Topology optimization empowered dual-band second-order photonic topological insulators

Dual-band second-order photonic topological insulators (SPTIs), characterized by multiple corner states, offer exceptional potential for robust multiband manipulation of electromagnetic waves in lower dimensions. However, previous theoretical implementations of dual-band SPTIs have been constrained by limited flexibility, hindering their adaptability for diverse applications. Additionally, experimental validation of these dual-band SPTIs has been lacking. In this study, we introduce a topology optimization method to design SPTIs with customizable dual-band corner states tailored for specific multiband applications. Dual-band SPTIs with customized corner states for manipulating electromagnetic waves of transverse magnetic and electric modes are created. Furthermore, multiple corner states within dual bandgaps are experimentally confirmed. This work opens new avenues for creating customizable photonic devices with dual-band topological features, enabling versatile multiband applications.