In 2007 CEO Jørgen Korsgaard from OPDI asked if we could come up with an idea to make a water-insensitive touch control panel for a stove. We raised 7 Mio DKK from Innovationsstyrelsen and came up with an optical waveguide solution that could be used as an inexpensive touch screen for mobile phones. And – it works under water!
PROBLEM
Even though the project started out aiming for a new touch panel for a stove, it quickly evolved into investigating new touch screen technologies for the cell phone and tablet markets, markets that were sky-rocketing by the introduction of the iPhone. At the time, a touch screen for an iPhone had an assumed cost price of 38 USD. By using molded plastic parts, a cheap laser and a CMOS line camera, we believed to be able to make a touch module for less than 5 USD.
SOLUTION
The touch module is based on a thin piece of plastic that covers the screen of, say, a smart phone. An infrared fan of light is launched into the plastic sheet through one of the corners, so that the light is guided in the plane of the plastic sheet. The sheet now acts as a waveguide that guides the light until it hits one of the opposing sides of the waveguide. Being metal coated and Fresnel shaped the sides redirect and collimate the light towards the remaining two sides of the waveguide. These are also metal coated and Fresnel shaped in a way so that the light fans are focused towards the corner being opposite to the laser. Here a CMOS sensor receives the light fans. When a finger touches the sheet, light is coupled out of the sheet locally, which leaves two dark spots at the CMOS sensor. The positions of these two spots reveal the location of the finger.
