Extreme Asymmetry in Metasurfaces via Evanescent Fields Engineering: Angular-Asymmetric Absorption

Area of Science:

• Wave propagation and control
• Metasurface engineering
• Evanescent wave phenomena

Background:

• Achieving asymmetric wave response in compact planar structures is a significant challenge.
• Conventional methods like diffraction gratings and reflectarrays have limitations in engineering asymmetry.
• Controlling wave propagation directionally is crucial for advanced optical and electromagnetic applications.

Purpose of the Study:

• To introduce a novel paradigm for engineering asymmetry in planar structures.
• To demonstrate angular-asymmetric absorption using a designed metasurface.
• To explore the potential of evanescent waves for wave manipulation.

Main Methods:

• Development of a new metasurface concept based on unilateral excitation of evanescent waves.
• Experimental characterization of the metasurface's absorption properties.
• Engineering the contrast ratio of absorption for waves from opposite angles.

Main Results:

• Demonstrated arbitrary engineering of absorption contrast ratio from zero to infinity.
• Showcased angular-asymmetric absorption for waves incident from two oppositely tilted angles.
• Confirmed that these asymmetry effects are unattainable with conventional diffraction gratings, reflectarrays, and phase-gradient metasurfaces.

Conclusions:

• The proposed metasurface offers unprecedented control over wave propagation asymmetry.
• Evanescent wave engineering provides a powerful tool for designing advanced wave manipulation devices.
• Potential applications include one-side detection, sensing, angle-encoded steganography, and nonlinear devices.