Electrically Tunable Graphene Terahertz Isolator Assisted by Nonreciprocal Plasmon

Abstract Nonreciprocal isolators enable unidirectional light propagation without back-reflection. Typical terahertz isolators require magnetic fields to break the time-reversal symmetry. Herein, we propose a nonmagnetic isolator in the terahertz range based on nonreciprocal graphene plasmons operated in a reflection configuration. The bias voltage generates a drift current in graphene, which breaks the time-reversal symmetry and induces nonreciprocal reflection. The isolator device exhibited a high isolation exceeding 20 dB with an insertion loss of less than 3 dB. Moreover, the bandwidth wit isolation exceeding 20 dB can be broadened five times to 1.7 THz by tuning the carrier density. The indexes, including the isolation, insertion loss and bandwidth of the isolator, show a strong dependence on the drift velocity and mobility of graphene, as well as the air-gap thickness. Our study shows great potential in the burgeoning terahertz technology, where nonmagnetic and electrically tunable isolators are still lacking.