On-Chip Active Supercoupled Topological Cavity.

On-chip photonic resonant cavity plays a critical role in widespread applications including lasing, sensing, and spectroscopy. However, the excitation of these cavities typically relies on evanescent coupling within sub-wavelength distances, limiting flexible and precise chip integration. Here, an on-chip supercoupled topological cavity is demonstrated which is critically coupled at 2.3-wavelength distance from a bus waveguide and remains excited even at 3.2 wavelengths, based on the supercoupling mechanism enabled by the valley vortex flow. Optothermal heating facilitates tunable quality factors and dynamic control of the supercoupling condition, allowing transitions from overcoupling to undercoupling through the critical point. The discovery extends the waveguide-cavity excitation distance to multiple wavelengths, unlocking new possibilities for designing and controlling on-chip resonant devices, including supercoupled lasers, sensors, and modulators.