Topological Band Engineering in q-BICs and EPs Derived from Visible Range Plasmons

Topological photonics, owing to its band topology, has substantial potential in applications such as quantum computation and photonic chips. However, attaining flexible control over band topology for effective light-matter interactions at the subwavelength scale remains elusive. In this study, we present a metal-insulator-metal (MIM) dimerized grating structure based on the one-dimensional (1D) Su-Schrieffer-Heeger model (SSH). This structure is designed for tuning optical band topology with a relatively high quality factor and small mode volume. Specifically, by variation of the grating thickness, topological band inversion with plasmonic quasi-bound states in the continuum (q-BICs) can be achieved. Moreover, through the modulation of gain-loss and coupling strength, the corresponding exceptional points (EPs) can emerge near the Brillouin zone center (Γ point). Consequently, this MIM dimerized grating structure offers a novel approach for the design of advanced topological devices.