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Fabry-Pérot quasinormal modes for topological edge states
Phys. Rev. B 113, L140102 – Published 20 April, 2026
DOI: https://doi.org/10.1103/1hy4-j86q
Abstract
Topological waveguides supporting quantum valley Hall edge states confine waves to interfaces and, due to topological protection, are resistant to backscattering even in the presence of defects. These topological insulators are typically studied by means of an infinite spectral problem. However, practical implementations are necessarily finite. In this work, we propose an alternative framework for analyzing topologically nontrivial states in open, finite systems. Our approach is based on a quasinormal modal expansion method, which directly characterizes the existence and excitation of these modes within the open system. The resulting spectrum is complex and discrete and fully describes the topologically nontrivial states, revealing an analogy of topological mode steering as a dispersive Fabry-Pérot cavity, with a dispersion relation closely related to that of the corresponding infinite (Floquet-Bloch) ribbon problem. Our results illustrate how topologically protected waveguiding can be understood in terms of leaky cavity modes and offers a powerful framework for analyzing finite topological devices.
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References (38)
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