Defect-localized bound states in the continuum in topological photonic alloys

Optical bound states in the continuum (BICs), characterized by extremely high quality factors, can significantly enhance light–matter interaction and pave the way for the development of various types of optical cavities. However, even slight perturbations in the system can degrade BICs into leaky modes. Therefore, in optical systems supporting BICs, perturbations are generally considered detrimental and should be strictly avoided. Contrary to this expectation, here we demonstrate that random magnetic doping combined with a single point defect in a photonic crystal can give rise to BICs. Furthermore, these BICs exhibit exceptional resilience to structural disorders, offering new design principles for stable and practical optical devices.