Ultra-thin flat lenses suitable for photography are one step closer after a team of researchers at Harvard University made a major leap forward with its prototype wafer-thin flat lens. The new lens builds on the original prototype, which we first heard about in 2012, by using an achromatic metasurface to focus different wavelengths of light at the same point.

When the team from the Harvard School of Engineering and Applied Sciences (SEAS) initially revealed its ultra-thin, flat lens, it was able to focus light without distortions, despite being effectively two-dimensional at just 60 nanometers thick. However, light at different wavelengths responded very differently to its nanoantennas, meaning it could only work with a single wavelength of light at a time.

The new model uses a dielectric material rather than a metal for the nanoantennas. This is said to improve its efficiency and, combined with a new design approach, means it is able to produce a consistent effect by focusing multiple wavelengths of light at the same point to achieve instant color correction. This change allows the new lens to create a color image by focusing red, green, and blue at the same point.

The development also means the new flat lens, dubbed an "achromatic metasurface," does not suffer from the chromatic aberrations, or color fringing, that plague refractive lenses. As such, it will not require the additional bulky lens elements traditionally used to compensate for this chromatic dispersion in higher quality lenses.

Applications for the technology could see the development of photography, astronomy, and microscopy lenses which are far smaller and lighter than traditional optics, without compromising on quality. It could also allow the creation of new miniature optical communications devices.

"What this now means is that complicated effects like color correction, which in a conventional optical system would require light to pass through several thick lenses in sequence, can be achieved in one extremely thin, miniaturized device," said principal investigator Federico Capasso, the Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering at Harvard SEAS.

A paper outlining the research was published in the journal Science.

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