Nonreciprocal Coupling Induced by Nonlocal Loss Engineering

Nonreciprocal coupling between photonic modes enables a range of advanced functionalities, though the available approaches for its practical implementation remain limited. Here, we introduce a novel strategy for achieving nonreciprocal coupling via nonlocal, nonlinear loss. We prove that robust, broadband, and continuously tunable nonreciprocal coupling can be realized by engineering the loss rate as a function of the state of a nonlocal mode, as validated through effective Hamiltonian modeling and numerical simulations. Our results suggest a promising route toward scalable, power-independent, and potentially integrable nonreciprocal photonic systems, with promising applications in non-Hermitian devices and topological photonics.