Anomalous Floquet non-Hermitian skin effect in a ring resonator lattice

Abstract

We present a simple and easy-to-implement approach for realizing the non-Hermitian skin effect (NHSE) in one-dimensional coupled ring resonator lattices. Unlike existing proposals based on engineering gain and loss on different ring segments to achieve nonreciprocal couplings, each ring in our design can have fixed on-site gain or loss. The lattice hosts a variant of the NHSE that we call the anomalous Floquet NHSE, whereby skin modes occur for every value of the Floquet quasienergy, allowing for broadband asymmetric transmission. Varying the gain/loss can induce a non-Hermitian topological phase transition that reverses the localization direction of the skin modes. An experimental implementation in an acoustic lattice yields good agreement with theoretical predictions.