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Liquid Crystal Improves Metalens Design

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CLEVELAND, Aug. 24, 2020 — An effort led by Federico Capasso of Harvard University and Giuseppe Strangi of Case Western Reserve University is using liquid crystals to improve the reconfigurability of metalenses. This advancement brings the viability of metalenses for commercial use closer to reality.

The researchers harnessed nanoscale forces to infiltrate liquid crystals between the microscopic pillars that allow metalenses to focus light. This allowed them to shape and diffract light in new ways, “tuning” the focus power, Strangi said.
Metalenses use microscopic pillars to focus light. Courtesy of Giuseppe Strangi and Federico Capasso.
Metalenses use microscopic pillars to focus light. Courtesy of Giuseppe Strangi and Federico Capasso.

Liquid crystals can be manipulated thermally, electrically, magnetically, or optically, which creates the potential for flexible or reconfigurable lenses.

“We believe that this holds the promise to revolutionize optics as we know it since the 16th century,” said Strangi, who leads the Nanoplasm Lab at Case Western Reserve.

Until recently, once a glass lens was shaped, it could only bend light in one way, unless combined with another lens or physically moved, Strangi said.

Metalenses, on the other hand, allow for the engineering of the wavefront by controlling phase, amplitude, and polarization of the light.
Giuseppe Strangi views a metalens array. Courtesy of Giuseppe Strangi and Federico Capasso.
Giuseppe Strangi views a metalens array. Courtesy of Giuseppe Strangi and Federico Capasso.

According to research paper co-author Andrew Lininger, part of the problem with current applications of metasurfaces is that their shape is fixed at the point of production, but “by enabling reconfigurability in the metasurface, these limitations can be overcome.”

With the liquid crystal, the researchers are able to control the lens further, which moves the technology closer toward the ability to generate reconfigurable structured light.

“This is just the first step, but there are many possibilities for using these lenses, and we have already been contacted by companies interested in this technology,” Strangi said.

Capasso, a pioneer in the flat optics research field who in 2014 first published research on metalenses, credited Strangi for the idea to infiltrate metalenses with liquid crystals, stating that the innovation represents a step toward even bigger things.

“Our ability to reproducibly infiltrate with liquid crystals state-of-the art metalenses made of over 150 million nanoscale-diameter glass pillars and to significantly change their focusing properties is a portent of the exciting science and technology I expect to come out of reconfigurable flat optics in the future,” Capasso said.

The collaboration included researchers from the United States and Europe, including fellow Case Western Reserve researchers Lininger and Jonathan Boyd; Giovanna Palermo of Universita’ della Calabria in Italy; and Capasso, Alexander Zhu, and Joon-Suh Park of the John A. Paulson School of Engineering and Applied Sciences at Harvard University.

The research was published in the Proceedings of the National Academy of Sciences (www.doi.org/10.1073/pnas.2006336117).

Photonics.com
Aug 2020
GLOSSARY
lens
A transparent optical component consisting of one or more pieces of optical glass with surfaces so curved (usually spherical) that they serve to converge or diverge the transmitted rays from an object, thus forming a real or virtual image of that object.
liquid crystal
A type of material that possesses less geometrical regularity or order than normal solid crystals, and whose order varies in response to alterations in temperature and other quantities. Liquid crystals are characterized by phase varieties, including cholesteric, nematic and smectic. The optical properties of liquid crystals are familiar from their use in displays, known as LCDs.
Research & TechnologyopticslensesmetalenslensmetasurfaceFlat Opticsliquid crystalFederico CapassoHarvard UniversityJohn A. Paulson School of Engineering and Applied SciencesCapasso LabCapasso GroupGiussepe Strangi

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