Quasi-Bound States in the Continuum in Disordered Systems

Disorders are often considered harmful defects in a system, which are unavoidable in sample fabrication and lead to the disappearance of high-quality states in experiments. Massive research aims to improve fabrication methods to minimize the adverse effects of disorder in the system. Here, a system with a high-quality state that is immune to disorder in the system is proposed, where q-BIC (quasi-bound states in the continuum) could be induced by topological phase transitions in disordered systems. In the proposed structure, the emergence of q-BIC could be controlled by the degree of disorder, providing new insights into how to control q-BIC. Such a mechanism can be realized in both one-dimensional grating systems and two-dimensional photonic crystal slabs. In addition, simulations and theoretical studies suggest that OAM (orbital angular momentum) light could also be generated with q-BIC in disordered systems. This study indicates that the exploration of BIC could be extended from periodic structures to disordered systems, giving researchers more freedom to explore the properties of BIC.