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Scientists engineer a functional optical lens out of 2D materials



http://www.washington.edu/news/2018/11/13/metalens-2d- Materials /

FROM: James Urton

University of Washington

206-543-2580

jurton@uw.edu

(NOTE: researcher contact information at end

For Immediate Release

November 13, 2018

Scientists engineer a functional optical lens out of 2D materials

In recent years, physicists and engineers have been designing, constructing, and testing different types of ultrathin materials in cameras and imaging systems. Critically, these engineered lenses ̵

1; known as metalenses – are not made of glass. Instead, they are constructed at the nanoscale into arrays of columns or fin-like structures.

But even though metalenses are much better than glass lenses, they still rely on "high aspect ratio" structures, in which the column or fin -like structures are much taller than they are wide, making them look to collapsing and falling over. Furthermore, they are now in the process of being used in the meantime.

In a paper published Oct. 8 in the journal Nano Letters a team from the University of Washington and the National Tsing Hua University of Taiwan, announced that it has become one of the most widely used technologies in the world light that they focus.

"This is the first time that anyone has seen it." metalens out of 2D materials, said Arka Majumdar, Senior Associate and Associate Professor, a UW assistant professor of physics and of electrical and computer engineering.

Their design principles can be used for the creation of more complex, tunable features , added Majumdar, who is now a faculty researcher with the UW's Molecular Engineering & Sciences Institute.

Majumdar's team has been studying the design principles of metalenses for years, and previously constructed metals for full-color imaging. As the light in the material is at work, the light in the material is at a certain temperature. In mathematical terms, this restriction ensures that a full zero to two-phase shift range is achievable. For example, a metalens for a 500-nm lightwave – which in the visual spectrum is green light – would need about 500 nanometers in thickness, but this thickness may decrease as the refractive index of the material increases.

Majumdar and his team were able to synthesize functional metals that were much better than this theoretical limit – one-tenth to one-half the wavelength. First, they constructed the sheets of 2D layered material. The team used 2D materials as hexagonal boron nitride and molybdenum disulfide. A single atomic layer of these materials provides a very small phase shift, unsuitable for efficient lensing.

"We had to make the best performance given the incomplete phase, "said co-author Jiajiu Zheng, a doctoral student in electrical and computer engineering.

To make up for the shortfall, the team employed mathematical models that were originally formulated for liquid-crystal optics. Thesis, in conjunction with the metalens structural elements, allows the researchers to achieve their efficiency. They tested the metalens' efficacy by using it to capture different test images.

In addition to achieving a wholly new approach to metalsens design at record-thin levels, the team believes that it's the promise of making new devices for imaging and optics entirely out of 2D materials.

"These results open up an entirely new platform for studying the properties of 2D materials, as well as constructing fully functional nanophotonic devices made entirely from these materials, said Majumdar. Additionally, Chang Hao Liu, who started this work as a UW postdoctoral researcher, has published a paper entitled "The Lead and Co-corresponding Author on the Paper."

researcher and is now a faculty member at the National Tsing Hua University in Taiwan. Additional co-authors are doctoral students Shane Colburn, Taylor Fryett, and Yueyang Chen in the Department of Electrical and Computer Engineering; and Xiaodong Xu, a UW professor of physics and materials science and engineering. The team's prototype metalenses were all built at the Washington Nanofabrication Facility on the UW campus. The research was funded by the U.S. Air Force Office of Scientific Research, the National Science Foundation, the Washington Research Foundation, the M.J. Murdock Charitable Trust, GCE Market, Class One Technologies and Google.

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For more information, contact Majumdar at arka@uw.edu.

Grant numbers: FA9550-18-1-0104, 1719797, 0335765, 1337840

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