The resolution of the projector is close to that of a WVGA projector, which has 800 by 480 pixels. The new projector has a brightness of 11 lumens, says Sieler, compared to 10 to 15 lumens for existing pico projectors. Sieler says that if the prototype were the same size as an existing pico projector, it would produce about 90 lumens. The next challenge is to make the LCD pixels smaller, from 8.5 microns each to less than three microns, says Sieler.
Microlens arrays are not new, notes Tim Holt, executive director of the Institute of Photonics at the University of Strathclyde. But Holt says that molding each lens in a way that focuses light at a single convergent point is novel.
The LCD behind each lens is sandwiched inside a transparent material, allowing the entire lens to be more compact. To make this kind of integration possible, the researchers needed a new transparent material. Glass wasn’t suitable because its melting point is so high that the LCD components would be destroyed during the molding process, says Michael Popall, head of the Fraunhofer Institute for Silicate Research, who helped develop the new pico projector. Transparent polymers tend to have the opposite problem: their melting point is so low they would melt and deform under the projector’s light source.
Popall and colleagues developed what he calls a hybrid organic-inorganic material. “This is an optical material that is totally transparent in the visual range, and which you can process like a polymer,” he says.
In February, the new prototype will be demonstrated at the Nano Tech 2011 conference in Tokyo.