“…[16,20,21] Optical nonreciprocity has the potential application in information processing, e.g., all-optical diodes [22,23] and unidirectional light transport. [24] So far, most studies on the optical nonreciprocity effect are based on the laser induced atomic coherence, [16,20,21] and it is necessary to have at least one coupling field to form the atom coherence. However, spontaneously generated coherence (SGC) can also create the atomic coherence, while SGC refers to the quantum interference between spontaneous decay channels from closely placed upper levels to a ground level.…”