Strategic Communications and Marketing News Bureau

Silicon photonic crystals key to optical cloaking, researchers say

Harley Johnson, left, a mechanical science and engineering professor, and Dong Xiao, a postdoctoral researcher, have demonstrated an approximate cloaking effect created by concentric rings of silicon photonic crystals.

Harley Johnson, left, a mechanical science and engineering professor, and Dong Xiao, a postdoctoral researcher, have demonstrated an approximate cloaking effect created by concentric rings of silicon photonic crystals.

CHAMPAIGN, Ill. – Now you see it, soon you might not, researchers at the University of Illinois say.

In computer simulations, the researchers have demonstrated an approximate cloaking effect created by concentric rings of silicon photonic crystals. The mathematical proof brings scientists a step closer to a practical solution for optical cloaking.

“This is much more than a theoretical exercise,” said Harley Johnson, a Cannon Faculty Scholar and professor of mechanical science and engineering at Illinois. “An optical cloaking device is almost within reach.”

In October 2006, an invisibility cloak operating in the microwave region of the electromagnetic spectrum was reported by researchers at Duke University, Imperial College in London, and Sensor Metrix in San Diego. In their experimental demonstration, microwave cloaking was achieved through a thin coating containing an array of tiny metallic structures called ring resonators.

To perform the same feat at much smaller wavelengths in the visible portion of the spectrum, however, would require ring resonators smaller than can be made with current technology, Johnson said. In addition, because metallic particles would absorb some of the incident light, the cloaking effect would be incomplete. Faintly outlined in the shape of the container, some of the background objects would appear dimmer than the rest.

To avoid these problems, postdoctoral research associate Dong Xiao came up with the idea of using a coating of concentric rings of silicon photonic crystals. The width and spacing of the rings can be tailored for specific wavelengths of light.

“When light of the correct wavelength strikes the coating, the light bends around the container and continues on its way, like water flowing around a rock,” Xiao said. “An observer sees what is behind the container, as though it isn’t there. Both the container and its contents are invisible.”

Currently simulated in two dimensions, the cloaking concept could be extended to three dimensions, Xiao said, by replacing the concentric rings with spherical shells of silicon, separated by air or some other dielectric.

The researchers’ optical cloaking technique is not perfect, however. “The wave fronts are slightly perturbed as they pass around the container,” said Johnson, who also is affiliated with the university’s Beckman Institute and the Frederick Seitz Materials Research Laboratory. “Because the wave fronts don’t match exactly, we refer to the technique as ‘approximate’ cloaking.”

Xiao and Johnson’s work is highlighted in the June issue of the Materials Research Society Bulletin. The researchers describe their work in a paper published in the April 15 issue of the journal Optics Letters.

Funding was provided by the U.S. Department of Energy.

 

Editor’s note: To reach Harley Johnson, call 217-265-5468; e-mail: htj@illinois.edu.

Read Next

Announcements Marcelo Garcia, professor of civil and environmental engineering at The Grainger College of Engineering.

Illinois faculty member elected to National Academy of Engineering

Champaign, Ill. — Marcelo Garcia, a professor of civil and environmental engineering in The Grainger College of Engineering, has been elected to the National Academy of Engineering.

Social sciences Male and female student embracing on the quad with flowering redbud tree and the ACES library in the background. Photo by Michelle Hassel

Dating is not broken, but the trajectories of relationships have changed

CHAMPAIGN, Ill. — According to some popular culture writers and online posts by discouraged singles lamenting their inability to find romantic partners, dating is “broken,” fractured by the social isolation created by technology, pandemic lockdowns and potential partners’ unrealistic expectations. Yet two studies of college students conducted a decade apart found that their ideas about […]

Engineering Civil and Environmental Engineering Professor Nishant Garg, center, is joined by fellow researchers, from left: Yujia Min, Hossein Kabir, Nishant Garg, center, Chirayu Kothari and M. Farjad Iqbal, front right. In front are examples of clay samples dissolved at different concentrations in a NaOH solution. The team invented a new test that can predict the performance of cementitious materials in mere 5 minutes. This is in contrast to the standard ASTM tests, which take up to 28 days. This new advance enables real-time quality control at production plants of emerging, sustainable materials. Photo taken at the University of Illinois Urbana-Champaign on Monday, Feb. 3, 2025. (Photo by Fred Zwicky / University of Illinois Urbana-Champaign)

Researchers develop a five-minute quality test for sustainable cement industry materials

A new test developed at the University of Illinois Urbana-Champaign can predict the performance of a new type of cementitious construction material in five minutes — a significant improvement over the current industry standard method, which takes seven or more days to complete. This development is poised to advance the use of next-generation resources called supplementary cementitious materials — or SCMs — by speeding up the quality-check process before leaving the production floor.

Strategic Communications and Marketing News Bureau

507 E. Green St
MC-426
Champaign, IL 61820

Email: stratcom@illinois.edu

Phone (217) 333-5010