Manipulating electromagnetic waves in magnetic-controllable topological cavity-waveguide systems

Topological photonic crystals (TPhcs), enabling unprecedented capability in manipulating electromagnetic (EM) waves using the nontrivial edge state (ES) and corner state (CS), provide a flexible platform to develop integrated photonic devices, leading to unique applications in optical communications and information processing. However, current approaches for manipulating EM waves in TPhcs, i.e., a topological cavity-waveguide system, can only enable fixed functions, which inevitably degrade its practical applications. Here, we propose a magnetic-field controllable platform consisting of a magnetic field-tunable TCS cavity coupled with an ES waveguide to dynamically modulate the transmission behaviors of EM waves. First, a topological cavity-waveguide system mimicking tunable and topologically protected filter function is demonstrated. Furthermore, the tunable electromagnetically induced transparency-like (EIT-like) phenomenon can also be achieved based on the magnetic-field controllable platform. The robust approach for dynamically controlling EM waves in a topological cavity-waveguide system may open a window to design multi-functional devices and time-varying systems.