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FROM: James Urton
University of Washington
(Note: Contact information at the end of the researcher)
November 13, 2018
Scientists design functional optical lenses as 2D materials.
The age of glass lenses in optics can weaken.
In recent years, physicists and engineers have been designing, manufacturing, and testing a variety of ultra-thin materials that can replace thick glass lenses used in cameras and imaging systems. Critically, these metalenses are not made of glass. Instead, they consist of materials made from nanoscale arrays of structures such as pillars or fins. These formations can interact with incoming light to point to a single focus to create an image.
However, metal lenses tend to collapse or fall because they are much thinner than glass lenses, but structures such as heat and fins rely on a "high aspect ratio" structure that is much larger than the width. In addition, this structure is always close to the wavelength of light interacting with the thickness.
Articles published in the journal on October 8 Nano letterThe University of Washington and the Tsing Hua University team in Taiwan have created functional metal lenses that are 1 / 10th to 1 / 2th of the wavelength of light to focus on. Made of layered 2D material, the metal sense was thinner than 190 nanometers – 1 / 100,000 inches.
Arka Majumdar, assistant professor of physics and electrical and computer engineering at UW, said, "This is the first time anyone has shown that it is possible to make metal from 2D materials."
Their design principles can be combined with Majumdar, a professor at UW's Institute of Molecular and Scientific Research, to create metal lenses with more complex and adjustable functions.
The Majumdar team has been studying the design principles of metal lenses for many years and previously produced metal lenses for full color imaging. But the challenge for the project was to overcome the inherent design limitations of metal lenses. In order for the metal material to interact with the light to achieve optimal imaging quality, the material had to be about the same thickness as the light's wavelength. Mathematically, this restriction ensures a complete 0 to 2π phase shift range, ensuring that all optical elements can be designed. For example, in a visual spectrum, a metal for a 500 nm light wave, which is a green light, may decrease as the refractive index of the material increases, but should be about 500 nanometers thick.
Majumdar and his team have been able to synthesize functional metal lenses that are much thinner than half the wavelength at 1/10 of the theoretical limit. First, they made the metal into a sheet of layered 2D material. The team has extensively studied 2D materials such as hexagonal boron nitride and molybdenum disulfide. The single atomic layer of these materials provides very small phase shifts and is unsuitable for efficient lens action. So the team was too thick to reach the full 2-pi phase shift, but we used several layers to increase the thickness.
"We have to figure out the type of design that can deliver the best performance at an incomplete level," said Jiajiu Zheng, a Ph.D. student in electrical and computer engineering.
To compensate for the shortfall, the team originally used a mathematical model formulated for liquid crystal optics. These, along with metalens structural elements, were able to achieve high efficiency even when the overall phase change was not addressed. They have tested the effectiveness of metal lenses by capturing a variety of test images, including the Mona Lisa and block letters W. The team has proven that the focal length of the lens can be adjusted by increasing the metal lens.
In addition to achieving a completely new type of metallic design at a thin level, the team believes that this experiment has shown promise to make a new device for imaging and optics complete with 2D material.
"This result not only opens up an entirely new platform for studying the properties of 2D materials, but also allows us to construct fully functional nanopot devices made from these materials," Majumdar said. These materials are also easily transferred to all materials including flexible materials, opening the way to flexible photons.
Co-author Chang-Hua Liu began his research as a postdoctoral researcher at UW and is currently a professor at National Tsing Hua University in Taiwan. Additional coauthors are Shane Colburn, Taylor Fryett and Yueyang Chen, Ph.D. students in Electrical and Computer Engineering. And Xiaodong Xu, professor of physics and materials science and engineering. The team's prototypes were all produced by the Washington Nanofabrication Facility at UW campus. The study was conducted by the US Air Force Science Research Office, the National Science Foundation, the Washington Research Foundation, and M.J. Murdock Charity Trust, GCE Markets, Class One Technologies and Google.
For more information, please contact Majumdar ([email protected]).
No .: FA9550-18-1-0104, 1719797, 0335765, 1337840
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