Originally Posted by FastCompany.com
Inspiration came in the form of an ordinary glass of water. Han noticed when he looked down on the water that light reflected differently in areas where his hand contacted the glass. He remembered that in fiber optics, light bounces on the inside of the cable until it emerges from the other end miles away. If the surface was made of glass, and the light was interrupted by, say, a finger, the light wouldn't bounce anymore, it would diffuse--some of it would bleed into the finger, some would shoot straight down, which was happening with his water glass. Physicists call the principle "frustrated total internal reflection" (it sounds like something your therapist might say).
Han decided to put these errant light beams to work. It took him just a few hours to come up with a prototype. "You have to have skills to build," he says. "You can't be strictly theoretical. I felt fortunate. I walked into a lab with crude materials and walked out with a usable model."
He did it by retrofitting a piece of clear acrylic and attaching LEDs to the side, which provided the light source. To the back, he mounted an infrared camera. When Han placed his fingers on the makeshift screen, some light ricocheted straight down, just as he thought it would, and the camera captured the light image pixel for pixel. The harder he pressed, the more information the camera captured. Han theorized he could design software that would measure the shape and size of each contact and assign a series of coordinates that defined it. In essence, each point of contact became a distinct region on a graph. "It's like a thumbprint scanner, blown up in scale and encapsulating all 10 or more fingers. It converts touch to light." It could also scale images appropriately, so if he pulled a photo apart with two fingers, the image would grow.