On‐Chip Active High‐<i>Q</i> Slow Light Topological Cavities

Abstract Topological photonic waveguides for lossless transport through edge states have enabled the design of cavities with sharp bends in a closed‐loop configuration, where the confinement of photons in topological cavities has typically been controlled by varying the cavity size. Here, a slow light topological cavity is presented, where the light confinement and the quality ( Q ) factor are controlled through engineered dispersion of the slow light waveguide mode and its group velocity, introducing a new degree of freedom to design high‐ Q photonic cavities. It is experimentally demonstrated that topological slow light in valley photonic crystals with bearded interfaces enhances light‐matter interactions, resulting in improved cavity Q ‐factor. In addition, active Q ‐factor control of slow light topological cavities is achieved through optical excitation of the silicon cavity chip, offering promising applications in communications, sensing, and polaritonics.