▎ 摘　　要

We propose a graphene Ramsey interferometer to study the non-reciprocal phase shift and modulation of surface plasmon polaritons (SPPs). The Ramsey interferometer is constructed by a spatially separated graphene pair that can support two SPP modes. By dynamically modulating the surface conductivity of graphene, the SPP modes will undergo uncompleted cross conversion and an additional phase shift. When adopting two modulation regions in the interferometer, the converted mode will jump back with a nonreciprocal phase shift which can be controlled by the modulation length or phase. The SPP mode of phase shift will interfere with the throughout unconverted one, resulting in arbitrary power arrangement between the two SPP modes. The study may find great applications in plasmonic isolators, phase detectors, and one-way mode converters.