Picture the Louvre pyramid: the iconic glass pyramid that serves as main entrance and skylight to the landmark museum. The pyramid is illuminated at night, creating a magical ambience. Imagine strolling next to it while a video about the museum is projected on the glass in front of you, adding information while preserving the elegance of the structure. This seems like a scene taken from The Avengers or other sci-fi movies: although some technology for transparent displays exists, in practice it has many limitations. Using the 20 thousand square feet of glass of the Louvre pyramid as a transparent display with existing methods would be expensive and difficult. Closer to home, one could wish to have a simple method to use a storefront glass, or a subway window as a projection screen.
A team from the MIT and Harvard departments of Physics, and the US Army Edgewood Chemical Biological Center, has developed a new approach to produce transparent projection screens. Their result paves the way for a new class of transparent displays with many attractive features, including wide viewing angle, scalability to large size, and low cost.
The team members are graduate students Chia Wei Hsu, Bo Zhen, Wenjun Qiu, research scientists Dr. Ofer Shapira, Dr. Brendan G. DeLacy, and Prof. John Joannopoulos (Francis Wright Davis Chair and director of ISN), led by Prof. Marin Soljacic. The work has been published in the 21st January 2014 issue of Nature Communications.
Color sensitive players
White light is composed of all the colors of the rainbow. A white projector screen looks white because all the colors of the ambient light interact with it and get reflected. On the other hand, a window appears transparent because the same ambient light doesn't interact with glass and is free to go through. This is also the reason why you cannot project onto a regular glass: the light that you are trying to project simply passes through. One can envision the components of a material to be like tennis players, and the light to be like tennis balls of different colors. A material that looks white is made up of players that intercept light-balls of all colors and hit them back; a clear glass is made up by players that do not hit any at all.
