Active formation of Friedrich-Wintgen bound states in the continuum in dielectric dimerized grating borophene heterostructure

Abstract: The Friedrich-Wintgen bound state in the continuum (FW BIC) provides a unique approach for achieving high quality factor (Q-factor) resonance, which has attracted wide attention and promoted the development of various applications. However, the FW BIC is usually considered as accident BIC resulting from the continuous parameters tuning, and a systematic approach to generate the FW BIC is still lacking. To address this, a method of actively forming FW BIC by matching the damping rate and resonance frequency of the coupling mode is proposed. As a proof-of-principle example, we propose a dielectric dimerized grating borophene heterostructure that generates a FW BIC near the commercially important communication wavelength. The coupling system comprises an electrically tunable borophene plasmon mode and a BIC supported by a dielectric dimer grating that can be attributed to the Brillouin zone folding. More interestingly, the BIC can be excited by the localized borophene plasmon (LBP) mode through near-field coupling as LBP mode can be considered as the dipole source. The interaction between them can further form the FW BIC, and support electromagnetically induced transparency (EIT)-like with maximum group index up to 2043, indicating its great potential for slow light applications. Our results provide a promising strategy and theoretical support for the generation of FW BIC in active plasmonic optical devices.