Broadband Modulation of Terahertz Waves With Non-Resonant Graphene Meta-Devices

Single-layer graphene absorbs a small fraction of incident terahertz waves by intraband transition of Dirac fermions. The amounts of absorption, reflection, and transmission of terahertz waves depend on the doping level of graphene, i.e., the Fermi level, and they exhibit relatively weak frequency dependency at terahertz frequencies. By hybridizing gated single-layer graphene with a non-resonant meta-atom structure, we show that the effective surface conductivity of meta-atom hybridized graphene can be significantly enhanced, and large intensity modulation of transmitted terahertz waves can be achieved without sacrificing the broadband modulation feature of single-layer graphene. For a frequency insensitive response, the meta-atoms are designed so that their resonance is positioned outside the frequencies of interest. Exploiting the enhanced effective surface conductivity with a non-resonant feature, larger modulation was possible over broad operating frequency from 0.3 to 2.3 THz. We anticipate that this electrically controlled graphene meta-device may play an important role in the realization of practical terahertz modulators.