Abstract
Topologically engineered optical materials support robust light transport. Herein, the investigated non-Hermitian lattice is trimerized and inhomogeneously coupled using uniform intracell coupling. The topological properties of the coupled waveguide lattice are evaluated, the PT-symmetric phase of a PT-symmetric lattice can have different topologies; the edge states depend on the lattice size, boundary configuration, and competition between the coupling and degree of non-Hermiticity. The topologically nontrivial region extends in the presence of periodic gain and loss. The nonzero geometric phases accumulated by the Bloch bands indicate the existence of topologically protected edge states between the band gaps. The unidirectional amplification and attenuation zero modes appear above a threshold degree of non-Hermiticity, which facilitate the development of a robust optical diode.
Highlights
Topological insulators are novel states of solid-state materials that have an insulating bulk band gap and a conducting edge or surface [1]
The PT -symmetric phases, band structure, and topologically protected edge states of a trimerized coupled waveguide lattice with universal non-Hermiticity are demonstrated. This lattice possesses topologies that are dependent on the degree of non-Hermiticity
In the topologically nontrivial region, the edge states are related to the configurations at the lattice boundary and depend on the coupling strengths
Summary
Topological insulators are novel states of solid-state materials that have an insulating bulk band gap and a conducting edge or surface [1]. The topologically protected unidirectional interface state propagates robustly against local impurities This was experimentally demonstrated in coupled waveguide ring resonators [6]. As progress on topological photonics has advanced, tremendous interest has been paid to parity-time (PT ) symmetric non-Hermitian systems in coupled optical waveguides [22,23,24,25], resonators [26,27,28,29,30,31,32], atoms, and atomic lattices [33,34]. In PT -symmetric configurations, the PT -symmetric regions possess different topologies depending on the coupling configuration and universal non-Hermiticity. We discover a non-Hermitian threshold above which there exist unidirectional amplified and damped edge states, which are located at opposite boundaries with identical resonant frequency.
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