Waveguide-induced coalescence of exceptional points

In non-Hermitian systems, multiple eigenstates can merge into one state at so-called exceptional points (EPs). This paper presents the coalescence of the multiple EPs based on a waveguide. For the ring cavities located at the second-order EPs with desired chiral modes, the waveguide provides unidirectional couplings among the modes of the second-order EPs, which merges the second-order EPs into one high-order EP. The principle of this framework and properties of this system are presented by analyzing the effective Hamiltonian of the system, a mode-coupling diagram, and numerical simulations.