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Meta-Lens Works in the Visible Spectrum, Sees Smaller Than a Wavelength of Light

posted by martyb on Sunday June 05 2016, @02:23AM   
from the see-what-he-did-there? dept.

Phoenix666 writes:

Curved lenses, like those in cameras or telescopes, are stacked in order to reduce distortions and resolve a clear image. That's why high-power microscopes are so big and telephoto lenses so long.

While lens technology has come a long way, it is still difficult to make a compact and thin lens (rub a finger over the back of a cellphone and you'll get a sense of how difficult). But what if you could replace those stacks with a single flat -- or planar -- lens?

Researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have demonstrated the first planar lens that works with high efficiency within the visible spectrum of light -- covering the whole range of colors from red to blue. The lens can resolve nanoscale features separated by distances smaller than the wavelength of light. It uses an ultrathin array of tiny waveguides, known as a metasurface, which bends light as it passes through, similar to a curved lens.

The article's description of the lens sounds reminiscent of a Fresnel lens. Perhaps Soylentils more familiar with the field can comment?

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Original Submission

• It is an improved fensnel lens (Score: 3, Informative) by Scruffy Beard 2 on Sunday June 05 2016, @05:08AM

  by Scruffy Beard 2 (6030) on Sunday June 05 2016, @05:08AM (#355406)

  Looks like this new lens avoids chromatic aberration by having nano-scale features.

  From Wikipedia:

  There are two main types of Fresnel lens: imaging and non-imaging. Imaging Fresnel lenses use segments with curved cross-sections and produce sharp images, while non-imaging lenses have segments with flat cross-sections, and do not produce sharp images.[11] As the number of segments increases, the two types of lens become more similar to each other. In the abstract case of an infinite number of segments, the difference between curved and flat segments disappears.
  ...
  A spherical Fresnel lens is equivalent to a simple spherical lens, using ring-shaped segments that are each a portion of a sphere, that all focus light on a single point. This type of lens produces a sharp image, although not quite as clear as the equivalent simple spherical lens due to diffraction at the edges of the ridges.

  From TFA:

  "Correcting for chromatic spread over the visible spectrum in an efficient way, with a single flat optical element, was until now out of reach," said Bernard Kress, Partner Optical Architect at Microsoft, who was not part of the research.
  ...
  n order to focus red, blue and green light -- light in the visible spectrum -- the team needed a material that wouldn't absorb or scatter light, said Rob Devlin, a graduate student in the Capasso lab and co-author of the paper.

  "We needed a material that would strongly confine light with a high refractive index," he said. "And in order for this technology to be scalable, we needed a material already used in industry."

  The team used titanium dioxide, a ubiquitous material found in everything from paint to sunscreen, to create the nanoscale array of smooth and high-aspect ratio nanostructures that form the heart of the metalens.

  Psuedo-edit: not sure how they solve the diffraction problem.

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