Interface state-based bound states in continuum and below-continuum-resonance modes with high-Q factors in the rotational periodic system

We have introduced a new approach to calculate the orbital angular momentum (OAM) of bound states in continuum (BICs) and below-continuum-resonance (BCR) modes in the rotational periodic system nested inside and outside by transforming the Bloch wave number from the translational periodic system. We extensively classify and study these BICs and BCR modes, which exhibit high-quality (high-Q) factors, in different regions relative to the interface of the system. These BICs and BCR modes with a high-Q factor have been studied in detail based on distinctive structural parameters and scattering theory. The outcomes of this research break the periodic limitation of interface state-based BICs, and realize more and higher symmetry interface state-based BICs and BCR modes. Moreover, we can control the region where light is captured by adjusting the frequency, and show that the Q factor of BICs is more closely related to the ordinal number of rings and the rotational symmetry number of the system.