Four-Channel Asymmetric Retroreflection via a Passive Non-Hermitian Metasurface

Abstract

Exceptional points (EPs) in non-Hermitian systems possess increased sensitivity and counterintuitive physical properties, thus offering a wide range of potential applications. Here, a passive non-Hermitian metasurface with four-channel asymmetric retroreflection at microwave region is proposed. Noninterleaved birefringent elements featuring adjustable losses are employed to encode dual independent phase gradients for incident waves along orthogonal planes. By introducing localized loss, the phase-gradient metasurface operates at two distinct second-order EPs and demonstrates markedly asymmetric retroreflection across two orthogonal planes. Specifically, the right-side port mode exhibits strong retroreflection, whereas the left-side port mode is nearly completely suppressed. As a proof of concept, the far-field scattering intensities of the prototype are demonstrated, which exhibits the extremely asymmetric performance across four channels. Our research opens new avenues for realize multifunctional performance of metasurfaces by exploring the new degree of freedom of loss and the multichannel asymmetric retroreflection performance has promising applications in establishing asymmetric channels in wireless communications and controlling radar cross section.