Metasurface optics and flat lenses

In plain language

Ordinary lenses work because curved glass bends light. A metasurface does the same job with a flat layer covered in tiny structures, each much smaller than a wavelength of light. Each structure delays the light passing through it by a precise amount, and the pattern of delays steers the light in the direction the designer wants. Yu and colleagues (2011) showed that surfaces with engineered phase changes of this kind can generalise the laws of reflection and refraction.

A flat lens built this way can be far thinner than a conventional lens. Harvard researchers reported in 2015 a dielectric metasurface that brought red, green and blue light to the same focus, and in 2018 a single metalens that focuses the entire visible spectrum to one spot. The 2018 release does not give the diameter of that lens, and the team's stated next goal is a lens about 1 cm across.

Technical explanation

Each nanostructure on a metasurface imparts a local phase shift to the light passing through it. Arranging the structures with spatially varying phase produces focusing, beam steering or other wavefronts. Because the phase delay of a single structure depends on wavelength, a simple metalens focuses different colours to different distances, which is called chromatic aberration. The Harvard release describing the 2018 work reports titanium dioxide nanofins arranged in pairs, which bring the visible wavelengths to one focal spot (Harvard, 2018; the research paper is Chen and colleagues, 2018).

Material choice affects efficiency. Aieta and colleagues (2015) used dielectric nanoantennas in place of metal, and the Harvard release for that work states that the change greatly improves efficiency, although it gives no numerical value. The same group reported in 2016 metalenses that achieve diffraction-limited focusing at visible wavelengths (Khorasaninejad and colleagues, 2016), showing that metasurface lenses can work at the resolution limit of ordinary optics.

The main open questions are scale and performance. The 2018 Harvard release does not give the diameter of the demonstrated lens or any efficiency figure, and states the team's next goal is to scale to about 1 cm. The 2015 simulations suggest the approach could extend beyond three wavelengths, but that projection has not been tested in the sources reviewed here.

What the evidence says

Each statement is typed by the strength of its evidence and linked to the source that supports it.

Limitations and open problems

• The 2018 Harvard release does not state the diameter of the demonstrated lens. The stated next goal is to scale the lens to about 1 cm across.
• The 2015 Harvard release gives only qualitative efficiency comparisons, with no numerical efficiency for the achromatic lens.
• The claim that the approach could extend to many more wavelengths comes from simulations, not from tested devices.
• The sources reviewed here describe research prototypes and give no verified production volumes or commercial product performance.

Possible future uses

Timeline

1. 21 Oct 2011Yu and colleagues publish generalised laws of reflection and refraction for surfaces with engineered phase changes in Science. Sources: [1]
2. 20 Mar 2015Aieta and colleagues publish a multiwavelength achromatic metasurface using dielectric nanoantennas in Science. Sources: [2], [6]
3. 3 Jun 2016Khorasaninejad and colleagues report metalenses with diffraction-limited focusing at visible wavelengths in Science. Sources: [3]
4. Jan 2018Chen and colleagues report a single broadband achromatic metalens that focuses the whole visible spectrum to one point in Nature Nanotechnology. Sources: [4], [5]

Futures this could help bring about

How far away?

A probe to another star

Science demonstrated · 1 of 8 steps done

Related breakthroughs

• Coloured-resist flat lenses focus 550 nm light to a 1.1 µm spot without etching (16 Jan 2025)

Glossary

Metasurface

A flat layer patterned with structures smaller than the wavelength of light, which control the phase, direction and shape of light passing through or reflecting from it.

Metalens

A flat lens built from a metasurface, in place of curved glass.

Achromatic

Producing the same focus or behaviour for light of different colours (wavelengths).

Diffraction-limited focusing

Focusing light to the smallest spot that the wavelength and aperture allow.

Sources

1. peer reviewed paper
   Light Propagation with Phase Discontinuities: Generalized Laws of Reflection and Refraction
   Nanfang Yu, Patrice Genevet, Mikhail A. Kats et al.. Science, 21 Oct 2011. DOI: 10.1126/science.1210713. Accessed 21 Oct 2026.
2. peer reviewed paper
   Multiwavelength achromatic metasurfaces by dispersive phase compensation
   Francesco Aieta, Mikhail A. Kats, Patrice Genevet et al.. Science, 20 Mar 2015. DOI: 10.1126/science.aaa2494. Accessed 21 Oct 2026.
3. peer reviewed paper
   Metalenses at visible wavelengths: Diffraction-limited focusing and subwavelength resolution imaging
   Mohammadreza Khorasaninejad, Wei Ting Chen, Robert C. Devlin et al.. Science, 3 Jun 2016. DOI: 10.1126/science.aaf6644. Accessed 21 Oct 2026.
4. peer reviewed paper
   A broadband achromatic metalens for focusing and imaging in the visible
   Wei Ting Chen, Alexander Y. Zhu, Vyshakh Sanjeev et al.. Nature Nanotechnology, Jan 2018. DOI: 10.1038/s41565-017-0034-6. Accessed 21 Oct 2026.
5. university press release
   Single metalens focuses all colors of the rainbow in one point
   Leah Burrows. Harvard John A. Paulson School of Engineering and Applied Sciences, 1 Jan 2018. Accessed 21 Oct 2026.
6. university press release
   Perfect colors, captured with one ultra-thin lens
   Caroline Perry. Harvard John A. Paulson School of Engineering and Applied Sciences, 19 Feb 2015. Accessed 21 Oct 2026.

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