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Paper-Thin Lenses Could Shrink Cameras and Holographic Displays

Nanostructured sheets of silicon can bend light in unusual ways, eliminating the need for bulky lenses.
February 19, 2015

A new nanostructured material makes it possible to replace bulky lenses and other optical devices with a thin sheet of material such as silicon.

The advance, described in the journal Science, could make it possible to shrink some professional-quality camera lenses to the thickness of a credit card. It might also enable lighter-weight, more compact full-color holographic 3-D goggles, the sort being developed by Microsoft and the Google-acquired company Magic Leap (see “Magic Leap” and “Microsoft’s New Idea: A Hologram Headset to Rewrite Reality”).

The work was inspired a year ago when Google approached Federico Capasso, a professor of applied physics at Harvard, with a challenge. He’d recently demonstrated that he could build thin, nanostructured films that could manipulate light. The films worked well with only one color, and Google wanted to know if he could he make the technology work with red, green, and blue light—the colors needed to produce full-color displays.

Google says the work would be especially important for work related to Google Glass, but didn’t specify how (Google has stopped selling its Glass device as it works on improving it—see “Google Glass Is Dead; Long Live Smart Glasses”).

Capasso has an agreement with Google not to talk about details of possible applications, but says his materials are useful for holographic 3-D imaging and augmented reality, in which computer-generated images appear to be overlaid on the real world. The ability to manipulate multiple colors might help Google make a full-color wearable version of the Magic Leap technology—the compact version it’s demonstrated so far only displays a green image.

One problem with most optical materials is that they bend light of different wavelengths at different angles—the reason prisms create rainbows. This makes it hard to produce clear images in a camera, for example, since not all wavelengths of light get focused on the same spot. It’s possible to correct for the problem, but that involves adding extra lenses, which is why the high-end lenses professionals use are so bulky.

Capasso and his colleagues found ways to make all the wavelengths bend at the same angle. It’s long been known that you can produce ultrafine patterns in a sheet of metal, or some other material, that will split light up into different colors the way a prism does. Capasso found that varying that pattern at the nanoscale in a precise way causes light of three different wavelengths to bend at the same angle. His experimental device manipulates infrared wavelengths, but the principles could be adopted for visible wavelengths as well, so that light entering the thin sheet of material could remain white instead of being broken up into a rainbow. Yet the light comes out at a different angle than it went in. The end result is the ability to manipulate light using very thin materials. 

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