Researchers at Nvidia have developed a method to produce low-cost, high-resolution displays by simply layering two LCD panels on top of each other. The technique can quadruple the effective resolution of a standalone display, and could lead to cheap screens for head-mounted devices like the Oculus Rift.
The idea behind what Nvidia calls 'cascaded displays' is that there are transparent gaps between the individual pixels in an LCD panel. By placing another LCD panel behind the first one, and offsetting it by a quarter-pixel, additional pixels can shine through the gaps to provide extra resolution.
The way images are created on the cascaded display is quite complex, with each display providing a fragment of subpixels used for a single effective pixel. Custom display software is necessary to drive this screen, as you might imagine, and some clever coding can achieve refresh rates above 60 Hz.
For testing purposes, Nvidia used two seven-inch 1280 x 800 LCD panels from a cheap Chinese manufacturer in their cascaded display. While the spatial resolution is quadrupled through the layering of the panels, the true resolution isn't four times as large; images produced look sharper and of a higher resolution, but not as good as a true 2560 x 1600 display.
There are some issues with stacking displays, including distortion (which can be corrected in software), a reduction in display brightness and narrow viewing angles. However, it could be a viable solution for producing cheap head-mounted displays for virtual reality systems.