Electrically Tunable Graphene Terahertz Isolator Assisted by Nonreciprocal Plasmon

<正>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 d B with an insertion loss of less than 3 d B.Moreover, the bandwidth wit isolation exceeding 20 d B 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.