Some near eye displays (NEDs) are used in virtual reality (VR) devices. NEDs of VR devices have eyes enclosed from external view to effect immersive display. VR devices are optimal with minimum of 80 degrees field-of-view (FOV) so that the viewer does not seem to be looking out from the window with the edges of the view showing. NEDs in VR devices use combination of lenses to focus on small display or image source. The problem is that this train of lenses are uncomfortably long, complex and bulky to achieve the minimum FOV and large eye box. An eye has a FOV of around 200 degrees horizontal and around 135 degrees vertical with eye rotation included (no head movement relative to NED). The pupil of the eye can be in locations covering around ¾ of an inch cube eye box with eye rotation and being slightly far or near the NED.
NEDs having wide FOV and large eye box approaching these extents are ideal. Unfortunately, even the largest lens in NEDs that can be used in VR devices prohibits the NED from achieving a very wide FOV. Optical problems arise when the eye starts to rotate from the optical axis or move away from the focal plane. Attempts to solve these problems using concentric optical system did not produce satisfactory FOV or image quality. Prior concentric optical system for NEDs use combination of see-thru mirrors, polarizers, quarterwave retarders, and lens system to cut and fold the optical path. Unfortunately, light from the image source passes through and reflected from these elements so many times that the image quality becomes degraded so much.
There are NEDs used for see-thru or augmented reality (AR) devices. AR NEDs are similar to VR NEDs except AR NEDs can overlay the image to the external view. NEDs in AR devices have displays or image sources placed away from line of sight and use angled see-thru mirror or beam splitter to see the local display overlaid to the external view. These AR NEDs have an unsatisfactory FOV because the angled see-thru mirror prohibits the NED from having wide FOV. Prior concentric optical system for NEDs of AR devices have failed to produce wide FOV with good image quality.
NEDs in AR devices have an image from a local display overlaid against the external view. Dark parts of the image unfortunately turn light when set against bright external view. The image could be very hard to see against brightly colored external view. Masking or occluding systems to cover parts or the whole image of the local display from external view to control the opacity against the external view have been tried. Unfortunately, these attempts have met limited success.
In view of the foregoing, improvements to NEDs are wanted by the industry.