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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   Printer-friendly
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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  • (Score: 2) by kanweg on Sunday June 05 2016, @04:56AM

    by kanweg (4737) on Sunday June 05 2016, @04:56AM (#355401)

    "Perhaps Soylentils more familiar with the field can comment?"

    And can that person also say something about whether that the lens suffers from chromatic aberration quite a bit, as I suspect?

    Bert

  • (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.

  • (Score: 3, Informative) by inertnet on Sunday June 05 2016, @09:30AM

    by inertnet (4071) on Sunday June 05 2016, @09:30AM (#355457) Journal

    Simulation video here: http://www.bbc.com/news/science-environment-36438686 [bbc.com]

  • (Score: 0) by Anonymous Coward on Sunday June 05 2016, @12:06PM

    by Anonymous Coward on Sunday June 05 2016, @12:06PM (#355486)

    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).

    What am I supposed to sense by rubbing a finger over the back of a cellphone?

    • (Score: 4, Interesting) by rleigh on Sunday June 05 2016, @12:29PM

      by rleigh (4887) on Sunday June 05 2016, @12:29PM (#355489) Homepage

      I assume a bump as seen on current thin phones, which is required to accommodate the bulk of the optics (already miniaturised and making significant compromises in image quality).

      If this does work as promised and is easy to scale up for bulk manufacture, it would be a revolution in optical engineering. Both for phones and other small devices--the "lens" could be laminated to the surface material and be small and unobtrusive, as well as cheaper. And also for serious optics like in microscopes, telescopes etc. In a good quality microscope, single lenses can cost several tens of thousands (and more); big telescope lenses are even more bulky and expensive. If you can replace these with something of comparable quality but which can be manufactured as a thin film, you could make billions.

      As someone else mentioned, chromatic and other aberrations might be something which needs more investigation. Glass lenses already make compromises to accommodate different wavelengths--they are only optimal at a single wavelength. Does this technology eliminate or reduce the problem, or is it worse?

      Either way, it certainly promises to be exciting for some applications, even if those applications are initially limited.

      • (Score: 0) by Anonymous Coward on Sunday June 05 2016, @01:05PM

        by Anonymous Coward on Sunday June 05 2016, @01:05PM (#355500)

        My guess -- the first big applications will be for spy satellites. The telescope mirrors they use now are fabricated from glass (or other materials) with internal cutouts to save launch weight.

  • (Score: 4, Informative) by cellocgw on Sunday June 05 2016, @03:38PM

    by cellocgw (4190) on Sunday June 05 2016, @03:38PM (#355526)

    Take a look at any info page: a Fresnell lens is essentially a regular convex lens with the "fat parts" cut out. You end up with a thin lens made up of concentric "circles" each of which has the curvature (tilt) that a full convex lens would have at that radius, but without the lens' thickness.

    The lens in this article is completely different: metamaterials are fabricated on a nano-scale, and work by way of interferometric interactions between the light's wavefront (phase front) and the structure of the nanomaterial. A classic lens, including Fresnell, works due to the difference in index of refraction between air and glass, and Snell's law thereof.

    (and yes, I am an optical physicist)

    --
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    • (Score: 2) by Fnord666 on Sunday June 05 2016, @06:43PM

      by Fnord666 (652) on Sunday June 05 2016, @06:43PM (#355564) Homepage

      The lens in this article is completely different: metamaterials are fabricated on a nano-scale, and work by way of interferometric interactions between the light's wavefront (phase front) and the structure of the nanomaterial. A classic lens, including Fresnell, works due to the difference in index of refraction between air and glass, and Snell's law thereof.
      (and yes, I am an optical physicist)

      Question for you. Some of the discussion of this lens seemed to indicate that the lens only worked for one wavelength of light. To work on a different wavelength the nanostructures would have to be reorganized. Is that correct?

      • (Score: 2) by cellocgw on Sunday June 05 2016, @07:56PM

        by cellocgw (4190) on Sunday June 05 2016, @07:56PM (#355579)

        Yes, that's my impression as well (that the current design is monochromatic). From what little I know of current metamaterial designs, the physical spacing of the layout only fits one wavelength. There's always some "bandwidth" the same way an FM receiver can handle a signal thats slightly off-center frequency, but that's about it.

        --
        Physicist, cellist, former OTTer (1190) resume: https://app.box.com/witthoftresume

    • (Score: 0) by Anonymous Coward on Monday June 06 2016, @03:30AM

      by Anonymous Coward on Monday June 06 2016, @03:30AM (#355706)

      The article's description reminds me of holographic lenses or zone plates.
      The innovation seems to be in the materials and manufacturing process, not some breakthrough in a new way of bending light.
      All the pop sci descriptions make it sound like both manufacturing and fundamental physics.

      Your thoughts?

    • (Score: 2) by takyon on Wednesday June 08 2016, @09:33AM

      by takyon (881) <reversethis-{gro ... s} {ta} {noykat}> on Wednesday June 08 2016, @09:33AM (#356772) Journal

      Can these be used to improve the capabilities of space-based or ground observatories while lowering the cost?

      --
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