Observation of Onsager–Casimir Reciprocal Relations in a Nonreciprocal Photonic System

Nonreciprocal systems have attracted broad interest in photonics for the ability to control light propagation and frequency conversion. The nonreciprocity in our system is induced by both the nonlinear susceptibility of the material (GaAs) and the external driving field. In this talk, we present a nonlinear photonic system in which reciprocity can be broken by an elliptically polarized drive, while the Onsager–Casimir reciprocal relations are preserved. Numerical analysis and experimental measurements show distinct responses when driven by left- and right-circular polarization, consistent with nonreciprocity while preserving Onsager–Casimir relations. These results reveal a new regime of reciprocity control in nonlinear photonic systems.