Breaking reciprocity in a non-Hermitian photonic coupler with saturable absorption

We study the breaking of reciprocity in non-Hermitian coupled photonic waveguides by the simultaneous action of the nonlinear effect of saturable absorption and the presence of exceptional points. The nonlinear response of such a system is studied in depth, giving physical insight into the operational principles and fundamental limitations while producing analytical and semianalytical results for the transmission and nonreciprocal intensity range. We numerically validate the theoretical results and assess important performance metrics for the nonreciprocal operation of such a device. This class of passive nonresonant devices can offer broadband on-chip nonreciprocal operation, with significant potential for high-speed applications.