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January 24, 2011

Six millimeters thick pico projector that is ten times brighter

Light fantastic: This prototype pico projector produces a sharp image without needing a bulky lens thanks to an ultra-thin array of micro-lenses.
Credit: Fraunhofer Institute for Applied Optics and Precision Engineering


MIT Technology Review reports that researchers in Germany have developed the world's thinnest "pico" video projector. The prototype device contains an array of carefully shaped microlenses, each with its own miniature liquid-crystal display (LCD). The device is just six millimeters thick, but it produces images that are 10 times brighter than would normally be possible with such a small device. The new lens system is small enough to be incorporated into a slim smart phone.



Sieler and colleagues created a novel type of lens that focuses light from a relatively large light source while remaining thin. The prototype video projector consists of 45 microlenses colored red, green, or blue. Each lens has an LCD with 200 by 200 pixels behind it. The light passing through each LCD is focused through a lens, and together each image is superimposed on top of each other to produce the final image. The design was inspired by a type of microlens array known as a "fly's eye condenser," which is normally used to mix light from different sources.

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.

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