Coherent control of wave beams via unidirectional evanescent modes excitation

TL;DR

This paper introduces a metasurface approach that enables coherent perfect absorption and reflection control for waves incident from arbitrary directions by utilizing unidirectional evanescent modes, expanding wave manipulation capabilities.

Contribution

It presents a novel metasurface paradigm that allows asymmetric wave excitation and control of reflection using unidirectional evanescent waves, surpassing traditional symmetric absorption methods.

Findings

Theoretically demonstrated control of reflected wave amplitude from zero to full reflection.

Experimentally confirmed tuning of reflection by phase difference adjustment.

Potential applications in optical switching and radar cross section management.

Abstract

Conventional coherent absorption occurs only when two incident beams exhibit mirror symmetry with respect to the absorbing surface, i.e., the two beams have the same incident angles, phases, and amplitudes. In this work, we propose a more general metasurface paradigm for coherent perfect absorption, with impinging waves from arbitrary asymmetric directions. By exploiting excitation of unidirectional evanescent waves, the output can be fixed at one reflection direction for any amplitude and phase of the control wave. We show theoretically and confirm experimentally that the relative amplitude of the reflected wave can be tuned continuously from zero to unity by changing the phase difference between the two beams, i.e. switching from coherent perfect absorption to full reflection. We hope that this work will open up promising possibilities for wave manipulation via evanescent waves engineering with applications in optical switches, one-side sensing, and radar cross section control.