Ultrahigh-Q and angle-robust chiroptical resonances beyond BIC splitting

Abstract

Chiroptical resonances inspired by bound states in the continuum (BICs) open a new, to the best of our knowledge, avenue to enhance chiral light–matter interaction. Symmetry breaking is the widely employed way, wherein the circularly polarized states (CPSs) arise from BIC splitting. Here, we utilize a far-field interference mechanism to create ultrahigh-Q (typically, 2.36 × 106) chiroptical resonance beyond BIC splitting, in which CPSs coexist with BICs in the momentum space. Accordingly, the spin-selective absorption with ultranarrow linewidth is achieved at the CPS points, which can be regulated by monolayer transition metal dichalcogenides (TMDCs). In addition, the chiral response of our scheme exhibits the incident-direction robustness and flexible tunability. Our findings may facilitate potential applications in light manipulation, spin–valley interaction, and chiral sensing.