Coherent Asymmetric Absorbers

Abstract

Most applications of metasurfaces require excitation and control of both electric and magnetic surface currents. For such purposes, the metasurface must have a finite thickness to handle magnetic surface currents. For metasurface sheets of negligible thickness that offer only electric response, coherent illumination can compensate the need to create discontinuities of the tangential electric field component using magnetic surface currents. Most of the known coherent metasurfaces are space uniform and can control only plane-wave absorption and specular reflection. However, it is also known that periodical space-modulated (inhomogeneous) metasurfaces can be used to realize anomalous reflection, refraction, and other useful effects. In this paper, we propose the concept of a coherently illuminated space-modulated metasurface that functions as a coherent asymmetric absorber. We study its behavior under nonideal illumination and suggest applications related to sensing.

Coherent control of wave beams via unidirectional evanescent modes excitation

“…However, in these previous works, the functionality of metasurfaces is designed only for one incident angle and the response for other illuminations is actually not considered. To design metasurfaces with coherent control functions for multiple simultaneously incident coherent beams from different directions, the matching conditions of amplitude, phase, and wavevector(direction) of the scattering modes between all incidences are required [35,39,40], which is almost an impossible task using traditional gradient phase methods [25,36] and brute-force numerical optimizations [37,41].…”

Emulating bianisotropic coupling through coherent illumination

“…Here, we ask ourselves the question if it is possible to emulate bianisotropic properties of metasurfaces using illumination of a simple nonbianisotropic metasurface by two or more coherent waves. The motivation is an analogy with other coherently-illuminated devices, such as coherent absorbers [6][7][8][9][10]. While perfect absorption of plane waves in thin layers requires excitation of both electric and magnetic surface currents in a finite-thickness layer [11], using coherent illumination by two waves it is possible to realize full absorption in a sheet of negligible thickness that supports only electric surface current [12].…”

A Dual-band Metasurface with Extreme Angular-Asymmetric Transmission and Frequency Selection Based on Resonant Coupling Effect

“…Angular-asymmetric reflections have been realized using spacemodulated metasurfaces [20]- [23]. A loss-assisted non-Hermitian electromagnetic metasurface was proposed to realize unidirectional retro-reflection, which exhibits different reflectance under two opposite oblique incident angles [20].…”

“…A loss-assisted non-Hermitian electromagnetic metasurface was proposed to realize unidirectional retro-reflection, which exhibits different reflectance under two opposite oblique incident angles [20]. In [23], a coherent asymmetric absorber using space-modulated metasurface was theoretically proposed, which behaves as an absorber or as a retro-reflector depending on the angle of incidence by two coherent waves. Three dimensional asymmetric meta-gratings were applied for angularasymmetric transmissions [24]- [25].…”