Super Quasibound State in the Continuum

Symmetry-protected bound states in the continuum (BICs) possessing nontrivial physical properties have facilitated the development of wave systems in various fields. However, limited by leakage from a finite photonic structure, the asymptotic behavior of the quality factor $Q$ for $N$ resonators is proportional to ${N}^{2}$. This Letter demonstrates a super quasibound state in the continuum, to manipulate the asymptotic behavior. Coordinating the avoided crossing of BICs in parameter space with the merging of BICs in momentum space can switch the asymptotic behavior from ${N}^{2}$ to ${N}^{3}$ proportionality, for applications such as lasing and optical sensing.