Sensitivity of topological edge states in a non-Hermitian dimer chain

Abstract

Photonic topological edge states in one-dimensional dimer chains have long been thought to be robust to structural perturbations by mapping the topological Su-Schrieffer-Heeger model of a solid-state system. However, the edge states at the two ends of a finite topological dimer chain will interact as a result of near-field coupling. This leads to deviation from topological protection by the chiral symmetry from the exact zero energy, weakening the robustness of the topological edge state. With the aid of non-Hermitian physics, the splitting frequencies of edge states can be degenerated again and topological protection recovered by altering the gain or loss strength of the structure. This point of coalescence is known as the exceptional point (EP). The intriguing physical properties of EPs in topological structures give rise to many fascinating and counterintuitive phenomena. In this work, based on a finite non-Hermitian dimer chain composed of ultra-subwavelength resonators, we propose theoretically and verify experimentally that the sensitivity of topological edge states is greatly affected when the system passes through the EP. Using the EP of a non-Hermitian dimer chain, we realize a new sensor that is sensitive to perturbation at the end of the structure and yet topologically protected from internal perturbation. Our demonstration of a non-Hermitian topological structure with an EP paves the way for the development of novel sensors that are not sensitive to internal manufacturing errors but are highly sensitive to changes in the external environment.

Photonic Band Inversion and Absorption Enhancement in Dirac Semi‐Metal Tamm Plasmon Multilayer System

“…[39] Guo et al experimentally studied the topological edge state in a non-hermitian system with exceptional points and designed a sensor having both the topological protection and the sensitivity of the exceptional points. [40] We investigated the sensing performance of this device by inserting an analyte layer at the PC hetero-junction. Air is chosen as the reference medium, and two absorption peaks appear at 7.01 THz and 7.10 THz.…”

“…It is clear from Figure11cthat absorption decreases with the increase in k values.Recently, the application of topological edge states in the design of various photonic devices has been studied on different platforms [39]. Guo et al experimentally studied the topological edge state in a non-hermitian system with exceptional points and designed a sensor having both the topological protection and the sensitivity of the exceptional points [40]. We investigated the sensing performance of this device by inserting an analyte layer at the PC hetero-junction.…”

Band structures and scattering properties of the simplest one-dimensional $${\mathscr {P}}{\mathscr {T}}$$-symmetric photonic crystal

“…Exceptional point is the coalescence point in general non-Hermitian system, where eigenstates become parallel with the same eigenvalue. Several novel properties near the exceptional point are disclosed and applied for the design of optical devices 28 – 30 . In the future, we intend to explore these properties and applications in the proposed model.…”

Rotation controlled topological edge states in a trimer chain composed of meta-atoms

“…The edge states of a finite SSH chain will be distributed at both ends of the chain. Moreover, edge states with topological protection are immune to the fabrication error of the chain, which have been used to realize many applications, such as the topological lasers [27][28][29], filter [4], sensors [30,31], and wireless power transfer (WPT) [32][33][34]. Normally, the construction of SSH chain in optical systems needs to change the separation of adjacent resonators or waveguides.…”