Equireflectionality and customized unbalanced coherent perfect absorption in asymmetric waveguide networks

TL;DR

This paper demonstrates broadband equireflectionality and tunable coherent perfect absorption in asymmetric waveguide networks, leveraging latent symmetry and scaled cospectrality, with validation through acoustic and microwave experiments.

Contribution

It introduces the concept of latent symmetry and scaled cospectrality to achieve broadband equireflectionality and tunable perfect absorption in asymmetric waveguide networks, a novel approach in wave manipulation.

Findings

Broadband equireflectionality observed in asymmetric waveguides.

Introduction of scaled cospectrality guarantees zero eigenvalue for perfect absorption.

Experimental validation with acoustic and microwave networks confirms theoretical predictions.

Abstract

We explore the scattering of waves in designed asymmetric one-dimensional waveguide networks. We show that the reflection between two ports of an asymmetric network can be identical over a broad frequency range, as if the network was mirror-symmetric, under the condition of so-called latent symmetry between the ports. This broadband equireflectionality is validated numerically for acoustic waveguides and experimentally through measurements on microwave transmission-line networks. In addition, introducing a generalization of latent symmetry, we study the properties of an $N$-port scattering matrix $S$. When the powers of $S$ fulfill certain relations, which we coin scaled cospectrality, the setup is guaranteed to possess at least one zero eigenvalue of $S$, so that the setup features coherent perfect absorption. More importantly, scaled cospectrality introduces a scaling factor which controls the asymmetry of the incoming wave to be absorbed. Our findings introduce a novel approach for designing tunable wave manipulation devices in asymmetric setups. As evidenced by our acoustic simulations and microwave experiments, the generality of our approach extends its potential applications to a wide range of physical systems.