Propagation and circulating modes of reciprocal non-Hermitian skin effect

TL;DR

This paper explores the propagation and circulation of non-Hermitian skin modes in reciprocal continuous media, revealing scattering-induced mode hopping and proposing a method to generate orbital angular momentum modes for optical applications.

Contribution

It demonstrates the scattering-induced hopping of skin modes and introduces a novel approach to generate circulating modes with orbital angular momentum in reciprocal media.

Findings

Scattering causes skin modes to hop between edges.

Proposes a new method to generate orbital angular momentum modes.

Paves the way for optical devices manipulating OAM.

Abstract

The non-Hermitian skin effect (NHSE) is a novel localization phenomenon, in which all bulk states in a non-Hermitian system under certain conditions are localized at the edge of the system. Conventionally, most studies of NHSE have dealt with discrete lattice systems with non-reciprocal couplings. However in recent years, NHSE in a reciprocal two-dimensional continuous medium, such as photonic crystal systems, has also been reported. In particular, we have previously shown that NHSE also occurs in two-dimensional uniform media. In such two-dimensional systems, skin modes propagate in a direction perpendicular to the localization direction, and especially, they have the property of propagating in only one direction. In this paper, we show numerically an intriguing scattering phenomenon: when a scatterer is placed in the path of a skin mode, the scattering causes the skin mode to hop between opposing edges. In addition, we propose a new method of generating circulating modes with orbital angular momentum using this scattering phenomenon. Our work paves the way for new applications of NHSE as micro-sized optical devices manipulating or generating OAM.