Tuning exceptional points towards switchable nonreciprocity

Exceptional points (EPs) have been extensively studied in tapered fiber-coupled microcavities, where their parameter coalescence can be engineered and manipulated through either gain/loss or coupling mechanisms. However, realizing and dynamically tuning EPs on a chip-based platform remains challenging, primarily due to the incompatibility of integrated gain materials and the lack of effective methods for controlling the extracavity coupling. Here, we propose an on-chip tunable EPs configuration based on a microring integrated with graphene and dual scatters. The states of the graphene-based dual-scatterer add-drop microring (GDS-ADM) configuration can be dynamically tuned among an EP with positive chirality (EP+), a non-exceptional point (non-EP) and an EP with negative chirality (EP-) by varying the bias voltage applied to graphene. The dynamics of the GDS-ADM are analyzed under both linear and thermo-optical nonlinear status. The results show that an optical nonreciprocal transmission can be achieved when thermo-optic nonlinearity is activated, and further switchable tuned by the bias voltage. The proposed configuration will find potential applications in on-chip optical communication and sensing.