Extreme Asymmetry in Metasurfaces

Gradient metasurfaces allow to engineer the contrast ratio of brightness for waves coming from two oppositely tilted angles. (Source: X. Wang, Aalto Univ.)

When we look at a mirror from an angle, we see the image of the object located at the opposite direc­tion. This specular reflection is angle-symmetric: if the person stands on the left side of mirror can see the right person, then the right person can always see the left one with the same clearness. Conven­tional mirrors always have symmetric responses for light coming from both sides of the mirrors. Recently, researchers at Aalto Univer­sity have success­fully broken the angle-symmetric response of a mirror using the concept of gradient meta­surfaces. The arti­ficially syn­thesized surfaces can be designed to look bright at one direction, while dark for the observer at the oppo­site direction.

Meta­surfaces are planar arti­ficial materials, composed of periodic arranged meta-atoms at subwave­length scale. Meta-atoms are made of tradi­tional materials but, if they are placed in a repeating patterns, the array can show many unusual effects which cannot be realized by the natural materials. Now, the team from Aalto use gradient meta­surfaces to engineer the contrast ratio of bright­ness for waves coming from two oppositely tilted angles.

“Our findings provide the first demon­stration that a flat surface can realize extreme optical asymmetry in angle spectrum. This is an important milestone in both physics and engi­neering commu­nities,” says Xuchen Wang, a doctoral student in Aalto Uni­versity, and also the responsible person of this work. (Source: Aalto Univ.)

Reference: X. Wang et al.: Extreme Asymmetry in Metasurfaces via Evanescent Fields Engineering: Angular-Asymmetric Absorption, Phys. Rev. Lett. 121, 256802 (2018); DOI: 10.1103/PhysRevLett.121.256802

Link: Dept. of Electronics and Nanoengineering, Aalto University, Aalto, Finland

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