displays

Abstract

An optical imaging assembly for imaging light from a display. The optical assembly is constructed from first and second linear polarization filters, first and second lenses that are preferably concave-convex lenses, and first and second ¼ wave plates. The first linear polarization filter passes light polarized in a first direction, and second linear polarization filter passes light polarized in a second direction that is orthogonal to the first direction. A folded imaging assembly is constructed from the first and second lenses and the first ¼ wave plate. The first and second lenses have partially reflecting coatings on one surface of each lens. The folded imaging assembly and the second ¼ wave plate are located between the first and second linear polarization filters. In the preferred embodiment of the present invention, the first ¼ wave plate has a birefringence axis that is orthogonal to the birefringence axis of the second ¼ wave plate and the two ¼ wave plates are constructed from the same material. The partially reflective coating of one of the first and second lenses preferably includes a material having a reflectivity that depends on the direction of linear polarization of light striking the reflective coating. The surfaces of the convex-concave lenses are preferably spherical. The lenses preferably provide a substantially telecentric optical imaging system.