Journal Article topological cavity 6G communication THz on‐chip cavity THz photonics THz topological integrated circuits (TTICs) THz topological photonic integrated circuits active non‐reciprocity bound states in the continuum flexible metasurfaces nanophotonic devices non‐reciprocal critical coupling state non‐volatile reconfiguration on-chip modulators on‐chip on‐chip integrated isolator on‐chip terahertz interconnects optothermal control phase‐change material quantum and topological photonics silicon photonics supercoupled cavity switchable active metasurfaces terahertz terahertz interfacial waveguide terahertz metamaterial sensors terahertz topological isolator terahertz topological photonic integrated circuit terahertz topological photonic integrated circuits topological non‐reciprocity