There are a number of approaches currently used to create transparent displays, such as transparent OLED and LCD displays or simple reflection, however, most are limited in terms of viewing angle. Researchers at MIT have come up with a new system that is low-cost and offers a wide angle of view with the projected image appearing on the transparent material itself.
The fact that OLED and LCD transparent displays integrate the necessary electronics directly into the transparent material limits their transparency and makes them complex and expensive. In comparison, the new system developed at MIT embeds only nanoparticles in the transparent material. These nanoparticles are tuned to scatter light of very specific wavelengths, or colors. When this particular wavelength of light is projected onto the display, it is scattered rather than passing through like all other wavelengths.
The MIT team has demonstrated a proof-of-concept system using commercially-available silver nanoparticles. These measure about 60 nanometers across and scatter blue light, resulting in a display capable of producing a blue image. However, the researchers say it should be possible to produce a full color display using nanoparticles tuned to scatter red, green and blue light. Because the nanoparticles are tuned to very specific wavelengths, most light would still pass through freely, including the red, green and blue hues not of the precise wavelength targeted by the nanoparticles.
Advertising on store windows or subway cars and HUDs on car windshields are just some of the potential applications envisaged by the team for the technology. Because the display material holds no electronics itself, the system has the potential to be cheap to produce. The team says existing windows or windshields would not even have to be replaced as the nanoparticles could be incorporated into a thin, inexpensive plastic coating that could be applied to a transparent surface, much like window tinting.
The transparent display technology is detailed in a paper published in the journal Nature Communications. It can be seen in action in the video below.
Source: MIT
However, there is a type of projection screen that is a hologram. These could be considered a "hologram of a screen." The effect is very similar to what is described in the article. These screens scatter all colors of light from a very specific angle--usually a very steep, off-axis angle, so that one is not staring into the lens of the projector. There are transparent versions, which do maintain a fair degree of transparency in areas where no light is striking it. One thing though, is that holographic screens are quite expensive, especially in sizes larger than a meter or so. I look forward to a lower-cost solution!