Fast encirclement of an exceptional point for highly efficient and compact chiral mode converters

Exceptional points (EPs) are degeneracies at which two or more eigenvalues and eigenstates of a physical system coalesce. Dynamically encircling EPs by varying the parameters of a non-Hermitian system enables chiral mode switching, i.e., the final state upon a closed loop in parameter space depends on the encircling handedness. Conventional schemes require sufficiently slow parameter evolution to ensure adiabaticity, limiting efficiency and device compactness. Here, we show that fast parametric evolution along the parameter space boundary of the system Hamiltonian relaxes this constraint. The proposed scheme enables highly efficient transmission and a more compact footprint for asymmetric mode converters. We experimentally demonstrate these principles in a 57 µm-long double-coupled silicon waveguide system, achieving chiral mode switching with near-unity transmission efficiency at 1550 nm, paving the way for high-efficiency, highly integrated chiral mode switching in practical applications.