Dual-mode tunable absorber based on quasi-bound states in the continuum

In this Letter, we propose a novel dual-mode tunable absorber that utilizes quasi-bound states in the continuum (q-BIC), based on the periodically arranged silicon cylinders tetramer. By introducing asymmetry perturbation through manipulating the diameters of diagonal cylinders in the all-dielectric structure, symmetry-protected BIC (SP-BIC) transforms into q-BIC, leading to the emergence of one transmission and one reflection Fano-like resonant mode. The relationship between the quality factor of each mode and the asymmetry parameterαis analyzed, revealing an exponential dependence with an exponent of -1.75, i.e., Q∝α^(-1.75). To explain the underlying physics, multipole decomposition analysis and Kutuzova's theory are applied. Subsequently, a monolayer of graphene is introduced to the all-dielectric structure to demonstrate the application of the dual-mode tunable absorber. When the critical coupling condition is satisfied, each mode can achieve the theoretical maximum absorption, demonstrating the distinctive capability of our proposed absorber for tunning and efficient light absorption. This research provides valuable insights into light-matter interactions and opens up possibilities for optical modulation and the development of graphene-based devices.