Topological switching via exceptional point pairs in optical microcavities

We present a topological method for deterministic control of the quality factor ( Q ) and mode conversion in optical microcavities using an exceptional-point (EP) pair. The transition between super- and subradiant modes is governed by braid-group topology on a two-sheet Riemann surface, enabling path-robust Q -tuning without relying on gain-loss balance, nonlinearity, or non-adiabatic encircling. Full-wave simulations demonstrate more than sixfold Q enhancement at a normalized frequency of k r ≈3, with higher gains expected at larger k r . The approach requires only a weak elliptical deformation and an engineered internal loss profile, maintaining compatibility with standard photonic platforms. This EP-pair framework offers a scalable and fabrication-tolerant strategy for reconfigurable microlasers, sensors, and integrated photonic devices.